|
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NGC 6791: An Old, Large Open
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| Title |
NGC 6791: An Old, Large Open Cluster |
| Explanation |
NGC 6791 is one of the oldest and largest open clusters of stars [ http://antwrp.gsfc.nasa.gov/apod/ap970128.html ] known. But how did it get so dirty? Open star clusters [ http://www.seds.org/messier/open.html ] usually contain a few hundred stars each less than a billion years old. Open star cluster [ http://antwrp.gsfc.nasa.gov/apod/lib/open_clusters.html ] NGC 6791 [ http://xxx.lanl.gov/ps/astro-ph/9812097 ], however, contains thousands of stars recently measured to be about 8 billion years old. What's really confusing, though, is that the stars of NGC 6791 [ http://xxx.lanl.gov/abs/astro-ph/9503065 ] are relatively dirty - the minuscule amounts of heavy elements [ http://pearl1.lanl.gov/periodic/ ] (generically called metals) are high relative to most other star clusters [ http://antwrp.gsfc.nasa.gov/apod/ap981025.html ]. Older stars are supposed to be metal poor, since metals have only been slowly accumulating in our Milky Way Galaxy [ http://www.damtp.cam.ac.uk/user/gr/public/gal_milky.html ]. This enigma makes NGC 6791, pictured above [ http://www.astrouw.edu.pl/~mochejsk/gallery.html ], one of the most studied open clusters [ http://cfa-www.harvard.edu/~stauffer/opencl/ ] and a possible example of how stars might evolve in the centers of galaxies. |
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NGC 1499: The California Neb
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| 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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Barred Spiral Galaxy NGC 130
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| Title |
Barred Spiral Galaxy NGC 1300 |
| Explanation |
NGC 1300 is a large spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/spiral_galaxies.html ] that appears as a flattened figure eight. A huge bar that spans over 150,000 light-years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] across the galaxy center dominates its appearance. The picturesque galaxy [ http://www.aao.gov.au/images/captions/aatccd014.html ] lies about 75 million light-years distant, so that light that we see now left during the age [ http://www.austmus.gov.au/lostkingdoms/snapshots/cretaceous_late.htm ] of the dinosaurs [ http://pubs.usgs.gov/gip/dinosaurs/ ]. Although it is well known how fast different parts of NGC 1300 rotate [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1996ApJ...469..131E ], the specific orbits of many component stars -- including how they interact with the gigantic bar -- remains a topic of research [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26A...317...36L ]. Our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap971229.html ] is a spiral galaxy [ http://www.seds.org/messier/galaxy.html ] with a less prominent bar. NGC 1300 [ http://www.starlightccd.com/funstuff/flic/1999-11/12_f33_mx512/ngc1300.htm ] can be seen with a small telescope towards the constellation [ http://www.att.virtualclassroom.org/vc99/vc_04/cons_stars/cons/hist_cons.html ] of Eridanus [ http://www.astronomical.org/constellations/eri.html ]. |
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Dwarf Elliptical Galaxy NGC
…
| Title |
Dwarf Elliptical Galaxy NGC 205 in the Local Group |
| Explanation |
Our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ] is not alone. It is part of a gathering of about 25 galaxies known as the Local Group [ http://www.seds.org/messier/more/local.html ]. Members include the Great Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap991114.html ] (M31), M32 [ http://antwrp.gsfc.nasa.gov/apod/ap991103.html ], M33 [ http://antwrp.gsfc.nasa.gov/apod/ap980721.html ], the Large Magellanic Cloud [ http://antwrp.gsfc.nasa.gov/apod/ap000222.html ], the Small Magellanic Cloud [ http://antwrp.gsfc.nasa.gov/apod/ap000430.html ], Dwingeloo 1 [ http://antwrp.gsfc.nasa.gov/apod/ap000109.html ], several small irregular galaxies [ http://www.seds.org/messier/irre.html ], and many dwarf elliptical [ http://nedwww.ipac.caltech.edu/level5/Ferguson/frames.html ] and dwarf spheroidal galaxies [ http://www.astro.uu.se/~ns/review.html ]. Pictured [ http://www.cfht.hawaii.edu/Science/Astros/Imageofweek/ciw061299.html ] on the lower left is one of the many dwarf ellipticals [ http://www.astro.psu.edu/users/pdurrell/dE.html ]: NGC 205 [ http://www.seds.org/messier/m/m110.html ]. Like M32 [ http://www.seds.org/messier/m/m032.html ], NGC 205 [ http://nedwww.ipac.caltech.edu/level5/Hodge/Hodge5_5.html ] is a companion to the large M31, and can sometimes be seen to the south of M31 [ http://www.seds.org/messier/m/m031.html ]'s center in photographs. The above image [ http://www.cfht.hawaii.edu/Science/Astros/Imageofweek/ciw061299.html ] shows NGC 205 to be unusual [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...499..209W ] for an elliptical galaxy [ http://antwrp.gsfc.nasa.gov/apod/elliptical_galaxies.html ] in that it contains at least two dust clouds [ http://antwrp.gsfc.nasa.gov/apod/ap990919.html ] (at 1 and 4 o'clock - they are visible but hard to spot) and signs of recent star formation [ http://antwrp.gsfc.nasa.gov/apod/stellar_nurseries.html ]. This galaxy is sometimes known as M110, although it was actually not part of Messier [ http://antwrp.gsfc.nasa.gov/apod/ap960626.html ]'s original catalog [ http://antwrp.gsfc.nasa.gov/apod/messier.html ]. |
|
Barred Spiral Galaxy NGC 167
…
| Title |
Barred Spiral Galaxy NGC 1672 |
| Explanation |
Many spiral galaxies have bars across their centers. Even our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap000130.html ] is thought to have a modest central bar [ http://antwrp.gsfc.nasa.gov/apod/ap050825.html ]. Prominently barred spiral galaxy NGC 1672, pictured above [ http://hubblesite.org/newscenter/archive/releases/2007/15/image/a/ ], was captured in spectacular detail in this recently released image taken by the orbiting Hubble Space Telescope [ http://en.wikipedia.org/wiki/Hubble_Space_Telescope ]. Visible are dark filamentary dust lanes [ http://antwrp.gsfc.nasa.gov/apod/ap060219.html ], young clusters [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] of bright blue stars, red emission nebulas [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] of glowing hydrogen gas, a long bright bar of stars across the center, and a bright active nucleus [ http://en.wikipedia.org/wiki/Active_galactic_nucleus ] that likely houses a supermassive black hole [ http://antwrp.gsfc.nasa.gov/htmltest/rjn_bht.html ]. Light takes about 60 million years to reach us from NGC 1672 [ http://heritage.stsci.edu/2007/15/caption.html ], which spans about 75,000 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] across. NGC 1672, which appears toward the constellation of the Swordfish (Dorado [ http://www.astronomical.org/portal/modules/wfsection/article.php?articleid=33 ]), is being studied [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004hst..prop.6669J ] to find out how a spiral bar contributes to star formation in a galaxy's central regions. |
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Barred Spiral Galaxy NGC 290
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| Title |
Barred Spiral Galaxy NGC 2903 |
| Explanation |
NGC 2903 is a spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/spiral_galaxies.html ] similar to our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ]. Similarities include its general size and a central bar [ http://antwrp.gsfc.nasa.gov/apod/ap001004.html ]. One striking difference, however, is the appearance of mysterious hot spots [ http://antwrp.gsfc.nasa.gov/apod/ap010321.html http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1991ApJ...375..105J ] in NGC 2903's core. Upon inspection of the above image [ http://hubble.esa.int/hubble/news/imagecollection.cfm?oid=26173 ] and similar images taken by the Hubble Space Telescope, these hot spots [ http://hubble.esa.int/hubble/news/newsrelease.cfm?oid=26173 ] were found to be bright young globular clusters [ http://antwrp.gsfc.nasa.gov/apod/ap010311.html ], in contrast to the uniformly old globular clusters [ http://antwrp.gsfc.nasa.gov/apod/globular_clusters.html ] found in our Milky Way Galaxy [ http://www.seds.org/messier/more/mw.html ]. Further investigation [ http://arXiv.org/abs/astro-ph/0010522 ] has indicated that current star formation [ http://www.sciam.com/exhibit/102797stellar/hall.html ] is most rampant in a 2000 light-year [ http://chandra.harvard.edu/photo/cosmic_distance.html ] wide circumnuclear ring [ http://antwrp.gsfc.nasa.gov/apod/ap991212.html ] surrounding NGC 2903's center. Astronomers hypothesize [ http://hubble.esa.int/hubble/news/newsrelease.cfm?oid=26173 ] that the gravity of the central bar expedites star formation in this ring. NGC 2903 [ http://www.astro.princeton.edu/~frei/Gcat_htm/Sub_sel/gal_2903.htm ] lies about 25 million light-years [ http://www.pa.msu.edu/sci_theatre/ask_st/012292.html ] away and is visible with a small telescope towards the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] of Leo [ http://www.astronomical.org/constellations/leo.html ]. |
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Hot Gas Halo Detected Around
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| Title |
Hot Gas Halo Detected Around Galaxy NGC 4631 |
| Explanation |
Is our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ] surrounded by a halo of hot gas? A step toward solving this long-standing mystery was taken recently with Chandra [ http://www1.msfc.nasa.gov/NEWSROOM/background/facts/cxoquick.htm ] X-ray observations of nearby galaxy NGC 4631 [ http://www.seds.org/messier/xtra/ngc/n4631.html ]. In the above composite picture [ http://chandra.harvard.edu/photo/cycle1/1138/index.html ], newly resolved diffuse X-ray [ http://chandra.harvard.edu/edu/chandra1012.html ] emission is shown in blue, superposed on an HST [ http://www.stsci.edu/hst/ ] image showing massive stars in red. Since NGC 4631 [ http://www.allthesky.com/galaxies/ngc4631.html ] is similar to the Milky Way [ http://www.seds.org/messier/more/mw.html ], this observation indicates [ http://xxx.lanl.gov/abs/astro-ph/0105541 ] that our own Galaxy is indeed surrounded by a halo of hot X-ray emitting gas, although we are too close to clearly differentiate it from more nearby [ http://antwrp.gsfc.nasa.gov/apod/ap000412.html ] extended X-ray sources. The clusters of massive stars [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] probably heat the halo [ http://antwrp.gsfc.nasa.gov/apod/ap971105.html ] gas. Exactly how this gas gets ejected into a halo is a topic of continuing research [ http://antwrp.gsfc.nasa.gov/apod/ap000207.html ]. |
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NGC 1850: Not Found in the M
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| Title |
NGC 1850: Not Found in the Milky Way |
| Explanation |
A mere 168,000 light-years distant, this large, lovely cluster of stars, NGC 1850 [ http://antwrp.gsfc.nasa.gov/apod/ap000729.html ], is located near the outskirts of the central bar structure in our neighboring galaxy, the Large Magellanic Cloud [ http://www.seds.org/messier/xtra/ngc/lmc.html ]. A first glance at this [ http://oposite.stsci.edu/pubinfo/PR/2001/25/fastfacts.html ] Hubble Space Telescope composite image suggests [ http://oposite.stsci.edu/pubinfo/PR/2001/25/index.html ] that this cluster's size and shape are reminiscent of the ancient globular star clusters which roam our own Milky Way Galaxy's halo [ http://www.limber.org/globs.html ]. But NGC 1850's stars are young ... making it a type of star cluster [ http://csep10.phys.utk.edu/guidry/violence/ starclusters.html ] with no known counterpart in the Milky Way [ http://www.seds.org/messier/glob.html ]. NGC 1850 is also a double star cluster, with a second, compact cluster of stars visible here below and to the right of the large cluster's central region. Stars in the large cluster are estimated to be 50 million years young [ http://oposite.stsci.edu/pubinfo/PR/97/34/af4.html ], while stars in the compact cluster are younger still, with an age of about 4 million years. In fact, the smaller cluster contains T-Tauri stars [ http://xxx.lanl.gov/abs/astro-ph/0106321 ], thought to be low mass, solar-type stars still in the process [ http://etacha.as.arizona.edu/~eem/ttau/ ] of formation. The glowing nebula at the left, like the supernova remnants [ http://antwrp.gsfc.nasa.gov/apod/ap010623.html ] in our own galaxy, testifies to [ http://www.eso.org/outreach/press-rel/pr-1999/ phot-15-99.html ] violent stellar explosions, indicating short-lived massive stars [ http://antwrp.gsfc.nasa.gov/apod/ap991130.html ] were also present in NGC 1850 [ http://antwrp.gsfc.nasa.gov/apod/ap001224.html ]. |
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Galaxy NGC 474: Cosmic Blend
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| Title |
Galaxy NGC 474: Cosmic Blender |
| Explanation |
What's happening to galaxy NGC 474? The multiple layers of emission appear strangely complex and unexpected given the relatively featureless appearance of the elliptical galaxy in less deep images. The cause of the shells is currently unknown, but possibly tidal tails [ http://antwrp.gsfc.nasa.gov/apod/ap060108.html ] related to debris left over from absorbing numerous small galaxies in the past billion years. Alternatively the shells [ http://antwrp.gsfc.nasa.gov/apod/ap021111.html ] may be like ripples in a pond, where the ongoing collision with the spiral galaxy to the right of NGC 474 [ http://adsabs.harvard.edu/abs/1999IAUS..186..191T ] is causing density waves [ http://en.wikipedia.org/wiki/Density_wave_theory ] to ripple [ http://myspacetv.com/index.cfm?fuseaction=vids.individual&videoid=10103178 ] though the galactic giant. Regardless of the actual cause, the above image [ http://www.astro.uni-bonn.de/~mischa/mbo/gallery_ccd/ngc474.html ] dramatically highlights the increasing consensus that the outer halos of most large galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap061011.html ] are not really smooth but have complexities induced by frequent interactions with -- and accretions of -- smaller nearby galaxies [ http://en.wikipedia.org/wiki/Local_Group ]. The halo of our own Milky Way Galaxy [ http://en.wikipedia.org/wiki/Milky_Way_galaxy ] is one example of such unexpected complexity [ http://antwrp.gsfc.nasa.gov/apod/ap050529.html ]. NGC 474 spans about 250,000 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] and lies about 100 million light years distant toward the constellation of the Fish Pisces [ http://en.wikipedia.org/wiki/Pisces_%28constellation%29 ]. |
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NGC 4414: A Flocculent Spira
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| Title |
NGC 4414: A Flocculent Spiral Galaxy |
| Explanation |
How much mass do flocculent [ http://www.bartleby.com/61/6/F0190600.html ] spirals hide? The above true color image of flocculent spiral galaxy [ http://www.star.le.ac.uk/edu/galaxies/spirals.html ] NGC 4414 was taken with the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] to help answer this question. Flocculent spirals [ http://nedwww.ipac.caltech.edu/level5/Elmegreen/Elm3.html ] -- galaxies without well defined spiral arms -- are a quite common form of galaxy, and NGC 4414 is one of the closest. Stars and gas near the visible edge of spiral galaxies [ http://antwrp.gsfc.nasa.gov/apod/spiral_galaxies.html ] orbit the center so fast that the gravity from a large amount of unseen dark matter [ http://www.sciam.com/specialissues/0398cosmos/0398rubin.html ] must be present to hold them together. Pictured above is the photogenic center of NGC 4414. A bright foreground star from our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap000518.html ] shines in the foreground of the image. Although NGC 4414's center likely holds little dark matter [ http://chandra.harvard.edu/xray_astro/dark_matter.html ], understanding its matter distribution helps calibrate the rest of the galaxy and, by deduction, flocculent spirals in general. By determining a precise distance [ http://www.astro.virginia.edu/~jh8h/glossary/distanceladder.htm ] to NGC 4414 [ http://antwrp.gsfc.nasa.gov/apod/ap990609.html ], astronomers also hope to help calibrate the scale [ http://antwrp.gsfc.nasa.gov/debate/debate96.html ] to the more distant universe [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998ApJ...509...80S ]. |
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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 2440 Nucleus: The Hottes
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| Title |
NGC 2440 Nucleus: The Hottest Star? |
| Explanation |
In the center of the above photograph [ http://pao.gsfc.nasa.gov/gsfc/lithos/hst/ngc2440/ngc2440.htm ] lies a star [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#star ] with one of the hottest surface temperatures yet confirmed. This bright white dwarf [ http://antwrp.gsfc.nasa.gov/apod/ap950910.html ] star's surface has been measured at greater than 200,000 degrees Celsius - more than 30 times hotter than that of our own Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ]. The white dwarf [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#wd ]'s extreme heat makes it glow extraordinarily bright: intrinsically more than 250 times brighter than the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap951004.html ]. The star is at the center of the planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/ap950628.html ] titled NGC 2440, which lies inside our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap950908.html ]. The above computer sharpened image was taken by the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap950810.html ]. |
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Local Group Galaxy NGC 205
| Title |
Local Group Galaxy NGC 205 |
| Explanation |
The Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap950908.html ] is not alone. It is part of a gathering of about 25 galaxies known as the Local Group [ http://www.csc.fi/jpr/galaxy/lbang.html ]. Members include the Great Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap950724.html ] (M31), M32 [ http://antwrp.gsfc.nasa.gov/apod/ap960106.html ], M33 [ http://seds.lpl.arizona.edu/messier/m/m033.html ], the Large Magellanic Clouds [ http://antwrp.gsfc.nasa.gov/apod/ap950918.html ], the Small Magellanic Clouds [ http://antwrp.gsfc.nasa.gov/apod/ap950919.html ], Dwingeloo 1 [ http://antwrp.gsfc.nasa.gov/apod/ap951017.html ], several small irregular galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap950728.html ], and many dwarf elliptical galaxies [ http://www.physics.mcmaster.ca/Grads/PRD2.html ]. Pictured is one of the many dwarf ellipticals: NGC 205. Like M32, NGC 205 is a companion to the large M31, and can sometimes be seen to the south of M31 [ http://seds.lpl.arizona.edu/messier/m/m031.html ]'s center in photographs. The above image [ http://crux.astr.ua.edu/gifimages/m110r.html ] shows this galaxy to be unusual for an elliptical galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap950913.html ] in that it contains at least two dust clouds [ http://antwrp.gsfc.nasa.gov/apod/ap951107.html ] (at 7 and 11 o'clock - they are visible but hard to spot) and signs of recent star formation. This galaxy is sometimes known as M110, although it was actually not part of Messier [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#messier ]'s original catalog. |
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Spiral Galaxy NGC 2997 from
…
| Title |
Spiral Galaxy NGC 2997 from VLT |
| Explanation |
NGC 2997 is a grand design spiral galaxy [ http://www.seds.org/messier/spir.html ]. Its small nucleus and sprawling spiral arms give it a type Sc [ http://zebu.uoregon.edu/~js/ast123/lectures/lec13.html ] designation. NGC 2997, pictured above [ http://www.eso.org/outreach/press-rel/pr-1999/pr-06-99.html ], is speeding away [ http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/ExpandUni.html ] from us at about 1100 kilometers per second, which would place it at about 55 million light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] distant, given current estimates of the expansion rate [ http://csep1.phy.ornl.gov/guidry/violence/hubble_constant.html ] of our universe. NGC 2997 [ http://www.ast.cam.ac.uk/AAO/images/captions/aat017.html ] is thought to have a mass of about 100 billion times that of our Sun [ http://antwrp.gsfc.nasa.gov/apod/sun.html ], but is probably less massive than our own Milky Way galaxy [ http://casswww.ucsd.edu/public/tutorial/MW.html ]. NGC 2997 is not seen face-on [ http://antwrp.gsfc.nasa.gov/apod/ap011004.html ] - it is thought tilted by about 45 degrees. NGC 2997 is particularly notable [ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1989ApJ...341..722W ] for a nucleus [ http://antwrp.gsfc.nasa.gov/apod/ap020603.html ] surrounded by a chain of hot giant clouds of ionized [ http://csep10.phys.utk.edu/astr162/lect/light/ionization.html ] hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ]. |
|
Open Cluster NGC 6520 from C
…
| Title |
Open Cluster NGC 6520 from CFHT |
| Explanation |
Did you ever have a day when it felt like a dark cloud [ http://antwrp.gsfc.nasa.gov/apod/ap010923.html ] was following you around? For the open cluster [ http://www.seds.org/messier/open.html ] of stars NGC 6520, every day is like this. On the left of the above picture [ http://www.cfht.hawaii.edu/HawaiianStarlight/AIOM/English/CFHT-Coelum-AIOM.html ] are many of NGC 6520's bright blue stars. They formed only millions of years ago - much more recently than our ancient Sun which formed billions of years ago. On the right is an absorption nebula [ http://antwrp.gsfc.nasa.gov/apod/dark_nebulae.html ], molecular cloud [ http://origins.jpl.nasa.gov/poster/bigbang3.html ] Barnard 86 [ http://astro.uchicago.edu/yerkes/virtualmuseum/Barnard.html ], from which the stars of NGC 6520 surely formed. This nebula contains much opaque dust [ http://antwrp.gsfc.nasa.gov/apod/ap010813.html ] that blocks light from the many stars that would have been visible in the background. Surrounding NGC 6520 [ http://www.ast.cam.ac.uk/AAO/images/captions/aat092.html ] is part of the tremendously dense starscape in the bulge of our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap970315.html ], the extended halo of stars that surrounds the center [ http://antwrp.gsfc.nasa.gov/apod/ap010708.html ] of our Galaxy. NGC 6520 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1982S%26T....63..254M ] spans about 10 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] and lies about 5500 light years away toward the direction of Sagittarius [ http://www.astronomical.org/constellations/sgr.html ]. |
|
Nearby Spiral Galaxy NGC 494
…
| 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
…
| 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. |
|
Facing NGC 6946
| Title |
Facing NGC 6946 |
| Explanation |
From our vantage point in the Milky Way Galaxy [ http://www.astro.umd.edu/education/astro/mw/ mw.html ], we see NGC 6946 [ http://www.noao.edu/outreach/aop/observers/n6946.html ] face on. The big beautiful spiral galaxy [ http://www.seds.org/messier/spir.html ] is located just 10 million light-years away, behind a veil of foreground stars in the high and far-off constellation of Cepheus [ http://www.astropix.com/HTML/E_SUM_N/ CEPHEUSO.HTM ]. Looking from the bright core outward along the loose, fragmented spiral arms, the galaxy's colors show a striking change from the yellowish light of old stars in the galaxy's center to young blue star clusters and reddish star forming regions. NGC 6946 is also bright in infrared light [ http://antwrp.gsfc.nasa.gov/apod/ap990322.html ] and rich in gas and dust, exhibiting a high star birth and death rate. In fact, during the 20th century, at least six supernovae, the death explosions [ http://antwrp.gsfc.nasa.gov/apod/ap990515.html ] of massive stars, were discovered in NGC 6946 [ http://www.seds.org/messier/xtra/ngc/n6946.html ]. In this sharp composite [ http://www.robgendlerastropics.com/6946LRGB.html ] color digital image, a small barred structure [ http://antwrp.gsfc.nasa.gov/apod/ap990624.html ] is just visible at the gorgeous galaxy's core. |
|
NGC 1818: A Young Globular C
…
| Title |
NGC 1818: A Young Globular Cluster |
| Explanation |
Globular clusters [ http://antwrp.gsfc.nasa.gov/apod/ap020416.html ] once ruled the Milky Way [ http://antwrp.gsfc.nasa.gov/apod/ap980523.html ]. Back in the old days [ http://antwrp.gsfc.nasa.gov/apod/ap001029.html ], back when our Galaxy first formed, perhaps thousands of globular clusters roamed our Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ]. Today, there are perhaps 200 left [ http://www.faqs.org/faqs/astronomy/faq/part8/section-5.html ]. Many globular clusters were destroyed [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...474..223G ] over the eons by repeated fateful encounters with each other or the Galactic center [ http://antwrp.gsfc.nasa.gov/apod/ap010708.html ]. Surviving relics are older than any Earth fossil [ http://craton.geol.brocku.ca/faculty/rc/teaching/1F90/history/shorthistory2.html ], older than any other structures in our Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap990224.html ], and limit the universe [ http://liftoff.msfc.nasa.gov/academy/universe/age.html ] itself in raw age. There are few, if any, young globular clusters [ http://antwrp.gsfc.nasa.gov/apod/globular_clusters.html ] in our Milky Way Galaxy [ http://www.seds.org/messier/more/mw.html ] because conditions are not ripe for more to form. Things are different next door, however, in the neighboring LMC galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap010804.html ]. Pictured above is a "young" globular cluster residing there: NGC 1818 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995A%26A...295...54W ]. Observations show it formed only about 40 million years ago - just yesterday compared to the 12 billion year ages of globular clusters [ http://www.seds.org/messier/glob.html ] in our own Milky Way [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_ts?milky+way ] |
|
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 1365: A Nearby Barred Sp
…
| Title |
NGC 1365: A Nearby Barred Spiral Galaxy |
| Explanation |
Many spiral galaxies [ http://www.seds.org/messier/spir.html ] have bars across their centers. Even our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap000130.html ] is thought to have a bar [ http://adsabs.harvard.edu/cgi-bin/nph- bib_query?bibcode=1992ApJ...384...81W ], but perhaps not so prominent as the one in NGC 1365, shown above [ http://www.eso.org/outreach/press-rel/pr-1999/phot-08-99.html ]. The persistence and motion of the bar [ http://www.smv.org/hastings/bsmain.htm ] imply relatively massive spiral arms [ http://adsabs.harvard.edu/cgi-bin/nph- bib_query?bibcode=1997MNRAS.288..715R ]. The placements of bright young blue stars [ http://antwrp.gsfc.nasa.gov/apod/ap021201.html ] and dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] lanes also indicate a strong rotating density wave [ http://home.cc.umanitoba.ca/~ummccowa/density.htm ] of star formation. NGC 1365 is a member of the Fornax Cluster of Galaxies [ http://www.ast.cam.ac.uk/AAO/images/captions/uks013.html ]. Because NGC 1365 [ http://adsabs.harvard.edu/cgi-bin/nph- bib_query?bibcode=1999ApJ...515....1S ] is relatively nearby, simultaneous measurements [ http://antwrp.gsfc.nasa.gov/apod/ap960110.html ] of its speed and distance are possible, which help astronomers estimate how fast our universe is expanding [ http://antwrp.gsfc.nasa.gov/debate/debate96.html ]. |
|
Barred Spiral Galaxy NGC 136
…
| Title |
Barred Spiral Galaxy NGC 1365 |
| Explanation |
Many spiral galaxies have bars across their centers. Even our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap970315.html ] is thought to have a bar [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994ApJ%2E%2E%2E422%2E%2E111B&db_key=AST&nosetcookie=1 ], but perhaps not so prominent as the one in NGC 1365, shown above. The persistence and motion of the bar imply relatively massive spiral arms [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996A%26A%2E%2E%2E313%2E%2E%2E65L&db_key=AST&nosetcookie=1 ]. The placements of bright young blue stars and dark dust lanes also indicate a strong rotating density wave [ http://www.vyne.com/prototype/WEB/askexpert/astronomy.html#acs9 ] of star formation. NGC 1365 is a member of the Fornax Cluster of Galaxies [ http://www.astro.yorku.ca/~lee/fornax.html ]. Because NGC 1365 is relatively nearby, simultaneous measurements of its speed and distance are possible, which help astronomers estimate how fast our universe is expanding [ http://antwrp.gsfc.nasa.gov/apod/ap960513.html ]. |
|
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/ap971229.html ]: a spiral galaxy [ ftp://crux.astr.ua.edu/web/goodies/data_resources/galaxies.text ] seen nearly edge-on [ http://www.limber.org/eon0.html ]. However, recent high-resolution images 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/ap980104.html ] was probably thrown out of the galactic disk toward the halo [ http://www.bc.kern.cc.ca.us/programs/sea/Astronomy/milkyway.description/milkyway.description.html ] by stellar supernovae explosions [ http://antwrp.gsfc.nasa.gov/apod/ap980217.html ]. Because dust is so fragile, its appearance after surviving disk expulsion can be very telling [ http://www.astro.wisc.edu/~howk/Papers/N891/n891.html ]. Newly discovered phenomena, however, sometimes appear so complex [ http://antwrp.gsfc.nasa.gov/apod/ap980310.html ] that more questions are raised than are answered. |
|
Starbirth in NGC 1808
| Title |
Starbirth in NGC 1808 |
| Explanation |
The center of galaxy NGC 1808 is bursting with new stars, but why? Being a barred spiral galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap970519.html ] makes NGC 1808 [ http://sol.stsci.edu/~mutchler/ngc1808.html ] somewhat similar to our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap971229.html ]. But the disk of NGC 1808 [ http://www.atnf.csiro.au/~bkoribal/n1808_hi.html ] (inset) is quite warped, and its center is unusually bright and blue. The above picture [ http://oposite.stsci.edu/pubinfo/pr/1998/12/ ] of NGC 1808's center, in representative color, was recently taken by the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap950810.html ] and released [ http://oposite.stsci.edu/pubinfo/pr/1998/12/content/prc9812.txt ] yesterday. Perhaps gravitational pull [ http://antwrp.gsfc.nasa.gov/apod/ap970602.html ] from a recent pass of neighboring galaxy NGC 1792 has caused matter to move inward along NGC 1808's bar, triggering the burst of star formation [ http://antwrp.gsfc.nasa.gov/apod/ap960816.html ]. Also prominent are blue clusters of stars [ http://antwrp.gsfc.nasa.gov/apod/ap971018.html ] and filaments of dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap980116.html ] obscuring even more activity. |
|
NGC 1808: A Nearby Starburst
…
| Title |
NGC 1808: A Nearby Starburst Galaxy |
| Explanation |
NGC 1808 is a galaxy in turmoil. A barred spiral [ http://antwrp.gsfc.nasa.gov/apod/ap970519.html ] with marked similarities to our home Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap971229.html ], NGC 1808 [ http://www.atnf.csiro.au/~bkoribal/phd_thesis.html ] is distinguished by a peculiar nucleus [ http://antwrp.gsfc.nasa.gov/apod/ap980323.html ], an unusually warped disk [ http://galileo.ifa.hawaii.edu/faculty/barnes/ast626/wdg.html ], and strange flows [ http://www.atnf.csiro.au/~bkoribal/n1808_hi.html ] of hydrogen [ http://cst.lanl.gov/CST/imagemap/periodic/1.html ] gas out from the central regions. Amidst all of this, NGC 1808 is undergoing so much star formation it has been deemed a starburst galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap951016.html ]. In the above color-enhanced photograph [ http://sol.stsci.edu/~mutchler/ngc1808/ngc1808b.html ], regions of active star formation and shown by their blue glow. Here bright blue stars have recently formed and are energizing large clouds of surrounding hydrogen gas. The reddish brown regions indicate dense interstellar dust [ http://astro.gmu.edu/classes/a10695/notes/l08/l08.html ]. NGC 1808 is a relatively close 40 million light-years away, and stretches about 35,000 light-years across. The peculiar state of NGC 1808 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=J76-06426&db_key=AST&high=34f6e1de7f22220 ] may be caused by the gravity of neighboring galaxy NGC 1792 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=A95-71214&db_key=AST&high=34f6e1de7f22233 ]. |
|
NGC 6946: The Fireworks Gala
…
| Title |
NGC 6946: The Fireworks Galaxy |
| Explanation |
Why is this galaxy so active? Nearby spiral galaxy NGC 6946 [ http://www.noao.edu/outreach/aop/observers/n6946.html ] is undergoing a tremendous burst of star formation with no obvious cause. In many cases spirals light up when interacting with another galaxy, but NGC 6946 [ http://antwrp.gsfc.nasa.gov/apod/ap040410.html ] appears relatively isolated in space. Located just 10 million light years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away toward the constellation [ http://www.fillingthesky.com/id8.html ] of Cepheus [ http://www.astronomical.org/portal/modules/wfsection/article.php?articleid=20 ], this beautiful face-on spiral [ http://antwrp.gsfc.nasa.gov/apod/ap041216.html ] spans about 20,000 light years and is seen through a field of foreground stars from our Milky Way Galaxy [ http://cassfos02.ucsd.edu/public/tutorial/MW.html ]. The center of NGC 6946 [ http://www.gemini.edu/index.php?option=content&task=view&id=116 ] is home to a nuclear starburst itself, and picturesque dark dust is seen lacing the disk along with bright blue stars [ http://antwrp.gsfc.nasa.gov/apod/ap031227.html ], red emission nebulas [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ], fast moving gas clouds, and unusually frequent supernovas [ http://heasarc.gsfc.nasa.gov/docs/snr.html ]. The 8-meter Gemini North Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap990629.html ] in Hawaii, USA [ http://www.cia.gov/cia/publications/factbook/geos/us.html ], took the above image [ http://www.gemini.edu/index.php?set_albumName=Previous-Featured-Images&id=ngc6946_Small&option=com_gallery&Itemid=39&include=view_photo.php ]. A suggested explanation [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000MNRAS.319..821P ] for the high star formation rate is the recent accretion of many primordial low-mass neutral hydrogen clouds [ http://www.universetoday.com/am/publish/clouds_hydrogen_swarm_andromeda.html?422004 ] from the surrounding region. |
|
NGC 1499: California Nebula
| Title |
NGC 1499: California Nebula |
| Explanation |
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 on the west coast of the United States. 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. Also known as NGC 1499 [ http://www.seds.org/~spider/spider/ Misc/n1499.html ], the classic emission nebula is around 100 light-years 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 ]. |
|
NGC 6712: Galactic Globular
…
| Title |
NGC 6712: Galactic Globular Cluster |
| Explanation |
Following orbits which loop high above the galactic plane [ http://www.limber.org/globs.html ], globular star clusters are probably 12 to 14 billion years old - truly ancient denizens [ http://antwrp.gsfc.nasa.gov/apod/ap990117.html ] of our Milky Way Galaxy. After analyzing these new ESO/VLT [ http://antwrp.gsfc.nasa.gov/apod/ap960901.html ] images of portions of the globular cluster NGC 6712, astronomers report that [ http://www.eso.org/outreach/press-rel/pr-1999/pr-04-99.html ] this dense grouping of about 1 million stars seems to be slowly dissolving - steadily loosing fainter, lower mass stars into our Galaxy's halo. Their results offer strong evidence for gravitational stripping [ http://adsabs.harvard.edu/cgi-bin/ nph-bib_query?bibcode=1997ApJ...474..223G&db_key=AST&high=34f6e1de7f29652 ] of stars from clusters which pass through the plane and central regions of the Galaxy. One of about 150 globular clusters [ http://physun.physics.mcmaster.ca/GC/mwgc.dat ] known to be members of the Milky Way, NGC 6712 is thought to have crossed through the crowded galactic plane only a few million years ago. NGC 6712 is about 23,000 light-years away in the southern constellation Scutum [ http://www.astro.wisc.edu/~dolan/constellations/constellations/ Scutum.html ]. |
|
Nearby Spiral Galaxy NGC 494
…
| Title |
Nearby Spiral Galaxy NGC 4945 |
| Explanation |
For such a close galaxy, NGC 4945 is easy to miss. NGC 4945 [ http://www.aao.gov.au/local/www/dfm/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/ap971101.html ]. The thin disk galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap981220.html ] is oriented nearly edge-on, however, and shrouded in dark dust [ http://antwrp.gsfc.nasa.gov/apod/ap980104.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/E2p2M.html ] testing a new wide-angle, high-resolution CCD camera [ http://www.ls.eso.org/lasilla/Telescopes/2p2T/E2p2M/WFI/WFI.html ]. Most of the spots scattered about the frame are foreground stars in our own Galaxy, but some spots are globular clusters [ http://antwrp.gsfc.nasa.gov/apod/ap980719.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/ap981023.html ] 2 nucleus that might house a large black hole [ http://antwrp.gsfc.nasa.gov/apod/ap960911.html ]. |
|
The Colliding Galaxies of NG
…
| Title |
The Colliding Galaxies of NGC 520 |
| Explanation |
Is this one galaxy or two? The jumble of stars, gas, and dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] that is NGC 520 is now thought to incorporate the remains of two separate galaxies. A combination of observations and simulations indicate the NGC 520 [ http://www.kopernik.org/images/archive/n520.htm ] is actually the collision of two disk galaxies. Interesting features of NGC 520 include an unfamiliar looking tail of stars [ http://antwrp.gsfc.nasa.gov/apod/ap040515.html ] at the image bottom and a perhaps more familiar looking band of dust [ http://antwrp.gsfc.nasa.gov/apod/ap031008.html ] running diagonally across the image center. A similar looking collision might be expected were our disk Milky Way Galaxy [ http://www.seds.org/messier/more/mw.html ] to collide [ http://www.cita.utoronto.ca/~dubinski/merger/bigmerger.html ] with our large galactic neighbor Andromeda [ http://antwrp.gsfc.nasa.gov/apod/ap040718.html ] (M31). The collision that defines NGC 520 [ http://www.cv.nrao.edu/~jhibbard/n520/n520.html ] started about 300 million years ago and continues today. Although the speeds of stars are fast, the distances are so vast that the interacting pair will surely not change its shape noticeably during our lifetimes. NGC 520 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.359..455R ], at visual magnitude [ http://en.wikipedia.org/wiki/Apparent_magnitude ] 12, has been noted to be one of the brightest interacting galaxies on the sky, after interacting pairs of galaxies known as the Antennae [ http://antwrp.gsfc.nasa.gov/apod/ap971022.html ]. NGC 520 was imaged above [ http://www.gemini.edu/index.php?option=content&task=view&id=150&Itemid=0&limit=1&limitstart=1 ] in spectacular fashion by the Gemini Observatory [ http://antwrp.gsfc.nasa.gov/apod/ap030909.html ] in Hawaii [ http://en.wikipedia.org/wiki/Hawaii ], USA [ http://www.cia.gov/cia/publications/factbook/geos/us.html ]. Also known as Arp [ http://www.haltonarp.com/ ] 157, NGC 520 lies about 100 million light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] distant, spans about 100 thousand light years, and can be seen with a small telescope toward the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] of the Fish (Pisces [ http://www.astronomical.org/portal/modules/wfsection/article.php?articleid=66 ]). |
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NGC 1365: A Nearby Barred Sp
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| Title |
NGC 1365: A Nearby Barred Spiral Galaxy |
| Explanation |
Many spiral galaxies [ http://www.seds.org/messier/spir.html ] have bars across their centers. Even our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap971229.html ] is thought to have a bar [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1992ApJ...384...81W ], but perhaps not so prominent as the one in NGC 1365, shown above [ http://www.eso.org/outreach/press-rel/pr-1999/phot-08-99.html ]. The persistence and motion of the bar imply relatively massive spiral arms [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997MNRAS.288..715R ]. The placements of bright young blue stars and dark dust lanes also indicate a strong rotating density wave [ http://www.imsa.edu/edu/astro/astrostudents/97_98_1/t03p2/densitywave.html ] of star formation. NGC 1365 is a member of the Fornax Cluster of Galaxies [ http://www.astro.yorku.ca/~lee/fornax.html ]. Because NGC 1365 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999ApJ...515....1S ] is relatively nearby, simultaneous measurements [ http://antwrp.gsfc.nasa.gov/apod/ap960110.html ] of its speed and distance are possible, which help astronomers estimate how fast our universe is expanding [ http://antwrp.gsfc.nasa.gov/debate/debate96.html ]. |
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Interstellar Dust-Bunnies of
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| 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/ap971229.html ]: a spiral galaxy [ ftp://crux.astr.ua.edu/web/goodies/data_resources/galaxies.text ] seen nearly edge-on [ http://www.limber.org/eon0.html ]. However, recent high-resolution images 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://antwrp.gsfc.nasa.gov/apod/ap980217.html ]. Because dust is so fragile, its appearance after surviving disk expulsion can be very telling [ http://www.astro.wisc.edu/~howk/Papers/N891/n891.html ]. 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 1309 and Friends
| Title |
NGC 1309 and Friends |
| Explanation |
A gorgeous [ http://heritage.stsci.edu/ ] spiral galaxy some 100 million light-years distant, NGC 1309 [ http://seds.lpl.arizona.edu/~spider/ngc/ngc.cgi?NGC1309 ] lies on the banks of the constellation Eridanus [ http://www.hawastsoc.org/deepsky/eri/index.html ]. NGC 1309 spans about 30,000 light-years, one third the size of our larger Milky Way galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap050825.html ]. Bluish clusters of young stars [ http://antwrp.gsfc.nasa.gov/apod/ap990402.html ] and dust lanes are seen to trace out NGC 1309's spiral arms as they wind around an older yellowish star population at its core. Not just another pretty face-on [ http://antwrp.gsfc.nasa.gov/apod/ap040410.html ] spiral galaxy, observations of NGC 1309's recent [ http://www.rochesterastronomy.org/sn2002/ sn2002fk.html ] supernova and cepheid stars contribute to the calibration [ http://cassfos02.ucsd.edu/public/tutorial/ Distances.html ] of the expansion [ http://hubblesite.org/newscenter/newsdesk/archive/releases/ 2001/09/astrofile/ ] of the Universe. Still, after you get over this beautiful galaxy's grand [ http://curious.astro.cornell.edu/ question.php?number=199 ] design, check out [ http://hubblesite.org/newscenter/newsdesk/archive/releases/2006/07/ image/c+zoom ] the array of more distant background galaxies also recorded in the sharp Hubble Space Telescope view [ http://hubblesite.org/newscenter/newsdesk/ archive/releases/2006/07/ ]. |
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Elliptical Galaxy NGC 4881 i
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| Title |
Elliptical Galaxy NGC 4881 in Coma |
| Explanation |
Elliptical galaxies are unlike spiral galaxies and hence unlike our own Milky Way Galaxy. The giant elliptical galaxy named NGC 4881 on the upper left lies at the edge of the giant Coma Cluster of Galaxies. Elliptical galaxies are ellipsoidal in shape, contain no spiral arms, contain little interstellar gas or dust, and are found mostly in rich clusters of galaxies. Elliptical galaxies appear typically yellow-red, as opposed to spirals which have spiral arms that appear quite blue. Much speculation continues on how each type of galaxy can form, on whether ellipticals can evolve from colliding spirals, or spirals can be created from colliding ellipticals, or both. Besides the spiral galaxy on the right, all other images in this picture are of galaxies that lie well behind the Coma Cluster. |
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