Hubble spots blue star 'spat out' by Milky Way travelling through space at 1.6million mph



Nasa's Hubble Space Telescope has detected a rare hypervelocity star that was spat out of the centre of our galaxy and is travelling three times as fast as the Sun.

Scientists believe that it was created when three stars travelling together passed too close to the black hole at the centre of the Milky Way around a hundred million years ago.

One of the stars was captured while the other two were flung out of the galaxy and merged to form a super-hot blue star travelling at around 1.6 million miles per hour.

A Nasa graphic showing how the 'blue straggler' was spat out of the centre of our galaxy

Known as HE 0437-5439 it is one of the fastest stars ever detected and is the first to be directly linked with the centre of the galaxy.

'Using Hubble, we can for the first time trace back to where the star came from by measuring the star's direction of motion on the sky. Our measurements point directly to the Milky Way center.' said astronomer Warren Brown of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

Brown, a member of the Hubble team that observed the star, is the lead author on a paper about the finding published online in the Astrophysical Journal Letters.

Brown said, 'These exiled stars are rare in the Milky Way's population of 100 billion stars. For every 100 million stars in the galaxy, there lurks one hypervelocity star.'

The stellar outcast already is cruising in the Milky Way's distant outskirts about 200,000 light-years from the galaxy's centre.

Using Hubble to measure the runaway star's direction and determine the Milky Way's core as its starting point, Brown and Gnedin's team calculated how fast the star had to have been ejected to reach its current location.

'Studying these stars could provide more clues about the nature of some of the universe's unseen mass, and it could help astronomers better understand how galaxies form,' said team leader Oleg Gnedin of the University of Michigan in Ann Arbor.

The Hubble image which pinpoints the blue star as it hurtles through space at unimaginable speeds

The star's age is another mystery. Based on the speed and position of HE 0437-5439, the star would have to be 100 million years old to have journeyed from the Milky Way's core.

But its mass -nine times that of our sun - and blue colour mean that it should have burned out after only 20 million years far shorter than the transit time it took to get to its current location.

This concept for imparting an escape velocity on stars was first proposed in 1988. The theory predicted the Milky Way's black hole should eject a star about once every 100,000 years.

The triple-star system contained a pair of closely orbiting stars and a third outer member also gravitationally tied to the group. The black hole pulled the outer star away from the tight binary system.