X-ray binary

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Artist's impression of an X-ray Binary Accretion disk.jpg
Artist's impression of an X-ray Binary

X-ray binaries are a class of binary stars that are luminous in X-rays. The X-rays are produced by matter falling from one component, called the donor (usually a relatively normal star), to the other component, called the accretor, which is either a neutron star or black hole. The infalling matter releases gravitational potential energy, up to 30 percent of its rest mass, as X-rays. (Hydrogen 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. [1]

Contents

An estimated 1041 positrons escape per second from a typical low-mass X-ray binary. [2] [3]

Classification

Microquasar SS-433. A game-changer SS-433.tif
Microquasar SS-433.

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

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. [1] 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, [11] and of these, thirteen LMXBs have been discovered in globular clusters. The Chandra X-ray Observatory has revealed LMXBs in many distant galaxies. [12]

A typical low-mass X-ray binary emits almost all of its radiation in X-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. 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 bursters, but can sometimes be seen in the form of X-ray pulsars. The X-ray bursters are created by thermonuclear explosions created by the accretion of Hydrogen and Helium. [13]

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. [13] [14] 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. [1] A fraction of the stellar wind of the massive normal star is captured by the compact object, and produces X-rays 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 pulsars and not X-ray bursters. These X-ray pulsars are due to the accretion of matter magnetically funneled into the poles of the compact companion. [13] 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 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. [14]

Microquasar

Artist's impression of the microquasar SS 433. Ss433 art big.gif
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 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 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 jets, often showing apparent superluminal motion. [15]

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 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

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<span class="mw-page-title-main">Cygnus X-1</span> Galactic X-ray source in the constellation Cygnus that is very likely a black hole

Cygnus X-1 (abbreviated Cyg X-1) is a galactic X-ray source in the constellation Cygnus and was the first such source widely accepted to be a black hole. It was discovered in 1965 during a rocket flight and is one of the strongest X-ray sources detectable from Earth, producing a peak X-ray flux density of 2.3×10−23 W/(m2⋅Hz) (2.3×103 jansky). It remains among the most studied astronomical objects in its class. The compact object is now estimated to have a mass about 21.2 times the mass of the Sun and has been shown to be too small to be any known kind of normal star or other likely object besides a black hole. If so, the radius of its event horizon has 300 km "as upper bound to the linear dimension of the source region" of occasional X-ray bursts lasting only for about 1 ms.

A Thorne–Żytkow object, also known as a hybrid star, is a conjectured type of star wherein a red giant or red supergiant contains a neutron star at its core, formed from the collision of the giant with the neutron star. Such objects were hypothesized by Kip Thorne and Anna Żytkow in 1977. In 2014, it was discovered that the star HV 2112, located in the Small Magellanic Cloud (SMC), was a strong candidate. Another possible candidate is the star HV 11417, also located in the SMC.

<span class="mw-page-title-main">X-ray burster</span> Class of X-ray binary stars

X-ray bursters are one class of X-ray binary stars exhibiting X-ray bursts, periodic and rapid increases in luminosity that peak in the X-ray region of the electromagnetic spectrum. These astrophysical systems are composed of an accreting neutron star and a main sequence companion 'donor' star. There are two types of X-ray bursts, designated I and II. Type I bursts are caused by thermonuclear runaway, while type II arise from the release of gravitational (potential) energy liberated through accretion. For type I (thermonuclear) bursts, the mass transferred from the donor star accumulates on the surface of the neutron star until it ignites and fuses in a burst, producing X-rays. The behaviour of X-ray bursters is similar to the behaviour of recurrent novae. In the latter case the compact object is a white dwarf that accretes hydrogen that finally undergoes explosive burning.

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<span class="mw-page-title-main">47 Tucanae</span> Globular cluster in the constellation Tucana

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<span class="mw-page-title-main">Astrophysical jet</span> Beam of ionized matter flowing along the axis of a rotating astronomical object

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<span class="mw-page-title-main">SS 433</span> Binary star system in the constellation Aquila

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<span class="mw-page-title-main">Centaurus X-3</span> Binary star with an X-ray pulsar in the constellation Centaurus

Centaurus X-3 is an X-ray pulsar with a period of 4.84 seconds. It was the first X-ray pulsar to be discovered, and the third X-ray source to be discovered in the constellation Centaurus. The system consists of a neutron star orbiting a massive, O-type supergiant star dubbed Krzeminski's star after its discoverer, Wojciech Krzemiński. Matter is being accreted from the star onto the neutron star, resulting in X-ray emission.

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<span class="mw-page-title-main">Ultraluminous X-ray source</span>

An ultraluminous X-ray source (ULX) is an astronomical source of X-rays that is less luminous than an active galactic nucleus but is more consistently luminous than any known stellar process (over 1039 erg/s, or 1032 watts), assuming that it radiates isotropically (the same in all directions). Typically there is about one ULX per galaxy in galaxies which host them, but some galaxies contain many. The Milky Way has not been shown to contain a ULX, although SS 433 may be a possible source. The main interest in ULXs stems from their luminosity exceeding the Eddington luminosity of neutron stars and even stellar black holes. It is not known what powers ULXs; models include beamed emission of stellar mass objects, accreting intermediate-mass black holes, and super-Eddington emission.

<span class="mw-page-title-main">Vela X-1</span> X-ray emission source in the constellation Vela

Vela X-1 is a pulsing, eclipsing high-mass X-ray binary (HMXB) system, associated with the Uhuru source 4U 0900-40 and the supergiant star HD 77581. The X-ray emission of the neutron star is caused by the capture and accretion of matter from the stellar wind of the supergiant companion. Vela X-1 is the prototypical detached HMXB.

<span class="mw-page-title-main">GRS 1915+105</span> Binary system in the constellation Aquila

GRS 1915+105 or V1487 Aquilae is an X-ray binary star system which features a regular star and a black hole. It was discovered on August 15, 1992 by the WATCH all-sky monitor aboard Granat. "GRS" stands for "GRANAT source", "1915" is the right ascension and "105" reflects the approximate declination. The near-infrared counterpart was confirmed by spectroscopic observations. The binary system lies 11,000 parsecs away in Aquila. GRS 1915+105 is the heaviest of the stellar black holes so far known in the Milky Way Galaxy, with 10 to 18 times the mass of the Sun. It is also a microquasar, and it appears that the black hole rotates at least 950 times per second, close to the maximum of 1,150 times per second, with a spin parameter value between 0.82 and 1.00.

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<span class="mw-page-title-main">Astrophysical X-ray source</span> Astronomical object emitting X-rays

Astrophysical X-ray sources are astronomical objects with physical properties which result in the emission of X-rays.

<span class="mw-page-title-main">XTE J1118+480</span> Star system in the constellation Ursa Major

XTE J1118+480 is a low-mass X-ray binary in the constellation Ursa Major. It is a soft X-ray transient that most likely contains a black hole and is probably a microquasar.

OAO 1657-415 is a high-mass X-ray binary (HMXB) located in the constellation of Scorpius, over 20,000 light years away. It is believed to be composed of a compact object and a highly evolved massive slash star, with Wolf–Rayet and O-type features in its spectrum, with a spectral type of Ofpe/WN9. OAO 1657-415 is special as it has the largest eccentricity and orbital period of any HMXB, and also because its donor star is much more evolved than many other HMXB donor stars.

References

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  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. PMID   18185581. S2CID   4333175.
  3. ↑ "Mystery of Antimatter Source Solved – Maybe" by John Borland 2008
  4. ↑ "A game-changer". www.eso.org. Retrieved 15 July 2019.
  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, Berlin, Heidelberg: Springer, vol. 461, pp. 143–208, arXiv: 1206.2727 , Bibcode:2021ASSL..461..143P, doi:10.1007/978-3-662-62110-3_4, ISBN   978-3-662-62110-3, S2CID   118471125 , retrieved 2022-06-16
  7. ↑ "Millisecond Pulsar Catalog - Black Sidus". 2013-09-30. Retrieved 2022-06-16.
  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 . S2CID   118475703.
  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. S2CID   14673570.
  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 . S2CID   118833989.
  13. 1 2 3 Tauris, 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. PMID   10655173. S2CID   17772120.
  14. 1 2 Podsiadlowski, 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. S2CID   16381236.
  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. ISSN   0028-0836. S2CID   4347263.
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