Editing 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 [[binary star]]s that are luminous in [[X-ray]]s. 
The X-rays are produced by matter falling from one component, called the ''donor'' (usually a relatively common [[main sequence]] [[star]]), to the other component, called the ''accretor'', which can be a [[white dwarf]], [[neutron star]] or [[black hole]]. 
The infalling matter releases [[gravitational energy|gravitational potential energy]], up to 30 percent of its rest mass, as X-rays.  (Hydrogen [[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> [[positron]]s escape per second from a typical [[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 binary|Low-mass X-ray binaries]] (LMXBs)
** [[Soft X-ray transient]]s (SXTs)
** [[Symbiotic variable star|Symbiotic X-ray binaries]]
** [[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 binary|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 binary|High-mass X-ray binaries]] (HMXBs)
** [[Be X-ray binaries|Be/X-ray binaries]] (BeXRBs)
** [[X-ray astronomy#Analytical X-ray astronomy|Supergiant X-ray binaries]] (SGXBs)
** [[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
** [[X-ray burster]]s
** [[X-ray pulsar]]s
** [[#Microquasar|Microquasar]]s (radio-jet X-ray binaries that can house either a neutron star or a black hole)

== Low-mass X-ray binary ==
[[File:X-Ray binary.jpg|thumb|Artist's impression of an X-ray binary system]]
A '''low-mass X-ray binary''' ('''LMXB''') is a [[binary star]] system where one of the components is either a [[black hole]] or [[neutron star]].{{r|Tauris}}  The other component, a donor, usually fills its [[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 [[main sequence]], a degenerate dwarf ([[white dwarf]]), or an evolved star ([[red giant]]). Approximately two hundred LMXBs have been detected in the [[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 [[globular cluster]]s.  The [[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 [[electromagnetic radiation|radiation]] in [[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 [[apparent magnitude]] is typically around 15 to 20. The brightest part of the system is the [[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 [[X-ray burster]]s, but can sometimes be seen in the form of [[X-ray pulsar]]s. The [[X-ray burster]]s are created by [[thermonuclear explosion]]s 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 [[binary star]] system that is strong in X rays, and in which the normal stellar component is a massive [[star]]: usually an O or B star, a blue [[supergiant]], or in some cases, a red supergiant or a [[Wolf–Rayet star]]. 
The compact, X-ray emitting, component is a [[neutron star]] or [[black hole]].{{r|Tauris}}
A fraction of the [[stellar wind]] of the massive normal star is captured by the compact object, and produces [[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 [[Cygnus X-1]], which was the first identified black hole candidate.  
Other HMXBs include [[Vela X-1]] (not to be confused with [[Vela X]]), and [[4U 1700-37]].

The variability of HMXBs are observed in the form of [[X-ray pulsar]]s and not [[X-ray burster]]s. These [[X-ray pulsar]]s are due to the accretion of matter magnetically funneled into the poles of the compact companion.<ref name=":1" /> The [[stellar wind]] and [[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 [[Thorne%E2%80%93%C5%BBytkow_object|red giant with a neutron core]] or a single [[neutron star]]. With a longer periodicity, a year and beyond, the HMXB can become a double [[neutron star]] binary if uninterrupted by a [[supernova]].<ref name=":0" />

== Be star binaries ==
=== Be/X-ray binaries ===
[[Be/X-ray binary|Be/X-ray binaries]] (BeXRBs) are a class of high-mass X-ray binaries that consist of a [[Be star]] and a [[neutron star]]. The neutron star is usually in a wide highly elliptical orbit around the Be star. The Be [[stellar wind]] forms a disk confined to a plane often different from the orbital plane of the neutron star. When the neutron star passes through the Be disk, it accretes a large mass of hot gas in a short time. As the gas falls onto the neutron star, a bright flare in hard X-rays is seen.<ref>{{cite journal|bibcode=2011Ap&SS.332....1R|title=Be/X-ray binaries|journal=Astrophysics and Space Science|volume=332|pages=1–29|last1=Reig|first1=Pablo|year=2011|issue=1 |doi=10.1007/s10509-010-0575-8|arxiv=1101.5036}}</ref>

=== Be–white dwarf X-ray binary systems ===
[[File:A Tale of two stars ESA506449.jpg|thumb|upright=1.5|ESA infographic of BeWD EP J0052 formation, observed by the [[Einstein Probe]]<ref>{{Cite web|url=https://www.esa.int/Science_Exploration/Space_Science/Einstein_Probe_catches_X-ray_odd_couple|title=Einstein Probe catches X-ray odd couple|website=www.esa.int}}</ref>]]
[[Be–white dwarf X-ray binary system]]s (BeWDs) are a rare type of X-ray binary consisting of a [[white dwarf]] that accretes matter from a rapidly-rotating [[Be star]]. These systems form through binary evolution where mass transfer spins up the accretor to become a Be star while the donor evolves into a white dwarf.<ref name=ep>{{cite journal |doi=10.3847/2041-8213/ad9580 |doi-access=free |title=Einstein Probe Discovery of EP J005245.1−722843: A Rare Be–White Dwarf Binary in the Small Magellanic Cloud? |date=2025 |last1=Marino |first1=A. |last2=Yang |first2=H. N. |last3=Coti Zelati |first3=F. |last4=Rea |first4=N. |last5=Guillot |first5=S. |last6=Jaisawal |first6=G. K. |last7=Maitra |first7=C. |last8=Ness |first8=J.-U. |last9=Haberl |first9=F. |last10=Kuulkers |first10=E. |last11=Yuan |first11=W. |last12=Feng |first12=H. |last13=Tao |first13=L. |last14=Jin |first14=C. |last15=Sun |first15=H. |last16=Zhang |first16=W. |last17=Chen |first17=W. |last18=Van Den Heuvel |first18=E. P. J. |last19=Soria |first19=R. |last20=Zhang |first20=B. |last21=Weng |first21=S.-S. |last22=Ji |first22=L. |last23=Zhang |first23=G. B. |last24=Pan |first24=X. |last25=Lv |first25=Z. |last26=Zhang |first26=C. |last27=Ling |first27=Z. X. |last28=Chen |first28=Y. |last29=Jia |first29=S. |last30=Liu |first30=Y. |journal=The Astrophysical Journal Letters |volume=980 |issue=2 |pages=L36 |display-authors=1 }}</ref> Only eight BeWDs are known, though theoretical models say they should be 7 times more common than Be/neutron star binaries.

== 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 [[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 [[accretion disk]] surrounding a [[compact object]] which is either a [[black hole]] or a [[neutron star]]. In quasars, the black hole is supermassive (millions of [[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 [[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 jet]]s, often showing apparent [[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 jet]]s. 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 [[SS 433]], in which atomic emission lines are visible from both jets; [[GRS 1915+105]], with an especially high jet velocity and the very bright [[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 [[Fermi acceleration]] and [[Centrifugal mechanism of acceleration]]).

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

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

== Further reading ==
* {{Cite journal |url=https://link.springer.com/article/10.12942/lrr-2014-3 |journal=Living Reviews in Relativity |title=The Evolution of Compact Binary Star Systems |date=5 May 2014 |volume=17 |first1=Konstantin A. |last1=Postnov |first2=Lev R. |last2=Yungelson}}
* {{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}}

==External links==
* 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]

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