Hypervelocity Star Breaks Universal Speed Record

1,200 Km / s.  That’s fast.  Fast enough to race around the entire Earth in 30 seconds.  Except that it’s not a bullet, it’s a star, larger and more massive than the Earth. And a multinational team of astronomers has discovered it, and more importantly, where it came from and why it’s moving so fast.

Artist’s conception of US-708. Credit: ESA / Hubble / NASA / S. Geier

Hypervelocity stars (HVS’) are an uncommon phenomenon, since the conditions necessary to accelerate them to incredible speeds are rare.  There are only about 20 HVS known, and the first was found only ten years ago.  So where do they come from?

There are only a few hypotheses to explain the origin of HVS’ right now, but they all involve very close binary systems.  One scenario is proposed where a binary system falls in toward a black hole, where one of the binary members is captured by the black hole and the other is shot away at high speed.

With the new discovery of HVS US 708, a Helium-rich star with rapid rotation, the proposed origin is a bit different.  Now nearly 62,000 light years away, the researchers were able to determine its direction of travel, and show that it did not originate at the centre of the Milky Way galaxy. Astronomers are suggesting that the star originated in a tight binary system where it was losing mass to a companion, which eventually exploded as a supernova.  The resulting explosion ejected the star at high velocity.

Image credit: Centre de Données astronomiques de Strasbourg / SIMBAD

I have read articles in the past about stars that are ‘wanderers,’ having been found in the vast darkness between galaxies.  I would expect many of these to be HVS,’ since they often are fired away during a collision of galaxies.  If modern galaxies formed from mergers of many protogalaxies, we should expect to see many stars hidden in intergalactic space.  But being so relatively small and distant, it is very hard to find such stars unless they are close to the Milky Way.  Further proof that we always can find something new and amazing to study when observing technology takes a leap forward.


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