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Hubble Maps the Cosmic Web o
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| Title |
Hubble Maps the Cosmic Web of "Clumpy" Dark Matter in 3-D |
| General Information |
What is an American Astronomical Society Meeting release? A major news announcement issued at an American Astronomical Society meeting, the premier astronomy conference. An international team of astronomers using NASA's Hubble Space Telescope has created a three-dimensional map that provides the first direct look at the large-scale distribution of dark matter in the universe. Read more: * NASA Press Release [ http://hubblesite.org/newscenter/archive/releases/2007/01/text/ ] * The Full Story [ http://hubblesite.org/newscenter/archive/releases/2007/01/full/ ] |
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RCW 86: Historical Supernova
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| Title |
RCW 86: Historical Supernova Remnant |
| Explanation |
In 185 AD, Chinese astronomers [ http://en.wikipedia.org/wiki/Chinese_astronomy ] recorded the appearance of a new star in the Nanmen asterism - a part of the sky identified with Alpha and Beta Centauri on modern star charts. The new star [ http://www.tass-survey.org/richmond/answers/historical.html ] was visible for months and is thought to be the earliest recorded supernova [ http://arxiv.org/abs/astro-ph/0301603 ]. Data from two orbiting X-ray telescopes of the 21st century, XMM-Newton [ http://heasarc.gsfc.nasa.gov/docs/xmm/xmmgof.html ] and Chandra [ http://chandra.harvard.edu/about/index.html ], now offer evidence that supernova remnant RCW 86 is indeed the debris from that stellar explosion [ http://antwrp.gsfc.nasa.gov/apod/ap060728.html ]. Their composite, false-color view of RCW 86 [ http://chandra.harvard.edu/photo/2006/rcw86/index.html ] shows the expanding shell of material glowing in x-rays [ http://chandra.harvard.edu/xray_astro/index.html ] with high, medium, and low energies shown in blue, green, and red hues. Shock velocities measured in [ http://arxiv.org/abs/astro-ph/0607307 ] the x-ray emitting shell and an estimated radius of about 50 light-years can be used to find the apparent age of the remnant. The results indicate that light from the initial explosion could well have first reached planet Earth in 185 AD. Near the plane of our Milky Way [ http://antwrp.gsfc.nasa.gov/apod/ap010202.html ] Galaxy, RCW 86 is about 8,200 light-years away. |
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Molecular Torus Surrounds Bl
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| Title |
Molecular Torus Surrounds Black Hole |
| Explanation |
Why do some black hole surroundings appear brighter than others? In the centers of active galaxies [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/active_galaxies.html ], supermassive black holes [ http://antwrp.gsfc.nasa.gov/apod/ap021128.html ] at least thousands of times the mass of our Sun [ http://antwrp.gsfc.nasa.gov/apod/sun.html ] dominate. Many, called Seyfert Type I [ http://www.astro.umd.edu/education/astro/actgal/seyfert.html ], are very bright in visible light. Others, called Seyfert Type II [ http://www.astro.umd.edu/education/astro/actgal/seyfert.html ], are rather dim. The difference might be caused by some black holes accreting [ http://antwrp.gsfc.nasa.gov/apod/ap030601.html ] much more matter than others. Alternatively, the black holes in the center of Seyfert [ http://antwrp.gsfc.nasa.gov/apod/ap000215.html ] Type II galaxies might be obscured by a surrounding torus [ http://mathworld.wolfram.com/Torus.html ]. To help choose between these competing hypotheses, the nearby Seyfert II galaxy NGC 4388 [ http://antwrp.gsfc.nasa.gov/apod/ap020603.html ] has been observed in X-ray light [ http://chandra.harvard.edu/xray_astro/xrays.html ] recently by many recent Earth-orbiting X-ray observatories, including CGRO [ http://antwrp.gsfc.nasa.gov/apod/ap000408.html ], SIGMA [ http://hea.iki.rssi.ru/GRANAT/sigma/sigma.html ], BeppoSAX [ http://www.asdc.asi.it/bepposax/ ], INTEGRAL [ http://www.esa.int/export/esaSC/120374_index_0_m.html ], Chandra [ http://chandra.harvard.edu/about/axaf_mission.html ], and XMM-Newton [ http://antwrp.gsfc.nasa.gov/apod/ap991221.html ]. Recent data [ http://arxiv.org/abs/astro-ph/0406553 ] from INTEGRAL and XMM-Newton have found [ http://www.gsfc.nasa.gov/topstory/2004/0720donutcloud.html ] that the X-ray flux in some X-ray colors varies rapidly, while flux in other X-ray colors is quite steady. The constant flux and apparent absorption of very specific X-ray colors by cool iron [ http://pearl1.lanl.gov/periodic/elements/26.html ] together give evidence [ http://www.esa.int/esaSC/SEM962V4QWD_index_0.html ] that the central black hole in NGC 4388 is seen through a thick torus [ http://www.esa.int/esaSC/SEM962V4QWD_index_1.html ] composed of molecular gas and dust [ http://antwrp.gsfc.nasa.gov/apod/ap030202.html ]. |
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