Extragalactic planet

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An extragalactic planet, also known as an extragalactic exoplanet or an extroplanet, [1] [2] [3] is a star-bound planet or rogue planet located outside of the Milky Way Galaxy. Due to the immense distances to such worlds, they would be very hard to detect directly. However, indirect evidence suggests that such planets exist. [4] [5] [6] Nonetheless, the most distant known planets are SWEEPS-11 and SWEEPS-04, located in Sagittarius, approximately 27,710 light-years from the Sun, while the Milky Way is about 87,400 light-years in diameter. This means that even galactic planets located further than that distance have not been detected.

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Candidate extragalactic planets

Candidates from gravitational microlensing

A microlensing event in the Twin Quasar gravitational lensing system was observed in 1996, by R. E. Schild, in the "A" lobe of the lensed quasar. It is predicted that a 3-Earth-mass planet in the lensing galaxy, YGKOW G1, caused the event. This was the first extragalactic planet candidate announced. This, however, is not a repeatable observation, as it was a one-time chance alignment. This predicted planet lies 4 billion light years away. [7] [8]

PA-99-N2

A team of scientists has used gravitational microlensing to come up with a tentative detection of an extragalactic exoplanet in Andromeda, the Milky Way's nearest large galactic neighbor. The lensing pattern fits a star with a smaller companion, PA-99-N2, weighing just around 6.34 times the mass of Jupiter. This suspected planet is the first announced in the Andromeda Galaxy. [9] [10]

Evidence of a population of rogue planets

A population of unbound planets between stars, with masses ranging from Lunar to Jovian masses, was indirectly detected, for the first time, by astrophysicists from the University of Oklahoma in 2018, in the lensing galaxy that lenses quasar RX J1131-1231 by microlensing. [4] [5] [6]

Candidates around extragalactic black-holes and X-ray binaries

IGR J12580+0134 b

In 2016, a candidate planet was found orbiting a 9,150,000 M☉ supermassive black hole, [11] indicating that it might also be a blanet. IGR J12580+0134 b could be a brown dwarf or planet as it has a mass of 8-40 MJ, it is located in the galaxy of NGC 4845. IGR J12580+0134 b is 17 million parsecs (55 million light years) away. [12]

M51-ULS-1b

In September 2020, the detection of a candidate planet orbiting the high-mass X-ray binary M51-ULS-1 in the Whirlpool Galaxy was announced. The planet was detected by eclipses of the X-ray source, [1] which consists of a stellar remnant (either a neutron star or a black hole [2] ) and a massive star, likely a B-type supergiant. The planet is 0.7 RJ in size or around 50,000 kilometers in radius. [13] and orbit at a distance of some tens of AU. [14] [15] The study of M51-ULS-1b as the first known extragalactic planet candidate was published in Nature in October 2021. [16]

Disrupted planets of runaway stars

The subdwarf star HD 134440, which is currently located in galactic halo and has extragalactic origin, was found to have a significantly higher metallicity than the similar star HD 134439. This was believed to resulted from an engulfment of orbiting planets by HD 134440. [17]

Refuted extragalactic planets

HIP 13044 b

A planet with a mass of at least 1.25 times that of Jupiter had been potentially discovered by the European Southern Observatory (ESO) orbiting a star of extragalactic origin, even though the star currently has been absorbed by our own galaxy. HIP 13044 is a star about 2,000 light years away in the southern constellation of Fornax, [18] part of the Helmi stream of stars, a leftover remnant of a small galaxy that collided with and was absorbed by the Milky Way over 6 billion years ago. [19]

However, subsequent analysis of the data revealed problems with the potential planetary detection: for example an erroneous barycentric correction had been applied (the same error had also led to claims of planets around HIP 11952 that were subsequently refuted). After applying the corrections, there is no evidence for a planet orbiting the star. [20] If it had been real, the Jupiter-like planet would have been particularly interesting, orbiting a star nearing the end of its life and seemingly about to be engulfed by it, potentially providing an observational model for the fate of our own planetary system in the distant future (cf. Future of Earth).

See also

Related Research Articles

<span class="mw-page-title-main">Exoplanet</span> Planet outside the Solar System

An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not then recognized as such. The first confirmation of the detection occurred in 1992. A different planet, first detected in 1988, was confirmed in 2003. According to statistics from the NASA Exoplanet Archive, As of 17 October 2024, there are 5,780 confirmed exoplanets in 4,314 planetary systems, with 969 systems having more than one planet. The James Webb Space Telescope (JWST) is expected to discover more exoplanets, and to give more insight into their traits, such as their composition, environmental conditions, and potential for life.

<span class="mw-page-title-main">Planetary system</span> Set of non-stellar objects in orbit around a star

A planetary system is a set of gravitationally bound non-stellar bodies in or out of orbit around a star or star system. Generally speaking, systems with one or more planets constitute a planetary system, although such systems may also consist of bodies such as dwarf planets, asteroids, natural satellites, meteoroids, comets, planetesimals and circumstellar disks. For example, the Sun together with the planetary system revolving around it, including Earth, form the Solar System. The term exoplanetary system is sometimes used in reference to other planetary systems.

<span class="mw-page-title-main">Rogue planet</span> Planets not gravitationally bound to a star

A rogue planet, also termed a free-floating planet (FFP) or an isolated planetary-mass object (iPMO), is an interstellar object of planetary mass which is not gravitationally bound to any star or brown dwarf.

<span class="mw-page-title-main">Whirlpool Galaxy</span> Galaxy in the constellation Canes Venatici

The Whirlpool Galaxy, also known as Messier 51a (M51a) or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. It is 7.22 megaparsecs away and 23.58 kiloparsecs (76,900 ly) in diameter.

<span class="mw-page-title-main">Gravitational microlensing</span> Astronomical phenomenon due to the gravitational lens effect

Gravitational microlensing is an astronomical phenomenon caused by the gravitational lens effect. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit much light (stars) or large objects that block background light. These objects make up only a minor portion of the mass of a galaxy. Microlensing allows the study of objects that emit little or no light.

<span class="mw-page-title-main">Exomoon</span> Moon beyond the Solar System

An exomoon or extrasolar moon is a natural satellite that orbits an exoplanet or other non-stellar extrasolar body.

<span class="mw-page-title-main">OGLE-2005-BLG-390Lb</span> Super-Earth orbiting OGLE-2005-BLG-390L

OGLE-2005-BLG-390Lb is a super-Earth exoplanet orbiting OGLE-2005-BLG-390L, a star 21,500 ± 3,300 light-years from Earth near the center of the Milky Way, making it one of the most distant planets known. On January 25, 2006, Probing Lensing Anomalies NETwork/Robotic Telescope Network (PLANET/Robonet), Optical Gravitational Lensing Experiment (OGLE), and Microlensing Observations in Astrophysics (MOA) made a joint announcement of the discovery. The planet does not appear to meet conditions presumed necessary to support life.

<span class="mw-page-title-main">Optical Gravitational Lensing Experiment</span> Long-term variability sky survey

The Optical Gravitational Lensing Experiment (OGLE) is a Polish astronomical project based at the University of Warsaw that runs a long-term variability sky survey (1992–present). The main goals are the detection and classification of variable stars, discovery of microlensing events, dwarf novae, and studies of the structure of the Galaxy and the Magellanic Clouds. Since the project began in 1992, it has discovered a multitude of extrasolar planets, together with the first planet discovered using the transit method (OGLE-TR-56b) and gravitational microlensing. The project has been led by professor Andrzej Udalski since its inception.

OGLE-2003-BLG-235L (MOA-2003-BLG-53L) is a star in the constellation of Sagittarius. The first gravitational microlensing event for which a planet orbiting the lens was detected around this star. The event occurred in during July 2003. Two groups observed and independently detected the event: the Optical Gravitational Lensing Experiment (OGLE) and the Microlensing Observations in Astrophysics (MOA), hence, the double designation. It is an orange dwarf star of spectral type K, which is accompanied by a giant planet.

<span class="mw-page-title-main">Methods of detecting exoplanets</span>

Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty of detecting such a faint light source, the light from the parent star causes a glare that washes it out. For those reasons, very few of the exoplanets reported as of January 2024 have been observed directly, with even fewer being resolved from their host star.

<span class="mw-page-title-main">Super-Earth</span> Type of exoplanet

A Super-Earth or super-terran is a type of exoplanet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively. The term "super-Earth" refers only to the mass of the planet, and so does not imply anything about the surface conditions or habitability. The alternative term "gas dwarfs" may be more accurate for those at the higher end of the mass scale, although "mini-Neptunes" is a more common term.

The Microlensing Follow-Up Network is an informal group of observers who monitor high magnification gravitational microlensing events in the Milky Way's Galactic Bulge. Its goal is to detect extrasolar planets via microlensing of the parent star by the planet. μFUN is a follow-up network - they monitor microlensing events identified by survey groups such as OGLE and Microlensing Observations in Astrophysics (MOA).

<span class="mw-page-title-main">Discoveries of exoplanets</span> Detecting planets located outside the Solar System

An exoplanet is a planet located outside the Solar System. The first evidence of an exoplanet was noted as early as 1917, but was not recognized as such until 2016; no planet discovery has yet come from that evidence. What turned out to be the first detection of an exoplanet was published among a list of possible candidates in 1988, though not confirmed until 2003. The first confirmed detection came in 1992, with the discovery of terrestrial-mass planets orbiting the pulsar PSR B1257+12. The first confirmation of an exoplanet orbiting a main-sequence star was made in 1995, when a giant planet was found in a four-day orbit around the nearby star 51 Pegasi. Some exoplanets have been imaged directly by telescopes, but the vast majority have been detected through indirect methods, such as the transit method and the radial-velocity method. As of 24 July 2024, there are 7,026 confirmed exoplanets in 4,949 planetary systems, with 1007 systems having more than one planet. This is a list of the most notable discoveries.

HIP 13044 is a red horizontal-branch star about 2,300 light years from Earth in the constellation Fornax. The star is part of the Helmi stream, a former dwarf galaxy that merged with the Milky Way between six and nine billion years ago. As a result, HIP 13044 circles the Galactic Center at a highly irregular orbit with respect to the galactic plane. HIP 13044 is slightly less massive than the Sun, but is approximately seven times its size. The star, which is estimated to be at least nine billion years old, has passed the red-giant phase. The relatively fast rotation of the star may be due to having engulfed one or more planets during the red-giant phase.

The Helmi Stream is a stellar stream of the Milky Way galaxy. It started as a dwarf galaxy, now absorbed by the Milky Way as a stream. It was discovered in 1999, is formed of old stars deficient in heavy elements, and has a mass of 10 to 100 million solar masses. It was absorbed by the Milky Way some 6 to 9 billion years ago.

PA-99-N2 is a microlensing event detected in the direction of the Andromeda Galaxy in 1999.

<span class="mw-page-title-main">Disrupted planet</span> Planet or related being destroyed by a passing object

In astronomy, a disrupted planet is a planet or exoplanet or, perhaps on a somewhat smaller scale, a planetary-mass object, planetesimal, moon, exomoon or asteroid that has been disrupted or destroyed by a nearby or passing astronomical body or object such as a star. Necroplanetology is the related study of such a process.

A blanet is a member of a hypothetical class of exoplanets that directly orbit black holes.

References

  1. 1 2 Smith, Kiona (26 October 2021). "Extroplanet: Astronomers may have just found the first planet outside our galaxy". Inverse. Retrieved 2021-11-08.
  2. 1 2 Planet Song M51 ULS 1b Messier 51 Whirlpool Galaxy, 6 November 2021, retrieved 2021-11-08
  3. ↑ Sandhya Ramesh (2021-10-29). "NASA telescope may have just helped find the first planet spotted outside Milky Way". ThePrint. Retrieved 2021-11-08.
  4. 1 2 Dai, Xinyu; Guerras, Eduardo (2 February 2018). "Probing Planets in Extragalactic Galaxies Using Quasar Microlensing". The Astrophysical Journal. 853 (2): L27. arXiv: 1802.00049 . Bibcode:2018ApJ...853L..27D. doi: 10.3847/2041-8213/aaa5fb . S2CID   119078402.
  5. 1 2 Zachos, Elaine (5 February 2018). "More Than a Trillion Planets Could Exist Beyond Our Galaxy - A new study gives the first evidence that exoplanets exist beyond the Milky Way". National Geographic Society . Archived from the original on February 5, 2018. Retrieved 5 February 2018.
  6. 1 2 Mandelbaum, Ryan F. (5 February 2018). "Scientists Find Evidence of Thousands of Planets in Distant Galaxy". Gizmodo . Retrieved 5 February 2018.
  7. ↑ Schilling, Govert (6 July 1996). "Do alien worlds throng faraway galaxy?". New Scientist. No. 2037.
  8. ↑ Extrasolar Visions, "The Q0957+561 Planet" Archived 2012-03-30 at the Wayback Machine (accessed 1 September 2009)
  9. ↑ "First extragalactic exoplanet may have been found by gravitational microlensing". Thaindian News. 11 June 2009. Archived from the original on 2009-06-24.
  10. ↑ Battersby, Stephen (10 June 2009). "First extragalactic exoplanet may have been found". New Scientist.
  11. ↑ Martin, Pierre-Yves (2016). "Planet IGR J12580+0134 b". exoplanet.eu. Retrieved 2024-10-16.
  12. ↑ Lei, Wei-Hua; Yuan, Qiang; Zhang, Bing; Wang, Daniel (December 2015). "Igr J12580+0134: The First Tidal Disruption Event with an Off-Beam Relativistic Jet". The Astrophysical Journal. 816 (1): 20. arXiv: 1511.01206 . doi: 10.3847/0004-637X/816/1/20 . ISSN   0004-637X.
  13. ↑ https://exoplanet.eu/catalog/m51_uls_1_b--7496
  14. ↑ Di Stefano, R.; et al. (18 September 2020). "M51-ULS-1b: The First Candidate for a Planet in an External Galaxy". arXiv: 2009.08987 [astro-ph.HE].
  15. ↑ Crane, Leah (23 September 2020). "Astronomers may have found the first planet in another galaxy". New Scientist . Retrieved 25 September 2020.
  16. ↑ Di Stefano, Rosanne; Berndtsson, Julia; Urquhart, Ryan; Soria, Roberto; Kashyap, Vinay L.; Carmichael, Theron W.; Imara, Nia (2021-10-25). "A possible planet candidate in an external galaxy detected through X-ray transit". Nature Astronomy. 5 (12): 1297–1307. arXiv: 2009.08987 . Bibcode:2021NatAs...5.1297D. doi:10.1038/s41550-021-01495-w. ISSN   2397-3366. S2CID   256726097.
  17. ↑ Reggiani, Henrique; Meléndez, Jorge (December 1, 2018). "Evidences of extragalactic origin and planet engulfment in the metal-poor twin pair HD 134439/HD 134440". Monthly Notices of the Royal Astronomical Society. 475 (3): 3502–3510. arXiv: 1802.07469 . Bibcode:2018MNRAS.475.3502R. doi: 10.1093/mnras/sty104 . ISSN   0035-8711 . Retrieved 10 May 2018.
  18. ↑ "Planet from another galaxy discovered". ESO Press Release. 18 November 2010. Retrieved 17 November 2011.
  19. ↑ Klement, R.; Setiawan, J.; Thomas Henning; Hans-Walter Rix; Boyke Rochau; Jens Rodmann; Tim Schulze-Hartung; MPIA Heidelberg; ESTEC (2011). "The visitor from an ancient galaxy: A planetary companion around an old, metal-poor red horizontal branch star". The Astrophysics of Planetary Systems: Formation, Structure, and Dynamical Evolution. IAU Symposium. Vol. 276. Proceedings of the International Astronomical Union. pp. 121–125. arXiv: 1011.4938 . Bibcode:2011IAUS..276..121K. doi:10.1017/S1743921311020059.
  20. ↑ Jones, M. I.; Jenkins, J. S. (2014). "No evidence of the planet orbiting the extremely metal-poor extragalactic star HIP 13044". Astronomy & Astrophysics. 562: id.A129. arXiv: 1401.0517 . Bibcode:2014A&A...562A.129J. doi:10.1051/0004-6361/201322132. S2CID   55365608.
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