Hills mechanism

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The Hills mechanism [1] is a phenomenon that occurs when a binary star system is disrupted by a supermassive black hole.

Tidal forces from the black hole cause one of the stars to be captured by it, and fall into an orbit around it. The other star is thrown away from the black hole at very high speeds. The phenomenon was proposed by astronomer Jack Hills in 1988 and confirmed in 2019, when an example of such a jettisoned star was observed. [2] This ejected star, namely S5-HVS1, an A-type main-sequence star, notable as the fastest star detected as of November 2019, has been determined to be traveling at nearly four million miles an hour (more specifically, 1,755 km/s (3,930,000 mph), almost 0.6% of the speed of light) away from the galactic core of the Milky Way. [3] [4] [5] [6] [7] [8] [9] [10] [11]

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S5-HVS1 is an A-type main-sequence star notable as the fastest one detected as of November 2019, and has been determined to be traveling at 1,755 km/s (3,930,000 mph). The star is in the Grus constellation in the southern sky, and about 29,000 light-years from Earth. According to astronomers, S5-HVS1 was ejected from the Milky Way galaxy after interacting with Sagittarius A*, the supermassive black hole at the center of the galaxy. It is possible that it was originally part of a binary system that was tidally disrupted by the supermassive black hole, causing it to be ejected. If this is the case, that it was flung out of the galaxy by the central black hole, it is then the first example of a star that has undergone the Hills mechanism.

References

  1. Hills, J. G (25 February 1988). "Hyper-velocity and tidal stars from binaries disrupted by a massive Galactic black hole". Nature. 331 (6158): 687–689. Bibcode:1988Natur.331..687H. doi:10.1038/331687a0. S2CID   4250308.
  2. Gohd, Chelsea (November 13, 2019). "A Star Ejected from the Milky Way's 'Heart of Darkness' Has Reached a Mind-Blowing Speed". Space.com. Retrieved November 14, 2019.
  3. Overbye, Dennis (14 November 2019). "A Black Hole Threw a Star Out of the Milky Way Galaxy - So long, S5-HVS1, we hardly knew you". The New York Times . Retrieved 18 November 2019.
  4. Koposov, Sergey E.; et al. (11 November 2019). "Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A*". Monthly Notices of the Royal Astronomical Society. arXiv: 1907.11725 . doi:10.1093/mnras/stz3081.
  5. Starr, Michelle (31 July 2019). "Bizarre Star Found Hurtling Out of Our Galaxy Centre Is Fastest of Its Kind Ever Seen". ScienceAlert.com. Retrieved 18 November 2019.
  6. Irving, Michael (13 November 2019). "Fastest star ever found is being flicked out of the Milky Way". NewAtlas.com. Retrieved 18 November 2019.
  7. Imster, Imster (18 November 2019). "Black hole hurls star out of Milky Way - Astronomers have spotted a star – S5-HVs1 – speeding out of the Milky Way at around 4 million miles (more than 6 million km) per hour. They believe it's being ejected from our galaxy after venturing too near the giant black hole at the Milky Way's heart about 5 million years ago". Earth & Sky . Retrieved 18 November 2019.
  8. Gohd, Chelsea (12 November 2019). "A Star Ejected from the Milky Way's 'Heart of Darkness' Has Reached a Mind-Blowing Speed - It is a visitor from a strange land". Space.com . Retrieved 18 November 2019.
  9. Staff (15 November 2019). "A Runaway Star Ejected from the Galactic Heart of Darkness". Carnegie-Mellon University . Retrieved 18 November 2019.
  10. Lincoln, Don (13 November 2019). "Supermassive Black Hole Ejects Star From Milky Way Galaxy". Forbes . Retrieved 18 November 2019.
  11. Plait, Phil (13 November 2019). "Our Local Supermassive Black Hole Shot A Star Right Out Of THe Galaxy". Bad Astronomy . Retrieved 19 November 2019.

See also