ผลต่างระหว่างรุ่นของ "หลุมดำ"
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บรรทัด 217:
ในทางกลับกันถ้าหลุมดำมีขนาดเล็กมาก คาดว่าผลจากรังสีจะเพิ่มขึ้น แม้หลุมดำจะถูกเปรียบเทียบว่าหนักเท่ากับมนุษย์นั้นจะระเหยในทันที โดยหลุดดับที่มีน้ำหนักเท่ากับรถ (~ 10<sup>-24</sup> m) ก็จะใช้เวลาประมาณเสี้ยววินาทีในการระเหย ในช่วงนั้นจะปรากฏความสว่างมากกว่า 200 เท่าของดวงอาิทิตย์ หลุมดำที่เบากว่าจะระเหยได้เร็วกว่า เช่นถ้ามีขนาด 1 TeV/c<sup>2</sup> จะใช้เวลาน้อยกว่า 10<sup>-88</sup> วินาทีที่จะระเหย และแน่นอนว่าแรงโน้มถ่วงควอนตัมในหลุมดำที่มีขนาดเล็กกว่าจะมีบทบาทแม้ว่าการพัฒนาความโน้มถ่วงควอนตัมจะทำให้หลุมดำขนาดเล็กคงที่ตามสมมติฐาน
==เทคนิคการหาหลุมดำ==
===วงแหวนก๊าซและลำก๊าซ===
[[Image:Black hole jet diagram.jpg|left|thumb|Formation of extragalactic jets from a black hole's [[Accretion disc|accretion disk]]]]
แอคเครชั่นดีสค์ [[Accretion disc|accretion disks]] เป็นก๊าซร้อนที่ประกอบด้วยอะตอม และไอออนซ์ของธาตุต่างๆ รวมทั้งอิเลคตรอนอิสระ และอนุภาคพลังงานสูงมากมาย และก๊าซที่พุ่งออกมา [[Relativistic jet|gas jets]] ไม่ได้เป็นตัวพิสูจน์ว่าหลุมดำจากดาวฤกษ์ ([[stellar-mass black hole]]) มีอยู่จริง เพราะวัตถุขนาดใหญ่และมีความหนาแน่นมาก เช่น ดาวนิวตรอน ([[neutron star]]) และดาวแคระขาว ([[white dwarf]]) ทำให้วงแหวนก๊าซ และลำก๊าซก่อตัวและมีประพฤติตัวเหมือน ๆ กัน รอบ ๆ หลุมดำ
ในทางกลับกัน วงแหวนก๊าซและลำก๊าซอาจจะเป็นหลักฐานที่ดีสำหรับการปรากฏของหลุมดำยักษ์([[supermassive black hole]]) เพราะเรารู้ว่ามวลมีขนาดใหญ่พอจะทำให้เกิดปรากฎการณ์นี้ได้ก็มีแต่หลุมดำเท่านั้น
===Strong radiation emissions===
[[Image:Black hole quasar NASA.jpg|thumb|right|A "Quasar" Black Hole.]]
Steady [[X-ray]] and [[gamma ray]] emissions also do not prove that a black hole is present, but can tell astronomers where it might be worth looking for one - and they have the advantage that they pass fairly easily through [[nebula]]e and gas clouds.
But strong, irregular emissions of [[X-ray]]s, [[gamma ray]]s and other [[electromagnetic radiation]] can help to prove that a massive, ultra-dense object is ''not'' a black hole, so that "black hole hunters" can move on to some other object. Neutron stars and other very dense stars have surfaces, and matter colliding with the surface at a high percentage of the speed of light will produce intense flares of radiation at irregular intervals. Black holes have no material surface, so the absence of irregular flares around a massive, ultra-dense object suggests that there is a good chance of finding a black hole there.
Intense but one-time [[gamma ray burst]]s (GRBs) may signal the birth of "new" black holes, because astrophysicists think that GRBs are caused either by the [[gravitational collapse]] of giant stars<ref>{{
cite journal
|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002AJ....123.1111B&db_key=AST
|author=Bloom, J.S., Kulkarni, S. R., & Djorgovski, S. G.
|year=2002
|title=The Observed Offset Distribution of Gamma-Ray Bursts from Their Host Galaxies: A Robust Clue to the Nature of the Progenitors
|journal=Astronomical Journal
|volume=123
|pages=1111-1148
}}</ref> or by collisions between neutron stars,<ref name = "Harvard.edu-NeutronStars">{{
cite journal
|url=http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984SvAL...10..177B&db_key=AST&link_type=ABSTRACT&high=4322390bbe18728
|author=Blinnikov, S., ''et al.''
|year=1984
|title=Exploding Neutron Stars in Close Binaries
|journal=Soviet Astronomy Letters
|volume=10
|pages=177
}}</ref> and both types of event involve sufficient mass and pressure to produce black holes. But it appears that a collision between a neutron star and a black hole can also cause a GRB,<ref>{{
cite journal
|url=http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976ApJ...210..549L&db_key=AST&link_type=ABSTRACT&high=4322390bbe17313
|author=Lattimer, J. M. and Schramm, D. N.
|year=1976
|title=The tidal disruption of neutron stars by black holes in close binaries
|journal=Astrophysical Journal
|volume=210
|pages=549
}}</ref> so a GRB is not proof that a "new" black hole has been formed.
All known GRBs come from outside our own galaxy, and most come from billions of [[light year]]s away<ref>{{
cite journal
|url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995PASP..107.1167P
|author=Paczynski, B.
|year=1995
|title=How Far Away Are Gamma-Ray Bursters?
|journal=Publications of the Astronomical Society of the Pacific
|volume=107
|pages=1167
}}</ref> so the black holes associated with them are actually billions of years old.
Some astrophysicists believe that some [[ultraluminous X-ray source]]s may be the [[Accretion disc|accretion disks]] of [[intermediate-mass black hole]]s.<ref>{{
cite journal
|url=http://arxiv.org/abs/astro-ph/0512480
|author= Winter, L.M., Mushotzky, R.F. and Reynolds, C.S.
|date=2005, revised 2006
|title=XMM-Newton Archival Study of the ULX Population in Nearby Galaxies
|journal=Astrophysical Journal
|volume=649
|pages=730
}}</ref>
[[Quasars]] are thought to be the accretion disks of [[supermassive black hole]]s, since no other known object is powerful enough to produce such strong emissions. Quasars produce strong emission across the [[electromagnetic spectrum]], including [[UV]], [[X-rays]] and [[gamma-rays]] and are visible at tremendous distances due to their high [[luminosity]]. Between 5 and 25% of quasars are "radio loud," so called because of their powerful [[radio]] emission.<ref>{{
cite journal
|url=http://adsabs.harvard.edu/cgi-bin/bib_query?2007ApJ...656..680J
|author=Jiang, L., Fan, X., Ivezić, Ž., Richards, G.~T., Schneider, D.~P., Strauss, M.~A., Kelly, B.~C.
|year=2007
|title=The Radio-Loud Fraction of Quasars is a Strong Function of Redshift and Optical Luminosity
|journal=Astrophysical Journal
|volume=656
|pages=680-690
}}</ref>
===Gravitational lensing===
[[Image:Black hole lensing web.gif|170px|left|thumb|Simulation of [[Gravitational lensing]] by a black hole which distorts a [[galaxy]] in the background.]]
A [[gravitational lens]] is formed when the light from a very distant, bright source (such as a [[quasar]]) is "bent" around a massive object (such as a black hole) between the source object and the observer. The process is known as '''gravitational lensing''', and is one of the [[tests of general relativity|predictions]] of the general theory of relativity. According to this theory, [[mass]] "warps" [[space-time]] to create [[gravitational field]]s and therefore bend [[light]] as a result.
A source image behind the lens may appear as multiple images to the observer. In cases where the source, massive lensing object, and the observer lie in a straight line, the source will appear as a ring behind the massive object.
Gravitational lensing can be caused by objects other than black holes, because any very strong gravitational field will bend light rays. Some of these multiple-image effects are probably produced by distant galaxies.
===Objects orbiting possible black holes===
{{See also|Kepler problem in general relativity}}
[[Image:Cygx1 spectrum.jpg|right|thumb|A [[Chandra X-ray Observatory|Chandra]] X-ray spectrum of Cygnus X-1 showing a characteristic peak near 6.4 [[Electron volt|keV]] due to [[ion]]ized [[iron]] in the accretion disk, but the peak is gravitationally red-shifted, broadened by the [[Doppler effect]], and skewed toward lower energies.<ref>{{cite web
| author=Staff | date=August 30, 2006
| url=http://chandra.harvard.edu/photo/2003/bhspin/more.html
| title=More Images of Cygnus X-1, XTE J1650-500 & GX 339-4
| publisher=Harvard-Smithsonian Center for Astrophysics/Chandra X-ray Center
| accessdate=2008-03-30 }}</ref>]]
Objects orbiting black holes probe the gravitational field around the central object. An early example, discovered in the 1970s, is the accretion disk orbiting the putative black hole responsible for [[Cygnus X-1]], a famous X-ray source. While the material itself cannot be seen directly, the X rays flicker on a millisecond time scale, as expected for hot clumpy material orbiting a ~10 solar-mass black hole just prior to accretion. The X-ray spectrum exhibits the characteristic shape expected for a disk of orbiting relativistic material, with an iron line, emitted at ~6.4 keV, broadened to the red (on the receding side of the disk) and to the blue (on the approaching side).
Another example is the [[S2 (star)|star S2]], seen orbiting the [[Galactic center]]. Here the star is several light hours from the ~3.5×10<sup>6</sup> solar mass black hole, so its orbital motion can be plotted. Nothing is observed at the center of the observed orbit, the position of the black hole itself——as expected for a black object.
===Determining the mass of black holes===
[[Quasi-periodic oscillations]] can be used to determine the mass of black holes.<ref>{{cite web|url=http://www.eurekalert.org/pub_releases/2008-04/nsfc-nsi040108.php|title=NASA scientists identify smallest known black hole}}</ref> The technique uses a relationship between black holes and the inner part of their surrounding disks, where gas spirals inward before reaching the event horizon. As the gas collapses inwards, it radiates X-rays with an intensity that varies in a pattern that repeats itself over a nearly regular interval. This signal is the Quasi-Periodic Oscillation, or QPO. A QPO’s frequency depends on the black hole’s mass; the event horizon lies close in for small black holes, so the QPO has a higher frequency. For black holes with a larger mass, the event horizon is farther out, so the QPO frequency is lower.
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