Astronomers discover hypervelocity star ejected from Milky Way's heart of darkness

Around five million years ago, a star was ejected by a supermassive black hole the heart at the Milky Way at a staggering speed of 3.7 million mph (6 million km/hour). 

The newfound super-fast star named S5-HVS1 is located in the constellation of Grus. The star was observed to be moving ten times faster than most of the stars of the galaxy. S5-HVS1 was discovered by Sergey Koposov of the Carnegie Mellon University as part of the Southern Stellar Stream Spectroscopic Survey. The discovery also appeared in the monthly Journal Notices of the  Royal Astronomical Society.

"The velocity of the discovered star is so high that it will inevitably leave the galaxy and never return," said study co-author Douglas Boubert, University of Oxford.

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Discovery was made 2 decades ago

The astronomers have been wondering about the high-velocity stars ever since the discovery was made almost two decades ago. The star remains to be unprecedented due to its high speed and close passage to the Earth which is ‘only’ 29 thousand light-years away.

With this available information, the astronomers can trace the star’s journey back to the center of the Milky Way, where a 4 million solar mass black hole known as Sagittarius A*, lies.

"This is super exciting, as we have long suspected that black holes can eject stars with very high velocities. However, we never before had a clear association of such a fast star with the galactic center," said lead author Koposov.

"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," Koposovsaid adding further.

As proposed by astronomer Jack Hills almost 30 years ago, superfast stars can be ejected through the black holes by the Hills Mechanism. S5-HSV1 star originally lived with a companion in a binary system, but they strayed too close to Sagittarius A*. Then during the gravitational tussle, the companion star was captured by the black hole, while S5-HVS1 was thrown out of it at extremely high speed.

"This is the first clear demonstration of the Hills mechanism in action," explained Ting Li from Carnegie Observatories and Princeton University, and leader of the S5 Collaboration.

"Seeing this star is amazing as we know it must have formed in the galactic center, a place very different from our local environment. It is a visitor from a strange land," Li added.

The star’s discovery was made through a 3.9-meter Anglo-Australian Telescope (AAT) near Coonabarabran, NSW, Australia, and was combined with the fascinating observations made by the European Space Agency's Gaia satellite. The satellite allowed the astronomers to reveal the full speed of the star and its journey from 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 a member of the S5 Executive Committee.

"While the main science goal of S5 is to probe the stellar streams -- disrupting dwarf galaxies and globular clusters -- we dedicated spare resources of the instrument to search for interesting targets in the Milky Way, and voila, we found something amazing for 'free,” said Kyler Kuehn, at Lowell Observatory and a member of the S5 Executive Committee.

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(With inputs from ANI)