Stellar collision

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 such contact binary systems are stable, some do become unstable and either eject one partner or eventually merge.

Astronomers predict that events of this type occur in the globular clusters of our galaxy about once every 10,000 years.{{Citation |last= Chang |first= Kenneth |url= http://partners.nytimes.com/library/national/science/061300sci-stars-collisions.html |title=Two Stars Collide; New Star is Born |newspaper=The New York Times |date=13 June 2000 |access-date= 14 November 2010 }} 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.{{cite journal | last1 = Tylenda | first1 = R. | last2 = Hajduk | first2 = M. | last3 = Kamiński | first3 = T. | display-authors = etal | title = V1309 Scorpii: merger of a contact binary | journal = Astronomy and Astrophysics | volume = 528 | pages = A114 | date = 11 April 2011 | doi = 10.1051/0004-6361/201016221 | bibcode=2011A&A...528A.114T |arxiv = 1012.0163 | s2cid = 119234303 }}

{{main|Type Ia supernova}}

White dwarfs are the remnants of low-mass stars which, if they form a binary system with a star on a sufficiently close orbit, 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.{{cite journal | last = González Hernández | first = J. I. |author2=Ruiz-Lapuente, P. |author3=Tabernero, H. M. |author4=Montes, D. |author5=Canal, R. |author6=Méndez, J. |author7= Bedin, L. R. | title = No surviving evolved companions of the progenitor of SN 1006 | journal = Nature | volume = 489 | issue = 7417| pages = 533–536 | date = 26 September 2012 | doi = 10.1038/nature11447 |arxiv = 1210.1948 |bibcode = 2012Natur.489..533G | pmid=23018963| hdl = 2445/127740 | s2cid = 4431391 }} 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. In a matter of seconds, all of the white dwarf's mass is thrown into space.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}}

{{Main|Neutron star merger}}

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{{cite journal |doi=10.1038/500535a|pmid=23985867|title=Astrophysics: Radioactive glow as a smoking gun|journal=Nature|volume=500|issue=7464|pages=535–6|year=2013|last1=Rosswog|first1=Stephan|bibcode=2013Natur.500..535R|doi-access=free}} and kilonovae.{{cite journal |author=Metzger, B. D. |author2=Martínez-Pinedo, G. |author3=Darbha, S. |author4=Quataert, E. |author5=Arcones, A. |author6=Kasen, D. |author7=Thomas, R. |author8=Nugent, P. |author9=Panov, I. V. |author10=Zinner, N. T. |display-authors=4 |title=Electromagnetic counterparts of compact object mergers powered by the radioactive decay of r-process nuclei |journal=Monthly Notices of the Royal Astronomical Society |volume=406 |issue=4 |page=2650 |date=August 2010 |doi=10.1111/j.1365-2966.2010.16864.x |doi-access=free |bibcode=2010MNRAS.406.2650M |arxiv=1001.5029 |s2cid=118863104 }}

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.{{citation |last= Overbye |first=Dennis |author-link=Dennis Overbye |date= 16 October 2017 |title= LIGO Detects Fierce Collision of Neutron Stars for the First Time |newspaper=The New York Times |url=https://www.nytimes.com/2017/10/16/science/ligo-neutron-stars-collision.html}}{{cite journal |last=Casttelvecchi |first=Davide |title=Rumours swell over new kind of gravitational-wave sighting |url=https://www.nature.com/news/rumours-swell-over-new-kind-of-gravitational-wave-sighting-1.22482 |date=25 August 2017 |journal=Nature |doi=10.1038/nature.2017.22482 |access-date=27 August 2017 |url-access=subscription }}{{cite magazine |last=Sokol |first=Josha |title=What Happens When Two Neutron Stars Collide? |url=https://www.wired.com/story/what-happens-when-two-neutron-stars-collide-scientific-revolution/ |date=25 August 2017 |magazine=Wired |access-date=27 August 2017 }}{{cite web |last=Drake |first=Nadia |author-link=Nadia Drake |title=Strange Stars Caught Wrinkling Spacetime? Get the Facts. |url=http://news.nationalgeographic.com/2017/08/new-gravitational-waves-neutron-stars-ligo-space-science/ |archive-url=https://web.archive.org/web/20170827011832/http://news.nationalgeographic.com/2017/08/new-gravitational-waves-neutron-stars-ligo-space-science/ |url-status=dead |archive-date=August 27, 2017 |date=25 August 2017 |magazine=National Geographic |access-date=27 August 2017 }}

{{main article|Thorne–Żytkow object}}

If a neutron star collides with red giant of sufficiently low mass and density, the merger is conjectured to produce a Thorne–Żytkow object, a hypothetical type of compact star containing a neutron star enveloped by a red giant.

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.{{Cite journal|arxiv=1102.3336|last1= Martin|first1= E. L.|title= A binary merger origin for inflated hot Jupiter planets|journal= Astronomy & Astrophysics|volume= 535|pages= A50|last2= Spruit|first2= H. C.|last3= Tata|first3= R.|year= 2011|doi= 10.1051/0004-6361/201116907|bibcode= 2011A&A...535A..50M|s2cid= 118473108}}

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.[http://www.thefreelibrary.com/Stellar+collisions+and+vampirism+give+blue+straggler+stars+a+%22cosmic...-a0215188997 "Stellar Collisions and vampirism give blue stragglers stars a 'cosmic facelift'"], Asian News International, 29 December 2009 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. 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.

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.{{cite web | url = http://www.space.com/scienceastronomy/stellar_collisions_000601.html | title = Researchers Claim First Proof That Stars Collide | access-date = 15 January 2014 | last = Lucentini | first = Jack | date = 1 June 2000 | website = Space.com | archive-url = https://web.archive.org/web/20040419035725/http://www.space.com/scienceastronomy/stellar_collisions_000601.html | archive-date = 19 April 2004|quote=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.}}

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.{{citation | contribution = Perturbation of the Oort Cloud by Close Stellar Approaches | display-authors=1 | date=24 August 1998 | last1=Garcia-Sanchez | first1=J. | last2=Weissman | first2=P. R. | last3=Preston | first3=R. A. | last4=Jones | first4=D. L. | last5=Lestrade | first5=J. F. | last6=Latham | first6=D. W. | last7=Stefanik | first7=R. P. | title=Asteroid and Comet Dynamics | location=Tatrauska Lomnica, Slovak Republic | hdl=2014/19368}} For comparison, the mean radius of the Earth's orbit, 1 AU, is {{nowrap|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.

The explosion that created the Kleinmann–Low Nebula nebula, located in the Orion Nebula, is suspected to have involved a dynamical interaction between multiple stars and might have involved a protostellar merger. The radio source I is suspected to be either a close binary or the result of such a merger.

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.

{{Cite arXiv|last=Kinemuchi |first=Karen |date=1 October 2013 |title=To Pulsate or to Eclipse? Status of KIC 9832227 Variable Star |eprint=1310.0544 |class=astro-ph.SR}}{{cite web|last1=Byrd|first1=Deborah |title=Star predicted to explode in 2022 |url=http://earthsky.org/space/star-predicted-to-explode-in-2022|website=EarthSky |date=6 January 2017 |publisher=EarthSky Communications |access-date=6 January 2017}}

{{Cite news|url=https://www.science.org/content/article/colliding-stars-will-light-night-sky-2022-rev2 |title=Colliding stars will light up the night sky in 2022 |date=1 May 2017 |journal=Science|access-date=7 January 2017 }}

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.

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.

{{Reflist|refs=

{{cite web|url=http://www.astronomy.com/news/2018/09/two-stars-will-not-merge-and-explode-into-red-fury-in-2022|title=Two stars will NOT merge and explode into red fury in 2022|first=Jake |last=Parks|date=7 September 2018|website=astronomy.com}}

{{Cite journal|last1=Molnar|first1=Lawrence A.|last2=Noord|first2=Daniel M. Van|last3=Kinemuchi|first3=Karen|last4=Smolinski|first4=Jason P.|last5=Alexander|first5=Cara E.|last6=Cook|first6=Evan M.|last7=Jang|first7=Byoungchan|last8=Kobulnicky|first8=Henry A.|last9=Spedden|first9=Christopher J.|date=2017|title=Prediction of a Red Nova Outburst in KIC 9832227|journal=The Astrophysical Journal|language=en|volume=840|issue=1|pages=1|doi=10.3847/1538-4357/aa6ba7|issn=0004-637X|arxiv=1704.05502|bibcode=2017ApJ...840....1M|s2cid=118970956 |doi-access=free }}

{{cite web|last1=Molnar|first1=Lawrence A.|url=http://www.calvin.edu/academic/phys/observatory/MergingStar/2018Update.html|title=Supplementary material to Calvin College press release "Team of researchers challenge bold astronomical prediction", September 7, 2018|website=calvin.edu|date=7 September 2018|access-date=8 September 2018}}

{{cite web|url=https://calvin.edu/news/archive/team-of-researchers-challenge-bold-astronomical-prediction|title=Team of researchers challenge bold astronomical prediction|first=Matt |last=Kucinski|website=calvin.edu|date=7 September 2018|access-date=8 September 2018}}

{{cite journal|title=KIC 9832227: Using Vulcan Data to Negate the 2022 Red Nova Merger Prediction|first1=Quentin J.|last1=Socia|first2=William F.|last2=Welsh|first3=Donald R.|last3=Short|first4=Jerome A.|last4=Orosz|first5=Ronald J.|last5=Angione|first6=Gur|last6=Windmiller|first7=Douglas A.|last7=Caldwell|first8=Natalie M.|last8=Batalha|journal=Astrophysical Journal Letters|date=11 September 2018|volume=864|issue=2|pages=L32|doi=10.3847/2041-8213/aadc0d|arxiv=1809.02771|bibcode=2018ApJ...864L..32S|s2cid=56134618 |doi-access=free }}

{{Cite journal |last1=Bally |first1=John |last2=Cunningham |first2=Nathaniel J. |last3=Moeckel |first3=Nickolas |last4=Burton |first4=Michael G. |last5=Smith |first5=Nathan |last6=Frank |first6=Adam |last7=Nordlund |first7=Ake |date=2011-02-01 |title=Explosive Outflows Powered by the Decay of Non-hierarchical Multiple Systems of Massive Stars: Orion BN/KL |url=https://ui.adsabs.harvard.edu/abs/2011ApJ...727..113B/abstract |journal=The Astrophysical Journal |volume=727 |issue=2 |pages=113 |arxiv=1011.5512 |bibcode=2011ApJ...727..113B |doi=10.1088/0004-637X/727/2/113 |issn=0004-637X}}

{{Cite journal |last1=Bally |first1=John |last2=Ginsburg |first2=Adam |last3=Forbrich |first3=Jan |last4=Vargas-González |first4=Jaime |date=2020-02-01 |title=The Orion Protostellar Explosion and Runaway Stars Revisited: Stellar Masses, Disk Retention, and an Outflow from the Becklin-Neugebauer Object |journal=The Astrophysical Journal |volume=889 |issue=2 |pages=178 |arxiv=2001.00899 |bibcode=2020ApJ...889..178B |doi=10.3847/1538-4357/ab65f2 |doi-access=free |issn=0004-637X}}

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• {{cite web| url=http://astro-gr.org/stellar-collisions| title=Pau Amaro Seoane MODEST working group 4 "Stellar Collisions"| access-date=20 May 2013 }}

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