View source for Astronomy:X-ray binary

{{Short description|Class of binary stars}}
[[Image:Accretion disk.jpg|300px|thumb|Artist's impression of an X-ray Binary]]

'''X-ray binaries''' are a class of [[Astronomy:Binary star|binary star]]s that are luminous in [[Physics:X-ray|X-ray]]s. 
The X-rays are produced by matter falling from one component, called the ''donor'' (usually a relatively normal [[Astronomy:Star|star]]), to the other component, called the ''accretor'', which is either a [[Astronomy:Neutron star|neutron star]] or [[Astronomy:Black hole|black hole]]. 
The infalling matter releases [[Physics:Gravitational energy|gravitational potential energy]], up to 30 percent of its rest mass, as X-rays.  (Hydrogen [[Physics:Nuclear fusion|fusion]] releases 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.<ref name=Tauris>{{cite book
 |first1=Thomas M. |last1=Tauris  |first2=Ed |last2=van den Heuvel
 |title=Compact Stellar X-ray Sources |chapter=Chapter 16: Formation and evolution of compact stellar X-ray sources
 |bibcode=2006csxs.book..623T
 |volume=39  |editor1-first=Walter |editor1-last=Lewin  |editor2-first=Michiel |editor2-last=van der Klis
 |series=Cambridge Astrophysics Series
 |year=2006
 |pages=623–665
 |doi=10.1017/CBO9780511536281.017
|arxiv=astro-ph/0303456 |isbn=978-0-521-82659-4|s2cid=18856214 }}</ref>

An estimated 10<sup>41</sup> [[Physics:Positron|positron]]s escape per second from a typical [[Astronomy:X-ray binary#Low-mass X-ray binary|low-mass X-ray binary]].<ref>{{Cite journal
  | last = Weidenspointner
  | first = Georg
  | title = An asymmetric distribution of positrons in the Galactic disk revealed by gamma-rays
  | journal = Nature
  | date = 2008
  | doi = 10.1038/nature06490
  |bibcode = 2008Natur.451..159W
  | pmid=18185581
  | volume=451
  | issue = 7175
  | pages=159–62| s2cid = 4333175
 }}</ref><ref>[https://www.wired.com/wiredscience/2008/01/mystery-of-anti/ "Mystery of Antimatter Source Solved – Maybe"] by John Borland 2008</ref>

==Classification==
[[File:A game-changer SS-433.tif|thumb|Microquasar SS-433.<ref>{{cite web |title=A game-changer |url=https://www.eso.org/public/images/potw1928a/ |website=www.eso.org |access-date=15 July 2019 |language=en}}</ref>]]

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 binaries (LMXBs)
** [[Astronomy:Soft X-ray transient|Soft X-ray transient]]s (SXTs)
** Symbiotic X-ray binaries
** [[Astronomy:Super soft X-ray source|Super soft X-ray source]]s or Super soft sources<ref>[http://heasarc.gsfc.nasa.gov/docs/objects/cvs/cvstext.html Introduction to Cataclysmic Variables (CVs)], NASA, 2006.</ref> (SSXs), (SSXB)
** Accreting millisecond X-ray pulsars (AMXPs)<ref>{{Citation |last1=Patruno |first1=Alessandro |title=Accreting Millisecond X-ray Pulsars |date=2021 |url=https://doi.org/10.1007/978-3-662-62110-3_4 |work=Timing Neutron Stars: Pulsations, Oscillations and Explosions |pages=143–208 |editor-last=Belloni |editor-first=Tomaso M. |place=Berlin, Heidelberg |publisher=Springer |language=en |doi=10.1007/978-3-662-62110-3_4 |isbn=978-3-662-62110-3 |access-date=2022-06-16 |last2=Watts |first2=Anna L. |volume=461 |editor2-last=Méndez |editor2-first=Mariano |editor3-last=Zhang |editor3-first=Chengmin|arxiv=1206.2727 |bibcode=2021ASSL..461..143P |s2cid=118471125 }}</ref><ref>{{Cite web |date=2013-09-30 |title=Millisecond Pulsar Catalog - Black Sidus |url=https://blacksidus.com/millisecond-pulsar-catalogue/ |access-date=2022-06-16 |language=en-US}}</ref>
* Intermediate-mass X-ray binaries (IMXBs)
** Ultracompact X-ray binaries (UCXBs)<ref>{{Cite journal |arxiv = 1608.02088|bibcode = 2016ApJ...830..131C|title = Evolution of Intermediate-mass X-Ray Binaries Driven by the Magnetic Braking of AP/BP Stars. I. Ultracompact X-Ray Binaries|journal = The Astrophysical Journal|volume = 830|issue = 2|pages = 131|last1 = Chen|first1 = Wen-Cong|last2 = Podsiadlowski|first2 = Philipp|year = 2016|doi = 10.3847/0004-637X/830/2/131|s2cid = 118475703 | doi-access=free }}</ref>
* High-mass X-ray binaries (HMXBs)
** Be/X-ray binaries (BeXRBs)
** [[Astronomy:X-ray astronomy#Analytical X-ray astronomy|Supergiant X-ray binaries]] (SGXBs)
** [[Astronomy:X-ray astronomy#Exotic X-ray sources|Supergiant Fast X-ray Transients]] (SFXTs)<ref>{{Cite journal |arxiv = astro-ph/0511088|bibcode = 2006ESASP.604..165N|title = Supergiant Fast X-ray Transients: A New Class of High Mass X-ray Binaries Unveiled by INTEGRAL|journal = The X-Ray Universe 2005|volume = 604|issue = 2006|pages = 165|last1 = Negueruela|first1 = I|last2 = Smith|first2 = D. M|last3 = Reig|first3 = P|last4 = Chaty|first4 = S|last5 = Torrejón|first5 = J. M|year = 2006}}</ref><ref>{{Cite journal |arxiv = 0809.3157|bibcode = 2008cosp...37.2892S|title = Transient outburst mechanisms|journal = 37th Cospar Scientific Assembly|volume = 37|pages = 2892|last1 = Sidoli|first1 = Lara|year = 2008|author2 = Ed van den Heuvel}}</ref>
* Others
** [[Astronomy:X-ray burster|X-ray burster]]s
** [[Astronomy:X-ray pulsar|X-ray pulsar]]s
** Microquasars (radio-jet X-ray binaries that can house either a neutron star or a black hole)

== Low-mass X-ray binary ==
A '''low-mass X-ray binary''' ('''LMXB''') is a [[Astronomy:Binary star|binary star]] system where one of the components is either a [[Astronomy:Black hole|black hole]] or [[Astronomy:Neutron star|neutron star]].{{r|Tauris}}  The other component, a donor, usually fills its [[Physics:Roche lobe|Roche lobe]] and therefore transfers mass to the compact star.  In LMXB systems the donor is less massive than the compact object, and can be on the [[Astronomy:Main sequence|main sequence]], a degenerate dwarf ([[Astronomy:White dwarf|white dwarf]]), or an evolved star ([[Astronomy:Red giant|red giant]]). Approximately two hundred LMXBs have been detected in the [[Astronomy:Milky Way|Milky Way]],<ref>{{Cite journal |arxiv = 0707.0544|bibcode = 2007A&A...469..807L|title = A catalogue of low-mass X-ray binaries in the Galaxy, LMC, and SMC (Fourth edition)|journal = Astronomy and Astrophysics|volume = 469|issue = 2|pages = 807|last1 = Liu|first1 = Q. Z|last2 = Van Paradijs|first2 = J|last3 = Van Den Heuvel|first3 = E. P. J|year = 2007|doi = 10.1051/0004-6361:20077303|s2cid = 14673570}}</ref> and of these, thirteen LMXBs have been discovered in [[Astronomy:Globular cluster|globular cluster]]s.  The [[Astronomy:Chandra X-ray Observatory|Chandra X-ray Observatory]] has revealed LMXBs in many distant galaxies. <ref>{{cite journal | last1=Tetarenko  | first1=B. E. | last2=Sivakoff | first2=G. R. | last3=Heinke | first3=C. O. | last4=Gladstone | first4=J. C. | title=Watchdog: A Comprehensive All-Sky Database of Galactic Black Hole X-Ray Binaries | date= February 10, 2010 | journal= The Astrophysical Journal Supplement Series | volume= 222 | issue= 2 | page=15 | doi=10.3847/0067-0049/222/2/15| arxiv=1512.00778 | s2cid=118833989 | doi-access=free }}</ref>

A typical low-mass X-ray binary emits almost all of its [[Physics:Electromagnetic radiation|radiation]] in [[Physics:X-ray|X-ray]]s, 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. The [[Astronomy:Apparent magnitude|apparent magnitude]] is typically around 15 to 20. The brightest part of the system is the [[Astronomy:Accretion disk|accretion disk]] around the compact object. The orbital periods of LMXBs range from ten minutes to hundreds of days.

The variability of LMXBs are most commonly observed as [[Astronomy:X-ray burster|X-ray burster]]s, but can sometimes be seen in the form of [[Astronomy:X-ray pulsar|X-ray pulsar]]s. The [[Astronomy:X-ray burster|X-ray burster]]s are created by thermonuclear explosions created by the accretion of Hydrogen and Helium.<ref name=":1" />

== Intermediate-mass X-ray binary ==
An '''intermediate-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.<ref name=":1">{{Cite journal |bibcode = 2000ApJ...530L..93T|title = Formation of Millisecond Pulsars with Heavy White Dwarf Companions:Extreme Mass Transfer on Subthermal Timescales|journal = The Astrophysical Journal|volume = 530|issue = 2|pages = L93–L96|last1 = Tauris|first1 = Thomas M|last2 = Van Den Heuvel|first2 = Edward P. J|last3 = Savonije|first3 = Gerrit J|year = 2000|doi = 10.1086/312496|pmid = 10655173|arxiv = astro-ph/0001013|s2cid = 17772120}}</ref><ref name=":0">{{Cite journal |arxiv = astro-ph/0107261|bibcode = 2002ApJ...565.1107P|title = Evolutionary Sequences for Low- and Intermediate-Mass X-Ray Binaries|journal = The Astrophysical Journal|volume = 565|issue = 2|pages = 1107|last1 = Podsiadlowski|first1 = Ph|last2 = Rappaport|first2 = S|last3 = Pfahl|first3 = E. D|year = 2002|doi = 10.1086/324686|s2cid = 16381236}}</ref> An intermediate-mass X-ray binary is the origin for Low-mass X-ray binary systems.

== High-mass X-ray binary ==
A '''high-mass X-ray binary''' ('''HMXB''') is a [[Astronomy:Binary star|binary star]] system that is strong in X rays, and in which the normal stellar component is a massive [[Astronomy:Star|star]]: usually an O or B star, a blue [[Astronomy:Supergiant|supergiant]], or in some cases, a red supergiant or a [[Astronomy:Wolf–Rayet star|Wolf–Rayet star]]. 
The compact, X-ray emitting, component is a [[Astronomy:Neutron star|neutron star]] or [[Astronomy:Black hole|black hole]].{{r|Tauris}}
A fraction of the [[Astronomy:Stellar wind|stellar wind]] of the massive normal star is captured by the compact object, and produces [[Physics:X-ray|X-ray]]s as 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 is [[Astronomy:Cygnus X-1|Cygnus X-1]], which was the first identified black hole candidate.  
Other HMXBs include [[Astronomy:Vela X-1|Vela X-1]] (not to be confused with Vela X), and [[Astronomy:4U 1700-37|4U 1700-37]].

The variability of HMXBs are observed in the form of [[Astronomy:X-ray pulsar|X-ray pulsar]]s and not [[Astronomy:X-ray burster|X-ray burster]]s. These [[Astronomy:X-ray pulsar|X-ray pulsar]]s are due to the accretion of matter magnetically funneled into the poles of the compact companion.<ref name=":1" /> The [[Astronomy:Stellar wind|stellar wind]] and [[Physics:Roche lobe|Roche lobe]] overflow 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 single red giant with a neutron core or a single [[Astronomy:Neutron star|neutron star]]. With a longer periodicity, a year and beyond, the HMXB can become a double [[Astronomy:Neutron star|neutron star]] binary if uninterrupted by a [[Astronomy:Supernova|supernova]].<ref name=":0" />

== Microquasar ==
[[Image:Ss433 art big.gif|250px|thumb|Artist's impression of the microquasar SS 433.]]
A '''microquasar''' (or radio emitting X-ray binary) is the smaller cousin of a [[Astronomy:Quasar|quasar]].  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 an [[Astronomy:Accretion disk|accretion disk]] surrounding a [[Astronomy:Compact object|compact object]] which is either a [[Astronomy:Black hole|black hole]] or a [[Astronomy:Neutron star|neutron star]]. In quasars, the black hole is supermassive (millions of [[Astronomy:Solar mass|solar mass]]es); 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 and [[Physics:X-ray|X-ray]] regions. Microquasars are sometimes called ''radio-jet X-ray binaries'' to distinguish them from other X-ray binaries. A part of the radio emission comes from relativistic jets, often showing apparent [[Astronomy:Superluminal motion|superluminal motion]].<ref>{{Cite journal |last1=Mirabel |first1=I. F. |last2=Rodríguez |first2=L. F. |date=1994-09-01 |title=A superluminal source in the Galaxy |url=https://ui.adsabs.harvard.edu/abs/1994Natur.371...46M |journal=Nature |volume=371 |issue=6492 |pages=46–48 |doi=10.1038/371046a0 |bibcode=1994Natur.371...46M |s2cid=4347263 |issn=0028-0836}}</ref>

Microquasars are very important for the study of relativistic 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 include [[Astronomy:SS 433|SS 433]], in which atomic emission lines are visible from both jets; [[Astronomy:GRS 1915+105|GRS 1915+105]], with an especially high jet velocity and the very bright [[Astronomy:Cygnus X-1|Cygnus X-1]], detected up to the High Energy gamma rays (E > 60 MeV). Extremely high energies of particles emitting in the VHE band might be explained by several mechanisms of particle acceleration (see [[Physics:Fermi acceleration|Fermi acceleration]] and [[Astronomy:Centrifugal mechanism of acceleration|Centrifugal mechanism of acceleration]]).

== See also ==
* [[Astronomy:4U 0614+091|4U 0614+091]]
* [[Astronomy:LS I +61 303|LS I +61 303]]
* [[Astronomy:SS 433|SS 433]]
* [[Astronomy:Quasar|Quasar]]

==References==
{{Reflist|30em}}

==External links==
* {{Cite conference |arxiv=0801.3863 |title=Supergiant Fast X-ray Transients and Other Wind Accretors |conference=A Population Explosion: The Nature & Evolution of X-Ray Binaries in Diverse Environments |volume=1010 |pages=252–256 |first1=Ignacio |last1=Negueruela |first2=Jose Miguel |last2=Torrejon |first3=Pablo |last3=Reig |first4=Marc |last4=Ribo |first5=David M. |last5=Smith |year=2008|bibcode=2008AIPC.1010..252N |doi=10.1063/1.2945052 |s2cid=18941968 }} {{doi|10.1063/1.2945052}} {{bibcode|2008AIPC.1010..252N}}
* Audio Cain/Gay (2009) [http://www.astronomycast.com/astronomy/ep-135-x-ray-astronomy/ Astronomy Cast episode 135: X-ray Astronomy]
* [https://students.iiserkol.ac.in/~adc15rs019/ulx_pulsar_catalogue.html Ultraluminous X-ray Pulsar (ULXP) Catalogue]

{{Neutron star}}

[[Category:X-ray binaries| ]]
[[Category:Binary stars|*]]
[[Category:Semidetached binaries|*]]
[[Category:Astronomical X-ray sources|*]]
[[Category:Compact stars]]

{{Sourceattribution|X-ray binary}}