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Topic: Compact object

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	Compact star - Wikipedia, the free encyclopedia
		In astronomy, a compact star (sometimes called a compact object) is a star that is a white dwarf, a neutron star, an exotic star, or a fl hole.
		"Compact star" is often used when the exact nature of the star is not known, but evidence suggests it is very massive and has small radius, thus leaving the above-mentioned possibilities.
		At low density (planets and the like) the object is held up by electromagnetic forces (chemical bonds between atoms and repulsion between electrons), which allow stiff objects such as rocks.
	en.wikipedia.org /wiki/Compact_star (1398 words)

	ELCAT Object List
		Compact PN of NGC6565 3-04 5 moderate-excit AKF3_2.
		Compact PN of NGC6644 8-07 2 moderate-excit AKF3_2.
		Compact PN Hb6 7+01 1 VV285, IRAS17521-2144 KON_2.
	stsdas.stsci.edu /elcat/objects.html (8172 words)

	The Astrophysics Spectator: Compact Binary Stars as X-ray Sources
		The consequence of this compactness is that matter from the companion star flows to the surface of the compact star, usually through an accretion disk, converting gravitational potential energy into thermal energy, and then into electromagnetic radiation.
		Compact binary systems are subdivided into two groups: the cataclysmic variables, which contain a degenerate dwarf, and the x-ray binaries, which contain a neutron star or a fl-hole candidate.
		Above this upper limit, the compact object under the theory of general relativity must be a fl-hole because the pressure at the center of such a massive star cannot counteract the force of gravity.
	www.astrophysicsspectator.com /topics/observation/XRayBinaryStars.html (1351 words)

	Massive compact halo object - Wikipedia, the free encyclopedia
		Massive compact halo object, or MACHO, is a general name for any kind of astronomical body that might explain the apparent presence of dark matter in galaxy halos.
		However, red and white dwarfs are not completely dark; they do emit some light, and so can be searched for with the Hubble Telescope and with proper motion surveys.
		Recent work has also suggested that ancient MACHOs are not likely to account for the large amounts of dark matter now thought to be present in the universe; the Big Bang as it is currently understood simply couldn't produce enough baryons without causing major problems in the observed elemental abundances, particularly the abundance of deuterium.
	en.wikipedia.org /wiki/Massive_compact_halo_object (801 words)

	Compact PDF Specification
		Compact PDF is in valid PDF syntax, although non-Compact-aware PDF libraries won't know how to extract objects from the Compact stream.
		Compact format is at odds with Linearization (aka Fast Web View), since Linearization allows parts of the PDF to be trasmitted as needed, whereas Compact puts most of the PDF in a single stream.
		The objects in the Compact stream are not represented in the cross-reference stream.
	multivalent.sourceforge.net /Research/CompactPDF.html (883 words)

	Mystery compact object producing high energy radiation (Site not responding. Last check: 2007-10-31)
		Depending on the mass of the star that produced it, this compact object is either a neutron star or a fl hole, but either way its strong gravitational pull draws in matter from its companion star.
		It is not clear what the compact object is. Some of the characteristics suggest it is a neutron star, some that it is a fl hole.
		This matter is then captured by the compact object's strong gravitational field and spirals down towards the surface.
	www.mpi-hd.mpg.de /hfm/HESS/public/PressRelease/LS5039Press/LS5039_Press_E.htm (1209 words)

	Discovering Black Holes - Week 4
		The trick is to measure the orbital period, and the velocity of the companion object.
		Determining the velocity of the companion object is done using the Doppler shift.
		In the case of an X-ray binary, if the mass function is greater than three solar masses, the compact object must be a fl hole.
	cmi.yale.edu /demo/bh/week4/pages/page2.html (462 words)

	XTE J1550-564 Microquasar
		The falling and spiraling of the matter toward the compact object releases large amounts of gravitational energy and heats the accretion disk.
		XTE J1550-564's rapidly spinning, compact object has an estimated mass of around 10.6 Solar, which is well above the maximum mass of a stable neutron star and so it appears to be a fl hole (Orosz et al, 2002).
		Because the spin of a stellar object was concentrated into a city-sized object (e.g., maybe 10 miles wide) during the collapse of the progenitor star's core, the fl hole created by a supernova is spinning very rapidly.
	www.solstation.com /x-objects/xte-bh.htm (1120 words)

	massive compact halo object concept from the Astronomy knowledge base (Site not responding. Last check: 2007-10-31)
		fl hole (7 kinds, 22 facts) - An object that is maximally gravitationally collapsed, and from which not even light can escape., An object with such a strong gravitational field that even light cannot escape.
		If an object with the mass of the Sun had a radius of 2.5 km, it would be a fl hole.
		Such objects are expected to have a mass less than 7% of the Sun's mass and represent a "missing link" between low-mass stars and gas giant planets like Jupiter (at 0.1% of the Sun's mass).
	www.site.uottawa.ca:4321 /astronomy/massivecompacthaloobject.html (660 words)

	Compact Objects (Site not responding. Last check: 2007-10-31)
		The group is actively involved in the theoretical and observational study of compact objects, from neutron stars to wormholes.
		These systems are formed by a compact object (fl hole or neutron star) and by a stellar companion that can be a high-mass and young star (in which case we talk about `high-mass microquasars') or a low-mass and old star (`low-mass microquasars´).
		The distance and relative velocity between the compact object and the star varies along the orbit (due to the excentricity) imprinting the same variability in the accretion rate, and further, in the light curve of the high-energy photons emerging from the jet-wind interaction.
	www.iar.unlp.edu.ar /garra/garra-comp.html (1897 words)

	Astron. Astrophys. 346, 91-100 (1999)
		Population of the compact object binaries in the four categories: double neutron star binaries that merge within the Hubble time (empty squares), and these that do not (empty circles), neutron star fl hole binaries that merge within the Hubble time (filled squares), and these that do not (filled circles).
		The actual compact object merger rate in the Galaxy can be calculated given the observed supernova rate, the fraction of stars that exist in binaries, and assuming some form of the star formation history.
		Thus mergers of heavy objects like a neutron star and a fl hole, or a pair of fl holes are visible in a larger volume and may yield a similar observational rate despite the fact that they are not as frequent as the double neutron star mergers.
	aa.springer.de /papers/9346001/2300091/sc3.htm (2287 words)

	ESA Science & Technology: Rapid heartbeat in Andromeda indicates a new kind of object
		Most of these sources are likely to be X-ray binary systems, where a compact object such as a fl hole or neutron star is tearing matter from a companion star.
		While not many of these objects have been observed - only two dozen in the whole Universe in the past 30 years - the observed behaviour of the new source is characteristic of an X-ray nova.
		This new source (referenced as XMMU J004319.4+411758) could be a white dwarf, a remarkably dense and compact star, with an extremely short orbital period sucking matter from a secondary star.
	sci.esa.int /science-e/www/object/index.cfm?fobjectid=27568 (1045 words)

	Massive Compact Halo Object
		The total mass of all the objects might even be enough to account for the so-called "missing mass" in the universe, though this is a matter of some debate, as are all "dark matter" candidates.
		Three light sources were used: One to illuminate the backdrop, one to illuminate the dwarf star from the direction of the galaxie's central buldge, and one at the upper right to give the subtle hint of the light from another galaxy coming from off-frame.
		The saturation of the dwarf star's color was boosted in Photoshop to simulate the subtle glow these objects would have due to their infrared and near-infrared emissions.
	www.imaginationbox.com /steve/astro/macho.htm (284 words)

	RX J1856.5-3754 and 3C58 Pulsar
		On the other hand, by November 2002, more accurate size estimates of another compact object named EXO 0748-676 (which has a stellar companion transferring mass to it that was leading to x-ray outbursts) left astronomers more certain that it was a neutron star (discussion and illustrations at NASA's Goddard Space Flight Center).
		As the coordinates for the remnant object from that explosion are not known precisely, the temperature estimates actually may apply to another object.
		If it is the right object, however, even a neutron star's high density would not be enough to produce cooling particles fast enough to reduce its temperature to such a low level in the eight centuries that have elapsed since its birth.
	www.solstation.com /x-objects/rxj1856.htm (2118 words)

	Massive compact halo object
		Massive compact halo objects, or MACHOs, are a type of astronomical body proposed as one possible explanation for the presence of dark matter in galactic halos.
		A MACHO is a small chunk of normal baryonic matter, far smaller than a star, which drifts through interstellar space unassociated with any solar system.
		However, some MACHOs may still exist (at the upper end of their size scale they would be brown dwarfs) and there are some attempts being made to detect them by the gravitational lensing they would cause in the light of stars as they pass in front of them.
	www.ebroadcast.com.au /lookup/encyclopedia/ma/MACHO.html (155 words)

	Gamma microquasar
		The matter falling into the compact object is ejected in the form of jets of relativistic particles.
		In addition, the collapse of matter from the disk into the compact object produces the ejection of jets of particles that travel in opposite directions at velocities close to the speed of light.
		Quasars display also jets of relativistic particles, but in their case the compact object is a fl hole of millions of solar masses located at the center of a galaxy.
	www.meta-religion.com /Astronomy/Gamma_rays/gamma_microquasar.htm (789 words)

	NASA - Black Hole
		To prove that a compact object is a fl hole, scientists would have to measure effects that only a fl hole could produce.
		The mass of each of those objects is thought to be between 1 million and 1 billion solar masses.
		The only known object that could be that massive and fit inside the star's orbit is a fl hole.
	www.nasa.gov /worldbook/blackhole_worldbook.html (837 words)

	ESA Portal - ESA's Integral discovers hidden black holes
		Also, after some analysis, researchers concluded that the new object could be a binary system comprising a compact object, such as a neutron star or a fl hole, and a very massive companion star.
		When gas from the companion star is accelerated and swallowed by the more compact object, energy is released at all wavelengths, from the gamma rays through to visible and infrared light.
		Astronomers, who have been observing the object regularly, guess that it had remained invisible because there must be a very thick shell of obscuring material surrounding it.
	www.esa.int /export/esaCP/SEMPHV1P4HD_index_0.html (714 words)

	Curious About Astronomy: How are black holes discovered?
		So, if we detect a compact object in space which is more than this critical mass, then we can be confident that it is a fl hole.
		Hence, a celestial object cannot change its luminosity on a time scale shorter than the time taken for the light to reach from one side of it to the other.
		Finally, astronomers used the binary star system to determine the mass of the compact object and found that it was greater than the critical mass, so that it was most likely a fl hole.
	curious.astro.cornell.edu /question.php?number=50 (918 words)

	Mystery compact object producing high energy radiation
		The object that is producing the high energy radiation is thought to be a 'microquasar'.
		Not only that, but the jet isn't much of a jet; although it is moving at about 20% of the speed of light, which might seem a lot, in the context of these objects it's actually quite slow.
		The H.E.S.S. array is ideal for finding new VHE gamma ray objects; because it's wide field of view (ten times the diameter of the Moon) means that it can survey the sky and discover previously unknown sources.
	www.pparc.ac.uk /Nw/hess.asp (1119 words)

	Astromart News - Mystery compact object producing high energy radiation.
		The instrument was inaugurated in September 2004 by the Namibian Prime Minister, Theo-Ben Guirab, and its first data have already resulted in a number of important discoveries, including the first astronomical image of a supernova shock wave at the highest gamma-ray energies.
		Objet compact de mystère produisant le rayonnement d'énergie élevée.
		Selon la masse de l'étoile qui l'a produite, cet objet compact est une étoile neutron ou un trou noir, mais l'une ou l'autre manière que sa gravitation forte dessine dans la matière de sa étoile de compagnon.
	www.astromart.com /news/news.asp?news_id=302 (3898 words)

	Curious About Astronomy: Why aren't accretion disks around giant stars as hot as accretion disks around black holes? (Site not responding. Last check: 2007-10-31)
		Since you can get closer to a fl hole (or other compact object, such as a neutron star) than you can to a giant star, accretion disks around compact objects are hotter.
		Closer to the massive object, the force of gravity will be stronger so the particles there get pulled around in faster orbits than the particles which are further away.
		But if you imagine a compact object of the same mass as the giant star, then by definition it is a lot smaller so you can have an accretion disk extending much closer to the object's center.
	curious.astro.cornell.edu /question.php?number=314 (697 words)

	Measuring the Mass of the Compact Object from Companion Star Data (Site not responding. Last check: 2007-10-31)
		The mass of the compact object in GRO J1655-40 has been derived via the radial velocity curves of the secondary star (Bailyn et al.
		Table 1: Compact object and companion star mass estimates derived for GRO J1655-40.
		are the semi-amplitude of the radial velocity curves of the compact object and companion star, respectively, and i is the inclination of the binary.
	www.atnf.csiro.au /pasa/18_1/buxton/paper/node2.html (329 words)

	Integral reveals new class of 'supergiant' X-ray binary stars
		The new class of double star systems is characterised by a very compact object that produces highly energetic, recurrent and fast-growing X-ray outbursts, and a very luminous 'supergiant' companion.
		In the latter case, the long duration of the outburst is consistent with a 'viscous' mass exchange between the star and an accreting compact object.
		Alternatively, the flow of material transported by the wind may become, for reasons not very well understood, very turbulent and irregular when falling into the enormous gravitational potential of the compact object.
	www.eurekalert.org /pub_releases/2005-11/esa-irn111605.php (896 words)

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