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| An artist's impression of the star S5-HVS1 being ejected by the Milky Way galaxy's supermassive black hole, Sagittarius A*. (Image credit: James Josephides (Swinburne Astronomy Productions)) |
An international study has discovered a star traveling at more than six
million km/h through the Milky Way after being flung from the center of our
galaxy by a supermassive black hole.
The eviction occurred about five million years ago, around the time when our
ancestors were just learning to walk upright.
Emeritus Professor Gary Da Costa, an astronomer at The Australian National
University (ANU), said the star is moving so fast that it will leave the
Milky Way in about 100 million years, never to return.
“We traced this star’s journey back to the center of our galaxy, which is
pretty exciting,” said Professor Da Costa from the ANU Research School of
Astronomy and Astrophysics.
“This star is traveling at record-breaking speed — 10 times faster than most
stars in the Milky Way, including our Sun.
“In astronomical terms, the star will be leaving our galaxy fairly soon and
it will likely travel through the emptiness of intergalactic space for
eternity. It’s great to be able to confirm a 30-year-old prediction that
stars can be flung out of a galaxy by the supermassive black hole at its
center.”
The giant black hole at the center of the Milky Way, Sagittarius A*, has a
mass equivalent to more than four million Suns.
Professor Da Costa and his ANU colleagues Dr. Dougal Mackey and Dr. Thomas
Nordlander were involved with the study, which was led by Dr. Sergey Koposov
from Carnegie Mellon University as part of the Southern Stellar Streams
Spectroscopic Survey.
The survey involves astronomers from Australian universities including ANU,
Macquarie University, the University of Sydney, and UNSW, as well as
researchers from the US, UK, and Chile. Dr. Ting Li from the Carnegie
Observatories and Princeton University leads the survey.
Dr. Mackey said the team spotted the fast-moving star serendipitously while
searching for the shredded remains of small galaxies orbiting the Milky Way.
“The star is only 29,000 light-years away, quite close by galactic
standards, which means the team could measure its trajectory very
precisely,” Dr. Mackey said.
Dr. Nordlander said supermassive black holes can slingshot stars by
interacting with a binary stellar system, whereby two stars orbit around
each other.
“If such a binary system approaches a black hole too closely, the black hole
can capture one of the stars into a close orbit and kick out the other at
very high speed.”
The team made the discovery of the star using the 3.9-meter (12.8-foot)
Anglo-Australian Telescope at the ANU Siding Spring Observatory. The
facility’s 2dF instrument is the best in the world for studying the sparsely
distributed stars in the outskirts of the Milky Way, due to its ability to
obtain simultaneous measurements for up to 400 targets at a time.
Follow-up observations made with the ANU 2.3-meter (7.5-foot) telescope
played an important role in confirming the star’s extreme speed.
The results of the study are published in the Monthly Notices of the Royal
Astronomical Society.
Reference:
Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A*”
by Sergey E Koposov, Boubert Douglas, S Li Ting, Denis Erkal, Gary S Da
Costa, Daniel B Zucker, Alexander P Ji, Kyler Kuehn, Geraint F Lewis and
Dougal Mackey, 4 November 2019, Monthly Notices of the Royal Astronomical
Society.
DOI: 10.1093/mnras/stz3081
Tags:
Space & Astrophysics