Hypervelocity star
Closest bright hypervelocity star LAMOST-HVS1Ben Bromley, University of Utah

The discovery of a hypervelocity star travelling at 1 million mph may offer clues about the halo of mysterious dark matter surrounding our galaxy.

Found by a team from the University of Utah, the celestial body is the closest, second-brightest and among the largest of the 20 so-called hypervelocity stars discovered in the last decade.

Named LAMOST–HVS1, the star may also provide clues about the supermassive black hole at the centre of our Milky Way.

"The hypervelocity star tells us a lot about our galaxy – especially its centre and the dark matter halo," said Zheng Zheng, an assistant professor of physics and astronomy and lead author of the study.

"We can't see the dark matter halo, but its gravity acts on the star," Zheng added. "We gain insight from the star's trajectory and velocity, which are affected by gravity from different parts of our galaxy."

Hypervelocity stars appear to be remaining pairs of binary stars that once orbited each other before moving too close to the black hole at the galaxy's centre. Intense gravity from the black hole – which has the mass of 4 million stars like our sun – captures one star and places it into the hole's orbit, while the other is cast out onto a trajectory beyond the galaxy.

The team discovered the new star while conducting other research into stars with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope in China.

LAMOST–HVS1 was found because its speed is almost three times the 500,000mph pace of a star. Its speed is about 1.1 million mph relative to the speed of the centre of the Milky Way.

Despite being the closest hypervelocity star, it is still 249 quadrillion miles, or 42,400 light-years from Earth.

"If you're looking at a herd of cows, and one starts going 60 mph, that's telling you something important," Ben Bromley, a University of Utah physics and astronomy professor told Sciencecodex.com. "You may not know at first what that is. But for hypervelocity stars, one of their mysteries is where they come from – and the massive black hole in our galaxy is implicated."

The star is located above the disk of our Milky Way galaxy, within a cluster of many. Their distribution in the sky suggests they originated near the galaxy's centre.

The diameter of the visible part of our spiral-shaped galaxy is at least 100,000 light-years. According to Zheng, when the halo of dark matter is added, the estimated diameter is roughly 1 million light years.

Dark matter is a type of matter hypothesized in astronomy and cosmology to account for effects that appear to be the result of mass where no such mass can be seen.

Astronomers say only 5% of the universe is made of visible matter, while 27% is invisible and yet-unidentified dark matter and 68% is dark energy, responsible for accelerating the expansion of the universe.

The findings were published in Astrophysical Journal Letters.