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The Compton Gamma Ray Observ
…
| Title |
The Compton Gamma Ray Observatory |
| Explanation |
The Compton Gamma Ray Observatory [ http://cossc.gsfc.nasa.gov/cossc/descriptions/cgro.html ] (CGRO) was the most massive instrument ever launched by a NASA Space Shuttle [ http://spaceflight.nasa.gov/shuttle/index.html ] in 1991 and continues to revolutionize gamma-ray astronomy [ http://cossc.gsfc.nasa.gov/gamma/gamma.html ]. Before Compton loses more stabilizing gyroscopes, NASA is considering [ http://cnn.com/2000/TECH/space/01/14/satellite.deorbit/index.html ] firing onboard rockets to bring it on a controlled reentry into the ocean. This orbiting observatory sees the sky in gamma-ray photons [ http://cossc.gsfc.nasa.gov/cossc/descriptions/espec1.html ] - light so blue humans can't see it. These photons are blocked by the Earth's atmosphere from reaching the Earth's surface. Results from CGRO, pictured above [ http://images.jsc.nasa.gov/images/pao/STS37/10064038.htm ], have shown the entire universe to be a violent and rapidly changing place - when viewed in gamma-rays. Astronomers using CGRO data continue to make monumental discoveries [ http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?&text=CGRO&query_type=PAPERS ], including identifying mysterious gamma-ray bursts [ http://antwrp.gsfc.nasa.gov/cgi-bin/cossc/apod_search?gamma+ray+burst ] that uniquely illuminate the early universe, discovery of a whole new class of QSOs [ http://cossc.gsfc.nasa.gov/cossc/descriptions/egret_blazars.html ], and discovery of objects so strange [ http://cossc.gsfc.nasa.gov/cossc/descriptions/egret_src.html ] that astronomers can't yet figure out what they are. |
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A Mystery In Gamma Rays
| Title |
A Mystery In Gamma Rays |
| Explanation |
Gamma rays [ http://cossc.gsfc.nasa.gov/cossc/outreach/nasm/VU/ ] are the most energetic form of light, packing a million or more times the energy of visible light photons. What if you could see [ http://cossc.gsfc.nasa.gov/cossc/outreach/images/ ] gamma rays? If you could, the familiar skyscape [ http://antwrp.gsfc.nasa.gov/apod/ap990410.html ] of steady stars would be replaced [ http://antwrp.gsfc.nasa.gov/apod/ap980321.html ] by some of the most bizarre objects known [ http://www.skypub.com/tips/basics/dsonames.html ] to modern astrophysics [ http://ads.harvard.edu/ ] -- and some which are "unknown". When the EGRET [ http://lheawww.gsfc.nasa.gov/docs/gamcosray/EGRET/ instrument_description.html ] instrument on the orbiting Compton Gamma-ray Observatory [ http://antwrp.gsfc.nasa.gov/apod/ap000116.html ] surveyed the sky in the 1990s, it cataloged 271 celestial sources [ http://cossc.gsfc.nasa.gov/cossc/descriptions/ egret_src.html ] of high-energy gamma-rays. These sources are very different from the powerful gamma-ray bursters [ http://antwrp.gsfc.nasa.gov/apod/ap991104.html ] that flash and fade rapidly from view, and researchers identified some with exotic black holes [ http://antwrp.gsfc.nasa.gov/apod/ap980729.html ], neutron stars [ http://cossc.gsfc.nasa.gov/cossc/outreach/descriptions/ egret_pulsars.html ], and distant flaring galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap981226.html ]. But 170 of the cataloged sources, shown in the above all-sky [ http://antwrp.gsfc.nasa.gov/apod/ap980523.html ] map, remain unidentified. Many sources [ http://pao.gsfc.nasa.gov/gsfc/spacesci/structure/cgro.htm ] in this gamma-ray mystery map likely belong to the already known classes of gamma-ray emitters and are simply obscured or too faint to be otherwise positively identified. However, astronomers recently called attention [ http://pao.gsfc.nasa.gov/gsfc/spacesci/structure/cgro.htm#press ] to the ribbon of sources winding through the plane of the galaxy, projected here along the middle of the map, which may represent a large unknown class of galactic gamma-ray emitters. In any event, the unidentified sources could remain a mystery until the planned launch of the more sensitive Gamma-ray Large Area Space Telescope [ http://www-glast.sonoma.edu/ ] in 2005. |
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Gamma-Ray Earth
| Title |
Gamma-Ray Earth |
| Explanation |
The pixelated planet above is actually our own planet Earth seen in gamma rays [ http://universe.nasa.gov/press/2005/050325b.html ] - the most energetic form of light. In fact, the gamma rays [ http://cossc.gsfc.nasa.gov/epo/vu/overview/whatare/ process.html ] used to construct this view [ http://heasarc.gsfc.nasa.gov/docs/objects/heapow/archive/ solar_system/cgro_earth.html ] pack over 35 million electron volts [ http://hyperphysics.phy-astr.gsu.edu/hbase/ electric/ev.html#c1 ] (MeV) compared to a mere two electron volts (eV) for a typical visible light photon. The Earth's gamma-ray glow [ http://antwrp.gsfc.nasa.gov/apod/ap060527.html ] is indeed very faint, and this image was constructed by combining data from seven years of exposure during the life of the Compton Gamma Ray Observatory [ http://cossc.gsfc.nasa.gov/ ], operating [ http://cossc.gsfc.nasa.gov/epo/vu/overview/gro/ gro.html ] in Earth orbit from 1991 to 2000. Brightest near the edge and faint near the center, the picture indicates that the gamma rays are coming from high in Earth's atmosphere. The gamma rays are produced as the atmosphere interacts with high energy cosmic rays [ http://antwrp.gsfc.nasa.gov/apod/ap001202.html ] from space, blocking [ http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ multiwavelength_astronomy/multiwavelength_astronomy/ orbit.html ] the harmful radiation from reaching the surface. Astronomers need to understand [ http://xxx.lanl.gov/abs/astro-ph/0410487 ] Earth's gamma-ray glow well as it can interfere with observations of cosmic gamma-ray sources [ http://cossc.gsfc.nasa.gov/epo/vu/index.html ] like pulsars, supernova remnants [ http://antwrp.gsfc.nasa.gov/apod/ap041105.html ], and distant active galaxies powered by supermassive black holes [ http://csep10.phys.utk.edu/astr162/lect/active/ smblack.html ]. |
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Gamma-Ray Moon
| Title |
Gamma-Ray Moon |
| Explanation |
If you could see gamma rays [ http://antwrp.gsfc.nasa.gov/apod/ap000722.html ] - photons with a million or more times the energy of visible light - the Moon would appear brighter than the Sun! The startling notion is demonstrated by this image of the Moon from the Energetic Gamma Ray Experiment Telescope (EGRET [ http://cossc.gsfc.nasa.gov/docs/cgro/cgro/egret.html ]) in orbit on NASA's Compton Gamma Ray Observatory [ http://cossc.gsfc.nasa.gov/docs/cgro/index.html ] from April 1991 to June 2000. Then, the most sensitive instrument of its kind, even EGRET could not see the quiet Sun which is extremely faint at gamma-ray energies. So why [ http://www.aas.org/publications/baas/v28n4/aas189/abs/ S025002.html ] is the Moon bright? High energy charged particles, known as cosmic rays [ http://imagine.gsfc.nasa.gov/docs/features/topics/snr_group/ cosmic_rays.html ], constantly bombard the unprotected lunar surface generating gamma-ray photons. EGRET's gamma-ray vision [ http://cossc.gsfc.nasa.gov/docs/cgro/epo/vu/ index.html ] was not sharp enough to resolve a lunar disk or any surface features, but its sensitivity reveals the induced gamma-ray [ http://antwrp.gsfc.nasa.gov/apod/ap050331.html ] moonglow. So far unique [ http://glast.gsfc.nasa.gov/ ], the image was generated from eight exposures made during 1991-1994 and covers a roughly 40 degree wide field of view with gamma-ray intensity represented in false color. |
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GLAST Gamma Ray Sky Simulati
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| Title |
GLAST Gamma Ray Sky Simulation |
| Explanation |
What shines in the gamma-ray sky? This simulated image models the intensities of gamma rays [ http://cossc.gsfc.nasa.gov/epo/nasm/VU/index.html ] with over 40 million times the energy of visible light, and represents how the sky might appear to the Gamma-ray Large Area Space Telescope [ http://glast.gsfc.nasa.gov ] (GLAST) after its first year in orbit. Familiar steady stars are absent from the dramatic 80x80 degree field which looks directly away from the center of the Galaxy. Instead, the Geminga [ http://imagine.gsfc.nasa.gov/docs/science/how_l2/timing.html ] and Crab pulsars [ http://oposite.stsci.edu/pubinfo/pr/96/22.html ] - bizarre, spinning stellar corpses known to be neutron stars [ http://antwrp.gsfc.nasa.gov/apod/ap980425.html ] - are the two brightest gamma-ray sources. These and other gamma-ray bright objects in the field, monstrous active galaxies [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ active_galaxies.html ] and still unknown [ http://antwrp.gsfc.nasa.gov/apod/ap000324.html ] sources, have been detected by the Energetic Gamma-Ray Experiment Telescope [ http://cossc.gsfc.nasa.gov/cossc/egret/ ] (EGRET) on the orbiting Compton Gamma-Ray Observatory [ http://cossc.gsfc.nasa.gov ]. However, most of the simulated sources are new - extrapolating current ideas and anticipating discoveries resulting from GLAST's improved gamma-ray vision [ http://glast.gsfc.nasa.gov/ Anticen/ ]. The central broad band of faint gamma-ray emission is due to high-energy cosmic rays [ http://antwrp.gsfc.nasa.gov/apod/ap980618.html ] colliding with interstellar gas in the outer spiral arms of the Milky Way [ http://antwrp.gsfc.nasa.gov/apod/ap980523.html ], while below is a diffuse energetic glow from prominent molecular clouds [ http://antwrp.gsfc.nasa.gov/apod/ap970430.html ] in Monoceros, Orion, Auriga, and Taurus. Intended to explore [ http://www-glast.sonoma.edu/ ] extreme environments in the distant cosmos [ http://universe.gsfc.nasa.gov/ ] and planned for launch in 2005, GLAST is under development by NASA, U.S., and international partners. |
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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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A Mystery In Gamma Rays
| Title |
A Mystery In Gamma Rays |
| Explanation |
Gamma rays [ http://cossc.gsfc.nasa.gov/epo/nasm/VU/index.html ] are the most energetic form of light, packing a million or more times the energy of visible light photons. If you could see gamma rays, the familiar skyscape [ http://antwrp.gsfc.nasa.gov/apod/ap990410.html ] of steady stars would be replaced [ http://antwrp.gsfc.nasa.gov/apod/ap980321.html ] by some of the most bizarre objects known [ http://www.skypub.com/tips/basics/dsonames.html ] to modern astrophysics [ http://ads.harvard.edu/ ] -- and some which are "unknown". When the EGRET [ http://lheawww.gsfc.nasa.gov/docs/gamcosray/EGRET/ instrument_description.html ] instrument on the orbiting Compton Gamma-ray Observatory [ http://antwrp.gsfc.nasa.gov/apod/ap000116.html ] surveyed the sky in the 1990s, it cataloged 271 celestial sources [ http://cossc.gsfc.nasa.gov/gamcat/catform.html ] of high-energy gamma-rays. Researchers identified some with exotic black holes [ http://antwrp.gsfc.nasa.gov/apod/ap980729.html ], neutron stars [ http://antwrp.gsfc.nasa.gov/apod/ap010719.html ], and distant flaring galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap981226.html ]. But 170 of the cataloged sources, shown in the above all-sky [ http://antwrp.gsfc.nasa.gov/apod/ap980523.html ] map, remain unidentified. Many sources [ http://pao.gsfc.nasa.gov/gsfc/spacesci/structure/cgro.htm ] in this gamma-ray mystery map likely belong to already known classes of gamma-ray emitters and are simply obscured or too faint to be otherwise positively identified. However, astronomers have called attention [ http://pao.gsfc.nasa.gov/gsfc/spacesci/structure/cgro.htm#press ] to the ribbon of sources winding through the plane of the galaxy, projected here along the middle of the map, which may represent a large unknown class [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query? bibcode=2000HEAD...32.4007G&db_key=AST&high=3af6c03e8125794 ] of galactic gamma-ray emitters. In any event, the unidentified sources could remain a mystery until the planned launch of the more sensitive Gamma-ray Large Area Space Telescope [ http://www-glast.sonoma.edu/ ] in 2005. |
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The Crab Nebula and Geminga
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| Title |
The Crab Nebula and Geminga in Gamma Rays |
| Explanation |
What if you could "see" in gamma-rays? If you could, these two spinning neutron stars [ http://antwrp.gsfc.nasa.gov/apod/lib/ns.html ] or pulsars would be among the brightest objects in the sky. This computer processed image shows the Crab Nebula pulsar (below and right of center) and the Geminga pulsar (above and left of center) in the "light" of gamma-rays. Gamma-ray photons are more than 10,000 times more energetic than visible light photons and are blocked from the Earths's surface by the atmosphere. This image was produced by the high energy gamma-ray telescope "EGRET" on board NASA's orbiting Compton Observatory satellite. For more information see Compton Science Support Center release. [ http://cossc.gsfc.nasa.gov/cossc/descriptions/egret_anti.html ] |
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Gamma Ray All Sky Map
| Title |
Gamma Ray All Sky Map |
| Explanation |
What if you could "see" gamma rays? This computer processed image represents a map of the entire sky at photon energies above 100 million electron Volts. These gamma-ray photons are more than 40 million times more energetic than visible light photons and are blocked from the Earth's surface by the atmosphere. In the early 1990s NASA's Compton Gamma Ray Observatory, in orbit around the Earth, scanned the entire sky to produce this picture. A diffuse gamma-ray glow from the plane of our Milky Way Galaxy is clearly seen across the middle. The nature and even distance to some of the fainter sources remain unknown. For more information see Compton Science Support Center release. [ http://cossc.gsfc.nasa.gov/cossc/descriptions/egret_allsky.html ] |
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The Gamma Ray Sky
| Title |
The Gamma Ray Sky |
| Explanation |
What if you could see gamma rays [ http://cossc.gsfc.nasa.gov/epo/vu/ ]? If you could, the sky would seem to be filled with a shimmering high-energy glow from the most exotic and mysterious objects [ http://www.pbs.org/wgbh/nova/gamma/ ] in the Universe. In the early 1990s NASA's orbiting Compton Observatory [ http://antwrp.gsfc.nasa.gov/apod/ap000408.html ], produced this premier vista of the entire sky in gamma rays [ http://www.gamma.mpe-garching.mpg.de/~rod/public/ tvuniv.htm ], photons with more than 40 million times the energy of visible light [ http://www.pbs.org/wgbh/nova/gamma/spectrum.html ]. The diffuse gamma-ray glow from the plane of our Milky Way [ http://antwrp.gsfc.nasa.gov/apod/ap970517.html ] Galaxy runs horizontally through the false-color image. The brightest spots in the galactic plane (right of center) are pulsars [ http://antwrp.gsfc.nasa.gov/apod/ap000609.html ], spinning magnetized neutron stars formed in the violent crucibles of stellar explosions [ http://antwrp.gsfc.nasa.gov/apod/ap980425.html ]. Above and below the plane, quasars [ http://antwrp.gsfc.nasa.gov/apod/ap971206.html ], believed to be powered by supermassive black holes, produce gamma-ray beacons at the edges of the universe. The nature of many [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query? 1996A%26AS%2E%2E120C%2E465M&db_key=AST ] of the fainter sources remains unknown [ http://antwrp.gsfc.nasa.gov/apod/ap010811.html ]. |
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The Compton Gamma Ray Observ
…
| Title |
The Compton Gamma Ray Observatory |
| Explanation |
The Compton Gamma Ray Observatory [ http://cossc.gsfc.nasa.gov/cossc/descriptions/cgro.html ] (CGRO) was the most massive instrument ever launched [ http://www.ksc.nasa.gov/shuttle/missions/sts-37/mission-sts-37.html ] by a NASA Space Shuttle and continues to revolutionize gamma-ray astronomy. This orbiting observatory sees the sky in gamma-ray photons - light so blue humans can't see it. These photons are blocked by the Earth's atmosphere from reaching the Earth's surface. Results from CGRO have shown the entire universe to be a violent and rapidly changing place - when viewed in gamma-rays. Astronomers using CGRO data continue to make monumental discoveries, including showing that mysterious flashes of gamma-rays are much more powerful than previously imagined [ http://cossc.gsfc.nasa.gov/cossc/descriptions/batse_src.html ], discovery of a whole new class of QSO [ http://cossc.gsfc.nasa.gov/cossc/descriptions/egret_blazars.html ], and discovery of objects so strange that astronomers can't yet figure out what they are [ http://cossc.gsfc.nasa.gov/cossc/descriptions/egret_src.html ]. Tomorrow's picture: Atlantis Landing |
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Gamma-Ray Quasars
| Title |
Gamma-Ray Quasars |
| Explanation |
Gamma rays are more than 10,000 times more energetic than visible light. If you could "see" gamma rays [ http://antwrp.gsfc.nasa.gov/apod/ap950623.html ], the night sky would seem very different indeed. The bright object in the center of the false color gamma-ray image above is quasar [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#qso ] 3C279, a nondescript, faint, starlike object [ http://antwrp.gsfc.nasa.gov/apod/ap951022.html ] in the visible sky. Yet, in June of 1991 a gamma-ray telescope onboard NASA's orbiting Compton Gamma Ray Observatory [ http://cossc.gsfc.nasa.gov/cossc/descriptions/cgro.html ] unexpectedly discovered [ http://cossc.gsfc.nasa.gov/cossc/descriptions/egret_blazars.html ] that it was one of the brightest objects in the gamma-ray sky. Shortly after this image was recorded the quasar faded from view at gamma-ray energies. Astronomers are still trying to understand what causes these enigmatic objects to flare so violently. Another quasar, 3C273, is faintly visible above and to the right of center. |
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The Compton Observatory Turn
…
| Title |
The Compton Observatory Turns Five |
| Explanation |
Earlier this April, NASA's Compton Gamma Ray Observatory [ http://antwrp.gsfc.nasa.gov/apod/ap950811.html ], completed its fifth successful year in orbit, exploring the gamma ray [ http://heasarc.gsfc.nasa.gov/cossc/descriptions/espec1.html ] sky [ http://antwrp.gsfc.nasa.gov/apod/ap950623.html ]. Pictured is astronaut Jay Apt [ http://www.jsc.nasa.gov/Bios/htmlbios/apt.html ] perched in the shuttle payload bay below the massive observatory. Compton [ http://heasarc.gsfc.nasa.gov/cossc/descriptions/cgro_info.html ] is the largest civilian instrument ever flown - the whole observatory is roughly the size of a school bus. Apt and colleague Jerry Ross [ http://www.jsc.nasa.gov/Bios/htmlbios/ross.html ] rescued the spacecraft from an unexpected problem by successfully freeing the stuck high gain antenna in an unplanned space walk. The second of NASA's planned Great Observatories for Space Astrophysics [ http://spacelink.msfc.nasa.gov/NASA.Projects/ Proposed.Projects/NASA.in.the.1990s ], the first being the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap950810.html ], the Compton Gamma Ray Observatory [ http://heasarc.gsfc.nasa.gov/cossc/cgro.html ] has exceeded expectations of scientific discovery [ http://heasarc.gsfc.nasa.gov/cossc/cossc.html ]. Compton continues to search the depths of the universe for such high energy phenomena as gamma-ray bursts [ http://antwrp.gsfc.nasa.gov/apod/ap950827.html ], blazars [ http://heasarc.gsfc.nasa.gov/cossc/descriptions/egret_blazars.html ], and pulsars [ http://heasarc.gsfc.nasa.gov/cossc/descriptions/egret_pulsars.html ]. Compton is still monitoring a new source [ http://antwrp.gsfc.nasa.gov/apod/ap960228.html ] it discovered just last December - the spectacular "bursting pulsar" [ http://space.mit.edu/%7Erutledge/TRANS/trans.html ] near the center of our Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap960213.html ]. |
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The Pulsar Powered Crab
| Title |
The Pulsar Powered Crab |
| Explanation |
In the Summer of 1054 A.D. Chinese astronomers reported [ http://www.stsci.edu/pubinfo/PR/96/22/crabhist.html ] that a star in the constellation of Taurus [ http://bradley.bradley.edu/~dware/taurus.html ] suddenly became as bright as the full Moon. Fading slowly, it remained visible for over a year. It is now understood that a spectacular supernova explosion [ http://antwrp.gsfc.nasa.gov/apod/ap951027.html ] - the detonation of a massive star whose remains [ http://antwrp.gsfc.nasa.gov/apod/ap960509.html ] are now visible as the Crab Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap951122.html ]- was responsible for the apparition. The core of the star collapsed [ http://www.stsci.edu/pubinfo/PR/96/22/pulsars.html ] to form a rotating neutron star [ http://astro.uchicago.edu/home/web/miller/nstar.html ] or pulsar [ http://pulsar.princeton.edu/rpr.shtml ], one of the most exotic objects known to 20th century astronomy. Like a cosmic lighthouse, the rotating Crab pulsar generates beams of radio, visible, x-ray and gamma-ray energy [ http://heasarc.gsfc.nasa.gov/cossc/descriptions/egret_pulsars.html ] which, as the name suggests, produce pulses as they sweep across our view. Using a stunning series of visible light images taken with the Hubble Space Telescope (HST) [ http://www.stsci.edu/pubinfo/PR/96/22.html ], astronomers have recently discovered spectacular pulsar powered motions within the Crab nebula. Highlights of this HST Crab "movie" [ http://www.stsci.edu/pubinfo/PR/96/22.html#Movies ] show wisps of material moving away from the pulsar at half the speed of light, a scintillating halo, and an intense knot of emission dancing, sprite-like, above the pulsar's pole. Only 6 miles wide but more massive than the sun, the pulsar's energy drives the dynamics and emission of the nebula itself which is more than 10 lightyears across. In the HST image above [ http://www.stsci.edu/pubinfo/PR/96/22/A.html ], the pulsar is the left most of the two bright central stars. |
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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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Tomorrow's picture: Space Wa
…
| Title |
Tomorrow's picture: Space Walz [ http://antwrp.gsfc.nasa.gov/apod/ap970211.html ] |
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Moon Occults Saturn
| Title |
Moon Occults Saturn |
| Explanation |
Many stargazers in the U. S. [ http://antwrp.gsfc.nasa.gov/apod/ap970830.html ] were able to watch a lovely lunar occultation [ http://www.skypub.com/whatsup/lunocc97.html ] early last Thursday morning as a bright Moon passed in front of Saturn [ http://www.skypub.com/whatsup/9709satu.html ]. Using a 1.2 meter reflector [ http://cfa-www.harvard.edu/cfa/oir/FLWO/FLWO/48/48.html ], astronomer Kris Stanek [ http://cfa-www.harvard.edu/~kstanek/index.html ] had an excellent view of this [ http://cfa-www.harvard.edu/~kstanek/Saturn/ ] dream-like event from the Whipple Observatory [ http://cfa-www.harvard.edu/cfa/oir/FLWO/FLWO/whipple.html ] atop Arizona's Mount Hopkins [ http://egret.sao.arizona.edu/mt.html ]. This animated gif image was constructed by Wes Colley [ http://www.astro.princeton.edu/~wes/research/ ] from 4 frames taken by Stanek at 35 second intervals as the ringed planet emerged from behind the Moon's [ http://antwrp.gsfc.nasa.gov/apod/ap970916.html ] dark limb. While lunar occultations of fairly bright stars [ http://antwrp.gsfc.nasa.gov/apod/ap970728.html ] and planets are not extremely rare events, their exact timing [ http://www.sky.net/~robinson/iotandx.htm ] depends critically on the observer's location. |
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The Milky Way's Gamma-Ray Ha
…
| Title |
The Milky Way's Gamma-Ray Halo |
| Explanation |
Our Milky Way galaxy appears to be surrounded by a halo of gamma rays [ http://tigre.ucr.edu/halo/halo.html ]. Gamma rays are the most energetic form of electromagnetic radiation [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ], with more than a hundred thousand times the energy of visible light, but known gamma-ray sources [ http://antwrp.gsfc.nasa.gov/apod/ap970222.html ] don't account for the diffuse distribution of this high-energy glow. This surprising result is based on data [ http://tigre.ucr.edu/halo/tipsh.html ] from the EGRET instrument onboard the Compton Gamma Ray Observatory [ http://antwrp.gsfc.nasa.gov/apod/ap970606.html ]. In this false color all-sky image centered on the Milky Way [ http://antwrp.gsfc.nasa.gov/apod/ap970517.html ], the brown and green regions indicate brighter, known sources of gamma-rays. The galactic center and plane clearly standout as do some distant galaxies seen near the top and bottom of the picture. The dim, blue regions above and below the plane correspond to our Galaxy's unexpected gamma-ray halo. " What causes the halo? " Future gamma-ray telescopes [ http://www-glast.stanford.edu ] could solve this mystery. However, the excitement has already inspired tantalizing speculation about the solution including, collisions of low energy photons with high-energy cosmic rays [ http://antwrp.gsfc.nasa.gov/apod/ap961016.html ], high energy electrons accelerated by a previous burst of Milky Way star formation [ http://antwrp.gsfc.nasa.gov/apod/ap971027.html ], and exotic interacting particles which make up Dark Matter [ http://antwrp.gsfc.nasa.gov/htmltest/gifcity/matter.html ]. |
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A Mystery In Gamma Rays
| Title |
A Mystery In Gamma Rays |
| Explanation |
Gamma rays [ http://cossc.gsfc.nasa.gov/epo/vu/ ] are the most energetic form of light, packing a million or more times the energy of visible light photons. If you could see gamma rays, the familiar skyscape [ http://antwrp.gsfc.nasa.gov/apod/ap040304.html ] of steady stars would be replaced [ http://antwrp.gsfc.nasa.gov/apod/ap980321.html ] by some of the most bizarre objects known [ http://skyandtelescope.com/howto/basics/ article_240_1.asp ] to modern astrophysics [ http://ads.harvard.edu/ ] -- and some which are "unknown". When the EGRET [ http://lheawww.gsfc.nasa.gov/docs/gamcosray/EGRET/ instrument_description.html ] instrument on the orbiting Compton Gamma-ray Observatory [ http://antwrp.gsfc.nasa.gov/apod/ap000408.html ] surveyed the sky in the 1990s, it cataloged 271 celestial sources [ http://cossc.gsfc.nasa.gov/gamcat/catform.html ] of high-energy gamma-rays. Researchers identified some with exotic black holes [ http://antwrp.gsfc.nasa.gov/apod/ap980729.html ], neutron stars [ http://antwrp.gsfc.nasa.gov/apod/ap010719.html ], and distant flaring galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap981226.html ]. But 170 of the cataloged sources, shown in the above all-sky map, remain unidentified. Many sources [ http://pao.gsfc.nasa.gov/gsfc/spacesci/structure/cgro.htm ] in this gamma-ray mystery map likely belong to already known classes of gamma-ray emitters and are simply obscured or too faint to be otherwise positively identified. However, astronomers have called attention [ http://pao.gsfc.nasa.gov/gsfc/spacesci/structure/cgro.htm#press ] to the ribbon of sources winding through the plane of the galaxy, projected here along the middle of the map, which may represent a large unknown class [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query? bibcode=2000HEAD...32.4007G&db_key=AST&high=3af6c03e8125794 ] of galactic gamma-ray emitters. In any event, the unidentified sources could remain a mystery until the planned launch of the more sensitive Gamma-ray Large Area Space Telescope [ http://www-glast.sonoma.edu/ ] in 2007. |
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The Gamma Ray Sky
| Title |
The Gamma Ray Sky |
| Explanation |
What if you could "see" gamma rays? [ http://cossc.gsfc.nasa.gov/cossc/nasm/VU/vu.html ] If you could, the sky would seem to be filled [ http://cossc.gsfc.nasa.gov/cossc/pics.html ] with a shimmering high-energy glow from the most exotic [ http://cossc.gsfc.nasa.gov/cossc/news.html ] and mysterious objects in the Universe [ http://antwrp.gsfc.nasa.gov/apod/ap971218.html ]. In the early 1990s NASA's orbiting Compton Observatory [ http://antwrp.gsfc.nasa.gov/apod/ap970606.html ], produced this premier vista of the entire sky in gamma rays [ http://cossc.gsfc.nasa.gov/cossc/nasm/VU/overview/ g_rayuni/g_rayuni.html ] - photons with more than 40 million times the energy of visible light [ http://cossc.gsfc.nasa.gov/cossc/whatgam.html ]. The diffuse gamma-ray glow from the plane of our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap970517.html ] runs horizontally through the false color image. The brightest spots in the galactic plane (right of center) are pulsars [ http://antwrp.gsfc.nasa.gov/apod/ap980211.html ] - spinning magnetized neutron stars formed in the violent crucibles of stellar explosions [ http://antwrp.gsfc.nasa.gov/apod/ap961114.html ]. Above and below the plane, quasars [ http://antwrp.gsfc.nasa.gov/apod/ap971206.html ], believed to be powered by supermassive black holes [ http://antwrp.gsfc.nasa.gov/apod/ap971019.html ], produce gamma-ray beacons at the edges of the universe. The nature of many [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996A%26AS%2E%2E120C%2E465M&db_key=AST ] of the fainter sources remains unknown [ http://www-glast.stanford.edu/ ]. |
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The Pulsar Powered Crab
| Title |
The Pulsar Powered Crab |
| Explanation |
In the Summer of 1054 [ http://www.chaco.com/park/archaeology/nebula.html ] A.D. Chinese astronomers reported [ http://www.stsci.edu/pubinfo/PR/96/22/crabhist.html ] that a star in the constellation of Taurus [ http://www.astro.wisc.edu/~dolan/constellations/ constellations/Taurus.html ] suddenly became as bright as the full Moon. Fading slowly, it remained visible for over a year. It is now understood that a spectacular supernova explosion [ http://antwrp.gsfc.nasa.gov/apod/ap980217.html ] - the detonation of a massive star whose remains [ http://antwrp.gsfc.nasa.gov/apod/ap980613.html ] are now visible as the Crab Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap951122.html ]- was responsible for the apparition. The core of the star collapsed [ http://www.stsci.edu/pubinfo/PR/96/22/pulsars.html ] to form a rotating neutron star [ http://astro.uchicago.edu/home/web/miller/nstar.html ] or pulsar [ http://pulsar.princeton.edu/rpr.shtml ], one of the most exotic objects known to 20th century astronomy. Like a cosmic lighthouse, the rotating Crab pulsar generates beams of radio, visible, x-ray and gamma-ray energy [ http://heasarc.gsfc.nasa.gov/cossc/descriptions/egret_pulsars.html ] which, as the name suggests, produce pulses as they sweep across our view. Using a stunning series of visible light images taken with the Hubble Space Telescope (HST) [ http://www.stsci.edu/pubinfo/PR/96/22.html ], astronomers have discovered spectacular pulsar powered motions within the Crab nebula. Highlights of this HST Crab "movie" [ http://www.stsci.edu/pubinfo/PR/96/22.html#Movies ] show wisps of material moving away from the pulsar at half the speed of light, a scintillating halo, and an intense knot of emission dancing, sprite-like, above the pulsar's pole. Only 6 miles wide but more massive than the sun, the pulsar's energy drives the dynamics and emission of the nebula itself which is more than 10 lightyears across. In this HST image [ http://www.stsci.edu/pubinfo/PR/96/22/A.html ], the pulsar is the left most of the two bright central stars. |
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GLAST Gamma-Ray Sky Simulati
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| Title |
GLAST Gamma-Ray Sky Simulation |
| Explanation |
This simulated image models the intensities of gamma rays [ http://cossc.gsfc.nasa.gov/cossc/outreach/nasm/VU/ ] with over 40 million times the energy of visible light, and represents how the sky might appear to the proposed Gamma-ray Large Area Space Telescope [ http://glast.gsfc.nasa.gov ] (GLAST) after its first year in orbit. Familiar steady stars are absent from the dramatic 80x80 degree field which looks directly away from the center of the Galaxy. Instead, the Geminga [ http://imagine.gsfc.nasa.gov/docs/science/how_l2/timing.html ] and Crab pulsars [ http://oposite.stsci.edu/pubinfo/pr/96/22.html ] - bizarre, spinning stellar corpses known to be neutron stars [ http://antwrp.gsfc.nasa.gov/apod/ap980425.html ] - are the two brightest gamma-ray sources. These and other bright objects in the field, dense pulsars [ http://antwrp.gsfc.nasa.gov/apod/ap980211.html ], monstrous active galaxies [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/active_galaxies.html ], and still unknown sources, have been detected by the Energetic Gamma-Ray Experiment Telescope [ http://cossc.gsfc.nasa.gov/cossc/egret/ ] (EGRET) on the orbiting Compton Gamma-Ray Observatory [ http://cossc.gsfc.nasa.gov ]. However, most of the simulated point sources are new - extrapolating current ideas and anticipating discoveries resulting from GLAST's improved gamma-ray vision [ http://glast.gsfc.nasa.gov/Anticen/ ]. The central broad band of faint gamma-ray emission is due to high-energy cosmic rays [ http://antwrp.gsfc.nasa.gov/apod/ap980618.html ] colliding with interstellar gas in the outer spiral arms of the Milky Way [ http://antwrp.gsfc.nasa.gov/apod/ap980523.html ], while below is a diffuse energetic glow from prominent molecular clouds [ http://antwrp.gsfc.nasa.gov/apod/ap970430.html ] in Monoceros, Orion, Auriga, and Taurus. Intended to explore [ http://perry.sonoma.edu/ ] the most extreme energy sources in the distant cosmos [ http://universe.gsfc.nasa.gov/ ] and planned for launch in 2005, the GLAST mission [ http://wwwmipd.gsfc.nasa.gov/glast/glast.htm ] is under development [ http://glast.gsfc.nasa.gov/Summary/ ] by NASA and a collaboration of U. S. and international partners. |
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Gamma-Ray Earth
| Title |
Gamma-Ray Earth |
| Explanation |
The pixelated planet above is actually our own planet Earth seen in gamma rays [ http://universe.nasa.gov/press/2005/050325b.html ] - the most energetic form of light. In fact, the gamma rays [ http://cossc.gsfc.nasa.gov/epo/vu/overview/whatare/ process.html ] used to construct this view [ http://heasarc.gsfc.nasa.gov/docs/objects/heapow/archive/solar_system/cgro_earth.html ] pack over 35 million electron volts [ http://hyperphysics.phy-astr.gsu.edu/hbase/ electric/ev.html#c1 ] (MeV) compared to a mere two electron volts (eV) for a typical visible light photon. The Earth's gamma-ray glow [ http://antwrp.gsfc.nasa.gov/apod/ap990417.html ] is indeed very faint, and this image was constructed by combining data from seven years of exposure during the life of the Compton Gamma Ray Observatory [ http://cossc.gsfc.nasa.gov/ ], operating [ http://cossc.gsfc.nasa.gov/epo/vu/overview/gro/ gro.html ] in Earth orbit from 1991 to 2000. Brightest near the edge and faint near the center, the picture indicates that the gamma rays are coming from high in Earth's atmosphere. The gamma rays are produced as the atmosphere interacts with high energy cosmic rays [ http://antwrp.gsfc.nasa.gov/apod/ap001202.html ] from space, blocking [ http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ multiwavelength_astronomy/multiwavelength_astronomy/ orbit.html ] the harmful radiation from reaching the surface. Astronomers need to understand [ http://xxx.lanl.gov/abs/astro-ph/0410487 ] Earth's gamma-ray glow well as it can interfere with observations of cosmic gamma-ray sources [ http://cossc.gsfc.nasa.gov/epo/vu/index.html ] like pulsars, supernova remnants [ http://antwrp.gsfc.nasa.gov/apod/ap041105.html ], and distant active galaxies powered by supermassive black holes [ http://csep10.phys.utk.edu/astr162/lect/active/ smblack.html ]. |
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