Astronomers from the United States and China have discovered a hypervelocity star (HVS) that is the closest bright HVS and one of the three most massive HVSs found so far.
This is an artist’s impression of the hypervelocity star LAMOST-HVS1 speeding away from the visible part of Milky Way Galaxy. Image credit: Ben Bromley / University of Utah.
HVSs appear to be remaining pairs of binary stars that once orbited each other and got too close to the supermassive black hole at the galaxy’s center.
Intense gravity from the black hole captures one star so it orbits the hole closely, and slingshots the other on a trajectory headed beyond the galaxy.
“The hypervelocity star tells us a lot about our Galaxy – especially its center and the dark matter halo. We can’t see the dark matter halo, but its gravity acts on the star. We gain insight from the star’s trajectory and velocity, which are affected by gravity from different parts of our Galaxy,” explained Dr Zheng Zheng from the University of Utah, the lead author of the study published in the Astrophysical Journal Letters (arXiv.org version).
Dr Zheng’s team discovered the new hypervelocity star, named LAMOST-HVS1, while conducting other research into stars with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST).
LAMOST-HVS1’s speed is almost three times the usual star’s 500,000-mph pace through space: 1.4 million mph relative to our Solar System and about 1.1 million mph relative to the speed of the center of the Milky Way Galaxy.
Despite being the closest HVS, it nonetheless is 42,400 light years away from Earth. It is also 62,000 light years from the center of our Galaxy.
LAMOST-HVS1 outshines our Sun – it is four times hotter and about 3,400 times brighter, if viewed from the same distance. But compared with the Sun, it is a youngster born only 32 million years ago, based on its speed and position.
It has a mass of about 9 times the Sun and an apparent magnitude of about 13, or 630 times fainter than stars that barely can be seen with the naked eye.
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Zheng Zheng et al. 2014. The First Hypervelocity Star from the LAMOST Survey. ApJ 785, L23; doi: 10.1088/2041-8205/785/2/L23
