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A New Class of X-ray Star?
| Title |
A New Class of X-ray Star? |
| 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. Teaming up space telescopes to make simultaneous ultraviolet and X-ray observations, astronomers may have solved a 20-year-old mystery and possibly discovered a new class of X-ray star. The unlikely suspect is a second-magnitude star 600 light-years from Earth in the constellation Cassiopeia. It turns out that the mild-mannered-looking star is ejecting 100-million-degree flares into space ? 10 times hotter than typical flares ejected from our Sun. The findings are based on observations by the Hubble telescope and the Rossi X-Ray Timing Explorer. Read more: * Release Text [ http://hubblesite.org/newscenter/archive/releases/1998/07/text/ ] |
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The X-Ray Sky
| Title |
The X-Ray Sky |
| Explanation |
What if you could see X-rays [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#X-ray ]? If you could, the night sky [ http://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/multiw_sky.html ] would be a strange and unfamiliar place. X-rays are about 1,000 times more energetic than visible light photons and are produced in violent and high temperature astrophysical environments. Instead of the familiar steady stars, the sky would seem to be filled with exotic binary star systems [ http://antwrp.gsfc.nasa.gov/apod/ap951226.html ] composed of white dwarfs [ http://antwrp.gsfc.nasa.gov/apod/ap950910.html ], neutron stars [ http://antwrp.gsfc.nasa.gov/apod/ap951122.html ], and black holes [ http://antwrp.gsfc.nasa.gov/apod/ap951127.html ], along with flare stars, X-ray bursters, pulsars [ http://pulsar.princeton.edu/rpr.shtml ], supernova remnants [ http://antwrp.gsfc.nasa.gov/apod/ap951203.html ] and active galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap951022.html ]. This X-ray image of the entire sky was constructed with Skyview [ http://skyview.gsfc.nasa.gov ], using data from the first High Energy Astronomy Observatory (HEAO 1) [ http://heasarc.gsfc.nasa.gov/docs/heao1/ heao1a2_gifbrowser.html ], and plotted in a coordinate system centered on the galactic center with the north galactic pole at the top. Sources near the galactic center are seen to dominate in this false color map which shows regions of highest X-ray intensity in yellow. Astronomers' ability to observe the sky at X-ray energies will be greatly enhanced by the recently launched X-ray Timing Explorer (XTE [ http://heasarc.gsfc.nasa.gov/docs/ xte/xte_1st.html ]) satellite. |
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The X-ray Timing Explorer
| Title |
The X-ray Timing Explorer |
| Explanation |
Launched Saturday [ http://heasarc.gsfc.nasa.gov/docs/xte/xte_1st.html ] on a Delta rocket [ http://antwrp.gsfc.nasa.gov/apod/ap951213.html ], the X-ray Timing Explorer [ http://heasarc.gsfc.nasa.gov/docs/xte/xte2.html ] (XTE) will watch the sky for rapid changes in X-rays [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#X-ray ]. XTE [ http://heasarc.gsfc.nasa.gov/docs/xte/XTE.html ] carries three separate X-ray telescopes. The Proportional Counter Array [ http://heasarc.gsfc.nasa.gov/docs/xte/PCA.html ] (PCA) and the High Energy X-ray Timing Experiment [ http://mamacass.ucsd.edu:8080/hexte/hexte.html ] (HEXTE) will provide the best timing information in the widest X-ray energy range yet available. They will observe stellar systems [ http://antwrp.gsfc.nasa.gov/apod/ap950624.html ] that contain black holes [ http://antwrp.gsfc.nasa.gov/apod/ap951127.html ], neutron stars [ http://antwrp.gsfc.nasa.gov/apod/ap951122.html ], and white dwarfs [ http://antwrp.gsfc.nasa.gov/apod/ap950910.html ] as well as study the X-ray properties of the centers of active galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap951205.html ]. XTE [ http://space.mit.edu/XTE/XTE.html ]'s All Sky Monitor [ http://heasarc.gsfc.nasa.gov/docs/xte/ASM.html ] (ASM) will scan the sky every 90 minutes to find new X-ray transients and track the variability of old ones. XTE has a planned life time of two years. |
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In the Center of the Keyhole
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| Title |
In the Center of the Keyhole Nebula |
| Explanation |
Stars, like people, do not always go gentle into that good night [ http://social.chass.ncsu.edu/~flowers/Thomas.htm ]. The above Keyhole Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap960404.html ] results from dying star Eta Carinae [ http://antwrp.gsfc.nasa.gov/apod/ap970712.html ]'s violently casting off dust [ http://antwrp.gsfc.nasa.gov/apod/ap961119.html ] and gas during its final centuries. Eta Carinae [ http://www.seds.org/messier/xtra/ngc/etacar.html ] is many times more massive than our own Sun [ http://antwrp.gsfc.nasa.gov/apod/ap960916.html ], and should eventually undergo a tremendous supernova [ http://www.gnacademy.org:8001/uu-gna/text/astro/stars/supernova.html ] explosion. Eta Carinae emits much light in colors outside the human visible range. This past week, X-ray [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#X-ray ] emission from Eta Carinae was verified by the orbiting Rossi X-Ray Timing Explorer [ http://heasarc.gsfc.nasa.gov/docs/xte/XTE.html ] to be periodic, peaking every 85.1 days [ http://lheawww.gsfc.nasa.gov/users/corcoran/eta_car/eta_car_xte.html ]. This, along with a previously hypothesized 5.52 year period [ http://www1.elsevier.nl/journals/newast/jnl/articles/S1384107697000080/ ], indicates that the dying star might be part of a multiple star system. |
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Evidence for Frame Dragging
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| Title |
Evidence for Frame Dragging Black Holes |
| Explanation |
Gravity can do more than floor you. According to recent measurements [ ftp://ftp.hq.nasa.gov/pub/pao/pressrel/1997/97-258.txt ] of a star system thought to contain a black hole [ http://wonka.physics.ncsu.edu/~blondin/Blackhole/title.html ], it can spin you too. This effect, called frame-dragging [ http://www.enews.com/magazines/discover/magtxt/9703-1.html ], is most prominent near massive, fast spinning objects. Now, a team led by W. Cui [ mailto:cui@space.mit.edu ] (MIT [ http://web.mit.edu/physics/www/physics.html ]) has used the orbiting Rossi X-ray Timing Explorer [ http://heasarc.gsfc.nasa.gov/docs/xte/learning_center/ ] to search for it near a system thought to contain a black hole [ http://antwrp.gsfc.nasa.gov/apod/ap970516.html ]. Cui's team claim that matter in this system gets caught up and spun around the black hole [ http://physics7.berkeley.edu/BHfaq.html ] at just the rate expected [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997ApJ%2E%2E%2E475%2E%2E%2E57B&db_key=AST&nosetcookie=1 ] from frame-dragging. Such discoveries help scientists better understand gravity [ http://www.ncsa.uiuc.edu/Cyberia/NumRel/NumRelHome.html ] itself. |
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X-Ray Pulsar
| Title |
X-Ray Pulsar |
| Explanation |
This dramatic artist's vision shows a city-sized neutron star [ http://astro.uchicago.edu/home/web/miller/nstar.html ] centered in a disk of hot plasma drawn from its enfeebled red companion star. Ravenously accreting material [ http://imagine.gsfc.nasa.gov/docs/dictionary.html ] from the disk, the neutron star spins faster and faster [ http://universe.gsfc.nasa.gov/videos/millisecond.html ] emitting powerful particle beams and pulses of X-rays [ http://heasarc.gsfc.nasa.gov/docs/xte/learning_center/ ASM/welcome.html ] as it rotates 400 times a second. Could such a bizarre and inhospitable star system really exist in our Universe [ http://antwrp.gsfc.nasa.gov/apod/ap980302.html ]? Based on data from the orbiting Rossi X-Ray Timing Explorer [ http://heasarc.gsfc.nasa.gov/docs/xte/learning_center/ ] (RXTE) satellite, research teams have recently announced a discovery [ http://universe.gsfc.nasa.gov/new/news/1998/98-129.html ] which fits this exotic scenario well - a "millisecond" X-ray pulsar. The newly detected celestial X-ray beacon [ http://antwrp.gsfc.nasa.gov/apod/ap980211.html ] has the unassuming catalog designation of SAX J1808.4-3658 and is located a comforting 12,000 light years away in the constellation Sagittarius [ http://www.astro.wisc.edu/~dolan/constellations/ constellations/Sagittarius.html ]. Its X-ray pulses offer evidence of rapid, accretion powered [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ cool_binary_fact.html ] rotation and provide a much sought after connection between known types of radio and X-ray pulsars [ http://astrosun.tn.cornell.edu/courses/astro201/pulsar.htm ] and the evolution [ http://astrosun.tn.cornell.edu/courses/astro201/pulsar_graph.htm ] and ultimate demise of binary star systems [ http://imagine.gsfc.nasa.gov/docs/features/movies/binaries.html ]. |
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