A team of international astronomers has detected a runaway star after it got ejected by the Milky Way’s supermassive black hole.
A team led by Sergey Koposov from Carnegie Mellon University spotted a runaway star. It was traveling through the Milky Way at about 3.7 million miles per hour. The gravitational forces of Sagittarius A* supermassive black hole caused the star to travel at such high speeds.
So, astronomers call this star S5-HVS1. It lies in the constellation of Grus—the Crane—and travels 10 times faster than most stars in our galaxy. The high-velocity star is on course to exit the Milky Way.
“The velocity of the discovered star is so high that it will inevitably leave the Galaxy and never return,” said co-author Douglas Boubert of the University of Oxford.
What makes S5-HVS1 so interesting is its high speed and close passage to the Earth, only 29 thousand light-years away. That’s practically next door by astronomical standards.
We never knew about these ultrafast stars until about two decades ago. They travel at sufficient speeds to escape the galaxy by overcoming its strong gravitational pull. It takes an incredibly massive object, like the 4-million-solar-mass Sagittarius A*, to accelerate these stars at such velocities.
“This is super exciting, as we have long suspected that black holes can eject stars with very high velocities. However, we never had an unambiguous association of such a fast star with the Galactic Centre,” said Sergey Koposov, the article’s lead author. “We think the black hole ejected the star with a speed of thousands of kilometers per second about five million years ago. This ejection happened at the time when humanity’s ancestors were just learning to walk on two feet.”
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Originally, S5-HSV1 was part of a binary system that got too close to Sagittarius A*. Therefore, the supermassive black hole swallowed one of the stars and ejected the other at high velocities. Scientists call this process the Hills Mechanism.
“This is the first clear demonstration of the Hills Mechanism in action,” said Ting Li from Carnegie Observatories and Princeton University, and leader of the S5 Collaboration. “Seeing this star is really amazing”, she added, “as we know it must have formed in the Galactic Centre, a place very different to our local environment. It is a visitor from a strange land.”
Astronomers discovered S5-HVS1, using the 3.9m Anglo-Australian Telescope (AAT) near Coonabarabran, NSW, Australia. With the help of the European Space Agency’s (ESA) Gaia satellite, the researchers also discovered the full speed of the star. Also, they even traced its journey right back to the center of the Milky Way.
“The observations would not be possible without the unique capabilities of the 2dF instrument on the AAT,” said Daniel Zucker, an astronomer at Macquarie University in Sydney, Australia, and S5 Executive Committee member. “It’s been conducting cutting-edge research for over two decades and still is the best facility in the world for our project.”
The researchers published the study in the journal Monthly Notices of the Royal Astronomical Society.