Stellar collision

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Simulated collision of two neutron stars

A stellar collision is the coming together of two stars [1] caused by stellar dynamics within a star cluster, or by the orbital decay of a binary star due to stellar mass loss or gravitational radiation, or by other mechanisms not yet well understood.

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Astronomers predict that events of this type occur in the globular clusters of our galaxy about once every 10,000 years. [2] On 2 September 2008 scientists first observed a stellar merger in Scorpius (named V1309 Scorpii), though it was not known to be the result of a stellar merger at the time. [3]

Any stars in the universe can collide, whether they are "alive", meaning fusion is still active in the star, or "dead", with fusion no longer taking place. White dwarf stars, neutron stars, black holes, main sequence stars, giant stars, and supergiants are very different in type, mass, temperature, and radius, and so react differently. [2]

A gravitational wave event that occurred on 25 August 2017, GW170817, was reported on 16 October 2017 to be associated with the merger of two neutron stars in a distant galaxy, the first such merger to be observed via gravitational radiation. [4] [5] [6] [7]

Types of stellar collisions and mergers

Type Ia supernovae

White dwarfs are the remnants of low-mass stars and, if they form a binary system with another star, they can cause large stellar explosions known as type Ia supernovae. The normal route by which this happens involves a white dwarf drawing material off a main sequence or red giant star to form an accretion disc. Much more rarely, a type Ia supernova occurs when two white dwarfs orbit each other closely. [8] Emission of gravitational waves causes the pair to spiral inward. When they finally merge, if their combined mass approaches or exceeds the Chandrasekhar limit, carbon fusion is ignited, raising the temperature. Since a white dwarf consists of degenerate matter, there is no safe equilibrium between thermal pressure and the weight of overlying layers of the star. Because of this, runaway fusion reactions rapidly heat up the interior of the combined star and spread, causing a supernova explosion. [8] In a matter of seconds, all of the white dwarf's mass is thrown into space. [9]

Neutron star mergers

Neutron star mergers occur in a fashion similar to the rare type Ia supernovae resulting from merging white dwarfs. When two neutron stars orbit each other closely, they spiral inward as time passes due to gravitational radiation. When they meet, their merger leads to the formation of either a heavier neutron star or a black hole, depending on whether the mass of the remnant exceeds the Tolman–Oppenheimer–Volkoff limit. This creates a magnetic field that is trillions of times stronger than that of Earth, in a matter of one or two milliseconds. Astronomers believe that this type of event is what creates short gamma-ray bursts [10] and kilonovae. [11]

Thorne–Żytkow objects

If a neutron star collides with red giant of sufficiently low mass and density, both can survive in the form of a peculiar hybrid known as Thorne–Żytkow object, with the neutron star surrounded by the red giant.

Binary star mergers

About half of all the stars in the sky are part of binary systems, with two stars orbiting each other. Some binary stars orbit each other so closely that they share the same atmosphere, giving the system a peanut shape. While most contact binary stars are stable, a few have become unstable and have merged in the past for reasons not well understood (see relevant section below).

Formation of planets

When two low-mass stars in a binary system merge, mass may be thrown off in the orbital plane of the merging stars, creating an excretion disk from which new planets can form. [12]

Discovery

While the concept of stellar collision has been around for several generations of astronomers, only the development of new technology has made it possible for it to be more objectively studied. For example, in 1764, a cluster of stars known as Messier 30 was discovered by astronomer Charles Messier. In the twentieth century, astronomers concluded that the cluster was approximately 13 billion years old. [13] The Hubble Space Telescope resolved the individual stars of Messier 30. With this new technology, astronomers discovered that some stars, known as blue stragglers, appeared younger than other stars in the cluster. [13] Astronomers then hypothesized that stars may have "collided", or "merged", giving them more fuel so they continued fusion while fellow stars around them started going out. [13]

Stellar collisions and the Solar System

While stellar collisions may occur very frequently in certain parts of the galaxy, the likelihood of a collision involving the Sun is very small. A probability calculation predicts the rate of stellar collisions involving the Sun is 1 in 1028 years. [14] For comparison, the age of the universe is of the order 1010 years. The likelihood of close encounters with the Sun is also small. The rate is estimated by the formula:

N ≈ 4.2 · D2 Myr−1

where N is the number of encounters per million years that come within a radius D of the Sun in parsecs. [15] For comparison, the mean radius of the Earth's orbit, 1 AU, is 4.82 × 10−6 parsecs.

Our star will likely not be directly affected by such an event because there are no stellar clusters close enough to cause such interactions. [14]

KIC 9832227 and binary star mergers

KIC 9832227 is an example of an eclipsing contact binary star system. It is mainly composed of two stars orbiting each other so closely that they share the same atmosphere, giving the system a peanut shape. As the orbits of the two stars decay due to stellar mass loss and internal viscosity, the two stars will eventually merge, resulting in a luminous red nova.

An analysis of the eclipses of KIC 9832227 initially suggested that its orbital period was indeed shortening, and that the cores of the two stars would merge in 2022. [16] [17] [18] [19] However subsequent reanalysis found that one of the datasets used in the initial prediction contained a 12-hour timing error, leading to a spurious apparent shortening of the stars' orbital period. [20] [21] [22] [23]

The mechanism behind binary star mergers is not yet fully understood, and remains one of the main focuses of those researching KIC 9832227 and other contact binaries.

Related Research Articles

<span class="mw-page-title-main">Globular cluster</span> Spherical collection of stars

A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member stars, all orbiting in a stable, compact formation. Globular clusters are similar in form to dwarf spheroidal galaxies, and the distinction between the two is not always clear. Their name is derived from Latin globulus. Globular clusters are occasionally known simply as "globulars".

<span class="mw-page-title-main">Neutron star</span> Collapsed core of a massive star

A neutron star is the collapsed core of a massive supergiant star, which had a total mass of between 10 and 25 solar masses (M☉), possibly more if the star was especially metal-rich. Except for black holes, neutron stars are the smallest and densest known class of stellar objects. Neutron stars have a radius on the order of 10 kilometers (6 mi) and a mass of about 1.4 M☉. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density to that of atomic nuclei.

<span class="mw-page-title-main">Star</span> Large self-illuminated object in space

A star is a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night; their immense distances from Earth make them appear as fixed points of light. The most prominent stars have been categorised into constellations and asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated 1022 to 1024 stars. Only about 4,000 of these stars are visible to the naked eye—all within the Milky Way galaxy.

<span class="mw-page-title-main">Binary star</span> System of two stars orbiting each other

A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in which case they are called visual binaries. Many visual binaries have long orbital periods of several centuries or millennia and therefore have orbits which are uncertain or poorly known. They may also be detected by indirect techniques, such as spectroscopy or astrometry. If a binary star happens to orbit in a plane along our line of sight, its components will eclipse and transit each other; these pairs are called eclipsing binaries, or, together with other binaries that change brightness as they orbit, photometric binaries.

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.

In astronomy, the term compact object refers collectively to white dwarfs, neutron stars, and black holes. It could also include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects have a high mass relative to their radius, giving them a very high density, compared to ordinary atomic matter.

<span class="mw-page-title-main">Intermediate-mass black hole</span> Class of black holes with a mass range of 100 to 100000 solar masses

An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range 102–105 solar masses: significantly more than stellar black holes but less than the 105–109 solar mass supermassive black holes. Several IMBH candidate objects have been discovered in the Milky Way galaxy and others nearby, based on indirect gas cloud velocity and accretion disk spectra observations of various evidentiary strength.

<span class="mw-page-title-main">Stellar black hole</span> Black hole formed by a collapsed star

A stellar black hole is a black hole formed by the gravitational collapse of a star. They have masses ranging from about 5 to several tens of solar masses. They are the remnants of supernova explosions, which may be observed as a type of gamma ray burst. These black holes are also referred to as collapsars.

Supernova nucleosynthesis is the nucleosynthesis of chemical elements in supernova explosions.

<span class="mw-page-title-main">Interacting galaxy</span> Galaxies with interacting gravitational fields

Interacting galaxies are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision, which may lead to a galaxy merger.

<span class="mw-page-title-main">Type Ia supernova</span> Type of supernova in binary systems

A Type Ia supernova is a type of supernova that occurs in binary systems in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.

<span class="mw-page-title-main">Binary pulsar</span> Two pulsars orbiting each other

A binary pulsar is a pulsar with a binary companion, often a white dwarf or neutron star. Binary pulsars are one of the few objects which allow physicists to test general relativity because of the strong gravitational fields in their vicinities. Although the binary companion to the pulsar is usually difficult or impossible to observe directly, its presence can be deduced from the timing of the pulses from the pulsar itself, which can be measured with extraordinary accuracy by radio telescopes.

<span class="mw-page-title-main">Gravitational wave</span> Propagating spacetime ripple

Gravitational waves are waves of the intensity of gravity that are generated by the accelerated masses of binary stars and other motions of gravitating masses, and propagate as waves outward from their source at the speed of light. They were first proposed by Oliver Heaviside in 1893 and then later by Henri Poincaré in 1905 as the gravitational equivalent of electromagnetic waves. Gravitational waves are sometimes called gravity waves, but gravity waves typically refer to displacement waves in fluids. In 1916 Albert Einstein demonstrated that gravitational waves result from his general theory of relativity as ripples in spacetime.

<span class="mw-page-title-main">Galaxy merger</span> Merger whereby at least two galaxies collide

Galaxy mergers can occur when two galaxies collide. They are the most violent type of galaxy interaction. The gravitational interactions between galaxies and the friction between the gas and dust have major effects on the galaxies involved. The exact effects of such mergers depend on a wide variety of parameters such as collision angles, speeds, and relative size/composition, and are currently an extremely active area of research. Galaxy mergers are important because the merger rate is a fundamental measurement of galaxy evolution. The merger rate also provides astronomers with clues about how galaxies bulked up over time.

<span class="mw-page-title-main">Gravitational-wave astronomy</span> Branch of astronomy using gravitational waves

Gravitational-wave astronomy is an emerging field of science, concerning the observations of gravitational waves to collect relatively unique data and make inferences about objects such as neutron stars and black holes, events such as supernovae, and processes including those of the early universe shortly after the Big Bang.

<span class="mw-page-title-main">Binary black hole</span> System consisting of two black holes in close orbit around each other

A binary black hole (BBH), or black hole binary, is a system consisting of two black holes in close orbit around each other. Like black holes themselves, binary black holes are often divided into stellar binary black holes, formed either as remnants of high-mass binary star systems or by dynamic processes and mutual capture; and binary supermassive black holes, believed to be a result of galactic mergers.

<span class="mw-page-title-main">Neutron star merger</span> Type of stellar collision

A neutron star merger is the stellar collision of neutron stars.

<span class="mw-page-title-main">KIC 9832227</span> Contact binary star system

KIC 9832227 is a contact binary star system in the constellation Cygnus, located about 2,060 light-years away. It is also identified as an eclipsing binary with an orbital period of almost 11 hours.

<span class="mw-page-title-main">GW170817</span> Gravitational-wave signal detected in 2017

GW 170817 was a gravitational wave (GW) signal observed by the LIGO and Virgo detectors on 17 August 2017, originating from the shell elliptical galaxy NGC 4993. The signal was produced by the last moments of the inspiral process of a binary pair of neutron stars, ending with their merger. It is the first GW observation that has been confirmed by non-gravitational means. Unlike the five previous GW detections—which were of merging black holes and thus not expected to produce a detectable electromagnetic signal—the aftermath of this merger was seen across the electromagnetic spectrum by 70 observatories on 7 continents and in space, marking a significant breakthrough for multi-messenger astronomy. The discovery and subsequent observations of GW 170817 were given the Breakthrough of the Year award for 2017 by the journal Science.

<span class="mw-page-title-main">NGC 4993</span> Galaxy in the constellation of Hydra

NGC 4993 is a lenticular galaxy located about 140 million light-years away in the constellation Hydra. It was discovered on 26 March 1789 by William Herschel and is a member of the NGC 4993 Group.

References

  1. ↑ Fred Lawrence Whipple (March 1939), "Supernovae and stellar collisions", Proceedings of the National Academy of Sciences of the United States of America, 25 (3): 118–25, Bibcode:1939PNAS...25..118W, doi: 10.1073/pnas.25.3.118 , PMC   1077725 , PMID   16577876
  2. 1 2 Chang, Kenneth (13 June 2000), "Two Stars Collide; New Star is Born", The New York Times , retrieved 14 November 2010
  3. ↑ Tylenda, R.; Hajduk, M.; Kamiński, T.; et al. (11 April 2011). "V1309 Scorpii: merger of a contact binary". Astronomy and Astrophysics . 528: A114. arXiv: 1012.0163 . Bibcode:2011A&A...528A.114T. doi:10.1051/0004-6361/201016221. S2CID   119234303.
  4. ↑ Overbye, Dennis (16 October 2017), "LIGO Detects Fierce Collision of Neutron Stars for the First Time", The New York Times
  5. ↑ Casttelvecchi, Davide (25 August 2017). "Rumours swell over new kind of gravitational-wave sighting". Nature . doi:10.1038/nature.2017.22482 . Retrieved 27 August 2017.
  6. ↑ Sokol, Josha (25 August 2017). "What Happens When Two Neutron Stars Collide?". Wired . Retrieved 27 August 2017.
  7. ↑ Drake, Nadia (25 August 2017). "Strange Stars Caught Wrinkling Spacetime? Get the Facts". National Geographic . Archived from the original on August 27, 2017. Retrieved 27 August 2017.
  8. 1 2 González Hernández, J. I.; Ruiz-Lapuente, P.; Tabernero, H. M.; Montes, D.; Canal, R.; Méndez, J.; Bedin, L. R. (26 September 2012). "No surviving evolved companions of the progenitor of SN 1006". Nature . 489 (7417): 533–536. arXiv: 1210.1948 . Bibcode:2012Natur.489..533G. doi:10.1038/nature11447. hdl:2445/127740. PMID   23018963. S2CID   4431391.
  9. ↑ Freedman, Roger A., Robert M. Geller, William J. Kaufmann III(2009). The Universe 9th Edition,p.543-545. W.H. Freeman and Company, New York. ISBN   1-4292-3153-X
  10. ↑ Rosswog, Stephan (2013). "Astrophysics: Radioactive glow as a smoking gun". Nature. 500 (7464): 535–6. Bibcode:2013Natur.500..535R. doi: 10.1038/500535a . PMID   23985867.
  11. ↑ Metzger, B. D.; Martínez-Pinedo, G.; Darbha, S.; Quataert, E.; et al. (August 2010). "Electromagnetic counterparts of compact object mergers powered by the radioactive decay of r-process nuclei". Monthly Notices of the Royal Astronomical Society. 406 (4): 2650. arXiv: 1001.5029 . Bibcode:2010MNRAS.406.2650M. doi:10.1111/j.1365-2966.2010.16864.x. S2CID   118863104.
  12. ↑ Martin, E. L.; Spruit, H. C.; Tata, R. (2011). "A binary merger origin for inflated hot Jupiter planets". Astronomy & Astrophysics. 535: A50. arXiv: 1102.3336 . Bibcode:2011A&A...535A..50M. doi:10.1051/0004-6361/201116907. S2CID   118473108.
  13. 1 2 3 "Stellar Collisions and vampirism give blue stragglers stars a 'cosmic facelift'", Asian News International, 29 December 2009
  14. 1 2 Lucentini, Jack (1 June 2000). "Researchers Claim First Proof That Stars Collide". Space.com . Archived from the original on 19 April 2004. Retrieved 15 January 2014. By one calculation, the sun is likely to have one crash per 10,000 trillion, trillion years (that's 28 zeros), and it will burn out on its own accord much sooner than that.
  15. ↑ Garcia-Sanchez, J.; et al. (24 August 1998), "Perturbation of the Oort Cloud by Close Stellar Approaches", Asteroid and Comet Dynamics, Tatrauska Lomnica, Slovak Republic, hdl:2014/19368 {{citation}}: CS1 maint: location missing publisher (link)
  16. ↑ Molnar, Lawrence A.; Noord, Daniel M. Van; Kinemuchi, Karen; Smolinski, Jason P.; Alexander, Cara E.; Cook, Evan M.; Jang, Byoungchan; Kobulnicky, Henry A.; Spedden, Christopher J. (2017). "Prediction of a Red Nova Outburst in KIC 9832227". The Astrophysical Journal. 840 (1): 1. arXiv: 1704.05502 . Bibcode:2017ApJ...840....1M. doi: 10.3847/1538-4357/aa6ba7 . ISSN   0004-637X. S2CID   118970956.
  17. ↑ Kinemuchi, Karen (1 October 2013). "To Pulsate or to Eclipse? Status of KIC 9832227 Variable Star". arXiv: 1310.0544 [astro-ph.SR].
  18. ↑ Byrd, Deborah (6 January 2017). "Star predicted to explode in 2022". EarthSky. EarthSky Communications. Retrieved 6 January 2017.
  19. ↑ "Colliding stars will light up the night sky in 2022". Science . 1 May 2017. Retrieved 7 January 2017.
  20. ↑ Molnar, Lawrence A. (7 September 2018). "Supplementary material to Calvin College press release "Team of researchers challenge bold astronomical prediction", September 7, 2018". calvin.edu. Retrieved 8 September 2018.
  21. ↑ Kucinski, Matt (7 September 2018). "Team of researchers challenge bold astronomical prediction". calvin.edu. Retrieved 8 September 2018.
  22. ↑ Socia, Quentin J.; Welsh, William F.; Short, Donald R.; Orosz, Jerome A.; Angione, Ronald J.; Windmiller, Gur; Caldwell, Douglas A.; Batalha, Natalie M. (11 September 2018). "KIC 9832227: Using Vulcan Data to Negate the 2022 Red Nova Merger Prediction". Astrophysical Journal Letters. 864 (2): L32. arXiv: 1809.02771 . Bibcode:2018ApJ...864L..32S. doi: 10.3847/2041-8213/aadc0d . S2CID   56134618.
  23. ↑ Parks, Jake (7 September 2018). "Two stars will NOT merge and explode into red fury in 2022". astronomy.com.
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