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Gravitational microlensing is an astronomical phenomenon due to 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.
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.
OGLE-2005-BLG-390L is a star thought to be a spectral type M. This dim magnitude 16 galactic bulge star is located in the Scorpius constellation at a far distance of about 21,500 light years.
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.
OGLE-2005-BLG-169L is a dim and distant magnitude 20 galactic bulge star located about 2,700 parsecs away in the constellation Sagittarius. If it is a main sequence star, then it is most likely a red dwarf with about half of the mass of the Sun. Other possibilities are a white dwarf star, or a neutron star or black hole.
OGLE-2005-BLG-071L is a distant, magnitude 19.5 galactic bulge star located in the constellation Scorpius, approximately 11,000 light years away from the Solar System. The star is probably a red dwarf with a mass 43% of that of the Sun.
MOA-2007-BLG-192Lb, occasionally shortened to MOA-192 b, is an extrasolar planet approximately 3,000 light-years away in the constellation of Sagittarius. The planet was discovered orbiting the brown dwarf or low-mass star MOA-2007-BLG-192L. At a mass of approximately 3.3 times Earth, it is one of the lowest-mass extrasolar planets at the time of discovery. It was found when it caused a gravitational microlensing event on May 24, 2007, which was detected as part of the MOA-II microlensing survey at the Mount John University Observatory in New Zealand.
MOA-2007-BLG-192L is a low-mass red dwarf star or brown dwarf, approximately 3,000 light-years away in the constellation of Sagittarius. It is estimated to have a mass approximately 6% of the Sun's. In 2008, an Earth-sized extrasolar planet was announced to be orbiting this object.
A circumbinary planet is a planet that orbits two stars instead of one. The two stars orbit each other in a binary system, while the planet typically orbits farther from the center of the system than either of the two stars. In contrast, circumstellar planets in a binary system have stable orbits around one of the two stars, closer in than the orbital distance of the other star. Studies in 2013 showed that there is a strong hint that a circumbinary planet and its stars originate from a single disk.
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).
MOA-2009-BLG-387Lb is an exoplanet in the orbit of the red dwarf MOA-2009-BLG-387L. Its discovery was announced on February 21, 2011, making it the eleventh planet discovered using gravitational microlensing. The planet is thought to be over twice the mass of Jupiter and to have an orbit 80 percent larger than that of Earth's, lasting approximately 1,970 days. However, its exact characteristics are difficult to constrain because the characteristics of the host star are not well known.
MOA-2009-BLG-387L is a red dwarf in the Sagittarius constellation that is host to the planet MOA-2009-BLG-387Lb. The star is estimated to be nearly 20,000 light years away and approximately one fifth the mass of the Sun, although large confidence intervals exist, reflecting the uncertainties in both the mass and distance. The star drew the attention of astronomers when it became the lens of gravitational microlensing event MOA-2009-BLG-387L, in which it eclipsed a background star and created distorted caustics, an envelope of reflected or refracted light rays. Analysis of the caustic events and of follow-up observational data led to the planet's discovery, which was reported in February 2011.
MOA-2010-BLG-477L is a star whose existence was detected when it caused a microlensing event in August, 2010. The microlensing event also revealed the existence of a planet orbiting the star. At first the star was thought to be about 0.67 times the mass of the Sun, in the main-sequence phase of its stellar evolution. But by the time the star should have been separated enough in the sky from the source star of the microlensing event it was not detected, implying that it is actually a dim white dwarf star.
OGLE-2007-BLG-349(AB)b is a circumbinary extrasolar planet about 8,000 light-years away in the constellation of Sagittarius. It is the first circumbinary exoplanet to be discovered using the microlensing method of detecting exoplanets.
OGLE-2016-BLG-1195Lb is an extrasolar planet located about 22,000 light-years from Earth, in the galactic bulge, orbiting the 0.57±0.06M☉ star OGLE-2016-BLG-1195L, discovered in 2017. The planet was detected using gravitational microlensing techniques managed by the Korea Astronomy and Space Science Institute and the Spitzer Space Telescope. Initially, it was believed the planet has a mass similar to Earth and is located about the same distance from its host star as the Earth is from the Sun, although it was expected to be much colder.
OGLE-2016-BLG-1190Lb is an extremely massive exoplanet, with a mass about 13.4 times that of Jupiter (MJ), or is, possibly, a low mass brown dwarf, orbiting the G-dwarf star OGLE-2016-BLG-1190L, located about 22,000 light years from Earth, in the constellation of Sagittarius, in the galactic bulge of the Milky Way.
MOA-2011-BLG-262L is an astronomical object of uncertain nature with an orbiting companion, detected through the gravitational microlensing event MOA-2011-BLG-262 in the constellation Sagittarius. Two different models fit the observation equally well - an object of ~3.2 MJ, likely a rogue planet, at a distance of about 0.56 kiloparsecs and orbited by a ~0.47 M🜨 exomoon; or an object of ~0.11 M☉, likely a red dwarf star, at a distance of about 7.2 kiloparsecs in the galactic bulge, and orbited by a ~17 M🜨 planet. The discovery team considers the latter scenario to be more likely.
References
- 1 2 Albrow, M. D.; et al. (2000). "Detection of Rotation in a Binary Microlens: PLANET Photometry of MACHO 97-BLG-41". The Astrophysical Journal. 534 (2): 894–906. arXiv: astro-ph/9910307 . Bibcode:2000ApJ...534..894A. doi:10.1086/308798. S2CID 3000437.
- ↑ Bennett, D. P.; et al. (1999). "Discovery of a planet orbiting a binary star system from gravitational microlensing". Nature. 402 (6757): 57–59. arXiv: astro-ph/9908038 . Bibcode:1999Natur.402...57B. doi:10.1038/46990. S2CID 205061885.
- ↑ Jung, Youn Kil; et al. (2013). "Reanalysis of the Gravitational Microlensing Event MACHO-97-BLG-41 Based on Combined Data". The Astrophysical Journal Letters. 768 (1). L7. arXiv: 1303.0952 . Bibcode:2013ApJ...768L...7J. doi:10.1088/2041-8205/768/1/L7. S2CID 118390991.