Nearest bright 'hypervelocity star' found: Speeding at 1 million mph, it probes black hole and dark matter

May 07, 2014
This is an astrophysicist-artist's conception of a hypervelocity star speeding away from the visible part of a spiral galaxy like our Milky Way and into the invisible halo of mysterious "dark matter" that surrounds the galaxy's visible portions. University of Utah researcher Zheng Zheng and colleagues in the US and China discovered the closest bright hypervelocity star yet found. Credit: Ben Bromley, University of Utah.

A University of Utah-led team discovered a "hypervelocity star" that is the closest, second-brightest and among the largest of 20 found so far. Speeding at more than 1 million mph, the star may provide clues about the supermassive black hole at the center of our Milky Way and the halo of mysterious "dark matter" surrounding the galaxy, astronomers say.

"The hypervelocity star tells us a lot about our galaxy – especially its center and the ," says Zheng Zheng, an assistant professor of physics and astronomy and lead author of the study published recently in Astrophysical Journal Letters by a team of U.S. and Chinese astronomers.

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

In the past decade, astronomers have found about 20 of these odd . Hypervelocity stars appear to be remaining pairs of binary stars that once orbited each other and got too close to the at the galaxy's center. Intense gravity from the black hole – which has the mass of 4 million stars like our sun – captures one star so it orbits the hole closely, and slingshots the other on a trajectory headed beyond the galaxy.

Zheng and his colleagues discovered the new hypervelocity star while conducting other research into stars with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, or LAMOST, located at the Xinglong Observing Station of the National Astronomical Observatories of China, about 110 miles northeast of Beijing. LAMOST boasts a 13.1-foot-wide aperture and houses 4,000 optical fibers, which capture "spectra" or light-wavelength readings from as many as 4,000 stars at once. A star's spectrum reveals information about its velocity, temperature, luminosity and size.

LAMOST's main purpose is to study the distribution of stars in the Milky Way, and thus the galaxy's structure. The new hypervelocity star – named LAMOST-HVS1 – stood out because its speed is almost three times the usual star's 500,000-mph pace through space: 1.4 million mph relative to our solar system. Its speed is about 1.1 million mph relative to the speed of the center of the Milky Way.

Despite being the closest hypervelocity star, it nonetheless is 249 quadrillion miles from Earth. (In U.S. usage, a quadrillion is 1,000,000,000,000,000 miles or 10 to the 15th power, or 1 million billion).

"If you're looking at a herd of cows, and one starts going 60 mph, that's telling you something important," says Ben Bromley, a University of Utah physics and astronomy professor who was not involved with Zheng's study. "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 Down-Low on a Fast and Loose Star

A cluster of known hypervelocity stars, including the new one, is located above the disk of our Milky Way galaxy, and their distribution in the sky suggests they originated near the galaxy's center, Zheng says.

The diameter of the visible part of our spiral-shaped galaxy is at least 100,000 , or 588 quadrillion miles. Zheng says that when the halo of dark matter is added, the estimated diameter is roughly 1 million light years, or 5,880 quadrillion miles.

Scientists know dark matter halos surround because the way their gravity affects the motion of a galaxy's visible stars and gas clouds. Researchers say only about 5 percent of the universe is made of visible matter, 27 percent is invisible and yet-unidentified dark matter and 68 percent is even more mysterious dark energy, responsible for accelerating the expansion of the universe. By traveling through the halo, the new hypervelocity star's speed and trajectory can reveal something about the mysterious halo.

Our solar system is roughly 26,000 light years or 153 quadrillion miles from the center of the galaxy – more than halfway out from the center of the visible disk.

By comparison, the new hypervelocity star is about 62,000 light years or 364 quadrillion miles from the galactic center, beyond as well as above the galaxy's visible disk. It is about 42,400 light years from Earth, or about 249 quadrillion miles away.

As far as that is – the star has a magnitude of about 13, or 630 times fainter than stars that barely can be seen with the naked eye – it nevertheless "is the nearest, second-brightest, and one of the three most massive hypervelocity stars discovered so far," Zheng says.

It is nine times more massive than our sun, which makes it very similar to another hypervelocity star known as HE 0437-5439, discovered in 2005, and both are smaller than HD 271791, which was discovered in 2008 and is 11 times more massive than the sun. As seen from Earth, only HD 271791 is brighter than LAMOST-HVS1, Zheng says.

The newly discovered hypervelocity star also outshines our own sun: It is four times hotter and about 3,400 times brighter (if viewed from the same distance). But compared with our 4.6-billion-year-old sun, the newly discovered LAMOST–HVS1 is a youngster born only 32 million years ago, based on its speed and position, Zheng says.

Is there any chance that the supermassive black hole might hurl a hypervelocity star in Earth's direction one day? Not really, Zheng says. First, astrophysicists estimate only one hypervelocity star is launched every 100,000 years. Second, possible trajectories of stars near the supermassive black hole don't forebode any danger, should any of them become a hypervelocity star in the future.

Explore further: Surprising new class of 'hypervelocity stars' discovered escaping the galaxy

More information: Paper: dx.doi.org/10.1088/2041-8205/785/2/L23 , preprint: arxiv.org/abs/1401.5063

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Dr_toad
May 07, 2014
This comment has been removed by a moderator.
verkle
1 / 5 (8) May 07, 2014
Scientists know dark matter halos surround galaxies....


Not true. We don't even know that dark matter exists. Complete postulation.

Regarding this HV star, we only think that it originated from the center of the galaxy because of its distribution? Can't we know what direction it is headed? Is it really moving away from the center of the galaxy? This article doesn't provide enough details.

arom
1 / 5 (7) May 07, 2014
"We can't see the dark matter halo, but its gravity acts on the star," Zheng says. "We gain insight from the star's trajectory and velocity, which are affected by gravity from different parts of our galaxy."
Scientists know dark matter halos surround galaxies because the way their gravity affects the motion of a galaxy's visible stars and gas clouds. Researchers say only about 5 percent of the universe is made of visible matter, 27 percent is invisible and yet-unidentified dark matter and 68 percent is even more mysterious dark energy, responsible for accelerating the expansion of the universe. By traveling through the dark matter halo, the new hypervelocity star's speed and trajectory can reveal something about the mysterious halo.

Maybe we could visualize the mysterious dark energy/matter via this new way of thought …
http://www.vacuum...14〈=en
sirchick
5 / 5 (6) May 09, 2014
Scientists know dark matter halos surround galaxies....


Not true. We don't even know that dark matter exists. Complete postulation.

Regarding this HV star, we only think that it originated from the center of the galaxy because of its distribution? Can't we know what direction it is headed? Is it really moving away from the center of the galaxy? This article doesn't provide enough details.



Dark matter is just a placeholder name for something that we have measured (there for DOES exist). But we know nothing of its properties other than how much of it there is, and its interaction with gravity.

It doesn't have to be matter or dark, we will likely rename it once we know more.. but something does exists... what ever it is, hopefully we will find out eventually what its properties are.

Same for dark energy, we have measured the universe expanding, so dark energy exists, what it is - we don't know.
yep
1.8 / 5 (5) May 10, 2014
Dark matter exists because of the religious belief in Big Bang the priori for all the other hypothetical "placeholder"s like Black Holes, Dark Energy, etc.

"we know nothing" Now there your saying something, and hopefully we can learn from it.
Protoplasmix
3 / 5 (1) May 11, 2014
When there's enough mass (for baryons), the force of gravity overwhelms the other forces combined. What is it about dark matter that it hasn't all just collapsed into black hole equivalents?
yep
2 / 5 (4) May 11, 2014

Primer Fields
https://www.youtu...lyiW-xGI
https://www.youtu...gyJ0k8Kw
https://www.youtu...6ikj1G-s
I believe these videos clearly show how magnetic fields would launch stars or star clusters across the cosmos without the need for black holes.

Read more at: http://phys.org/n...html#jCp
bearly
1 / 5 (2) May 11, 2014
Possibly not a star but a starship?
Protoplasmix
not rated yet May 11, 2014
"We can't see the dark matter halo, but its gravity acts on the star," Zheng says. "We gain insight from the star's trajectory and velocity, which are affected by gravity from different parts of our galaxy."

Mapping the DM distribution using gravitational lensing would provide a nice check. Also, knowing the distribution would help to provide additional insights/constraints on the nature of other interactions between DM and baryonic matter:
a) DM quenches nuclear reaction in star's core --> less outward pressure --> star contracts, luminosity decreases.
b) DM catalyzes nuclear reaction in star's core --> greater outward pressure --> star expands, luminosity increases.
c) DM has no measurable effect.
no fate
1 / 5 (1) May 12, 2014
"Primer Fields
https://www.youtu...lyiW-xGI"

You got alot of nerve posting videos of a model that accurately describes a staggering number of phenomena we observe on this forum sir. This is totally invalid as it has no accompanying math and was not produced by a peer reviewed physicist or mainstream facility.

I mean sure it may predict a few things accurately, have observational support examples that number in the thousands, produce structures in a lab that no other model can replicate and generally make sense of the current astrophysics debacle...but if you haven't described it mathematically what real use does it have?

LMAO! ( I did not make these videos I just wish I had. They make sense)

Well done YEP