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The Cosmic X-Ray Background
| Title |
The Cosmic X-Ray Background |
| Explanation |
Early on, x-ray satellites [ http://heasarc.gsfc.nasa.gov/docs/corp/ observatories.html ] revealed a surprising cosmic background [ http://chandra.harvard.edu/xray_sources/ background.html ] glow of x-rays and astronomers have struggled to understand its origin. Now, peering through [ http://sci.esa.int/content/news/ index.cfm?aid=23&cid=45&oid=25139 ] a hole in the obscuring gas and dust of our own Milky Way Galaxy, the powerful orbiting XMM-Newton telescope [ http://antwrp.gsfc.nasa.gov/apod/ap991221.html ] has recorded this deep image of the x-ray sky [ http://antwrp.gsfc.nasa.gov/apod/ap000819.html ], resolving some of the mysterious background [ http://antwrp.gsfc.nasa.gov/apod/ap000114.html ] into many faint individual sources. The tantalizing image [ http://sci.esa.int/content/searchimage/ searchresult.cfm?aid=23&cid=45&ooid=25141 ] is color-coded, with red representing relatively low energy x-rays, photons with 500 or so times the energy of visible light. Green and blue colors correspond to increasingly energetic x-rays with up to about 10,000 times visible light energies. Notably, the faint sources tend to be green and blue, showing x-ray characteristics of huge amounts of material falling into massive black holes in very distant galaxies. Do massive black holes [ http://oposite.stsci.edu/pubinfo/PR/2000/22/ index.html ] reside in the hearts of all large galaxies? The XMM-Newton results add [ http://arxiv.org/abs/astro-ph/0011271 ] to the growing consensus that they do and that, from across the universe [ http://universe.gsfc.nasa.gov/ ], x-rays produced as matter feeds these black holes account for [ http://xxx.lanl.gov/abs/astro-ph/0008019 ] the cosmic x-ray background. |
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X-Ray Rings Expand from a Ga
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| Title |
X-Ray Rings Expand from a Gamma Ray Burst |
| Explanation |
Why do x-ray [ http://www.colorado.edu/physics/2000/xray/ ] rings appear to emanate from a gamma-ray burst? The surprising answer has little to do with the explosion itself but rather with light reflected off sheets of dust [ http://antwrp.gsfc.nasa.gov/apod/ap030721.html ]-laden gas in our own Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ]. GRB 031203 [ http://www.ucolick.org/~xavier/GRB/031203/ ] was a tremendous explosion -- a gamma-ray burst [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/ bursts.html ] that occurred far across the universe with radiation just arriving in our Solar System last December 3. Since GRBs [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/ apod_search?GRB ] can also emit copious amounts of x-rays, a bright flash of x-rays [ http://www.arxiv.org/abs/astro-ph/0312603 ] likely arrived simultaneously with the gamma-radiation [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/ emspectrum.html ]. In this case [ http://www.star.le.ac.uk/~sav2/grb031203/ ], the x-rays also bounced off two slabs of cosmic dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] nearly 3500 light-years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/ question19.html ] distant and created the unusual reflections [ http://antwrp.gsfc.nasa.gov/apod/ap030402.html ]. The longer path from the GRB, to the dust slab, to the XMM-Newton telescope [ http://sci.esa.int/science-e/www/area/ index.cfm?fareaid=23 ] caused the x-ray light echoes [ http://antwrp.gsfc.nasa.gov/apod/ap971023.html ] to arrive well after the GRB. |
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