|
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NGC 2440: Cocoon of a New Wh
…
| Title |
NGC 2440: Cocoon of a New White Dwarf |
| Explanation |
Like a butterfly, a white dwarf star begins its life by casting off a cocoon that enclosed its former self. In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas would become the prettiest of all! In the above cocoon [ http://hubblesite.org/newscenter/newsdesk/archive/releases/1999/35/image/e ], the planetary nebula designated NGC 2440, contains one of the hottest white dwarf stars known. The white dwarf [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html ] can be seen as the bright dot near the photo's center. Our Sun will eventually become a "white dwarf butterfly", but not for another 5 billion years. The above false color image [ http://heritage.stsci.edu/1999/38/ ] was post-processed by Forrest Hamilton [ http://heritage.stsci.edu/commonpages/infoindex/ourproject/f_hamilton.html ]. |
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NGC 6888: A Tricolor Starfie
…
| Title |
NGC 6888: A Tricolor Starfield |
| Explanation |
NGC 6888 [ http://www.noao.edu/image_gallery/html/im0834.html ], also known as the Crescent Nebula, is a cosmic bubble [ http://arxiv.org/abs/astro-ph/0310311 ] about 25 light-years across, blown by winds [ http://www.sdsc.edu/GatherScatter/GSwinter97/owocki.html ] from its central, bright, massive star. Near the center of this intriguing widefield view of interstellar gas clouds and rich star fields [ http://antwrp.gsfc.nasa.gov/apod/ap031023.html ] of the constellation Cygnus, NGC 6888 is about 5,000 light-years away. The three color composite [ http://dg-imaging.astrodon.com/gallery/ display.cfm?imgID=56 ] image was created by stacking exposures through narrow band filters that transmit the light [ http://hubblesite.org/sci.d.tech/behind_the_pictures/ meaning_of_color/eagle.shtml ] from atoms in the clouds. Hydrogen is shown as green, sulfur as red, and oxygen as blue. NGC 6888's central star is classified as a Wolf-Rayet star [ http://www.peripatus.gen.nz/Astronomy/WolRaySta.html ] (WR 136) and is shedding its outer envelope in a strong stellar wind, ejecting the equivalent of our Sun's mass every 10,000 years. Burning fuel at a prodigious rate and near the end of its stellar life [ http://heasarc.gsfc.nasa.gov/docs/xmm_lc/edu/lessons/ background-lifecycles.html ], this star should ultimately go out with a bang in a spectacular supernova explosion [ http://antwrp.gsfc.nasa.gov/apod/ap060430.html ]. |
|
Blue Stragglers In NGC 6397
| Title |
Blue Stragglers In NGC 6397 |
| Explanation |
In our neck of the Galaxy [ http://www.limber.org/globs.html ] stars are too far apart [ http://antwrp.gsfc.nasa.gov/apod/ap991211.html ] to be in danger of colliding, but in the dense cores of globular star clusters [ http://antwrp.gsfc.nasa.gov/apod/ap990312.html ] star collisions may be relatively common. In fact, researchers have evidence [ http://www.aas.org/publications/baas/v32n2/aas196/ 265.htm ] that the row of six closely spaced blue stars just below the label in this Hubble Space Telescope [ http://hubble.stsci.edu/ ] image were formed when stars directly collided. Pictured is the central region of NGC 6397 [ http://www.seds.org/messier/xtra/ngc/n6397.html ], a globular cluster [ http://www.seds.org/messier/glob.html ] about 6,000 light-years distant, whose stars [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ stars.html ] all formed at about the same time. NGC 6397's [ http://dibonsmith.com/ngc6397.htm ] massive stars have long since evolved off the main sequence, exhausting their central supplies of nuclear fuel [ http://fusedweb.pppl.gov/default.html ]. This should leave the cluster with only old low mass stars, faint red main sequence stars and brighter blue and red giants [ http://plabpc.csustan.edu/astro/stars/giant.htm ]. However, spectroscopic data show that the indicated stars, descriptively dubbed blue stragglers [ http://antwrp.gsfc.nasa.gov/apod/ap971104.html ], are clearly main sequence stars which are too blue and too massive to still be there. Suggestively the stragglers appear to be two and occasionally three times as massive as the lower mass cluster stars otherwise present, supporting evidence [ http://www.boston.com/dailyglobe2/165/science/ Taking_measure_of_the_stars+.shtml ] for their formation from two and even three star collisions. |
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X-Ray Wind From NGC 3783
| Title |
X-Ray Wind From NGC 3783 |
| Explanation |
A black hole [ http://www.ncsa.uiuc.edu/Cyberia/NumRel/BlackHoles.html ] is supposed to inexorably attract matter. But the intense radiation generated as material swirls and plunges into its high gravity field also heats up surrounding gas and drives it away. In fact, measurements made using this recent Chandra Observatory [ http://chandra.harvard.edu/press/00_releases/ press_052500.html ] X-ray spectrum of active galaxy NGC 3783 reveal a wind of highly ionized atoms blowing away from the galaxy's suspected central black hole [ http://chandra.harvard.edu/xray_sources/quasars.html ] at a million miles per hour. Displayed in false color, the bright central spot is the X-ray image [ http://imagine.gsfc.nasa.gov/docs/science/how_l2/ xtelescopes_systems.html ] of NGC 3783 while the lines radiating away represent an X-ray spectrum [ http://imagine.gsfc.nasa.gov/docs/teachers/lessons/ xray_spectra/background-spectroscopy.html ] of this source produced by Chandra's High Energy Transmission Grating [ http://chandra.harvard.edu/about/science_instruments.html ] (HETG). An X-ray spectrum is the analog to the rainbow spread of colors in a visible light spectrum. It represents a detailed, spread out image of X-ray colors or energies arising from the source. Ionized atoms of iron, magnesium, oxygen, nitrogen and other elements [ http://www.webelements.com/ ] produce patterns of absorption at known X-ray energies. These patterns have been identified in the spectrum of NGC 3783 [ http://xxx.lanl.gov/abs/astro-ph/0004050 ] at slightly shifted energies and the measured shifts indicate the hot wind's velocity. |
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NGC 1499: The California Neb
…
| Title |
NGC 1499: The California Nebula |
| Explanation |
What's California doing in space? Drifting through the Orion Arm of the spiral Milky Way Galaxy, this cosmic cloud [ http://www.anzwers.org/free/universe/nebulae/ ngc1499.html ] by chance echoes the outline of California [ http://en.wikipedia.org/wiki/California ] on the west coast of the United States [ https://www.cia.gov/cia/publications/factbook/geos/us.html ]. Our own Sun also lies within the Milky Way's Orion Arm [ http://www.anzwers.org/free/universe/5000lys.html ], only about 1,500 light-years from the California Nebula [ http://en.wikipedia.org/wiki/California_Nebula ]. Also known as NGC 1499 [ http://www.seds.org/~spider/spider/ Misc/n1499.html ], the classic emission nebula is around 100 light-year [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ]s long. It glows with the red light characteristic of hydrogen atoms recombining with long lost [ http://antwrp.gsfc.nasa.gov/apod/lib/lament.html ] electrons, stripped away (ionized [ http://csep10.phys.utk.edu/ astr162/lect/light/ionization.html ]) by energetic starlight. In this case, the star most likely providing the energetic starlight is the bright, hot, bluish Xi Persei, just right of the nebula and above picture center. Fittingly, this composite [ http://www.astro.caltech.edu/~wsk/ngc1499.html ] picture was made with images from a telescope in California - the 48-inch (1.2-meter) Samuel Oschin Telescope [ http://www.astro.caltech.edu/~wsk/sot.html ] - taken as a part of the second National Geographic Palomar [ http://antwrp.gsfc.nasa.gov/apod/ap030807.html ] Observatory Sky Survey [ http://www.astro.caltech.edu/~wws/poss2.html ]. |
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NGC 6960: The Witch's Broom
…
| Title |
NGC 6960: The Witch's Broom Nebula |
| Explanation |
Ten thousand years ago, before the dawn of recorded human history [ http://news.bbc.co.uk/hi/english/sci/tech/newsid_334000/334517.stm ], a new light must suddenly have appeared in the night sky and faded after a few weeks. Today we know this light was an exploding star [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html ] and record the colorful expanding cloud as the Veil Nebula [ http://nineplanets.org/twn/cygnusx.html ]. Pictured above [ http://robgendler.astrodigitals.com/Nebulas.html ] is the west end of the Veil Nebula [ http://www.astropix.com/HTML/E_SUM_N/VEIL.HTM ] known technically as NGC [ http://www.ngcic.com/dss/dss_images.htm ] 6960 but less formally as the Witch's Broom Nebula. The rampaging gas gains its colors by impacting and exciting existing [ http://antwrp.gsfc.nasa.gov/apod/ap960307.html ] nearby gas. The supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/supernova_remnants.html ] lies about 1400 light-years away towards the constellation of Cygnus [ http://www.multimania.com/cdadfs/constellation/cygne/cygnus.htm ]. This Witch's Broom actually spans over three times the angular size of the full Moon [ http://antwrp.gsfc.nasa.gov/apod/moon.html ]. The bright blue star 52 Cygnus [ http://www.seds.org/Maps/Stars_en/Fig/cygnus.html ] is visible with the unaided eye from a dark location but unrelated to the ancient supernova [ http://www.chapman.edu/oca/benet/intro_sn.htm ]. |
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Gangly Spiral Galaxy NGC 318
…
| Title |
Gangly Spiral Galaxy NGC 3184 |
| Explanation |
NGC 3184 is a large spiral galaxy [ http://www.seds.org/messier/spir.html ] with a small nucleus and long sprawling spiral arms. Although NGC 3184 [ http://www.kopernik.org/images/archive/n3184.htm ] contains hundreds of billions of stars, the blue color of its spiral arms [ http://online.bc.cc.ca.us/sea/astronomy/ismnotesb/ismglxyc.htm ] comes mostly from relatively few bright young blue stars [ http://antwrp.gsfc.nasa.gov/apod/ap000227.html ]. The galaxy is not empty of matter between these spiral [ http://antwrp.gsfc.nasa.gov/apod/spiral_galaxies.html ] arms -- the bright stars that highlight the arms were created in huge density waves [ http://fuse.pha.jhu.edu/~danforth/spiral/ ] that circle the center. Visible [ http://www.ghg.net/akelly/ ] with a small telescope towards the constellation [ http://www.att.virtualclassroom.org/vc99/vc_04/cons_stars/cons/hist_cons.html ] of Ursa Major [ http://www.astronomical.org/constellations/uma.html ], light takes about 25 million years to reach us from NGC 3184 [ http://home.cc.umanitoba.ca/~umgonza4/histobserv.html ], and about 50,000 years just to cross it. NGC 3184 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26AS..124..129P ] (Hubble type [ http://www.seds.org/messier/xtra/supp/gal-ttab.html ] Sbc) is notable for its high abundance [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1982PhDT........35M ] of heavy elements [ http://casa.colorado.edu/~uvconf/white_final/node5.html ] and a supernova [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/supernovae.html ] that has occurred there recently [ http://cfa-www.harvard.edu/iauc/07300/07329.html#Item1 ]. |
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NGC 6960: The Witch's Broom
…
| Title |
NGC 6960: The Witch's Broom Nebula |
| Explanation |
Ten thousand years ago, before the dawn of recorded human history [ http://news.bbc.co.uk/hi/english/sci/tech/newsid_334000/334517.stm ], a new light must suddenly have appeared in the night sky and faded after a few weeks. Today we know this light was an exploding star [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html ] and record the colorful expanding cloud as the Veil Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap010928.html ]. Pictured above [ http://www.noao.edu/image_gallery/html/im0852.html ] is the west end of the Veil Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap030204.html ] known technically as NGC [ http://en.wikipedia.org/wiki/New_General_Catalog ] 6960 but less formally as the Witch [ http://antwrp.gsfc.nasa.gov/apod/ap061211.html ]'s Broom [ http://www.broomshop.com/history/ ] Nebula. The rampaging gas gains its colors by impacting and exciting existing [ http://www.seds.org/billa/twn/cygnusx.html ] nearby gas. The supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/supernova_remnants.html ] lies about 1400 light-years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away towards the constellation of Cygnus [ http://www.multimania.com/cdadfs/constellation/cygne/cygnus.htm ]. This Witch's Broom actually spans over three times the angular size [ http://imagine.gsfc.nasa.gov/YBA/HTCas-size/more-ang_size.html ] of the full Moon [ http://antwrp.gsfc.nasa.gov/apod/ap030810.html ]. The bright star 52 Cygnus [ http://www.seds.org/Maps/Stars_en/Fig/cygnus.html ] is visible with the unaided eye from a dark location but unrelated to the ancient supernova [ http://en.wikipedia.org/wiki/Supernova ]. |
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NGC 1850: Gas Clouds and Sta
…
| Title |
NGC 1850: Gas Clouds and Star Clusters |
| Explanation |
There's nothing like it in our own Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap000130.html ]. Globular clusters as young as NGC 1850 [ http://antwrp.gsfc.nasa.gov/apod/ap000729.html ] don't exist here. Globular clusters [ http://antwrp.gsfc.nasa.gov/apod/globular_clusters.html ] only 40 millions of years old can still be found in the neighboring LMC [ http://antwrp.gsfc.nasa.gov/apod/ap000222.html ] galaxy, though, but perhaps none so unusual as NGC 1850 [ http://oposite.stsci.edu/pubinfo/press-releases/94-40.txt ]. Close inspection of the above photograph [ http://www.eso.org/outreach/press-rel/pr-1999/phot-15-99.html ] will reveal two clusters. Below and right of the main group of stars known as NGC 1850 [ http://www.mso.anu.edu.au/~kim/thesis/node6.html ]A is a smaller, still younger group dubbed NGC 1850B [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1994ApJ...435L..43G ]. This cluster is made of stars only about four million years old. The large red cloud of gas surrounding the clusters may have been predominantly created by supernovae explosions [ http://heasarc.gsfc.nasa.gov/docs/snr.html ] of stars in the younger cluster. The red supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/supernova_remnants.html ] N57D is visible on the upper left. |
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Stars, Dust and Nebula in NG
…
| Title |
Stars, Dust and Nebula in NGC 2170 |
| Explanation |
When stars form, pandemonium reigns. A textbook [ http://zebu.uoregon.edu/text.html ] case is the star forming region NGC 2170 [ http://antwrp.gsfc.nasa.gov/apod/ap060805.html ]. Visible above [ http://www.rc-astro.com/photo/id1178.html ] are red glowing emission nebulas [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] of hydrogen [ http://periodic.lanl.gov/elements/1.html ], blue reflection nebulas [ http://en.wikipedia.org/wiki/Reflection_nebula ] of dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ], dark absorption nebulas [ http://www.glyphweb.com/esky/concepts/absorptionnebula.html ] of dust, and the stars that formed from them. The first massive stars formed from the dense gas will emit energetic light [ http://imagers.gsfc.nasa.gov/ems/uv.html ] and winds [ http://www.peripatus.gen.nz/Astronomy/SteWin.html ] that erode, fragment, and sculpt [ http://antwrp.gsfc.nasa.gov/apod/ap050425.html ] their birthplace. And then they explode [ http://heasarc.gsfc.nasa.gov/docs/snr.html ]. The resulting morass [ http://antwrp.gsfc.nasa.gov/apod/ap020424.html ] is often as beautiful as it is complex. After tens of millions of years, the dust boils away, the gas gets swept away, and all that is left is a naked open cluster [ http://antwrp.gsfc.nasa.gov/apod/ap040222.html ] of stars. |
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In the Center of Reflection
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| Title |
In the Center of Reflection Nebula NGC 1333 |
| Explanation |
The dust is so thick in the center of NGC 1333 that you can hardly see the stars forming. Conversely, the very dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] clouds that hide the stars also reflects their optical light [ http://fuse.pha.jhu.edu/~wpb/spectroscopy/em_spec.html ], giving NGC 1333 [ http://www.robgendlerastropics.com/NGC1333text.html ]'s predominantly blue glow the general designation of a reflection nebula [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ]. A highly detailed image of the nebula, shown above [ http://www.noao.edu/image_gallery/html/im1037.html ], was taken recently by the Mayall 4-meter telescope [ http://www.noao.edu/outreach/kptour/mayall.html ] on Kitt Peak [ http://www.noao.edu/kpno/ ] in Arizona [ http://en.wikipedia.org/wiki/Arizona ], USA [ http://en.wikipedia.org/wiki/United_States ] and released to honor astronomer Stephen Strom [ http://www.noao.edu/outreach/press/pr07/pr0706.html ] on his retirement. Visible near the image top are vast blue regions of dust [ http://antwrp.gsfc.nasa.gov/apod/ap061211.html ] predominantly reflecting the light from bright massive stars [ http://antwrp.gsfc.nasa.gov/apod/ap060109.html ]. Visible in the thick central dust are not only newly formed stars but red jets [ http://antwrp.gsfc.nasa.gov/apod/ap070430.html ] and red-glowing gas energized by the light and winds [ http://www-spof.gsfc.nasa.gov/Education/wsolwind.html ] from recently formed young stars. The NGC 1333 [ http://adsabs.harvard.edu/abs/2002ApJ...580..959N ] nebula contains [ http://antwrp.gsfc.nasa.gov/apod/ap061006.html ] hundreds of newly formed stars that are less than one million years old. Reflection nebula [ http://en.wikipedia.org/wiki/Reflection_nebula ] NGC 1333 lies about 1,000 light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away toward the constellation of Perseus [ http://chandra.harvard.edu/photo/constellations/perseus.html ]. |
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NGC 2264: Stars, Dust, and G
…
| Title |
NGC 2264: Stars, Dust, and Gas |
| Explanation |
The nebula surrounding bright star S Mon is filled with dark dust and glowing gas. The strange shapes [ http://antwrp.gsfc.nasa.gov/apod/ap000924.html ] that haunt this star forming region originate from fine interstellar dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] reacting in complex ways [ http://antwrp.gsfc.nasa.gov/apod/ap981118.html ] to the energetic light and hot gas being expelled by the young stars. The above picture [ http://www.mso.anu.edu.au/~bessell/thumbnails/ ], in representative color [ http://www.atnf.csiro.au/pasa/17_2/bessell/paper/ ], isolates the northern part of a greater nebula designated NGC 2264 [ http://www.aao.gov.au/images/captions/aat014.html ], which lies about 2500 light-years [ http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980211a.html ] away and includes the Cone Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap960301.html ]. The blue glow directly surrounding S Mon [ http://www.seds.org/messier/xtra/ngc/n2264.html ] results from reflection [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ], where neighboring dust reflects light from the bright star. The more diffuse red glow results from emission [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ], where starlight ionizes hydrogen [ http://antwrp.gsfc.nasa.gov/apod/ap010113.html ] gas. Pink areas are lit by a combination of the two processes. A small group of stars surrounds S Mon [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993PASP..105..324P ], the brightest star in the picture and a star visible with the naked eye toward the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] of Monoceros [ http://www.hawastsoc.org/deepsky/mon/index.html ]. |
|
Spiral Galaxy NGC 7742
| Title |
Spiral Galaxy NGC 7742 |
| Explanation |
This might resemble [ http://oposite.stsci.edu/pubinfo/pr/1998/28/index.html ] a fried egg you've had for breakfast [ http://antwrp.gsfc.nasa.gov/apod/ap980320.html ], but it's actually much larger. In fact, ringed by blue-tinted star forming [ http://antwrp.gsfc.nasa.gov/apod/ap980701.html ] regions and faintly visible spiral arms [ http://antwrp.gsfc.nasa.gov/apod/ap000920.html ], the yolk-yellow center of this face-on spiral galaxy, NGC 7742, is about 3,000 light-years across. About 72 million light-years [ http://www.treasure-troves.com/astro/Light-Year.html ] away in the constellation Pegasus [ http://www.seds.org/Maps/Stars_en/Fig/pegasus.html ], NGC 7742 is known to be a Seyfert galaxy [ http://www.astro.soton.ac.uk/PH308/AGN/Seyferts.html ] - a type of active spiral galaxy [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/active_galaxies.html ] with a center or nucleus which is very bright at visible wavelengths [ http://amazing-space.stsci.edu/light/index.html ]. Across the spectrum, the tremendous brightness [ http://seds.lpl.arizona.edu/messier/more/m077_hst.html ] of Seyferts [ http://www.seds.org/~spider/spider/ScholarX/seyferts.html ] can change over periods of just days to months and galaxies like NGC 7742 are suspected of harboring massive black holes at their cores [ http://oposite.stsci.edu/pubinfo/pr/97/18.html ]. This beautiful color picture is courtesy of the Hubble Space Telescope Heritage Project [ http://heritage.stsci.edu/public/commonpages/subjectindex.html ]. |
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NGC 4755: A Jewel Box of Sta
…
| Title |
NGC 4755: A Jewel Box of Stars |
| Explanation |
The great variety of star colors in this open cluster [ http://www.seds.org/messier/open.html ] underlies its name: The Jewel Box [ http://www.seds.org/messier/xtra/ngc/n4755.html ]. One of the bright central stars is a red supergiant, in contrast to the many blue stars that surround it. The cluster [ http://adsabs.harvard.edu/cgi-bin/nph- bib_query?bibcode=1963MNRAS.126...11F ], also known as Kappa Crucis [ http://adsabs.harvard.edu/cgi-bin/nph- bib_query?bibcode=1984A%26AS...56..373D ] contains just over 100 stars, and is about 10 million years old. Open clusters [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] are younger, contain few stars, and contain a much higher fraction of blue stars than do globular clusters [ http://antwrp.gsfc.nasa.gov/apod/globular_clusters.html ]. This Jewel Box [ http://www.iucaa.ernet.in/~vam/akksem/clusters/ngc4755.html ] lies about 7500 light-years [ http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980211a.html ] away, so the light that we see today was emitted from the cluster before even the Great Pyramids [ http://www.pbs.org/wgbh/nova/pyramid/ ] in Egypt [ http://www.cia.gov/cia/publications/factbook/geos/eg.html ] were built. The Jewel Box, pictured above [ http://www.mso.anu.edu.au/~bessell/thumbnails/ ], spans about 20 light-years, and can be seen with binoculars towards the southern constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.ht ml ] of Crux [ http://www.astronomical.org/constellations/cru.html ]. |
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The Bubbling Cauldron of NGC
…
| Title |
The Bubbling Cauldron of NGC 3079 |
| Explanation |
Edge-on [ http://antwrp.gsfc.nasa.gov/apod/ap010510.html ] spiral galaxy NGC 3079 is a mere 50 million light-years away toward the constellation Ursa Major. Shown in this [ http://oposite.stsci.edu/pubinfo/PR/2001/28/ index.html ] stunning false-color Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] image, the galaxy's disk - composed of spectacular star clusters in winding spiral arms and dramatic dark lanes of dust - spans some [ http://heasarc.gsfc.nasa.gov/docs/cosmic/cosmic.html ] 70,000 light-years. Still, NGC 3079's [ http://oposite.stsci.edu/pubinfo/PR/2001/28/ fastfacts.html ] most eye-catching features are the pillars of gas which tower above a swirling cosmic cauldron of activity at the galaxy's center. Seen in the close-up inset at lower right, the pillars rise to a height of about 2,000 light-years and seem to lie on the surface of an immense bubble rising from the galactic core. Measurements indicate that the gaseous pillars are streaming away from the core at 6 million kilometers per hour. What makes [ http://oposite.stsci.edu/pubinfo/PR/2001/28/ faq.html ] this galaxy's cauldron bubble [ http://tech-two.mit.edu/Shakespeare/macbeth/ macbeth.4.1.html ]? Astronomers are exploring [ http://xxx.lanl.gov/abs/astro-ph/0101010 ] the possibility that the superbubble [ http://antwrp.gsfc.nasa.gov/apod/ap991130.html ] is formed by winds [ http://www.physics.unc.edu/~cecil/science.html ] from massive stars. If so, these massive stars were likely born all at once as the galactic center underwent a sudden burst [ http://antwrp.gsfc.nasa.gov/apod/ap010124.html ] of star formation. |
|
Spiral Galaxy NGC 3310 Acros
…
| Title |
Spiral Galaxy NGC 3310 Across the Visible |
| Explanation |
The party is still going on in spiral galaxy NGC 3310. Roughly 100 million years ago, NGC 3310 [ http://antwrp.gsfc.nasa.gov/apod/ap010117.html ] likely collided with a smaller galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap001102.html ] causing the large spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/spiral_galaxies.html ] to light up with a tremendous burst of star formation [ http://archive.ncsa.uiuc.edu/Cyberia/Bima/StarForm.html ]. The changing gravity during the collision created density waves [ http://fuse.pha.jhu.edu/~danforth/spiral/ ] that compressed existing clouds of gas and triggered the star-forming party [ http://antwrp.gsfc.nasa.gov/apod/ap010812.html ]. The above image [ http://heritage.stsci.edu/public/2001sep/table.html ] composite by the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] was used to find the ages of many of the resulting clusters [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] of stars. To the surprise of many, some of the clusters [ http://antwrp.gsfc.nasa.gov/apod/globular_clusters.html ] are quite young, indicating that starburst galaxies [ http://chandra.harvard.edu/xray_sources/starburst.html ] may remain in star-burst mode for quite some time. NGC 3310 [ http://home.cc.umanitoba.ca/~umnorri1/ngc3310intro.html ] spans about 50,000 light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ], lies about 50 million light years away, and is visible with a small telescope [ http://es.rice.edu/ES/humsoc/Galileo/Things/telescope.html ] towards the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] of Ursa Major [ http://www.astronomical.org/constellations/uma.html ]. |
|
NGC 6992: A Glimpse of the V
…
| Title |
NGC 6992: A Glimpse of the Veil |
| Explanation |
After 5,000 years, the gorgeous Veil Nebula [ http://www.astropix.com/HTML/E_SUM_N/VEIL.HTM ] is still turning heads. Cataloged as NGC 6992, these glowing filaments [ http://antwrp.gsfc.nasa.gov/apod/ap000426.html ] of interstellar shocked gas are part of a larger spherical supernova remnant [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ supernova_remnants.html ] known as the Cygnus Loop [ http://www.seds.org/billa/twn/cygnusx.html ] or the Veil Nebula -- expanding debris from a star which exploded [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/ supernovae.html ] over 5,000 years ago. This color digital image of a bit of the Veil [ http://www.galaxyimages.com/bitoveil2.html ] has been processed and enhanced to reveal stunning details in the diaphanous cosmic cloud. Seen from our perspective against a rich Milky Way star field, the Veil Nebula is now known [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query? bibcode=1999AJ....118..942B&db_key=AST&high=3899d8d98207083 ] to lie some 1,400 light-years away toward the constellation Cygnus [ http://www.astro.wisc.edu/~dolan/constellations/ constellations/Cygnus.html ]. At that distance, witnesses [ http://www.wam.umd.edu/~tlaloc/archastro/ ] to the original stellar explosion would have seen a star in the heavens [ http://www.att.virtualclassroom.org/vc99/vc_04/ mainindex.html ] increase in brightness to about -8 magnitude [ http://www.projectpluto.com/ manual/app_g.htm ], roughly corresponding to the brightness of the crescent Moon [ http://antwrp.gsfc.nasa.gov/apod/ap010809.html ]. |
|
Emission and Reflection in N
…
| Title |
Emission and Reflection in NGC 6559 |
| Explanation |
Bright gas and dark dust permeate the space between stars in a nebula known as NGC 6559 [ http://robgendler.astrodigitals.com/6559.html ]. The gas, primarily hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ], is responsible for the diffuse red glow of the emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ]. As energetic light from neighboring stars ionizes interstellar hydrogen [ http://antwrp.gsfc.nasa.gov/apod/ap010113.html ], protons [ http://www.neutron.anl.gov/hyper-physics/proton.html ] and electrons [ http://www.aip.org/history/electron/ ] recombine to emit light [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] of very specific colors [ http://csep10.phys.utk.edu/astr162/lect/light/absorption.html ], including the red [ http://antwrp.gsfc.nasa.gov/apod/ap010214.html ] hue observed. Small dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] particles reflect blue starlight efficiently and so creates the blue reflection nebulosity [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ] seen near two of the bright stars. Dust [ http://nedwww.ipac.caltech.edu/level5/Mathis/Mathis9.html ] also absorbs visible light, causing the dark clouds [ http://antwrp.gsfc.nasa.gov/apod/ap010923.html ] and filaments [ http://antwrp.gsfc.nasa.gov/apod/ap990919.html ] visible. NGC 6559 [ http://www.aao.gov.au/images/captions/uks003.html ] lies about 5000 light-years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away toward the constellation of Sagittarius [ http://www.astronomical.org/constellations/sgr.html ]. |
|
Supernova Factory NGC 2770
| Title |
Supernova Factory NGC 2770 |
| Explanation |
The stellar explosions known as supernovae are [ http://en.wikipedia.org/wiki/Supernova] among the most powerful events [ http://antwrp.gsfc.nasa.gov/apod/ap990515.html ] in the universe. Triggered by the collapsing core of a massive star or the nuclear demise of a white dwarf, supernovae occur [ http://www.rochesterastronomy.org/SNIMAGES/ ] in average spiral galaxies only about once every century. But the remarkable spiral galaxy NGC 2770 has lately produced more than its fair share. Two still bright supernovae and the location of a third, originally spotted in 1999 but now faded from view, are indicated in this image of the edge-on spiral. All three supernovae are now thought to be of the core-collapse variety, but the most recent of the trio, SN2008D [ http://grad40.as.utexas.edu/ grblog.php?view-burst&GRB=080109A ], was first detected [ http://www.astronomerstelegram.org/?read=1353 ] by the Swift satellite [ http://swift.gsfc.nasa.gov/docs/swift/swiftsc.html ] at more extreme energies as an X-ray flash [ http://chandra.harvard.edu/press/03_releases/ press_091103.html ] (XRF) or possibly a low-energy version of a gamma-ray burst [ http://www.npr.org/templates/story/ story.php?storyId=4679036 ] on January 9th. Located a mere [ http://www.pbs.org/wgbh/nova/gamma/milkyway.html ] 90 million light-years away in the northern constellation Lynx, NGC 2770 is now the closest galaxy known to host such a powerful supernova event [ http://antwrp.gsfc.nasa.gov/apod/ap020228.html ]. |
|
Oddities of Star Cluster NGC
…
| Title |
Oddities of Star Cluster NGC 6397 |
| Explanation |
One of these stars is blinking. This star [ http://hubble.esa.int/hubble/gallery/new_searchresult.cfm?ooid=29458&imgid=12986 ], a member of globular cluster [ http://antwrp.gsfc.nasa.gov/apod/globular_clusters.html ] NGC 6397, is noteworthy not just because it blinks, but because it blinks so fast and because its companion star is so atypical. Speculation holds [ http://hubble.esa.int/hubble/news/newsrelease.cfm?oid=29454 ] that this might be a neutron star [ http://www.astro.umd.edu/~miller/nstar.html ] spun up to a rate of 274 rotations each second by the bloated red star [ http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/971016.html ] it orbits. Matter gravitationally pulled from the bloated star likely orbits [ http://antwrp.gsfc.nasa.gov/apod/ap010508.html ] the millisecond pulsar [ http://www.livingreviews.org/Articles/Volume1/1998-10lorimer/ ], making it spin faster when it crashes onto the surface. The odd system might have resulted when the neutron star [ http://antwrp.gsfc.nasa.gov/apod/ap981128.html ] captured a normal star after a near collision near the globular cluster [ http://www.seds.org/messier/glob.html ]'s dense center. Other collisions near the center of NGC 6397 [ http://antwrp.gsfc.nasa.gov/apod/ap000622.html ] are thought to have produced other oddities -- blue straggler stars [ http://antwrp.gsfc.nasa.gov/apod/ap971104.html ]. The Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] took the above image [ http://hubble.esa.int/hubble/gallery/new_searchresult.cfm?ooid=29460&imgid=12988 ] of the colorful globular cluster [ http://www.seds.org/messier/xtra/ngc/n6397.html ]. |
|
Galaxy NGC 4388 Expels Huge
…
| Title |
Galaxy NGC 4388 Expels Huge Gas Cloud |
| Explanation |
Why are huge clouds of gas billowing from spiral galaxy NGC 4388? The extent of the gas clouds, over 100,000 light-years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ], was unexpected before the Subaru Telescope [ http://www.naoj.org/Introduction/outline.html ] took the above image [ http://www.subaru.naoj.org/Latestnews/200204/NGC4388/index.html ]. NGC 4388 has a bright energetic nucleus and so is classified as an active galaxy [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/active_galaxies.html ]. The spiral [ http://antwrp.gsfc.nasa.gov/apod/spiral_galaxies.html ], relatively close by at 60 million light years, is a member of the nearest major cluster of galaxies [ http://www.seds.org/messier/gal_clus.html ]: the Virgo Cluster [ http://antwrp.gsfc.nasa.gov/apod/ap000220.html ]. One hypothesis [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002ApJ...567..118Y ] holds that the gas was stripped away as NGC 4388 [ http://www.seds.org/~spider/ngc/ngc.cgi?4388 ] made its way through the intergalactic medium of the Virgo Cluster [ http://antwrp.gsfc.nasa.gov/apod/ap960419.html ]. A competing hypothesis holds that the gas is all that remains of a smaller galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap991003.html ] that was gravitationally deconstructed [ http://antwrp.gsfc.nasa.gov/apod/ap001102.html ] by the larger NGC 4388. Further observations may better determine NGC 4388 [ http://www.pa.uky.edu/~shlosman/gals/SEYFERT/HTML_PAGES/n4388.html ]'s past and likely contribute to a better understanding of how galaxies evolve inside massive clusters [ http://www.astr.ua.edu/white/mug/cluster/clusters.html ]. |
|
NGC 2266: Old Cluster in the
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| Title |
NGC 2266: Old Cluster in the New General Catalog |
| Explanation |
The New General Catalog [ http://www.ngcic.org/ ] of star clusters and nebulae really isn't so new. In fact, it was published in 1888 [ http://www.ngcic.org/ngciccat.htm ] - an attempt by J. L. E. Dreyer [ http://star.arm.ac.uk/history/dreyer.html ] to consolidate the work of astronomers William [ http://www.seds.org/messier/xtra/similar/ herschel.html ], Caroline [ http://starchild.gsfc.nasa.gov/docs/StarChild/shadow/ whos_who_level2/herschel.html ], and John [ http://www-groups.dcs.st-and.ac.uk/~history/ Mathematicians/Herschel.html ] Herschel along with others into a useful single, complete catalog of astronomical discoveries and measurements [ http://www.seds.org/messier/xtra/history/ deepskyd.html ]. Dreyer's work was successful and is still important today as this famous catalog continues [ http://www.ngcic.org/history.htm ] to lend its "NGC" to bright clusters, galaxies, and nebulae. Take for example this star cluster known as NGC 2266 (item number 2,266 in the NGC compilation). It lies about 10,000 light-years distant in the constellation Gemini and represents an open or galactic cluster [ http://antwrp.gsfc.nasa.gov/apod/ap990305.html ]. With an age of about 1 billion years, NGC 2266 is old for a galactic cluster. Its evolved red giant stars [ http://antwrp.gsfc.nasa.gov/apod/ap990312.html ] are readily apparent in this gorgeous [ http://www.allthesky.com/clusters/n2266.html ] three-color [ http://www.allthesky.com/articles/ imagecolor.html ] image. |
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NGC 4697: X-Rays from an Ell
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| Title |
NGC 4697: X-Rays from an Elliptical Galaxy |
| Explanation |
The many bright, point-like sources in this Chandra Observatory x-ray image [ http://chandra.harvard.edu/photo/2002/1140/index.html ] lie within NGC 4697, an elliptical galaxy some 40 million light-years away towards Virgo [ http://www.seds.org/Maps/Stars_en/ Fig/virgo.html ]. Like other normal elliptical galaxies [ http://www.star.le.ac.uk/edu/galaxies/ellipticals.html ], NGC 4697 is a spherical ensemble of mainly older, fainter, low mass stars, with little star forming gas and dust compared to spiral galaxies. But the luminous x-ray [ http://chandra.harvard.edu/photo/ false_color.html ] sources in the Chandra image indicate that NGC 4697 had a wilder youth [ http://chandra.harvard.edu/press/02_releases/ press_060402.html ]. Powering the x-ray sources [ http://imagine.gsfc.nasa.gov/docs/science/ know_l1/history1_xray.html ] are neutron stars and black holes in binary star systems [ http://heasarc.gsfc.nasa.gov/docs/binary.html ], where x-rays are generated as matter from a more ordinary companion star falls in to these bizarre, compact objects. Since neutron stars [ http://www.astro.umd.edu/~miller/nstar.html ] and black holes [ http://antwrp.gsfc.nasa.gov/apod/ap010119.html ] are the endpoints in the lives of massive stars, NGC 4697 must have had many bright, massive stars in its past. An exceptionally large number of NGC 4697's x-ray binaries are found in the galaxy's globular star clusters, suggesting that dense star clusters [ http://antwrp.gsfc.nasa.gov/apod/ap010920.html ] are a good place for neutron stars and black holes [ http://antwrp.gsfc.nasa.gov/ htmltest/rjn_bht.html ] to capture a companion. Stellar winds and [ http://antwrp.gsfc.nasa.gov/apod/ap011019.html ] supernovae explosions of massive stars could also have produced the hot gas responsible for this galaxy's diffuse x-ray glow. |
|
Interstellar Dust Bunnies of
…
| Title |
Interstellar Dust Bunnies of NGC 891 |
| Explanation |
What is going on in NGC 891 [ http://antwrp.gsfc.nasa.gov/apod/ap970228.html ]? This galaxy appeared previously to be very similar to our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap000130.html ]: a spiral galaxy [ http://www.astr.ua.edu/goodies/data_resources/galaxies.text ] seen nearly edge-on. However, recent [ http://www.cfht.hawaii.edu/HawaiianStarlight/English/Poster-NGC891.html ] high-resolution images [ http://antwrp.gsfc.nasa.gov/apod/ap990919.html ] of NGC 891 [ http://www.seds.org/messier/xtra/ngc/n0891.html ]'s dust show unusual filamentary patterns extending well away from its Galactic disk. This interstellar dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] was probably thrown out of the galactic disk toward the halo [ http://www.eso.org/outreach/press-rel/pr-1999/pr-04-99.html ] by stellar supernovae explosions [ http://heasarc.gsfc.nasa.gov/docs/snr.html ]. Because dust is so fragile, its appearance after surviving disk expulsion can be very telling [ http://antwrp.gsfc.nasa.gov/apod/ap020703.html http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000A%26A...362..138P ]. Newly discovered phenomena, however, sometimes appear so complex [ http://antwrp.gsfc.nasa.gov/apod/ap980310.html ] that more questions are raised than are answered. |
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NGC 1569: Heavy Elements fro
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| Title |
NGC 1569: Heavy Elements from a Small Galaxy |
| Explanation |
For astronomers, elements other than hydrogen [ http://antwrp.gsfc.nasa.gov/apod/ap010113.html ] and helium [ http://antwrp.gsfc.nasa.gov/apod/ap010120.html ] are sometimes considered to be simply "heavy elements". It's understandable really, because even lumped all together heavy elements make up an exceedingly small fraction [ http://csep10.phys.utk.edu/astr162/lect/sun/ composition.html ] of the Universe. Still, heavy elements can profoundly influence galaxy and star formation ... not to mention [ http://www.europhysicsnews.com/full/14/article1/ article1.html ] the formation of planets and people. In this tantalizing [ http://chandra.harvard.edu/photo/2002/1060/index.html ] false-color x-ray image from the orbiting Chandra Observatory [ http://chandra.harvard.edu/about/whereis.html ], small dwarf galaxy NGC 1569 [ http://www.seds.org/~spider/ngc/ngc.cgi?1569 ] is surrounded by x-ray emitting [ http://chandra.harvard.edu/xray_astro/ ] clouds of gas thousands of light-years across. The gas has recently been observed [ http://arXiv.org/abs/astro-ph/0203513 ] to contain significant concentrations of astronomers' heavy elements such as oxygen, silicon, and magnesium, supporting the idea that dwarf galaxies, the most common type of galaxy in the Universe [ http://www.anzwers.org/free/ universe/galgrps.html ], are largely responsible for heavy elements in intergalactic space. A mere 7 million light-years distant toward the long-necked [ http://www.nature-wildlife.com/girtxt.htm ] constellation Camelopardalis [ http://www.dibonsmith.com/cam_con.htm ], NGC 1569 has undergone a recent burst of star formation and stellar supernova explosions [ http://curious.astro.cornell.edu/ supernovae.php ]. The furious cosmic activity [ http://heasarc.gsfc.nasa.gov/docs/xmm_lc/edu/ lessons/background-lifecycles.html ] has heated the expanding gas clouds to temperatures of millions of degrees while enriching them with newly synthesized [ http://antwrp.gsfc.nasa.gov/apod/ap011026.html ] heavy elements. |
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Nearby Spiral Galaxy NGC 494
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| Title |
Nearby Spiral Galaxy NGC 4945 |
| Explanation |
For such a close galaxy, NGC 4945 is easy to miss. NGC 4945 [ http://www.ast.cam.ac.uk/AAO/images/captions/aat101.html ] is a spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap980525.html ] in the Centaurus Group of galaxies, located only six times farther away than the prominent Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap991114.html ]. The thin disk galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap020703.html ] is oriented nearly edge-on, however, and shrouded in dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ]. Therefore galaxy-gazers searching the southern constellation of Centaurus [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Centaurus.html ] need a telescope to see it. The above picture [ http://www.eso.org/outreach/press-rel/pr-1999/phot-18-99.html ] was taken with a large telescope [ http://www.ls.eso.org/lasilla/Telescopes/2p2T/E2p2M/ ] testing a new wide-angle, high-resolution CCD camera [ http://www.ls.eso.org/lasilla/Telescopes/2p2T/E2p2M/WFI/ ]. Most of the spots scattered about the frame [ http://www.eso.org/outreach/epr/posters/ ] are foreground stars in our own Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ], but some spots are globular clusters [ http://antwrp.gsfc.nasa.gov/apod/globular_clusters.html ] orbiting the distant galaxy. NGC 4945 [ http://astro.ph.unimelb.edu.au/central/images/mbrown/ngc4945.html ] is thought to be quite similar to our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap971229.html ]. X-ray [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] observations reveal, however, that NGC 4945 has an unusual, energetic, Seyfert [ http://antwrp.gsfc.nasa.gov/apod/ap010701.html ] 2 nucleus that might house a large black hole [ http://antwrp.gsfc.nasa.gov/apod/ap960911.html ]. |
|
Giant Emission Nebula NGC 36
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| Title |
Giant Emission Nebula NGC 3603 in Infrared |
| Explanation |
NGC 3603 is the largest region of glowing gas in our Milky Way galaxy [ http://adc.gsfc.nasa.gov/mw/mmw_edu.html ]. Spanning over 20 light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] across, the giant emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] (HII region) is home to a massive star cluster [ http://antwrp.gsfc.nasa.gov/apod/ap010124.html ], thick dust pillars [ http://antwrp.gsfc.nasa.gov/apod/ap990604.html ], and a star about to explode [ http://antwrp.gsfc.nasa.gov/apod/ap011027.html ]. NGC 3603 was captured above in infrared light [ http://www.ipac.caltech.edu/Outreach/Edu/infrared.html ] by a Two Micron All Sky Survey [ http://www.ipac.caltech.edu/2mass/overview/about2mass.html ] (2MASS) telescope. The young star cluster near the center heats the region's mostly hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ] gas. Many stars in the cluster are estimated [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001RMxAA..37...39T ] to be about one million years old, much less than the five billion-year age of our Sun [ http://www.nineplanets.org/sol.html ]. NGC 3603 [ http://www.ipac.caltech.edu/2mass/gallery/powcap9.html#ngc3603 ] lies approximately 20,000 light years away toward the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] of Carina [ http://www.astronomical.org/constellations/car.html ]. |
|
Shell Game in NGC 300
| Title |
Shell Game in NGC 300 |
| Explanation |
Featured in color in yesterday's [ http://antwrp.gsfc.nasa.gov/apod/ap020821.html ] episode, big, beautiful, face-on spiral galaxy NGC 300 is seen here [ http://www.eso.org/outreach/press-rel/pr-2002/ phot-18-02.html#phot-18c-02 ] through a narrow filter that transmits only the red light of hydrogen atoms [ http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch6/ bohr.html#hydrogen ]. Ionized by energetic starlight, a hydrogen atom emits the characteristic red H-alpha [ http://antwrp.gsfc.nasa.gov/apod/ap980828.html ] light as its single [ http://antwrp.gsfc.nasa.gov/apod/lib/lament.html ] electron is recaptured and transitions to lower energy [ http://csep10.phys.utk.edu/astr162/lect/light/ absorption.html ] states. As a result, this image of NGC 300 [ http://www.vuw.ac.nz/~mackie/ atlas/index/n300/n300.html ] is dominated by regions filled with massive, young stars and shell-shaped [ http://antwrp.gsfc.nasa.gov/apod/ap020613.html ] clouds of hydrogen gas hundreds to thousands of light-years across. Formed in groups called OB associations [ http://www.mpifr-bonn.mpg.de/staff/ tpreibis/usco.html ], the stars are likely only a few million years young [ http://starchild.gsfc.nasa.gov/docs/ StarChild/StarChild.html ]. The hydrogen clouds are glowing nebulae or HII regions [ http://astrosun.tn.cornell.edu/courses/astro201/ stromgren_sphere.htm ] that have been sculpted by the strong stellar winds and ultraviolet radiation. While picking out your favorite cosmic shell [ http://antwrp.gsfc.nasa.gov/apod/ap990410.html ] in this picture, don't be misled by the relatively bright foreground stars located in our own Milky Way galaxy. They often show spikes [ http://antwrp.gsfc.nasa.gov/apod/ap010415.html ] and rings caused by the telescope and camera system. |
|
NGC 2359: Thor's Helmet
| Title |
NGC 2359: Thor's Helmet |
| Explanation |
NGC 2359 is a striking emission nebula [ http://www.noao.edu/outreach/aop/observers/ n2359.html ] with an impressive popular name - Thor's [ http://www.pantheon.org/ articles/t/thor.html ] Helmet. Sure, its suggestive winged appearance might lead some to refer to it as the "duck nebula", but if you were a nebula which name would you choose? By any name NGC 2359 [ http://www.kopernik.org/images/archive/ n2359.htm ] is a bubble-like nebula some 30 light-years across, blown by energetic winds from an extremely hot star [ http://www.star.ucl.ac.uk/~hsn/ ] seen near the center and classified as a Wolf-Rayet star. Wolf-Rayet stars [ http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/ 980603a.html ] are rare massive blue giants which develop stellar winds with speeds of millions of kilometers per hour. Interactions with [ http://antwrp.gsfc.nasa.gov/apod/ap970102.html ] a nearby large molecular cloud are thought to have contributed to this nebula's more complex shape and curved bow-shock [ http://antwrp.gsfc.nasa.gov/apod/ap010221.html ] structures. NGC 2359 is about 15,000 light-years distant toward the constellation [ http://www.hawastsoc.org/deepsky/cma/ ] Canis Major [ http://www.internal.org/view_poem.phtml?poemID=115 ]. |
|
Open Star Clusters M35 and N
…
| Title |
Open Star Clusters M35 and NGC 2158 |
| Explanation |
Open clusters of stars can be near or far, young or old, and diffuse or compact. Open clusters [ http://www.seds.org/messier/open.html ] may contain from 100 to 10,000 stars, all of which formed at nearly the same time. Bright blue stars [ http://antwrp.gsfc.nasa.gov/apod/ap021201.html ] frequently distinguish younger open clusters. M35 [ http://www.seds.org/messier/m/m035.html ], pictured above [ http://www.noao.edu/image_gallery/html/im0794.html ] on the upper left, is a relatively nearby at 2800 light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] distant, relatively young at 150 million years old, and relatively diffuse, with about 2500 stars spread out over a volume 30 light years across. An older and more compact open cluster, NGC 2158 [ http://www.sciencenet.org.uk/astron/const/Gemini/ngc2158.html ], is visible above [ http://www.noao.edu/image_gallery/html/im0794.html ] on the lower right. NGC 2158 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.332..705C ] is four times more distant that M35 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...546.1006B ], over 10 times older, and much more compact as it contains many more stars in roughly the same volume of space. NGC 2158's bright blue stars have self-destructed [ http://heasarc.gsfc.nasa.gov/docs/snr.html ], leaving cluster light to be dominated by older and yellower star [ http://antwrp.gsfc.nasa.gov/apod/ap000815.html ]s. Both clusters are visible toward the constellation [ http://www.adlerplanetarium.org/history/exhibits/constellations/timeline.html ] of Gemini [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Gemini.html ] -- M35 with binoculars and NGC 2158 with a small telescope. |
|
NGC 6960: The Witch's Broom
…
| Title |
NGC 6960: The Witch's Broom Nebula |
| Explanation |
Ten thousand years ago, before the dawn of recorded human history [ http://news.bbc.co.uk/hi/english/sci/tech/newsid_334000/334517.stm ], a new light must suddenly have appeared in the night sky and faded after a few weeks. Today we know this light was an exploding star [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html ] and record the colorful expanding cloud as the Veil Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap010928.html ]. Pictured above [ http://starryscapes.com/nebula/ngc6960.html ] is the west end of the Veil Nebula [ http://www.astropix.com/HTML/E_SUM_N/VEIL.HTM ] known technically as NGC [ http://www.ngcic.com/dss/dss_images.htm ] 6960 but less formally as the Witch's Broom Nebula. The rampaging gas gains its colors by impacting and exciting existing [ http://www.seds.org/billa/twn/cygnusx.html ] nearby gas. The supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/supernova_remnants.html ] lies about 1400 light-years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away towards the constellation of Cygnus [ http://www.multimania.com/cdadfs/constellation/cygne/cygnus.htm ]. This Witch's Broom actually spans over three times the angular size [ http://imagine.gsfc.nasa.gov/YBA/HTCas-size/more-ang_size.html ] of the full Moon [ http://antwrp.gsfc.nasa.gov/apod/moon.html ]. The bright blue star 52 Cygnus [ http://www.seds.org/Maps/Stars_en/Fig/cygnus.html ] is visible with the unaided eye from a dark location but unrelated to the ancient supernova [ http://www.chapman.edu/oca/benet/intro_sn.htm ]. |
|
NGC 1700: Elliptical Galaxy
…
| Title |
NGC 1700: Elliptical Galaxy and Rotating Disk |
| Explanation |
In spiral galaxies, majestic [ http://antwrp.gsfc.nasa.gov/apod/ap021004.html ] winding arms of young stars and interstellar gas and dust rotate [ http://antwrp.gsfc.nasa.gov/apod/ap020125.html ] in a disk around a bulging galactic nucleus. Elliptical galaxies [ http://www.star.le.ac.uk/edu/galaxies/ellipticals.html ] seem to be simpler, randomly swarming with old stars and lacking gas and dust. So astronomers were excited to find [ http://www.ohiou.edu/researchnews/science/xray_disk.html ] that NGC 1700, a young elliptical galaxy about 160 million light-years away, shows evidence for a 90,000 light-year wide rotating disk of multi-million degree hot gas. The evidence comes from data recorded by the orbiting Chandra [ http://chandra.harvard.edu/about/tracking.html ] Observatory, whose sharp x-ray image of NGC 1700 [ http://chandra.harvard.edu/photo/2002/n1700/ index.html ] is seen above. Balancing gravity, the rotation of the x-ray hot disk [ http://heasarc.gsfc.nasa.gov/docs/objects/heapow/archive/ normal_galaxies/ngc1700_chandra.html ], the largest of its type yet discovered, gives the galaxy a pronounced boxy profile in this false-color picture. Theories about the origin [ http://xxx.lanl.gov/abs/astro-ph/0208379 ] of the disk suggest that NGC 1700 may be the result of a cosmic scale galactic merger [ http://antwrp.gsfc.nasa.gov/apod/ap021017.html ], perhaps between a spiral and elliptical galaxy. NGC 1700 is just visible with small telescopes toward the flowing constellation Eridanus [ http://www.hawastsoc.org/ deepsky/eri/ ]. |
|
The Heart in NGC 346
| Title |
The Heart in NGC 346 |
| Explanation |
Yes, it's Valentine's Day [ http://antwrp.gsfc.nasa.gov/apod/ap020214.html ] (!) and looking toward star cluster NGC 346 [ http://www.seds.org/~spider/ngc/ngc.cgi?346 ] in our neighboring galaxy the Small Magellanic Cloud [ http://www.seds.org/messier/xtra/ngc/smc.html ], astronomers have noted this heart-shaped cloud [ http://chandra.harvard.edu/photo/2003/ngc346/ index.html ] of hot, x-ray emitting gas in the cluster's central region. The false-color Chandra Observatory x-ray image also shows [ http://xxx.lanl.gov/abs/astro-ph/0212197 ] a strong x-ray source just above the heart-shaped cloud which corresponds to HD 5980, a remarkable, massive binary star system that lies within the cluster. HD 5980 [ http://heasarc.gsfc.nasa.gov/docs/objects/heapow/archive/stars/ hd5980_chandra.html ] has been known to undergo dramatic brightness variations, in 1994 briefly outshining all other stars in the Small Magellanic Cloud, and has been likened to the luminous, eruptive variable star Eta Carinae [ http://antwrp.gsfc.nasa.gov/apod/ap021010.html ] in our own Milky Way galaxy. At about 100 light-years across, NGC 346's [ http://www.asnsw.com/observing/clouds/tsmc5.htm ] heart-shaped cloud is probably the result of an ancient supernova explosion. Alternatively it may have been produced during past eruptions from the HD 5980 system, analogous to the nebula associated with Eta Carinae [ http://lheawww.gsfc.nasa.gov/users/corcoran/eta_car/ eta_car.html ]. |
|
NGC 253: The Sculptor Galaxy
| Title |
NGC 253: The Sculptor Galaxy |
| Explanation |
NGC 253 [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search?ngc+253 ] is not only one of the brightest spiral galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap980922.html ] visible, it is also one of the dustiest [ http://antwrp.gsfc.nasa.gov/apod/ap980116.html ]. Discovered in 1783 by Caroline Herschel [ http://history.math.csusb.edu/Mathematicians/Herschel_Caroline.html ] in the constellation of Sculptor [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Sculptor.html ], NGC 253 [ http://astro.nmsu.edu/~choopes/research.html ] lies only about ten million light-years distant. NGC 253 [ http://seds.lpl.arizona.edu/messier/xtra/ngc/n0253.html ] is the largest member of the Sculptor Group of Galaxies [ http://seds.lpl.arizona.edu/messier/xtra/ngc/sclgr.html ], the nearest group to our own Local Group of Galaxies [ http://seds.lpl.arizona.edu/messier/more/local.html ]. The dense dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] accompanies a high star formation [ http://antwrp.gsfc.nasa.gov/apod/ap020717.html ] rate, giving NGC 253 [ http://antwrp.gsfc.nasa.gov/apod/ap990121.html ] the designation of starburst galaxy [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...505..639E ]. Visible in the above photograph [ http://oposite.stsci.edu/pubinfo/pr/1998/42/a.html ] from the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] is the active central nucleus [ http://www.astr.ua.edu/keel/agn/text.html ], also known to be a bright source of X-rays [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#X-ray ] and gamma rays [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ]. |
|
NGC 281: Cluster, Clouds, an
…
| Title |
NGC 281: Cluster, Clouds, and Globules |
| Explanation |
NGC 281 [ http://www.seds.org/~spider/ngc/ngc.cgi?ngc281 ] is a busy workshop of star formation. Prominent features include a small open cluster [ http://antwrp.gsfc.nasa.gov/apod/ap010909.html ] of stars, a diffuse red-glowing emission nebula [ http://www.seds.org/messier/nebula.html ], large lanes of obscuring gas [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#hydrogen ] and dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ], and dense knots of dust and gas in which stars may still be forming. The open cluster [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] of stars IC 1590 visible around the center has formed only in the last few million years. The brightest member of this cluster is actually a multiple-star system [ http://antwrp.gsfc.nasa.gov/apod/ap970219.html ] shining light that helps ionize the nebula's gas, causing the red glow visible throughout. The lanes of dust [ http://antwrp.gsfc.nasa.gov/apod/ap980121.html ] visible below the center are likely homes of future star formation [ http://antwrp.gsfc.nasa.gov/apod/ap011125.html ]. Particularly striking in the above photograph [ http://www.cfht.hawaii.edu/HawaiianStarlight/AIOM/English/CFHT-Coelum- AIOM-Apr2003.html ] are the dark Bok globules [ http://antwrp.gsfc.nasa.gov/apod/ap030127.html ] visible against the bright nebula. Stars are surely forming there right now. The entire NGC 281 [ http://adsabs.harvard.edu/cgi-bin/nph- bib_query?bibcode=1996AAS...188.4206G ] system lies about 10 thousand light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] distant. |
|
NGC 1275: A Galactic Collisi
…
| Title |
NGC 1275: A Galactic Collision |
| Explanation |
In NGC 1275, one galaxy is slicing through another. The disk of the dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ]y spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/spiral_galaxies.html ] near the image center is cutting through a large elliptical galaxy [ http://www.seds.org/messier/elli.html ], visible predominantly on the lower left. Galaxies [ http://www.damtp.cam.ac.uk/user/gr/public/gal_class.html ] can change significantly during a collision [ http://csep10.phys.utk.edu/astr162/lect/galaxies/colliding.html ] like this, with gravitational tides [ http://burro.astr.cwru.edu/Academics/Astr221/Gravity/tides.html ] distorting [ http://antwrp.gsfc.nasa.gov/apod/ap001102.html ] each galaxy and gas clouds being compressed [ http://www.aoc.nrao.edu/~smyers/courses/astro12/L14.html ] and lighting up with new star formation [ http://antwrp.gsfc.nasa.gov/apod/ap020611.html ]. Galaxy collisions [ http://antwrp.gsfc.nasa.gov/apod/ap020506.html ] occur in slow motion to the human eye [ http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/V/Vision.html ], with a single pass taking as much as 100 million years. NGC 1275 [ http://heritage.stsci.edu/2003/14/caption.html ] is a member of the Perseus cluster of galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap980815.html ] that lies about 230 million light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away toward the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] of Perseus [ http://www.astronomical.org/constellations/per.html ]. Each galaxy spans about 50,000 light years across. The above picture [ http://heritage.stsci.edu/2003/14/index.html ] is a composite of images [ http://hubblesite.org/newscenter/archive/2003/14/ ] taken by the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] in 1995 and 2001. |
|
NGC 1818: Pick A Star
| Title |
NGC 1818: Pick A Star |
| Explanation |
This is NGC 1818 [ http://antwrp.gsfc.nasa.gov/apod/ap980307.html ], a youthful, glittering cluster of 20,000 stars residing in the Large Magellanic Cloud [ http://seds.lpl.arizona.edu/messier/xtra/ngc/lmc.html ], 180,000 light-years away. Pick a star. Any star. Astronomers might pick [ http://oposite.stsci.edu/pubinfo/pr/1998/16/ ] the unassuming bluish-white one (circled) which appears [ http://hubblesite.org/sci.d.tech/behind_the_pictures/ wacky_shape/index.shtml ] to be a hot newly formed white dwarf star. What makes it so interesting? The standard astronomical wisdom suggests that stars over 5 times as massive as the sun rapidly exhaust [ http://archive.ncsa.uiuc.edu/Cyberia/Bima/ StarDeath.html ] their nuclear fuel and end their lives in a spectacular supernova explosion [ http://antwrp.gsfc.nasa.gov/apod/ap030528.html ]. With less than this critical mass [ http://heasarc.gsfc.nasa.gov/docs/ xmm_lc/edu/lessons/background-lifecycles.html ] they evolve into red giants, pass through a relatively peaceful planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/ap020302.html ] phase, and calmly fade away as white dwarf stars [ http://antwrp.gsfc.nasa.gov/apod/ap000910.html ] like this one. Except that as a member of the NGC 1818 cluster, this new white dwarf would have evolved from a red giant star [ http://www.historyoftheuniverse.com/starold.html ] over 7.6 times as massive as the sun -- which should have exploded! Its discovery [ http://xxx.lanl.gov/abs/astro-ph/9802117 ] will likely force astronomers to revise the limiting mass estimate for supernovae upward. |
|
Spiral Galaxy NGC 253 Almost
…
| Title |
Spiral Galaxy NGC 253 Almost Sideways |
| Explanation |
NGC 253 is a normal spiral galaxy [ http://www.seds.org/messier/spir.html ] seen here almost sideways. It is the largest member of the Sculptor Group of Galaxies [ http://www.seds.org/messier/xtra/ngc/sclgr.html ], the nearest group [ http://csep10.phys.utk.edu/astr162/lect/gclusters/groups.html ] to our own Local Group [ http://csep10.phys.utk.edu/astr162/lect/gclusters/localg.html ] of Galaxies. NGC 253 [ http://antwrp.gsfc.nasa.gov/apod/ap030316.html ], pictured above [ http://www.cfht.hawaii.edu/HawaiianStarlight/AIOM/English/CFHT-Coelum-AIOM-May2003.html ], appears visually as one of the brightest spirals [ http://antwrp.gsfc.nasa.gov/apod/spiral_galaxies.html ] on the sky, and is easily visible in southern hemisphere [ http://antwrp.gsfc.nasa.gov/apod/ap021222.html ] with a good pair of binoculars [ http://www.birdwatching.com/optics/binoculars1.html#How%20Binoculars%20Work ]. The type Sc galaxy [ http://zebu.uoregon.edu/~js/ast123/lectures/lec13.html ] is about 10 million light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] distant. NGC 253 [ http://antwrp.gsfc.nasa.gov/apod/ap010607.html ] is considered a starburst galaxy [ http://chandra.harvard.edu/xray_sources/starburst.html ] because of high star formation rates and dense dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] clouds in its nucleus. The energetic nuclear region is seen to glow in X-ray [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#X-ray ] and gamma-ray [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] light. |
|
NGC 7293: The Helix Nebula
| Title |
NGC 7293: The Helix Nebula |
| Explanation |
Will our Sun [ http://www.nineplanets.org/sol.html ] look like this one day? The Helix Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap000828.html ] is the closest example of a planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html ] created at the end of the life of a Sun-like star. The outer gasses of the star expelled into space [ http://www.seds.org/messier/planetar.html ] appear from our vantage point as if we are looking down a helix [ http://mathworld.wolfram.com/Helix.html ]. The remnant central stellar core, destined to become a white dwarf star [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html ], glows in light so energetic [ http://imagers.gsfc.nasa.gov/ems/uv.html ] it causes the previously expelled gas to fluoresce [ http://www.exploratorium.edu/xref/exhibits/fluorescent_tube.html ]. The Helix Nebula [ http://www.seds.org/messier/xtra/ngc/n7293.html ], given a technical designation of NGC 7293 [ http://www.astro.uiuc.edu/~akspeck/evolved-stuff/nebulae/Helix/ ], lies about 650 light-years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] away towards the constellation [ http://www.emufarm.org/~cmbell/myth/myth.html ] of Aquarius [ http://www.astronomical.org/constellations/aqr.html ] and spans about 2.5 light-years. The above picture [ http://hubblesite.org/newscenter/archive/2003/11/ ] is a composite [ http://archive.stsci.edu/hst/helix/ ] of newly released images from the ACS [ http://acs.pha.jhu.edu/ ] instrument on the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] and wide-angle images from the Mosaic Camera on the WIYN [ http://www.noao.edu/wiyn/ ] 0.9-m Telescope [ http://www.noao.edu/dir/09m/description.html ] at Kitt Peak National Observatory [ http://www.noao.edu/kpno/ ]. A close-up [ http://antwrp.gsfc.nasa.gov/apod/ap020512.html ] of the inner edge of the Helix Nebula [ http://hubblesite.org/newscenter/archive/2003/11/fastfacts ] shows complex gas knots of unknown origin [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002ApJ...573L..55H ]. |
|
NGC 1068 and the X-Ray Flash
…
| Title |
NGC 1068 and the X-Ray Flashlight |
| Explanation |
At night [ http://antwrp.gsfc.nasa.gov/apod/ap030307.html ], tilting a flashlight up under your chin hides the glowing bulb from the direct view of your friends. Light from the bulb still reflects from your face though, and can give you a startling appearance. Spiral Galaxy NGC 1068 [ http://www.kopernik.org/images/archive/m77.htm ] may be playing a similar trick on a cosmic scale [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ active_galaxies.html ], hiding a central powerful source of x-rays -- likely a supermassive black hole [ http://chandra.harvard.edu/xray_sources/ blackholes_sm.html ] -- from direct view. X-rays are [ http://imagine.gsfc.nasa.gov/docs/features/exhibit/ xray_anniversary.html ] still scattered into our line-of-sight though, by a dense torus of material surrounding the black hole. The scenario is [ http://arxiv.org/abs/astro-ph/0211406 ] supported by x-ray data from the Chandra Observatory [ http://chandra.harvard.edu/resources/misc/ special_features.html ] combined with a Hubble Space Telescope optical image in this false-color composite [ http://chandra.harvard.edu/photo/2003/ngc1068/index.html ] picture. Optical data in red shows spiral structure across NGC 1068's inner 7 thousand light-years with the x-ray data overlaid in blue and green. A hot wind of gas streaming from the galaxy's core is seen as the broad swath of x-ray emission while material lit up [ http://chandra.harvard.edu/photo/2003/ngc1068/more.html ] by the hidden black hole source is within the central cloud of more intense x-rays. Also well known [ http://www.seds.org/messier/m/m077.html ] as M77, NGC 1068 [ http://antwrp.gsfc.nasa.gov/apod/ap960911.html ] lies a mere 50 million light-years away toward the constellation Cetus. |
|
Spiral Galaxy NGC 7742
| Title |
Spiral Galaxy NGC 7742 |
| Explanation |
This might resemble [ http://oposite.stsci.edu/pubinfo/pr/1998/28/index.html ] a fried egg you've had for breakfast [ http://antwrp.gsfc.nasa.gov/apod/ap980320.html ], but it's actually much larger. In fact, ringed by blue-tinted star forming [ http://antwrp.gsfc.nasa.gov/apod/ap980701.html ] regions and faintly visible spiral arms [ http://antwrp.gsfc.nasa.gov/apod/ap000920.html ], the yolk-yellow center of this face-on spiral galaxy, NGC 7742, is about 3,000 light-years across. About 72 million light-years [ http://www.treasure-troves.com/astro/ Light-Year.html ] away in the constellation Pegasus [ http://www.seds.org/Maps/Stars_en/Fig/ pegasus.html ], NGC 7742 is known to be a Seyfert galaxy [ http://www.seds.org/~spider/spider/ScholarX/ seyferts.html ] - a type of active spiral galaxy [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ active_galaxies.html ] with a center or nucleus which is very bright at visible wavelengths [ http://amazing-space.stsci.edu/light/index.html ]. Across the spectrum, the tremendous brightness [ http://seds.lpl.arizona.edu/messier/more/ m077_hst.html ] of Seyferts can change over periods of just days to months and galaxies like NGC 7742 are suspected of harboring massive black holes at their cores [ http://oposite.stsci.edu/pubinfo/pr/97/18.html ]. This beautiful color picture is courtesy of the Hubble Space Telescope Heritage Project [ http://heritage.stsci.edu/public/commonpages/ subjectindex.html ]. |
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Blue Stragglers in NGC 6397
| Title |
Blue Stragglers in NGC 6397 |
| Explanation |
In our neck of the Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ] stars are too far apart [ http://antwrp.gsfc.nasa.gov/apod/ap991211.html ] to be in danger of colliding, but in the dense cores of globular star clusters [ http://antwrp.gsfc.nasa.gov/apod/ap010422.html ] star collisions may be relatively common. In fact, researchers have evidence [ http://www.aas.org/publications/baas/v32n2/aas196/ 265.htm ] that the closely spaced blue stars near the center of the above image [ http://heritage.stsci.edu/2003/21/caption.html ] taken by the orbiting Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] were formed when stars directly collided. Pictured is the central region of NGC 6397 [ http://www.seds.org/messier/xtra/ngc/n6397.html ], a globular cluster [ http://www.seds.org/messier/glob.html ] about 6,000 light-years distant, whose stars [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ stars.html ] all formed at about the same time. NGC 6397's [ http://dibonsmith.com/ngc6397.htm ] massive stars have long since evolved off the main sequence [ http://observe.arc.nasa.gov/nasa/space/stellardeath/stellardeath_1ai.html ], exhausting their central supplies of nuclear fuel [ http://zebu.uoregon.edu/textbook/energygen.html ]. This should leave the cluster with only old low mass stars, faint red main sequence stars and brighter blue and red giants [ http://www.historyoftheuniverse.com/starold.html ]. However, spectroscopic data show that the indicated stars, descriptively dubbed blue stragglers [ http://antwrp.gsfc.nasa.gov/apod/ap971104.html ], are clearly main sequence stars which are too blue and too massive to still be there. Suggestively [ http://antwrp.gsfc.nasa.gov/apod/ap000622.html ] the stragglers appear to be two and occasionally three times as massive as the lower mass cluster stars otherwise present, supporting evidence [ http://heritage.stsci.edu/2003/21/supplemental.html ] for their formation from two and even three star collisions. |
|
NGC 6888: X-Rays in the Wind
| Title |
NGC 6888: X-Rays in the Wind |
| Explanation |
NGC 6888, also known as the Crescent Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap030415.html ], is a cosmic bubble of interstellar gas about 25 light-years across. Created by winds [ http://www.peripatus.gen.nz/Astronomy/SteWin.html ] from the bright, massive star seen near the center of this composite image, the shocked filaments of gas glowing at optical wavelengths are represented in green and yellowish hues. X-ray image data [ http://chandra.harvard.edu/photo/2003/ngc6888/ ] from a portion of the nebula viewed by the Chandra Observatory is overlaid in blue. Such isolated stellar wind bubbles [ http://arxiv.org/abs/astro-ph/0310311 ] are not usually seen to produce energetic x-rays [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/ history1_xray.html ], which require heating gas to a million degrees celsius. Still, NGC 6888 seems to have accomplished this as slow moving winds from the central star's initial transition to a red supergiant [ http://hyperphysics.phy-astr.gsu.edu/hbase/astro/ redsup.html ] were overtaken and rammed by faster winds driven by the intense radiation from the star's exposed inner layers. Burning fuel [ http://www.sciam.com/askexpert_question.cfm? articleID=000607EA-5B27-1E56-A98A809EC5880105 ] at a prodigious rate and near the end of its stellar life [ http://heasarc.gsfc.nasa.gov/docs/xmm_lc/edu/lessons/ background-lifecycles.html ], NGC 6888's central star should ultimately go out with a bang, creating a supernova explosion in 100,000 years or so. NGC 6888 is about 5,000 light-years close, toward the constellation Cygnus [ http://www.astronomical.org/constellations/cyg.html ]. |
|
Spiral Galaxy NGC 3982 Befor
…
| Title |
Spiral Galaxy NGC 3982 Before Supernova |
| Explanation |
What do stars look like just before they explode? To find out, astronomers [ http://www.iau.org/ ] are taking detailed images of nearby galaxies now, before any supernova is visible. Hopefully, a star in one of the hundreds of high resolution galaxy images [ http://hubble.esa.int/science-e/www/object/index.cfm?fobjectid=33858 ] will explode in the coming years. If so, archival images like that taken above by the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] can be inspected to find what the star looked like originally. This information is likely important for better understanding of how and why supernovas occur, as well as why some supernovas [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html ] appear brighter than others. Pictured above [ http://hubble.esa.int/science-e/www/object/index.cfm?fobjectid=33854 ], beautiful spiral galaxy [ http://www.seds.org/messier/spir.html ] NGC 3982 displays numerous spiral arms [ http://antwrp.gsfc.nasa.gov/apod/ap020125.html ] filled with bright stars, blue star clusters [ http://antwrp.gsfc.nasa.gov/apod/ap030122.html ], and dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] lanes. NGC 3982 [ http://www.seds.org/~spider/spider/Misc/n3982.html ], which spans about 30,000 light years, lies about 60 million light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] from Earth and can be seen with a small telescope toward the constellation of Ursa Major [ http://www.astronomical.org/constellations/uma.html ]. |
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Open Star Clusters M35 and N
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| Title |
Open Star Clusters M35 and NGC 2158 |
| Explanation |
Open clusters of stars can be near or far, young or old, and diffuse or compact. Open clusters [ http://www.seds.org/messier/open.html ] may contain from 100 to 10,000 stars, all of which formed at nearly the same time. Bright blue stars [ http://antwrp.gsfc.nasa.gov/apod/ap021201.html ] frequently distinguish younger open clusters. M35 [ http://www.seds.org/messier/m/m035.html ], pictured above [ http://www.cfht.hawaii.edu/HawaiianStarlight/AIOM/English/CFHT-Coelum-AIOM.html ] on the upper left, is relatively nearby at 2800 light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] distant, relatively young at 150 million years old, and relatively diffuse, with about 2500 stars spread out over a volume 30 light years across. An older and more compact open cluster, NGC 2158 [ http://www.seds.org/~spider/spider/MWGC/n2158.html ], is visible above [ http://www.cfht.hawaii.edu/HawaiianStarlight/AIOM/English/CFHT-Coelum-AIOM.html ] on the lower right. NGC 2158 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002MNRAS.332..705C ] is four times more distant that M35 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...546.1006B ], over 10 times older, and much more compact as it contains many more stars in roughly the same volume of space. NGC 2158 [ http://antwrp.gsfc.nasa.gov/apod/ap021129.html ]'s bright blue stars have self-destructed [ http://heasarc.gsfc.nasa.gov/docs/snr.html ], leaving cluster light to be dominated by older and yellower star [ http://antwrp.gsfc.nasa.gov/apod/ap000815.html ]s. Both clusters are visible toward the constellation [ http://www.adlerplanetarium.org/history/exhibits/constellations/ ] of Gemini [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Gemini.html ] -- M35 with binoculars and NGC 2158 with a small telescope. |
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NGC 869 & NGC 884: A Double
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| Title |
NGC 869 & NGC 884: A Double Open Cluster |
| Explanation |
Most star clusters are singularly impressive. Open clusters [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] NGC 869 and NGC 884, however, are doubly impressive. Also known as "h and chi Persei", this unusual double cluster [ http://www.seds.org/messier/xtra/ngc/n0869.html ], shown above, is bright enough to be seen from a dark location without even binoculars. Although their discovery surely predates written history [ http://news.bbc.co.uk/1/hi/sci/tech/334517.stm ], the Greek astronomer Hipparchus [ http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Hipparchus.html ] notably cataloged the "double cluster [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26A...345..505K ]". The clusters are over 7000 light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] distant toward the constellation [ http://www.cogsci.princeton.edu/cgi-bin/webwn?stage=1&word=constellation ] of Perseus [ http://www.astronomical.org/constellations/per.html ], but are separated by only hundreds of light years. |
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NGC 604: Giant Stellar Nurse
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| Title |
NGC 604: Giant Stellar Nursery |
| Explanation |
Stars are sometimes born in the midst of chaos. About 3 million years ago in the nearby galaxy M33 [ http://antwrp.gsfc.nasa.gov/apod/ap030924.html ], a large cloud of gas spawned dense internal knots which gravitationally collapsed to form stars. NGC 604 [ http://www.seds.org/messier/more/m033_n604.html ] was so large, however, it could form enough stars to make a globular cluster [ http://antwrp.gsfc.nasa.gov/apod/globular_clusters.html ]. Many young stars from this cloud are visible [ http://hubblesite.org/newscenter/newsdesk/archive/releases/2003/30/image/ ] in the above image [ http://heritage.stsci.edu/2003/30/caption.html ] from the Hubble Space Telescope [ http://www.stsci.edu/hst/HST_overview/ ], along with what is left of the initial gas cloud [ http://heritage.stsci.edu/2003/30/supplemental.html ]. Some stars were so massive they have already evolved and exploded in a supernova [ http://heasarc.gsfc.nasa.gov/docs/snr.html ]. The brightest stars [ http://antwrp.gsfc.nasa.gov/apod/ap021102.html ] that are left emit light so energetic that they create one of the largest cloud of ionized hydrogen [ http://antwrp.gsfc.nasa.gov/apod/ap030410.html ] gas known, comparable to the Tarantula Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap030823.html ] in our Milky Way [ http://www.damtp.cam.ac.uk/user/gr/public/gal_milky.html ]'s close neighbor, the Large Magellanic Cloud [ http://antwrp.gsfc.nasa.gov/apod/ap010804.html ]. |
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NGC 6960: The Witch's Broom
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| Title |
NGC 6960: The Witch's Broom Nebula |
| Explanation |
Ten thousand years ago, before the dawn of recorded human history [ http://news.bbc.co.uk/hi/english/sci/tech/newsid_334000/334517.stm ], a new light must suddenly have appeared in the night sky and faded after a few weeks. Today we know this light was an exploding star [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html ] and record the colorful expanding cloud as the Veil Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap010928.html ]. Pictured above [ http://www.noao.edu/image_gallery/html/im0852.html ] is the west end of the Veil Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap030204.html ] known technically as NGC [ http://www.ngcic.com/dss/dss_images.htm ] 6960 but less formally as the Witch [ http://antwrp.gsfc.nasa.gov/apod/ap031229.html ]'s Broom [ http://www.broomshop.com/history/ ] Nebula. The rampaging gas gains its colors by impacting and exciting existing [ http://www.seds.org/billa/twn/cygnusx.html ] nearby gas. The supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/supernova_remnants.html ] lies about 1400 light-years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away towards the constellation of Cygnus [ http://www.multimania.com/cdadfs/constellation/cygne/cygnus.htm ]. This Witch's Broom actually spans over three times the angular size [ http://imagine.gsfc.nasa.gov/YBA/HTCas-size/more-ang_size.html ] of the full Moon [ http://antwrp.gsfc.nasa.gov/apod/ap030810.html ]. The bright star 52 Cygnus [ http://www.seds.org/Maps/Stars_en/Fig/cygnus.html ] is visible with the unaided eye from a dark location but unrelated to the ancient supernova [ http://www.chapman.edu/oca/benet/intro_sn.htm ]. |
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NGC 3372: The Great Nebula i
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| Title |
NGC 3372: The Great Nebula in Carina |
| Explanation |
In one of the brightest parts of the Milky Way [ http://antwrp.gsfc.nasa.gov/apod/ap990224.html ] lies a nebula where some of the oddest things occur. NGC 3372, known as the Great Nebula in Carina [ http://www.ast.cam.ac.uk/AAO/images/captions/aat009.html ], is home to massive stars and changing nebula. Eta Carina [ http://antwrp.gsfc.nasa.gov/apod/ap020428.html ], the most energetic star in the nebula was one of the brightest stars [ http://www.astro.wisc.edu/%7Edolan/constellations/extra/brightest.html ] in the sky in the 1830s, but then faded dramatically. The Keyhole Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap000613.html ], visible near the center, houses several of the most massive stars known and has also changed its appearance. The Carina Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap031126.html ] spans over 300 light years and lies about 7000 light-years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] away in the constellation of Carina [ http://www.astro.wisc.edu/%7Edolan/constellations/constellations/Carina.html ]. The above image [ http://www.starryscapes.com/nebula/eta_carinae.html ] was taken from La Frontera in Alcohuaz, Chile [ http://sunsite.dcc.uchile.cl/chile/chile.html ]. Eta Carina [ http://antwrp.gsfc.nasa.gov/apod/ap971129.html ] might explode in a dramatic supernova [ http://heasarc.gsfc.nasa.gov/docs/snr.html ] within the next thousand years, and has even flared in brightness [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999A%26A...346L..33S ] over just the past decade [ http://cfa-www.harvard.edu/iauc/07100/07146.html ]. |
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In the Center of NGC 6559
| Title |
In the Center of NGC 6559 |
| Explanation |
Bright gas and dark dust permeate the space between stars in the center of a nebula known as NGC 6559 [ http://www.noao.edu/outreach/aop/observers/n6559.html ]. The gas, primarily hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ], is responsible for the diffuse red glow of the emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ]. As energetic light from neighboring stars ionizes interstellar hydrogen [ http://antwrp.gsfc.nasa.gov/apod/ap010113.html ], protons [ http://www.neutron.anl.gov/hyper-physics/proton.html ] and electrons [ http://www.aip.org/history/electron/ ] recombine to emit light [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] of very specific colors [ http://csep10.phys.utk.edu/astr162/lect/light/absorption.html ], including the red [ http://antwrp.gsfc.nasa.gov/apod/ap010214.html ] hue observed. Small dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] particles reflect blue starlight efficiently and so creates the blue reflection nebulosity [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ] seen near two of the bright stars. Dust [ http://nedwww.ipac.caltech.edu/level5/Mathis/Mathis9.html ] also absorbs visible light, causing the dark clouds [ http://antwrp.gsfc.nasa.gov/apod/ap030202.html ] and filaments [ http://antwrp.gsfc.nasa.gov/apod/ap990919.html ] visible. NGC 6559 [ http://www.aao.gov.au/images/captions/uks003.html ] lies about 5000 light-years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away toward the constellation of Sagittarius [ http://www.astronomical.org/portal/modules/wfsection/article.php?articleid=72 ]. |
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