Hyperfast Star Ejected from the Large Magellenic Cloud

Occasionally, stars minding their own business around the supermassive black hole at the center of our galaxy get chucked out of the Milky Way, never to return. Fraser wrote about the discovery of two of these exiled stars, hurling away at the mind-blowing speed of over 1 million miles an hour. A recent study of another shows that not all of them originate in the center of our own galaxy.

New results from astronomers at the Carnegie Institute show that one star rocketing away from the Milky Way hearkens from the Large Magellanic Cloud, our neighboring galaxy. There have been ten such hypervelocity stars discovered, but where this one came from was quite a conunudrum.

Named HE 0437-5439, it’s nine times the mass of the Sun, and is traveling at 1.6 million miles an hour (2.6 million km an hour). The origin of the star has been a mystery until now because of its youth: it is 35 million years old, but it would have taken 100 million years to get to its current location if it were from the center of the Milky Way.

This meant that the star either came from somewhere else, or had to have formed out of the merger of two low-mass stars from the Milky Way, a so-called “blue straggler.”

Carnegie astronomers Alceste Bonanos and Mercedes López-Morales, and collaborators Ian Hunter and Robert Ryans from Queen’s University Belfast took measurements of the composition of the star – the first time this has been done on any hypervelocity star – and determined that its metal-poor makeup pointed towards the Large Magellanic Cloud as the former home of the castaway.

Bonanos said,“We’ve ruled out that the star came from the Milky Way. The concentration of [heavy] elements in Large Magellanic Cloud stars are about half those in our Sun. Like evidence from a crime scene, the fingerprints point to an origin in the Large Magellanic Cloud.�

Hypervelocity stars get their kick of energy from their interaction with a black hole. The stars were once part of a binary system, and as one star in the system gets captured by the black hole, the other is abruptly released, booting it clear out of the galaxy.

The mere fact that the Large Magellanic Cloud produced this hyperfast star hints at the presence of a black hole there, which has never previously been observed to exist.

Source: Carnegie Institute Press Release