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The Gum Nebula
| Title |
The Gum Nebula |
| Explanation |
Named for Australian astronomer Colin Stanley Gum [ http://en.wikipedia.org/wiki/Colin_Stanley_Gum ] (1924-1960), The Gum Nebula [ http://www.southernskyphoto.com/southern_sky/gum_nebula.htm ] is so large and close it is actually hard to see. In fact [ http://antwrp.gsfc.nasa.gov/apod/ap020217.html ], we are only about 450 light-years from the front edge and 1,500 light-years from the back edge of this cosmic cloud of glowing hydrogen gas. Covered in this 41 degree-wide [ http://canopus.physik.uni-potsdam.de/~axm/ photo.cgi?Image=images/Vela_50mm_HaRGB_1000 ] mosaic of H-alpha [ http://antwrp.gsfc.nasa.gov/apod/ap051223.html ] images, the faint emission region is otherwise easy to lose against the background of Milky Way stars. The complex [ http://adsabs.harvard.edu/cgi-bin/ nph-bib_query?bibcode=1993A%26A...280..231S ] nebula is thought to be a supernova remnant [ http://chandra.harvard.edu/xray_sources/ supernovas.html ] over a million years old, sprawling across [ http://hawastsoc.org/deepsky/car/index.html#Myth ] the southern constellations Vela and Puppis. Sliding your cursor over this spectacular wide field view will reveal the location of objects embedded in The Gum Nebula, including the Vela supernova remnant [ http://www.aao.gov.au/images/captions/ uks002.html ]. |
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Giant Cluster Bends, Breaks
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| Title |
Giant Cluster Bends, Breaks Images |
| Explanation |
What are those strange blue objects? Many are images of a "single," unusual, beaded, blue, ring-like galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap981219.html ] which just happens to line-up behind a giant cluster of galaxies. [ http://antwrp.gsfc.nasa.gov/apod/clusters_of_galaxies.html ] Cluster galaxies here appear yellow and -- together with the cluster's dark matter [ http://antwrp.gsfc.nasa.gov/apod/ap960419.html ] -- act as a gravitational lens [ http://antwrp.gsfc.nasa.gov/apod/ap951220.html ]. A gravitational lens [ http://cfa-www.harvard.edu/~jcohn/lens.html ] can create several images of background galaxies, analogous to the many points of light one would see while looking through a wine glass [ http://vela.astro.ulg.ac.be/themes/extragal/gravlens/bibdat/engl/DE/didac.html ] at a distant street light. The distinctive shape of this background galaxy [ http://www.journals.uchicago.edu/ApJ/journal/issues/ApJL/v461n2/5782/5782.html ] -- which is probably just forming -- has allowed astronomers to deduce that it has separate images at 4, 8, 9 and 10 o'clock, from the center of the cluster. Possibly even the blue smudge just left of center is yet another image! This spectacular photo from the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap970306.html ] was taken in October 1994. |
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Vela Pulsar: Neutron Star-Ri
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| Title |
Vela Pulsar: Neutron Star-Ring-Jet |
| Explanation |
This stunning image [ http://chandra.harvard.edu/photo/cycle1/vela/ ] from the orbiting Chandra X-ray Observatory [ http://chandra.harvard.edu/index.html ] is centered on the Vela pulsar -- the collapsed stellar core within the Vela supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/ap960612.html ] some 800 light-years distant. The Vela pulsar is a neutron star [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/ pulsars.html ]. More massive than the Sun, it has the density of an atomic nucleus. About 12 miles in diameter it spins 10 times a second as it hurtles through the supernova debris cloud [ http://antwrp.gsfc.nasa.gov/apod/ap980425.html ]. The pulsar's [ http://www.jb.man.ac.uk/~pulsar/Education/Sounds/ sounds.html ] electric and magnetic fields accelerate particles to nearly the speed of light, powering the compact x-ray [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/ history1_xray.html ] emission nebula revealed in the Chandra picture. The cosmic crossbow shape is over 0.2 light-years across, composed of an arrow-like jet emanating from the polar region of the neutron star [ http://astro.uchicago.edu/home/web/miller/nstar.html ] and bow-like inner and outer arcs believed to be the edges of tilted rings of x-ray emitting high energy particles. Impressively, the swept back compact nebula indicates the neutron star is moving up and to the right in this picture, exactly along the direction of the x-ray jet. The Vela pulsar (and associated supernova remnant [ http://www.seds.org/billa/twn/velax.html ]) was created by a massive star which exploded over 10,000 years ago. Its awesome x-ray rings and jet are reminiscent of another well-known pulsar powered system, the Crab Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap990929.html ]. |
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Gamma-Ray Burst: A Milestone
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| Title |
Gamma-Ray Burst: A Milestone Explosion |
| Explanation |
Gamma-Ray Bursts (GRBs) were discovered [ http://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/grbhist.html ] by accident. Thirty three years ago today, satellites first recorded a GRB [ http://antwrp.gsfc.nasa.gov/htmltest/ jbonnell/www/grbhist.html#firstburst ]. The data plotted here show that the count rate of the satellite gamma-ray instrument abruptly jumped [ http://antwrp.gsfc.nasa.gov/apod/ap991104.html ] indicating a sudden flash of gamma-rays. The Vela satellites [ http://leonardo.jpl.nasa.gov/msl/QuickLooks/velaQL.html ] that detected this and other GRBs were developed to test technology to monitor nuclear test ban treaties [ http://www.state.gov/www/global/arms/treaties/ltbt1.html ]. With on board sensors they watched [ http://antwrp.gsfc.nasa.gov/apod/ap951105.html ] for brief x-ray [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ history_xray.html ] and gamma-ray [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ history_gamma.html ] flashes, the telltale signatures of nuclear [ http://www.em.doe.gov/timeline/ ] explosions. As intended, the Velas found flashes of gamma-rays - but not from nuclear detonations near Earth. Instead, the flashes were determined to come from deep space! Dubbed "cosmic gamma-ray bursts" [ http://antwrp.gsfc.nasa.gov/apod/ap961123.html ] they are now known [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/ debate_1995.html ] to be the most powerful explosions originating in distant galaxies. What could power a gamma-ray burst [ http://www.sciam.com/0797issue/ 0797fishman.html ]? |
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ROSAT Explores The X-Ray Sky
| Title |
ROSAT Explores The X-Ray Sky |
| Explanation |
Launched in 1990, the orbiting ROSAT observatory [ http://heasarc.gsfc.nasa.gov/docs/rosat/rosat.html ] explored the Universe by viewing the entire sky in x-rays [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/ history1_xray.html ] -- photons with about 1,000 times more energy than visible light. This ROSAT survey [ http://www.xray.mpe.mpg.de/rosat/survey/sxrb/12/ass.html ] produced the sharpest, most sensitive image of the x-ray sky to date. The all-sky image is shown with the plane of our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap980523.html ] running horizontally through the center. Both x-ray brightness and relative energy are represented with red, green, and blue colors indicating three x-ray energy ranges (from lowest to highest). Bright x-ray spots near the galactic plane are within our own Milky Way. The brightest region (right of center) is toward the Vela Pulsar [ http://antwrp.gsfc.nasa.gov/apod/ap000609.html ] and the Puppis supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/ap991209.html ]. Bright sources beyond our Galaxy are also apparent, notably the Virgo cluster of galaxies [ http://www.seds.org/messier/more/virgo.html ] (near top right) and the Large Magellanic Cloud (LMC) [ http://www.seds.org/messier/xtra/ngc/lmc.html ]. The LMC is easy to find here as several of the black stripes (blank areas caused by missing data) seem to converge on its position (lower right). Over large areas of the sky a general diffuse background of x-rays [ http://chandra.harvard.edu/press/00_releases/ press_011400bg.html ] dominates. Hot gas in our own Galaxy provides much of this background and gives rise to the grand looping structures [ http://antwrp.gsfc.nasa.gov/apod/ap990503.html ] visible in the direction of the galactic center (image center). Unresolved extragalactic sources also add to this background, particularly above and below the plane. Despite the x-ray sky's exotic appearance, a very familiar feature is visible - the gas and dust clouds which line the plane of our galaxy absorb x-rays as well as optical light and produce the dark bands running through the galactic center [ http://antwrp.gsfc.nasa.gov/apod/ap000629.html ]. |
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The Gum Nebula Supernova Rem
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| Title |
The Gum Nebula Supernova Remnant |
| Explanation |
Because the Gum Nebula is the closest supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/supernova_remnants.html ], it is actually hard to see. Spanning 40 degrees [ http://math.rice.edu/~pcmi/sphere/drg_txt.html ] across the sky, the nebula is so large and faint [ http://antwrp.gsfc.nasa.gov/apod/ap000412.html ] it is easily lost in the din of a bright and complex background. The Gum Nebula [ http://www.britannica.com/bcom/eb/article/idxref/3/0,5716,363760,00.html ], highlighted nicely in the above wide angle photograph [ http://www.celestialimage.com/page107.html ], is so close that we are much nearer the front edge than the back edge, each measuring 450 and 1500 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] respectively. The complex nebula [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993A%26A...280..231S ] lies in the direction of the constellations [ http://aibn47.astro.uni-bonn.de/~gallery/constellations/const.html ] of Puppis [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Puppis.html ] and Vela [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Vela.html ]. Oddly, much remains unknown about the Gum Nebula [ http://www.edpsciences.org/articles/astro/abs/1997/07/ads1235/ads1235.html ], including the timing and even number of supernova explosions [ http://observe.ivv.nasa.gov/nasa/space/stellardeath/stellardeath_3.html ] that formed it. |
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Vela Supernova Remnant in Vi
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| Title |
Vela Supernova Remnant in Visible Light |
| Explanation |
The explosion is over but the consequences continue. About eleven thousand years ago a star in the constellation of Vela [ http://www.hawastsoc.org/deepsky/vel/index.html ] could be seen to explode [ http://www.youtube.com/watch?v=gL1xUWgBlFw ], creating a strange point of light briefly visible to humans living near the beginning of recorded history [ http://en.wikipedia.org/wiki/Cave_painting ]. The outer layers of the star crashed into the interstellar medium [ http://antwrp.gsfc.nasa.gov/apod/ap020210.html ], driving a shock wave [ http://antwrp.gsfc.nasa.gov/apod/ap020313.html ] that is still visible today. A roughly spherical, expanding shock wave is visible in X-rays [ http://antwrp.gsfc.nasa.gov/apod/ap960612.html ]. The above image [ http://www.skyfactory.org/vela/vela.htm ] captures much of that filamentary and gigantic shock in visible light [ http://imagers.gsfc.nasa.gov/ems/visible.html ], spanning almost 100 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] and appearing twenty times the diameter of the full moon [ http://antwrp.gsfc.nasa.gov/apod/ap051113.html ]. As gas flies away from the detonated star, it decays [ http://imagine.gsfc.nasa.gov/docs/features/exhibit/cgro_snr.html ] and reacts with the interstellar medium, producing light in many different colors and energy bands. Remaining at the center of the Vela Supernova Remnant [ http://en.wikipedia.org/wiki/Vela_Supernova_Remnant ] is a pulsar [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html ], a star as dense as nuclear matter that completely rotates more than ten times in a single second. |
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Illusion and Evolution in Ga
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| Title |
Illusion and Evolution in Galaxy Cluster Abell 2667 |
| Explanation |
What's happening to the galaxies of cluster Abell 2667? On the upper left, a galaxy appears to be breaking up into small pieces, while on the far right, another galaxy appears to be stretched like taffy. To start, most of the yellowish objects in the above image [ http://www.spacetelescope.org/news/html/heic0705.html ] from the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] are galactic members of a massive cluster of galaxies [ http://antwrp.gsfc.nasa.gov/apod/clusters_of_galaxies.html ] known as Abell 2667 [ http://en.wikipedia.org/wiki/Abell_2667 ]. The distortion of the galaxy on the upper left is real. As the galaxy plows through the intercluster medium [ http://www.physicsforums.com/archive/index.php/t-77572.html ], gas is stripped out and condenses to form bright new knots of stars. This detailed image of ram pressure [ http://en.wikipedia.org/wiki/Ram_pressure ] stripping helps astronomers understand why so many galaxies today have so little gas. The distortion of the galaxy on the far right, however, is an illusion [ http://en.wikipedia.org/wiki/Optical_illusion ]. This nearly normal galaxy is actually far behind the massive galaxy cluster. Light from this galaxy is gravitationally lensed [ http://www.astro.ucla.edu/~wright/cluster-lensing.html ] by Abell 2667, appearing much like a distant person would appear through [ http://vela.astro.ulg.ac.be/themes/extragal/gravlens/bibdat/engl/DE/didac.html ] a wine glass. Each distorted galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap040807.html ] gives important clues about how galaxies and clusters of galaxies evolve [ http://en.wikipedia.org/wiki/Galaxy_formation_and_evolution ]. |
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Pulsar Wind in the Vela Nebu
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| Title |
Pulsar Wind in the Vela Nebula |
| Explanation |
The Vela pulsar was born [ http://antwrp.gsfc.nasa.gov/apod/ap980425.html ] 10,000 years ago at the center of a supernova -- an exploding star [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ supernovae.html ]. In this Chandra Observatory x-ray image [ http://chandra.harvard.edu/photo/cycle1/velawv/ index.html ], the pulsar still produces a glowing nebula at the heart of the expanding cloud of stellar debris. The pulsar [ http://www.jb.man.ac.uk/~pulsar/Education/Sounds/ sounds.html ] itself is a neutron star [ http://heasarc.gsfc.nasa.gov/docs/objects/binaries/ neutron_star_structure.html ], formed as the stellar core was compacted [ http://observe.ivv.nasa.gov/nasa/space/stellardeath/ stellardeath_3a.html ] to nuclear densities. With a strong magnetic field, approximately the mass of the Sun, and a diameter of about 20 kilometers, the Vela pulsar rotates 11 times "a second". The sharp Chandra image aids astronomers [ http://xxx.lanl.gov/abs/astro-ph/0105128 ] in understanding such extreme systems as efficient high-voltage generators [ http://chandra.harvard.edu/chronicle/0201/vela.html ] which drive structured winds [ http://antwrp.gsfc.nasa.gov/apod/ap000609.html ] of electrically charged particles. An x-ray bright nebula is created as the pulsar winds slam into the surrounding material. This view spans about 6 light-years across the central region of the much larger Vela supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/ap960612.html ]. |
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The Local Bubble and the Gal
…
| Title |
The Local Bubble and the Galactic Neighborhood |
| Explanation |
What surrounds the Sun in this neck of the Milky Way Galaxy [ http://www.seds.org/messier/more/mw.html ]? Our current best guess is depicted in the above map [ http://www.sigmaxi.org/amsci/articles/00articles/Frischcap3.html ] of the surrounding 1500 light year [ http://chandra.harvard.edu/photo/cosmic_distance.html ]s constructed from various observations and deductions [ http://www.sigmaxi.org/amsci/articles/00articles/Frisch.html ]. Currently, the Sun is passing through a Local Interstellar Cloud [ http://antwrp.gsfc.nasa.gov/apod/ap020210.html ] (LIC), shown in violet, which is flowing away from the Scorpius-Centaurus Association [ http://www.mpifr-bonn.mpg.de/staff/tpreibis/scocen.html ] of young stars. The LIC resides in a low-density hole in the interstellar medium [ http://spacsun.rice.edu/~twg/lism.html ] (ISM) called the Local Bubble [ http://spacsun.rice.edu/~twg/pc120.html ], shown in black. Nearby, high-density molecular clouds [ http://antwrp.gsfc.nasa.gov/apod/ap010923.html ] including the Aquila Rift [ http://www.a.phys.nagoya-u.ac.jp/~ohnishi/aquila/aquila.html ] surround star forming regions, each shown in orange. The Gum Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap001107.html ], shown in green, is a region of hot ionized [ http://csep10.phys.utk.edu/astr162/lect/light/ionization.html ] hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ] gas. Inside the Gum Nebula [ http://www.edpsciences.org/articles/astro/abs/1997/07/ads1235/ads1235.html ] is the Vela Supernova Remnant [ http://antwrp.gsfc.nasa.gov/apod/ap960612.html ], shown in pink, which is expanding to create fragmented shells of material like the LIC [ http://antwrp.gsfc.nasa.gov/apod/ap020217.html http://www-ssg.sr.unh.edu/tof/Outreach/Interstellar/index.html ]. Future observations should help astronomers discern more about the local Galactic Neighborhood [ http://www.sigmaxi.org/amsci/articles/00articles/frischmaterial.html#environment ] and how it might have affected Earth's past climate [ http://whyfiles.news.wisc.edu/017planet/gas_cloud2.html ]. |
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Simulated Galaxy Cluster Vie
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| Title |
Simulated Galaxy Cluster View |
| Explanation |
Stunningly detailed, this picture is a computer simulated view [ http://oposite.stsci.edu/pubinfo/pr/2002/06/ index.html ] of a cluster of galaxies [ http://antwrp.gsfc.nasa.gov/apod/ clusters_of_galaxies.html ] in the distant cosmos [ http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/ HierarchUni.html ]. A large, elliptical galaxy dominates this hypothetical cluster's central region surrounded by a swarm of member galaxies. Other galaxies which lie far behind the cluster are seen as numerous visible concentric arcs [ http://antwrp.gsfc.nasa.gov/apod/ap011007.html ] - lensed by [ http://www.iam.ubc.ca/~newbury/lenses/ research.html ] the enormous gravitational [ http://vela.astro.ulg.ac.be/themes/extragal/gravlens/ bibdat/ ] field dominated by dark matter [ http://antwrp.gsfc.nasa.gov/apod/ap011024.html ] within the cluster itself. Such magnificent images are expected to be achieved by the Advanced Camera for Surveys [ http://www.ball.com/aerospace/acs.html ] (ACS), one of the upgrades [ http://sm3b.gsfc.nasa.gov/mission-critical/ objectives-part1.html ] being installed on the Hubble Space Telescope during the ongoing servicing mission [ http://spaceflight.nasa.gov/shuttle/crew/grunsfeldreports/ grunsfeldreports.html ]. Compared to Hubble's workhorse Wide Field Planetary Camera 2 [ http://hubble.stsci.edu/sci.d.tech/behind_the_pictures/ wacky_shape/constructing.shtml ] (WFPC2), whose achievements include the current deep field views [ http://www.stsci.edu/ftp/science/hdf/hdf.html ] of the Universe, the new technology ACS will be twice as sharp an imager with twice the field of view and five times the sensitivity. Along with extended views of the distant cosmos, enthusiastic astronomers also plan to use the ACS to monitor our own Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap020214.html ] and to search for planets orbiting stars [ http://www.generation.net/~mariob/astro/exoplan/ intro-e.htm ] beyond the Sun. |
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Vela Satellites: The Watcher
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| Title |
Vela Satellites: The Watchers |
| Explanation |
In October of 1963 the US Air Force [ http://www.dtic.dla.mil/airforcelink/ ] launched the first in a series of satellites inspired by a recently signed nuclear test ban treaty [ gopher://wealaka.okgeosurvey1.gov/11/nuke.treaties ]. Signatories of this treaty agreed not to test nuclear devices in the atmosphere or in space. These "Vela" (from the Spanish verb [ http://www.willamette.edu/~tjones/Language-Page.html ] velar, to watch) satellites were part of an unclassified program whose goal was to develop the technology to monitor nuclear tests from space. A Vela satellite [ http://heasarc.gsfc.nasa.gov/docs/heasarc/missions/vela5a.html ] is pictured above in an artist's conception, keeping watch over the Earth. The high energy radiation sensors onboard the Velas did not detect any clandestine nuclear explosions [ http://www.pal.xgw.fi/hew/ ]. Instead, in the most surprising discovery [ http://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/grbhist.html ] in the history of space based astronomy, they found bursts of gamma rays [ http://antwrp.gsfc.nasa.gov/apod/ap950827.html ] coming from deep space! The mysterious origin of these brief, intense flashes of gamma rays is one of the most hotly debated topics [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate.html ] in modern astrophysics. |
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Star-Forming Region RCW38 fr
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| Title |
Star-Forming Region RCW38 from 2MASS |
| Explanation |
The star cluster in RCW38 was hiding. Looking at the star forming region [ http://antwrp.gsfc.nasa.gov/apod/stellar_nurseries.html ] RCW38 [ http://www.ipac.caltech.edu/2mass/gallery/showcase/rcw38/caption.html ] will not normally reveal most of the stars in this cluster. The reason is that the open cluster [ http://antwrp.gsfc.nasa.gov/apod/open_clusters.html ] is so young that it is still shrouded in thick dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] that absorbs visible light. This dust typically accompanies the gas that condenses to form young stars. When viewed in infrared [ http://www.ipac.caltech.edu/Outreach/Edu/infrared.html ] light, however, many stars in RCW38 are revealed, because dust is less effective at absorbing infrared light. The above representative-color image [ http://www.ipac.caltech.edu/2mass/gallery/showcase/rcw38/index.html ] mosaic of RCW38 taken by the 2MASS sky survey [ http://www.ipac.caltech.edu/2mass/overview/about2mass.html#about ] in infrared light shows not only many bright blue stars from the star cluster but clouds of brightly emitting gas [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ] and dramatic lanes of dark dust. RCW38 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1987MNRAS.228..721M ] spans about 10 light-years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] and is located about 5500 light years away towards the constellation [ http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html ] of Vela [ http://www.astronomical.org/constellations/vel.html ]. |
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X-Ray Mystery in RCW 38
| Title |
X-Ray Mystery in RCW 38 |
| Explanation |
A mere 6,000 light-years distant and sailing through the constellation Vela [ http://www.hawastsoc.org/deepsky/vel/index.html ], star cluster RCW 38 [ http://antwrp.gsfc.nasa.gov/apod/ap020717.html ] is full of powerful stars. It's no surprise that these stars, only a million years young with hot outer atmospheres, appear as [ http://antwrp.gsfc.nasa.gov/apod/ap990828.html ] point-like x-ray sources dotting this x-ray image [ http://chandra.harvard.edu/photo/2002/rcw38/index.html ] from the orbiting Chandra Observatory [ http://chandra.harvard.edu/about/axaf_mission.html ]. But the diffuse cloud of x-rays surrounding them is a bit mysterious. The image is color coded by x-ray energy, with high energies in blue, medium in green, and low energy x-rays in red. Just a few light-years across, the cloud which pervades the cluster has colors suggesting the x-rays [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ history_xray.html ] are produced by high energy electrons moving through magnetic fields [ http://chandra.harvard.edu/xray_astro/xrays3.html ]. Yet a source of energetic electrons, such as shockwaves from exploding stars (supernova remnants [ http://chandra.harvard.edu/xray_sources/ supernovas.html ]), or rotating neutron stars (pulsars), is not apparent in the Chandra data. Whatever their origins, the energetic particles could leave an imprint on planetary systems forming in young star cluster RCW 38, just as nearby energetic [ http://www.pbs.org/wgbh/nova/gamma/ milkyway.html ] events seem to have affected the chemistry and isotopes found in our own solar system [ http://www.psrd.hawaii.edu/Mar00/ supernovaDebris.html ]. |
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The COMPTEL Gamma-Ray Sky
| Title |
The COMPTEL Gamma-Ray Sky |
| Explanation |
This premier gamma-ray view of the sky was produced by the COMPTEL instrument [ http://wwwgro.unh.edu:8080/comptel/comptel_main.html ] onboard NASA's orbiting Compton Gamma Ray Observatory [ http://antwrp.gsfc.nasa.gov/apod/ap951129.html ]. The entire sky is seen projected on a coordinate system centered on our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap960213.html ] with the plane of the Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap950908.html ] running across the middle of the picture. Gamma-ray intensity is represented by a false color map - low (blue) to high (white). COMPTEL's sensitivity to gamma-rays [ http://wwwgro.unh.edu:8080/comptel/comptel_highlights.html ] which have over 1 million times the energy of visible light photons reveals the locations of some of the Galaxy's most exotic objects. The brightest source, the Crab pulsar [ http://antwrp.gsfc.nasa.gov/apod/ap951122.html ], is located near the plane of the Galaxy on the far right. Moving along the plane from the Crab, more than halfway toward the galactic center, another bright gamma-ray source, the Vela pulsar [ http://heasarc.gsfc.nasa.gov/cossc/descriptions/egret_pulsars.html ], appears. The galactic center itself, along with the famous black hole candidate Cygnus X-1 [ http://www.owlnet.rice.edu/~spac250/steve/ident.html ] (near the plane, halfway from the center to the left edge) are also seen as bright sources. Both above and below the plane, spots of gamma-ray emission due to distant active galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap951023.html ] are also visible. |
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Vela Supernova Remnant in X-
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| Title |
Vela Supernova Remnant in X-ray |
| Explanation |
What happens when a star explodes? [ http://lheawww.gsfc.nasa.gov/users/jonathan/outreach_pages/supernova.html ] A huge fireball of hot gas [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#hydrogen ] shoots out in all directions. When this gas slams into the existing interstellar medium [ http://lsnt7.lightspeed.net/astronomy/ismnotes/ismnotes.html ], it heats up so much it glows in X-rays [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#X-ray ]. The above picture [ http://heasarc.gsfc.nasa.gov/Images/rosat/rosat08.html ] by the ROSAT satellite [ http://heasarc.gsfc.nasa.gov/docs/heasarc/missions/rosat.html ] has captured some of these X-rays and shown -- for the first time -- the Vela supernova explosion [ http://www.seds.org/billa/twn/velax.html ] was roughly spherical. Non-uniformity of the interstellar medium causes Vela's appearance to be irregular. [ http://adsabs.harvard.edu/cgi-bin/nph-article_query?bibcode=1994ApJ...437..209B&type=SCREEN_VIEW&data_type=GIF&page=1&db_key=AST ] The size of this X-ray emitting spherical shell is immense - 230 light years across, covering over 100 times the sky-area of the full Moon. The supernova [ http://antwrp.gsfc.nasa.gov/apod/lib/supernova.html ] that created this nebula occurred about 1500 light years away and about 11,000 years ago. Coincidently, a completely different supernova [ http://antwrp.gsfc.nasa.gov/htmltest/gifcity/msblues.html ] shell can also be seen in X-rays in this picture! It is visible as the bright patch near the upper right. This Puppis supernova remnant [ http://lheawww.gsfc.nasa.gov/users/jonathan/outreach_pages/neutron_stars.html ] nebula is actually about four times farther than the Vela nebula. |
|
ROSAT Explores the X-Ray Sky
| Title |
ROSAT Explores the X-Ray Sky |
| Explanation |
Launched in 1990, the orbiting ROSAT observatory [ http://legacy.gsfc.nasa.gov/docs/heasarc/missions/rosat.html ] explored the Universe by viewing the entire sky in x-rays [ http://heasarc.gsfc.nasa.gov/docs/learning_center/ basic/xray/xray_information.html ] - photons with about 1,000 times more energy than visible light [ http://heasarc.gsfc.nasa.gov/docs/learning_center/ basic/emspectrum.html ]. This ROSAT survey [ http://www.rosat.mpe-garching.mpg.de/survey/sxrb/ ] produced the sharpest, most sensitive image of the x-ray sky to date. The all-sky image is shown with the plane of our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap960213.html ] running horizontally through the center. Both x-ray brightness and relative energy are represented with red, green, and blue colors indicating three x-ray energy ranges (from lowest to highest). Bright x-ray spots near the galactic plane are within our own Milky Way. The brightest region (right of center) is toward the Vela Pulsar and the Puppis supernova remnant [ http://lheawww.gsfc.nasa.gov/users/jonathan/outreach_pages/ neutron_stars.html ]. Bright sources beyond our Galaxy are also apparent, notably the Virgo cluster of galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap960419.html ] (near top right) and the Large Magellanic Cloud (LMC) [ http://antwrp.gsfc.nasa.gov/apod/ap950918.html ]. The LMC is easy to find here as several of the black stripes (blank areas caused by missing data) seem to converge on its position (lower right). Over large areas of the sky a general diffuse background of x-rays dominates [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ%2E%2E%2E454%2E%2E643S&db_key=AST ]. Hot gas in our own Galaxy provides much of this background and gives rise to the grand looping structures visible in the direction of the galactic center (image center). Unresolved extragalactic sources also add to this background, particularly above and below the plane. Despite the x-ray sky's exotic appearance, a very familiar feature is visible - the gas and dust clouds which line the plane of our galaxy absorb x-rays as well as optical light and produce the dark bands running through the galactic center [ http://antwrp.gsfc.nasa.gov/apod/ap960605.html ]. |
|
The Gum Nebula Supernova Rem
…
| Title |
The Gum Nebula Supernova Remnant |
| Explanation |
Because the Gum Nebula is the closest supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/supernova_remnants.html ], it is actually hard to see. Spanning 40 degrees [ http://math.rice.edu/~pcmi/sphere/drg_txt.html ] across the sky, the nebula is so large and faint [ http://antwrp.gsfc.nasa.gov/apod/ap020217.html ] it is easily lost in the din of a bright and complex background. The Gum Nebula [ http://www.southernskyphoto.com/southern_sky/gum_nebula.htm ], highlighted nicely in the above wide angle photograph [ http://www.celestialimage.com/page107.html ], is so close that we are much nearer the front edge than the back edge, each measuring 450 and 1500 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] respectively. The complex nebula [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1993A%26A...280..231S ] lies in the direction of the constellations [ http://www.dibonsmith.com/stars.htm ] of Puppis [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Puppis.html ] and Vela [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Vela.html ]. Oddly, much remains unknown about the Gum Nebula [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001MNRAS.325.1213W ], including the timing and even number of supernova explosions [ http://heasarc.gsfc.nasa.gov/docs/snr.html ] that formed it. |
|
The Pencil Nebula Supernova
…
| Title |
The Pencil Nebula Supernova Shockwave |
| Explanation |
At 500,000 kilometers per hour, a supernova [ http://heasarc.gsfc.nasa.gov/docs/snr.html ] shockwave [ http://www.sciam.com/article.cfm?articleID=0004A908-9AAC-1CDC-B4A8809EC588EEDF ] plows through interstellar space. This shockwave is known as the Pencil Nebula [ http://www.ast.cam.ac.uk/AAO/images/captions/aat084.html ], or NGC 2736, and is part of the Vela supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/ap960612.html ], an expanding shell of a star that exploded about 11,000 years ago. Initially the shockwave [ http://heritage.stsci.edu/2003/16/caption.html ] was moving at millions of kilometers per hour, but the weight of all the gas it has swept up has slowed it considerably. Pictured above [ http://hubblesite.org/newscenter/archive/2003/16/image/a ], the shockwave [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003ApJ...589..242S ] moves from left to right, as can be discerned by the lack of gas on the left. The above region [ http://heritage.stsci.edu/2003/16/fast_facts.html ] spans nearly a light year [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] across, a small part of the 100+ light-year span of the entire Vela supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/ap990803.html ]. The Hubble Space Telscope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] ACS [ http://acs.pha.jhu.edu/ ] captured the above image last October. |
|
The Vela Pulsar's Dynamic Je
…
| Title |
The Vela Pulsar's Dynamic Jet |
| Explanation |
The Vela pulsar [ http://www.jb.man.ac.uk/~pulsar/Education/Sounds/ sounds.html ] is a neutron star born over 10,000 years ago in a massive supernova explosion [ http://antwrp.gsfc.nasa.gov/apod/ap030609.html ]. Above, false-color x-ray images [ http://chandra.harvard.edu/press/03_releases/ press_063003.html ] from the Chandra Observatory [ http://chandra.harvard.edu/about/top_ten.html ] reveal details of this remnant pulsar's x-ray bright nebula [ http://antwrp.gsfc.nasa.gov/apod/ap000609.html ] along with emission from a spectacular jet of high-energy particles. In this time-lapse series [ http://chandra.harvard.edu/photo/2003/vela_pulsar/ animations.html ] of pictures, the jet seems to dance [ http://xxx.lanl.gov/abs/astro-ph/0305510 ] around very much like an out-of-control firehose, shooting along the pulsar's direction of motion (toward the top right corner) to a length of about half a light-year while whipping back and forth at about half the speed of light. Highly magnetized and spinning over 10 times a second, the Vela pulsar is thought of as a cosmic high-voltage [ http://chandra.harvard.edu/chronicle/0201/vela.html ] generator, powering the x-ray nebula and dynamic cosmic jet. A mere [ http://antwrp.gsfc.nasa.gov/apod/ap000412.html ] 800 light-years away the pulsar itself is located near the lower left corner in the four panels. |
|
Composite Crab
| Title |
Composite Crab |
| Explanation |
The Crab Pulsar, a city-sized, magnetized neutron star [ http://antwrp.gsfc.nasa.gov/apod/ap030201.html ] spinning 30 times a second, lies at the center of this composite image of the inner region of the well-known Crab Nebula [ http://www.seds.org/messier/m/m001.html ]. The spectacular picture combines optical data (red) from the Hubble Space Telescope [ http://hubblesite.org/gallery/ ] and x-ray images (blue) from the Chandra Observatory [ http://chandra.harvard.edu/chronicle/0303/top_ten/ ], also used in the popular Crab Pulsar movies [ http://chandra.harvard.edu/photo/2002/0052/movies.html ]. Like a cosmic dynamo [ http://chandra.harvard.edu/chronicle/0201/vela.html ] the pulsar powers [ http://antwrp.gsfc.nasa.gov/apod/ap010602.html ] the x-ray and optical emission from the nebula, accelerating charged particles and producing the eerie, glowing x-ray jets. Ring-like structures are x-ray emitting regions where the high energy particles slam into the nebular material. The innermost ring is about a light-year across. With more mass than the Sun [ http://www.sunblock99.org.uk/sb99/fact/heavy.html ] and the density of an atomic nucleus [ http://hyperphysics.phy-astr.gsu.edu/hbase/ nuclear/nucuni.html#c2 ], the spinning pulsar is the collapsed core of a massive star that exploded, while the nebula is the expanding remnant of the star's outer layers. The supernova explosion was witnessed in the year 1054 [ http://www.seds.org/messier/more/m001_sn.html ]. |
|
Gamma-Ray Burst: A Milestone
…
| Title |
Gamma-Ray Burst: A Milestone Explosion |
| Explanation |
Gamma-Ray Bursts (GRBs) were discovered [ http://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/grbhist.html ] by accident. In fact, GRBs [ http://antwrp.gsfc.nasa.gov/apod/ap970625.html ] always seem to be where scientists least expect them. Thirty years ago today, satellites first recorded a GRB [ http://antwrp.gsfc.nasa.gov/htmltest/ jbonnell/www/grbhist.html#firstburst ]. The burst data plotted in this histogram [ http://www.stat.ufl.edu/~hyper/Sections/lect2/node17.html ] show that the count rate of the gamma-ray instrument abruptly jumped indicating a sudden flash of gamma-rays. The Vela satellites [ http://antwrp.gsfc.nasa.gov/apod/ap951105.html ] that detected this and other GRBs were developed to test technology to monitor nuclear test ban treaties [ gopher://wealaka.okgeosurvey1.gov:70/00/nuke.treaties/LTBT ]. With on board sensors they watched for brief X-ray and gamma-ray [ http://heasarc.gsfc.nasa.gov/docs/ learning_center/basic/emspectrum.html ] flashes, the telltale signs of nuclear explosions from the vicinity of the Earth [ gopher://wealaka.okgeosurvey1.gov:70/11/nuke.cat ]. As intended, the Velas found flashes of gamma-rays - but not from nuclear detonations near Earth. Instead, the flashes came from deep space! Dubbed "cosmic gamma-ray bursts" [ http://antwrp.gsfc.nasa.gov/apod/ap961123.html ] their origin was then unknown and is still controversial [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate_1995.html ]. However, the gamma-ray surprises were not over. Exploring the high-energy sky [ http://antwrp.gsfc.nasa.gov/apod/ap970222.html ] nearly 25 years later, the orbiting Compton Observatory's Burst and Transient Source Experiment (BATSE) [ http://www.batse.msfc.nasa.gov/astronomy/batse/harmon_allsky.html ], intentionally designed to detect cosmic gamma-ray bursts [ http://www.batse.msfc.nasa.gov/data/grb/skymap/ ], was searching for clues to the GRB mystery. But the second burst BATSE recorded did not come from deep space. It came from near the Earth! Don't worry, these terrestrial GRBs are not nuclear bombs exploding. They are a new phenomenon now thought [ http://www.batse.msfc.nasa.gov/astronomy/fishman_tgf.html ] to be related to a recently discovered type of high altitude lightning [ http://antwrp.gsfc.nasa.gov/apod/ap951111.html ]. Exploring new horizons continues to yield unexpected results. [ http://antwrp.gsfc.nasa.gov/apod/ap960915.html ] |
|
Vela Supernova Remnant in Op
…
| Title |
Vela Supernova Remnant in Optical Credit: Photograph made from plates taken with the UK Schmidt Telescope [ http://www.roe.ac.uk/ukstu/ukst.html ]. Color photography by David Malin. Copyright: Anglo-Australian Telescope Board [ http://www.aao.gov.au/images.html ] |
| Explanation |
About 11,000 years ago a star in the constellation of Vela [ http://galileo.gmu.edu/constellation/VEL.html ] exploded. This bright supernova [ http://antwrp.gsfc.nasa.gov/apod/lib/supernova.html ] may have been visible to the first human farmers. Today the Vela supernova remnant [ http://www.seds.org/billa/twn/velax.html ] marks the position of a relatively close and recent explosion in our Galaxy [ http://antwrp.gsfc.nasa.gov/apod/lib/milky_way.html ]. A roughly spherical, expanding shock wave is visible in X-rays [ http://antwrp.gsfc.nasa.gov/apod/ap960611.html ]. In the above optical photograph, the upper left corner of the spherical blast wave is shown in detail. As gas flies away from the detonated star [ http://lheawww.gsfc.nasa.gov/users/jonathan/outreach_pages/supernova.html ], it reacts with the interstellar medium [ http://www-dapnia.cea.fr/Phys/Sap/Report/interstellar_medium.html ], knocking away closely held electrons from even heavy elements [ http://pdg.lbl.gov/cpep/adventure.html ]. When the electrons recombine with these atoms [ http://adsabs.harvard.edu/cgi-bin/nph-article_query?bibcode=1995ApJ%2E%2E%2E440%2E%2E227J&page=1&plate_select=NO&type=GIF ], light in many different colors and energy bands [ http://heasarc.gsfc.nasa.gov/docs/learning_center/basic/emspectrum.html ] is produced. |
|
Young Star, Dark Cloud
| Title |
Young Star, Dark Cloud |
| Explanation |
High-speed outflows of molecular gas from a young stellar object glow in infrared light, revealing themselves in this recent false-color image from the Spitzer Space Telescope [ http://www.spitzer.caltech.edu/Media/releases/ssc2003-06/ ssc2003-06f.shtml ]. Cataloged as [ http://www-astro.phast.umass.edu/catalogs/HHcat/ HHintro.html ] HH (Herbig-Haro) 46/47 the infrared source [ http://coolcosmos.ipac.caltech.edu/image_galleries/ ir_zoo/horse.html ] is lodged within a dark nebula or Bok globule - near the lower right corner of the dark nebula in the optical inset - that is largely opaque when viewed [ http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ multiwavelength_astronomy/multiwavelength_astronomy/ index.html ] in visible light. The energetic outflow [ http://hubblesite.org/newscenter/newsdesk/archive/ releases/1995/24/image/a ] features extend for nearly a light-year, burrowing into the dark interstellar material, and are attributed to [ http://photojournal.jpl.nasa.gov/catalog/PIA04940 ] early stages in the life of a sun-like star. They may well represent a phase of our own Sun's evolution [ http://www.columbia.edu/~ah297/unesa/sun/ sun-chapter5.html ] which took place some 4.5 billion years ago, along with the formation of our solar system from a circumstellar disk [ http://antwrp.gsfc.nasa.gov/apod/ap030208.html ]. A tantalizing [ http://planetquest.jpl.nasa.gov/ ] object to explore with Spitzer's infrared [ http://www.spitzer.caltech.edu/science/whyir/ index.shtml ] capabilities, this young star system [ http://arxiv.org/abs/astro-ph/0304258 ] is relatively nearby, located only some 1,140 light-years distant in the nautical constellation Vela [ http://www.hawastsoc.org/deepsky/vel/index.html ]. |
|
Runaway Star
| Title |
Runaway Star |
| Explanation |
Runaway stars are massive stars [ http://www.eso.org/outreach/press-rel/pr-1997/pr-01-97.html ] traveling rapidly through interstellar space. Like a ship plowing through the interstellar medium [ http://antwrp.gsfc.nasa.gov/apod/ap961218.html ], runaway star HD 77581 has produced this graceful arcing bow wave or "bow shock" - compressing the gaseous material in its path. Located near the centre of this European Southern Observatory photograph [ http://www.eso.org/outreach/press-rel/pr-1997/phot-02-97.html ], HD 77581 itself is so bright that it saturates the sensitive camera and produces the spiky cross shape. This star is over 6,000 light-years away in the constellation Vela [ http://www.astro.wisc.edu/~dolan/constellations/ constellations/Vela.html ], and appears to move at over 50 miles per second. What force could set this star in motion [ http://www.aas.org/meetings/aas184/abs/S601.html ]? A clue to the answer may lie in its optically invisible companion star, an X-ray bright [ http://antwrp.gsfc.nasa.gov/apod/ap961008.html ] pulsar [ http://antwrp.gsfc.nasa.gov/apod/ap960531.html ] known as Vela X-1. This pulsar [ http://crazyhorse.msfc.nasa.gov/data/pulsar/sources/velax1nml.html ] is clearly the remnant of a supernova explosion [ http://legacy.gsfc.nasa.gov/docs/snr.html ] ... which seems to have given this massive star and its companion a mighty kick [ http://antwrp.gsfc.nasa.gov/apod/ap970225.html ]! |
|
Abell 2218: A Galaxy Cluster
…
| Title |
Abell 2218: A Galaxy Cluster Lens |
| Explanation |
Gravity can bend light [ http://antwrp.gsfc.nasa.gov/apod/ap951126.html ]. Almost all of the bright objects in this Hubble Space Telescope image [ http://oposite.stsci.edu/pubinfo/PR/95/14.html ] are galaxies in the cluster known as Abell 2218. The cluster is so massive and so compact that its gravity bends and focuses the light [ http://vela.astro.ulg.ac.be/themes/extragal/gravlens/ bibdat/engl/glc_homepage.html ] from galaxies that lie behind it. As a result, multiple images of these background galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap951220.html ] are distorted into faint stretched out arcs - a simple lensing effect analogous to viewing distant street lamps through a glass of wine. The Abell 2218 cluster itself is about 3 billion light-years away in the northern constellation Draco [ http://astro.gmu.edu/constellation/DRA.html ]. |
|
A Bulls-Eye Einstein Ring
| Title |
A Bulls-Eye Einstein Ring |
| Explanation |
Can one galaxy hide behind another? Not in the case of B1938+666 [ http://www.jb.man.ac.uk/ceres/1938/1938.html ]. Here the foreground galaxy acts like a huge gravitational lens [ http://antwrp.gsfc.nasa.gov/apod/ap970503.html ], pulling the light from the background object around it, keeping it visible. Here the alignment is so precise that the distant galaxy is distorted into a nearly perfect giant ring around the foreground galaxy, a formation known as an Einstein ring [ http://www.iam.ubc.ca/spider/newbury/lenses/Einstein_rings.html ]. The bright peak at the center of the bulls-eye is the nearer galaxy. The cosmic mirage [ http://vela.astro.ulg.ac.be/themes/extragal/gravlens/bibdat/engl/index.html ] was found initially with the MERLIN radio telescope array [ http://www.jb.man.ac.uk/merlin/about/layman/merlin.html ]. The follow-up image shown above from the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap950810.html ] was released [ http://www.jb.man.ac.uk/merlin/press/PR9801/press.html ] earlier today. Although appearing extremely small at 1 arcsecond [ http://proxima.astro.virginia.edu/~pai/Text/coords/subsection4_1.html ] diameter, the above Einstein ring [ http://antwrp.gsfc.nasa.gov/htmltest/gifcity/nslens_effects.html ] is really tens of thousands of light years across. |
|
X-Ray Mystery in RCW 38
| Title |
X-Ray Mystery in RCW 38 |
| Explanation |
A mere 6,000 light-years distant and sailing through the constellation Vela [ http://www.hawastsoc.org/deepsky/vel/index.html ], star cluster RCW 38 [ http://antwrp.gsfc.nasa.gov/apod/ap020717.html ] is full of powerful stars. It's no surprise that these stars, only a million years young with hot outer atmospheres, appear as [ http://antwrp.gsfc.nasa.gov/apod/ap990828.html ] point-like x-ray sources dotting this x-ray image [ http://chandra.harvard.edu/photo/2002/rcw38/index.html ] from the orbiting Chandra Observatory [ http://chandra.harvard.edu/ ]. But the diffuse cloud of x-rays surrounding them is a bit mysterious. The image is color coded by x-ray energy, with high energies in blue, medium in green, and low energy x-rays in red. Just a few light-years across, the cloud which pervades the cluster has colors suggesting the x-rays [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ history_xray.html ] are produced by high energy electrons moving through magnetic fields [ http://chandra.harvard.edu/xray_astro/xrays3.html ]. Yet a source of energetic electrons, such as shockwaves from exploding stars (supernova remnants [ http://chandra.harvard.edu/xray_sources/ supernovas.html ]), or rotating neutron stars (pulsars [ http://imagine.gsfc.nasa.gov/docs/science/ know_l1/pulsars.html ]), is not apparent in the Chandra data. Whatever their origins, the energetic particles could leave an imprint on planetary systems forming in young star cluster RCW 38, just as nearby energetic [ http://www.pbs.org/wgbh/nova/gamma/ milkyway.html ] events seem to have affected the chemistry and isotopes found in our own solar system [ http://www.psrd.hawaii.edu/Mar00/ supernovaDebris.html ]. |
|
PG 1115+080 A Ghost of Lensi
…
| Title |
PG 1115+080 A Ghost of Lensing Past |
| Explanation |
In this tangle of quasars and galaxies lies a clue to the expansion rate of the universe. A diffuse glow evident in the picture on the left reveals a normal elliptical galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap961106.html ]. Directly behind this galaxy lies a normal quasar [ http://antwrp.gsfc.nasa.gov/apod/ap980409.html ]. Because the quasar [ http://antwrp.gsfc.nasa.gov/apod/ap971206.html ] is directly behind the galaxy, however, the gravity of the galaxy deflects quasar light like a lens [ http://vela.astro.ulg.ac.be/themes/extragal/gravlens/bibdat/engl/index.html ], creating four bright images [ http://antwrp.gsfc.nasa.gov/apod/ap951220.html ] of the same distant quasar. When these images are all digitally subtracted, a distorted image of the background galaxy that hosts the quasar appears - here shown on the right in ghostly white. Each quasar [ http://www.student.nada.kth.se/~f93-cal/Qcontents.html ] image traces how the quasar looked at different times in the past, with the time between images influenced by the expansion rate [ http://antwrp.gsfc.nasa.gov/apod/ap960513.html ] of the universe itself. Assuming dark matter in the elliptical lens [ http://antwrp.gsfc.nasa.gov/apod/ap980111.html ] galaxy traces the visible matter, this expansion rate [ http://antwrp.gsfc.nasa.gov/debate/debate96.html ] can be characterized by a Hubble constant [ http://csep1.phy.ornl.gov/guidry/violence/hubble_constant.html ] of Ho near 65 km/sec/Mpc, a value close to that determined by other methods [ http://antwrp.gsfc.nasa.gov/apod/ap960110.html ]. Analysis [ http://xxx.lanl.gov/abs/astro-ph/9803207 ] of this image [ http://oposite.stsci.edu/pubinfo/pr/1998/37/ab.html ] by itself sheds little light on whether the global geometry of the universe [ http://antwrp.gsfc.nasa.gov/apod/ap980302.html ] is affected by a cosmological constant [ http://super.colorado.edu/~michaele/lambda.html ]. |
|
Composite Crab
| Title |
Composite Crab |
| Explanation |
The Crab Pulsar, a city-sized, magnetized neutron star [ http://antwrp.gsfc.nasa.gov/apod/ap030201.html ] spinning 30 times a second, lies at the center of this composite image of the inner region of the well-known Crab Nebula [ http://www.seds.org/messier/m/m001.html ]. The spectacular picture combines optical data (red) from the Hubble Space Telescope [ http://hubblesite.org/gallery/ ] and x-ray images (blue) from the Chandra Observatory [ http://chandra.harvard.edu/fifth/ ], also used in the popular Crab Pulsar movies [ http://chandra.harvard.edu/photo/2002/0052/movies.html ]. Like a cosmic dynamo [ http://chandra.harvard.edu/chronicle/0201/vela.html ] the pulsar powers [ http://antwrp.gsfc.nasa.gov/apod/ap010602.html ] the x-ray and optical emission from the nebula, accelerating charged particles and producing the eerie, glowing x-ray jets. Ring-like structures are x-ray emitting regions where the high energy particles slam into the nebular material. The innermost ring is about a light-year across. With more mass than the Sun [ http://www.sunblock99.org.uk/sb99/fact/heavy.html ] and the density of an atomic nucleus [ http://hyperphysics.phy-astr.gsu.edu/hbase/ nuclear/nucuni.html#c2 ], the spinning pulsar is the collapsed core of a massive star that exploded, while the nebula is the expanding remnant of the star's outer layers. The supernova explosion was witnessed in the year 1054 [ http://www.seds.org/messier/more/m001_sn.html ]. |
|
Star-Forming Region RCW38
| Title |
Star-Forming Region RCW38 |
| Explanation |
Star cluster RCW38 was hiding. This open cluster [ http://antwrp.gsfc.nasa.gov/apod/ap980329.html ] of stars is located about 5000 light years away towards the constellation of Vela [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Vela.html ]. Looking there will not normally reveal most of the stars in this cluster, though. The reason is that the open cluster [ http://antwrp.gsfc.nasa.gov/apod/ap980803.html ] is so young that it is still shrouded in thick dust [ http://antwrp.gsfc.nasa.gov/apod/ap980104.html ] that absorbs visible light. This dust typically accompanies the gas that condenses to form young stars [ http://antwrp.gsfc.nasa.gov/apod/ap980412.html ]. When viewed in infrared light [ http://www.ipac.caltech.edu/Outreach/Edu/discovery.html ], however, the star cluster in RCW38 [ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1987MNRAS.228..721M ] is revealed, because dust is less effective at absorbing infrared light. The above photograph [ http://www.eso.org/outreach/press-rel/pr-1998/pr-19-98.html ] was one of the first ever taken with the new Infrared Spectrometer and Array Camera [ http://www.eso.org/instruments/isaac/ ] (ISAAC) affixed to the 8.2-meter Very Large Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap960901.html ]. |
|
Ring Around the Galaxy
| Title |
Ring Around the Galaxy |
| Explanation |
It is difficult to hide one galaxy far behind another. The closer galaxy's gravity will act like a huge lens [ http://imagine.gsfc.nasa.gov/docs/features/news/grav_lens.html ], pulling images of the background galaxy around both sides. This is just the case observed in the above recently released image [ http://www.eso.org/outreach/press-rel/pr-1998/pr-20-98.html ] from the VLT [ http://antwrp.gsfc.nasa.gov/apod/ap960901.html ]: the red galaxy in the middle is in the foreground, lensing the image of the background green galaxy into surrounding contorted arcs [ http://antwrp.gsfc.nasa.gov/apod/ap981102.html ]. These images are more than sideshow [ http://vela.astro.ulg.ac.be/themes/extragal/gravlens/bibdat/engl/DE/DE106/didac106.html ]s, since the distance between background images increases [ http://vela.astro.ulg.ac.be/themes/extragal/gravlens/bibdat/engl/DE/DE103/didac103.html ] with the mass of the lens. This lens mass turns out to be much greater than the sum of all its stars - indicating the presence of dark matter [ http://www.sciam.com/specialissues/0398cosmos/0398rubin.html ]. The distorted galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap980614.html ] is said to appear as an Einstein ring [ http://antwrp.gsfc.nasa.gov/htmltest/gifcity/nslens_effects.html ], named after Albert Einstein [ http://antwrp.gsfc.nasa.gov/apod/ap980927.html ] who accurately predicted many attributes of the gravitational lens effect [ http://vela.astro.ulg.ac.be/themes/extragal/gravlens/bibdat/engl/index.html ] -- although he also guessed that such an effect was unlikely to be seen in practice. |
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Kitt Peak National Observato
…
| Title |
Kitt Peak National Observatory |
| Explanation |
At the top of Kitt Peak Mountain near Tucson [ http://www.ci.tucson.az.us/ ], Arizona [ http://www.state.az.us/ ] lies one of the world's great collections of telescopes. As pictured [ http://www.noao.edu/image_gallery/html/im0411.html ], in the dome at the far left lies the 3.5-meter WIYN Telescope [ http://www.noao.edu/kpno/40th/wiyn.html ], famous recently for tracking distant supernovae. The next major dome to the right houses a 36-inch telescope [ http://www.noao.edu/kpno/40th/small_tel.html ] now used mostly for imaging. Farther to the right beside a thin tower is a 2.1-meter Telescope [ http://www.noao.edu/kpno/40th/2.1m.html ] used currently for imaging and spectroscopy. The unusual triangular building houses the McMath-Pierce Solar Telescope [ http://www.noao.edu/kpno/40th/mcpierce.html ]. In front of it lies the Vacuum Tower Telescope [ http://www.noao.edu/image_gallery/html/im0216.html ] while in back are the Burrell-Schmidt Telescope [ http://www.noao.edu/image_gallery/html/im0341.html ] and the SARA 0.9-meter automated telescope. At the far right lies one of the world's largest telescopes: the 4-meter Mayall Reflector [ http://www.noao.edu/kpno/40th/4m.html ]. Kitt Peak recently celebrated its 40th year [ http://www.noao.edu/kpno/40th/ ] during which it helped establish the existence of dark matter [ http://www.sciam.com/specialissues/0398cosmos/0398rubin.html ] and the first gravitational lens [ http://vela.astro.ulg.ac.be/themes/extragal/gravlens/bibdat/engl/index.html ]. Kitt Peak National Observatory [ http://www.noao.edu/kpno/ ] is part of the United States' National Optical Astronomical Observatories [ http://www.noao.edu/noao.html ] and is operated under agreement with the National Science Foundation [ http://www.nsf.gov/ ]. |
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PG 1115+080: A Gravitational
…
| Title |
PG 1115+080: A Gravitational Cloverleaf |
| Explanation |
All four blue images in the above photograph [ http://www.subaru.naoj.org/outreach/press_releases/990128/ ] are the same object. The gravitational lens [ http://vela.astro.ulg.ac.be/themes/extragal/gravlens/bibdat/engl/index.html ] effect of the red, foreground, elliptical galaxy [ http://www.seds.org/messier/elli.html ] visible near image center creates a cloverleaf image of the single distant quasar [ http://antwrp.gsfc.nasa.gov/apod/ap980409.html ]. Light from the quasar [ http://www.student.nada.kth.se/~f93-cal/Qcontents.html ] is pulled around the massive galaxy in different paths, corresponding to different images. Light takes many billions of years to reach us from this quasar. Since light takes a different amount of time to traverse each path, each image shows the quasar as it appeared at a slightly different time in the past, creating time delays [ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1998PASJ...50..175A ] on the time scale of days. Since these time delays are influenced by the expansion rate of the universe [ http://antwrp.gsfc.nasa.gov/debate/debate96.html ], analysis of this image helps reveal Hubble's constant [ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1996PASP%2E%2E108%2E1073T ], the parameter that calibrates universe expansion [ http://www.astro.ucla.edu/~wright/cosmology_faq.html ]. This recent picture [ http://www.subaru.naoj.org/outreach/press_releases/990128/ ] by the new Subaru Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap990201.html ] is perhaps the clearest image yet of this famous optical mirage [ http://antwrp.gsfc.nasa.gov/apod/ap981102.html ]. |
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The Case of the Missing Supe
…
| Title |
The Case of the Missing Supernova |
| Explanation |
Would you notice a second Moon in the sky? About 700 years ago, light from a tremendous explosion [ ftp://pao.gsfc.nasa.gov/pub/pao/releases/1999/99-037.htm ] reached Earth that should have appeared almost as bright as a full Moon. The bright spot should have lasted for weeks, yet no notation of such an occurrence has been found in historical records. The mystery was uncovered by Wan Chen [ http://lheawww.gsfc.nasa.gov/users/chen/CV.html ] and Neil Gehrels [ http://lheawww.gsfc.nasa.gov/users/gehrels/ShtBio/gehrels.html ] (NASA/GSFC [ http://www.gsfc.nasa.gov/GSFC_homepage.html ]) when studying the source of radioactive elements [ http://nucleardata.nuclear.lu.se/nucleardata/ ] toward the Vela supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/ap960612.html ]. They deduced that an explosion much younger and closer than the supernova [ http://antwrp.gsfc.nasa.gov/apod/ap990209.html ] that caused Vela must have occurred, and even computed explosion characteristics from the amounts of radioactive elements [ http://antwrp.gsfc.nasa.gov/apod/ap960724.html ] present. They calculate that GRO/RX J0852 should have dazzled medieval stargazers [ http://www.astro.uni-bonn.de/~pbrosche/astoria.html ]. Perhaps people were too busy, surviving records are too incomplete, or the explosion was somehow too dim. The above picture of GRO/RX J0852 was taken in gamma-ray light [ http://cossc.gsfc.nasa.gov/cossc/outreach/bro/bro2.html ] with the Compton Gamma-Ray Observatory [ http://antwrp.gsfc.nasa.gov/apod/ap950811.html ] and is shown in false-color. Astronomers and historians continue to contemplate the clues. |
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Introducing Nova Velorum 199
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| Title |
Introducing Nova Velorum 1999 |
| Explanation |
A bright nova was discovered Saturday that is currently visible to the unaided eye in southern skies. Nova Velorum 1999 [ http://cfa-www.harvard.edu/iauc/07100/07176.html ] was recorded near visual magnitude 3 independently by discoverers Peter Williams and Alan C. Gilmore (Mt. John U. Obs. [ http://www.phys.canterbury.ac.nz/research/astronomy/astronomy_mjuo_facilities.html ]), making it more luminous than many famous bright stars. The last nova this bright was Nova Cygni 1975 [ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1976PASJ...28..163K ], which peaked just brighter than magnitude 2. Nova Velorum [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Vela.html ] 1999 is brighter now than the well-studied Nova Cygni 1992 [ http://antwrp.gsfc.nasa.gov/apod/ap951227.html ] ever appeared [ http://antwrp.gsfc.nasa.gov/apod/ap961216.html ]. A nova [ http://www.sciam.com/specialissues/0398cosmos/0398starrfield.html ] occurs when the surface of a white dwarf star [ http://antwrp.gsfc.nasa.gov/apod/ap971102.html ] undergoes a tremendous thermonuclear [ http://fusedweb.pppl.gov/ ] explosion, throwing off its outer layers. How the nova will appear over the next few weeks is uncertain, but the exploding debris will likely fade beyond detectability over the next few years. The above photograph [ http://www.ozemail.com.au/~loomberah/novavel.htm ] of Nova Velorum 1999 was taken yesterday from Australia. The cross-hair like spikes [ http://antwrp.gsfc.nasa.gov/apod/ap971119.html ] that appear around it were caused by the photographing telescope and camera. |
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A Gallery of Gravitational M
…
| Title |
A Gallery of Gravitational Mirages |
| Explanation |
The deeper you peer into the universe, the harder it is to see straight. The reason is that distant galaxies act as gravitational lenses [ http://vela.astro.ulg.ac.be/themes/extragal/gravlens/bibdat/engl/index.html ], deflecting light that passes nearby. These deflections result in the distortion of background sources [ http://antwrp.gsfc.nasa.gov/apod/ap980614.html ], and in some cases the creation of multiple images [ http://antwrp.gsfc.nasa.gov/apod/ap990331.html ]. Pictured above [ http://oposite.stsci.edu/pubinfo/pr/1999/18/index.html ], candidate artifacts of gravitational lensing [ http://imagine.gsfc.nasa.gov/docs/features/news/grav_lens.html ] have been found [ http://xxx.lanl.gov/abs/astro-ph/9902100 ] in images from the Medium Deep Survey [ http://archive.stsci.edu/mds/index.html ] being done with the Hubble Space Telescope [ http://www.stsci.edu/hst/ ]. Background source images that are lensed [ http://science.nasa.gov/newhome/headlines/ast14may99_1.htm ] by foreground galaxies include quasars, appearing as multiple blue smudges [ http://antwrp.gsfc.nasa.gov/apod/ap951220.html ], and galaxies, distorted into curving arcs [ http://antwrp.gsfc.nasa.gov/apod/ap981223.html ]. Unusual and interesting candidates [ http://oposite.stsci.edu/pubinfo/pr/1999/18/extra-photos.html ] for gravitational lensing include an edge-on galaxy disk [ http://antwrp.gsfc.nasa.gov/apod/ap981220.html ] which might be acting as a lens (upper left) and an image nicknamed London Underground [ http://www.jle.lul.co.uk/ ] (far left) which could well be the distortion of a background galaxy into an optical Einstein ring [ http://antwrp.gsfc.nasa.gov/apod/ap981102.html ]. |
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The Vela Supernova Remnant E
…
| Title |
The Vela Supernova Remnant Expands |
| Explanation |
The explosion is over but the consequences continue. About eleven thousand years ago a star in the constellation of Vela [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Vela.html ] exploded, creating a strange point of light [ http://www.aao.gov.au/local/www/dfm/uks002.html ] briefly visible to humans living near the beginning of recorded history [ http://warrensburg.k12.mo.us/ew/human.html ]. The outer layers of the star crashed into the interstellar medium [ http://spacsun.rice.edu/~twg/lism.html ], driving a shock wave [ http://www.fireplug.net/~rshand/streams/vela/vela.html ] that is still visible today [ http://antwrp.gsfc.nasa.gov/apod/ap970713.html ]. Different colors in the complex, right moving shock, pictured on the left [ http://www.aao.gov.au/local/www/dfm/aat078.html ], represent different energies [ http://antwrp.gsfc.nasa.gov/apod/ap960612.html ] of impact of the shock front [ http://www.aao.gov.au/local/www/dfm/aat084.html ]. The star on the left appears by chance in the foreground, and the long diagonal line is also unrelated. Remaining at the center of the Vela Supernova Remnant [ http://www.seds.org/billa/twn/velax.html ] is a pulsar [ http://antwrp.gsfc.nasa.gov/apod/ap990803.html http://universe.gsfc.nasa.gov/videos/millisecond.html ], a star as dense as nuclear matter [ http://user88.lbl.gov/NSD_docs/abc/home.html ] that completely rotates more than ten times in a single second. |
|
Runaway Star
| Title |
Runaway Star |
| Explanation |
Runaway stars are massive stars [ http://www.eso.org/outreach/press-rel/pr-1997/pr-01-97.html ] traveling rapidly through interstellar space. Like a ship plowing through the interstellar medium [ http://antwrp.gsfc.nasa.gov/apod/ap961218.html ], runaway star HD 77581 has produced this graceful arcing bow wave or "bow shock" - compressing the gaseous material in its path. Located near the centre of this European Southern Observatory photograph [ http://www.eso.org/outreach/press-rel/pr-1997/phot-02-97.html ], HD 77581 itself is so bright that it saturates the sensitive camera and produces the spiky cross shape [ http://antwrp.gsfc.nasa.gov/apod/ap971119.html ]. This star is over 6,000 light-years away in the constellation Vela [ http://www.astro.wisc.edu/~dolan/constellations/ constellations/Vela.html ], and appears to move at over 50 miles per second. What force could set this star in motion? A clue to the answer may lie in its optically invisible companion star, an X-ray bright [ http://chandra.harvard.edu/ ] pulsar [ http://antwrp.gsfc.nasa.gov/apod/ap980905.html ] known as Vela X-1. This pulsar is clearly the remnant of a supernova explosion [ http://legacy.gsfc.nasa.gov/docs/snr.html ] ... which seems to have given this massive star and its companion a mighty kick [ http://antwrp.gsfc.nasa.gov/apod/ap990515.html ]! |
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![Vela Supernova Remnant in Optical Credit: Photograph made from plates taken with the UK Schmidt Telescope [ http://www.roe.ac.uk/ukstu/ukst.html ]. Color photography by David Malin. Copyright: Anglo-Australian Telescope Board [ http://www.aao.gov.au/images.html ]](http://mm04.nasaimages.org/MediaManager/srvr?mediafile=/Size1/NVA2-4-NA/8325/vela_roe.jpg&userid=1&username=admin&resolution=1&servertype=JVA&cid=4&iid=NVA2&vcid=NA&usergroup=NASA_Astronomy_Picture_of_the_Day_Collecti-4-Admin&profileid=16)
