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X-ray binary

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Artist's impression of an X-ray Binary

X-ray binariesare a class ofbinary starsthat are luminous inX-rays. The X-rays are produced by matter falling from one component, called thedonor(usually a relatively commonmain sequencestar), to the other component, called theaccretor,which is either aneutron starorblack hole. The infalling matter releasesgravitational potential energy,up to 30 percent of its rest mass, as X-rays. (Hydrogenfusionreleases only about 0.7 percent of rest mass.) The lifetime and the mass-transfer rate in an X-ray binary depends on the evolutionary status of the donor star, the mass ratio between the stellar components, and their orbital separation.[1]

An estimated 1041positronsescape per second from a typicallow-mass X-ray binary.[2][3]

Classification[edit]

Microquasar SS-433.[4]

X-ray binaries are further subdivided into several (sometimes overlapping) subclasses, that perhaps reflect the underlying physics better. Note that the classification by mass (high, intermediate, low) refers to the optically visible donor, not to the compact X-ray emitting accretor.

Low-mass X-ray binary[edit]

Alow-mass X-ray binary(LMXB) is abinary starsystem where one of the components is either ablack holeorneutron star.[1]The other component, a donor, usually fills itsRoche lobeand therefore transfers mass to the compact star. In LMXB systems the donor is less massive than the compact object, and can be on themain sequence,a degenerate dwarf (white dwarf), or an evolved star (red giant). Approximately two hundred LMXBs have been detected in theMilky Way,[11]and of these, thirteen LMXBs have been discovered inglobular clusters.TheChandra X-ray Observatoryhas revealed LMXBs in many distant galaxies.[12]

A typical low-mass X-ray binary emits almost all of itsradiationinX-rays,and typically less than one percent in visible light, so they are among the brightest objects in the X-ray sky, but relatively faint in visible light. Theapparent magnitudeis typically around 15 to 20. The brightest part of the system is theaccretion diskaround the compact object. The orbital periods of LMXBs range from ten minutes to hundreds of days.

The variability of LMXBs are most commonly observed asX-ray bursters,but can sometimes be seen in the form ofX-ray pulsars.TheX-ray burstersare created bythermonuclear explosionscreated by the accretion of Hydrogen and Helium.[13]

Intermediate-mass X-ray binary[edit]

Anintermediate-mass X-ray binary(IMXB) is a binary star system where one of the components is a neutron star or a black hole. The other component is an intermediate-mass star.[13][14]An intermediate-mass X-ray binary is the origin for Low-mass X-ray binary systems.

High-mass X-ray binary[edit]

Ahigh-mass X-ray binary(HMXB) is abinary starsystem that is strong in X rays, and in which the normal stellar component is a massivestar:usually an O or B star, a bluesupergiant,or in some cases, a red supergiant or aWolf–Rayet star. The compact, X-ray emitting, component is aneutron starorblack hole.[1] A fraction of thestellar windof the massive normal star is captured by the compact object, and producesX-raysas it falls onto the compact object.

In a high-mass X-ray binary, the massive star dominates the emission of optical light, while the compact object is the dominant source of X-rays. The massive stars are very luminous and therefore easily detected. One of the most famous high-mass X-ray binaries isCygnus X-1,which was the first identified black hole candidate. Other HMXBs includeVela X-1(not to be confused withVela X), and4U 1700-37.

The variability of HMXBs are observed in the form ofX-ray pulsarsand notX-ray bursters.TheseX-ray pulsarsare due to the accretion of matter magnetically funneled into the poles of the compact companion.[13]Thestellar windandRoche lobeoverflow of the massive normal star accretes in such large quantities, the transfer is very unstable and creates a short lived mass transfer.

Once a HMXB has reached its end, if the periodicity of the binary was less than a year, it can become a singlered giant with a neutron coreor a singleneutron star.With a longer periodicity, a year and beyond, the HMXB can become a doubleneutron starbinary if uninterrupted by asupernova.[14]

Microquasar[edit]

Artist's impression of the microquasarSS 433.

Amicroquasar(or radio emitting X-ray binary) is the smaller cousin of aquasar.Microquasars are named after quasars, as they have some common characteristics: strong and variable radio emission, often resolvable as a pair of radio jets, and anaccretion disksurrounding acompact objectwhich is either ablack holeor aneutron star.In quasars, the black hole is supermassive (millions ofsolar masses); in microquasars, the mass of the compact object is only a few solar masses. In microquasars, the accreted mass comes from a normal star, and the accretion disk is very luminous in the optical andX-rayregions. Microquasars are sometimes calledradio-jet X-ray binariesto distinguish them from other X-ray binaries. A part of the radio emission comes fromrelativistic jets,often showing apparentsuperluminal motion.[15]

Microquasars are very important for the study ofrelativistic jets.The jets are formed close to the compact object, and timescales near the compact object are proportional to the mass of the compact object. Therefore, ordinary quasars take centuries to go through variations a microquasar experiences in one day.

Noteworthy microquasars includeSS 433,in which atomic emission lines are visible from both jets;GRS 1915+105,with an especially high jet velocity and the very brightCygnus X-1,detected up to the High Energygamma rays(E > 60 MeV). Extremely high energies of particles emitting in the VHE band might be explained by several mechanisms of particle acceleration (seeFermi accelerationandCentrifugal mechanism of acceleration).

See also[edit]

References[edit]

  1. ^abcTauris, Thomas M.; van den Heuvel, Ed (2006). "Chapter 16: Formation and evolution of compact stellar X-ray sources". In Lewin, Walter; van der Klis, Michiel (eds.).Compact Stellar X-ray Sources.Cambridge Astrophysics Series. Vol. 39. pp. 623–665.arXiv:astro-ph/0303456.Bibcode:2006csxs.book..623T.doi:10.1017/CBO9780511536281.017.ISBN978-0-521-82659-4.S2CID18856214.
  2. ^Weidenspointner, Georg (2008). "An asymmetric distribution of positrons in the Galactic disk revealed by gamma-rays".Nature.451(7175): 159–62.Bibcode:2008Natur.451..159W.doi:10.1038/nature06490.PMID18185581.S2CID4333175.
  3. ^"Mystery of Antimatter Source Solved – Maybe"by John Borland 2008
  4. ^"A game-changer".eso.org.Retrieved15 July2019.
  5. ^Introduction to Cataclysmic Variables (CVs),NASA, 2006.
  6. ^Patruno, Alessandro; Watts, Anna L. (2021), Belloni, Tomaso M.; Méndez, Mariano; Zhang, Chengmin (eds.),"Accreting Millisecond X-ray Pulsars",Timing Neutron Stars: Pulsations, Oscillations and Explosions,vol. 461, Berlin, Heidelberg: Springer, pp. 143–208,arXiv:1206.2727,Bibcode:2021ASSL..461..143P,doi:10.1007/978-3-662-62110-3_4,ISBN978-3-662-62110-3,S2CID118471125,retrieved2022-06-16
  7. ^"Millisecond Pulsar Catalog - Black Sidus".2013-09-30.Retrieved2022-06-16.
  8. ^Chen, Wen-Cong; Podsiadlowski, Philipp (2016)."Evolution of Intermediate-mass X-Ray Binaries Driven by the Magnetic Braking of AP/BP Stars. I. Ultracompact X-Ray Binaries".The Astrophysical Journal.830(2): 131.arXiv:1608.02088.Bibcode:2016ApJ...830..131C.doi:10.3847/0004-637X/830/2/131.S2CID118475703.
  9. ^Negueruela, I; Smith, D. M; Reig, P; Chaty, S; Torrejón, J. M (2006). "Supergiant Fast X-ray Transients: A New Class of High Mass X-ray Binaries Unveiled by INTEGRAL".The X-Ray Universe 2005.604(2006): 165.arXiv:astro-ph/0511088.Bibcode:2006ESASP.604..165N.
  10. ^Sidoli, Lara; Ed van den Heuvel (2008). "Transient outburst mechanisms".37th Cospar Scientific Assembly.37:2892.arXiv:0809.3157.Bibcode:2008cosp...37.2892S.
  11. ^Liu, Q. Z; Van Paradijs, J; Van Den Heuvel, E. P. J (2007). "A catalogue of low-mass X-ray binaries in the Galaxy, LMC, and SMC (Fourth edition)".Astronomy and Astrophysics.469(2): 807.arXiv:0707.0544.Bibcode:2007A&A...469..807L.doi:10.1051/0004-6361:20077303.S2CID14673570.
  12. ^Tetarenko, B. E.; Sivakoff, G. R.; Heinke, C. O.; Gladstone, J. C. (February 10, 2010)."Watchdog: A Comprehensive All-Sky Database of Galactic Black Hole X-Ray Binaries".The Astrophysical Journal Supplement Series.222(2): 15.arXiv:1512.00778.doi:10.3847/0067-0049/222/2/15.S2CID118833989.
  13. ^abcTauris, Thomas M; Van Den Heuvel, Edward P. J; Savonije, Gerrit J (2000). "Formation of Millisecond Pulsars with Heavy White Dwarf Companions:Extreme Mass Transfer on Subthermal Timescales".The Astrophysical Journal.530(2): L93–L96.arXiv:astro-ph/0001013.Bibcode:2000ApJ...530L..93T.doi:10.1086/312496.PMID10655173.S2CID17772120.
  14. ^abPodsiadlowski, Ph; Rappaport, S; Pfahl, E. D (2002). "Evolutionary Sequences for Low- and Intermediate-Mass X-Ray Binaries".The Astrophysical Journal.565(2): 1107.arXiv:astro-ph/0107261.Bibcode:2002ApJ...565.1107P.doi:10.1086/324686.S2CID16381236.
  15. ^Mirabel, I. F.; Rodríguez, L. F. (1994-09-01)."A superluminal source in the Galaxy".Nature.371(6492): 46–48.Bibcode:1994Natur.371...46M.doi:10.1038/371046a0.ISSN0028-0836.S2CID4347263.

External links[edit]

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