First Stellar Outcast Speeding at Over 1.5 Million Miles Per Hour

Feb 09, 2005

Using the MMT Observatory in Tucson, AZ, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) are the first to report the discovery of a star leaving our galaxy, speeding along at over 1.5 million miles per hour. This incredible speed likely resulted from a close encounter with the Milky Way's central black hole, which flung the star outward like a stone from a slingshot. So strong was the event that the speedy star eventually will be lost altogether, traveling alone in the blackness of intergalactic space.

"We have never before seen a star moving fast enough to completely escape the confines of our galaxy," said co-discoverer Warren Brown (CfA). "We're tempted to call it the outcast star because it was forcefully tossed from its home."

The star, catalogued as SDSS J090745.0+24507, once had a companion star. However, a close pass by the supermassive black hole at the galaxy's center trapped the companion into orbit while the speedster was violently flung out. Astronomer Jack Hills proposed this scenario in 1998, and the discovery of the first expelled star seems to confirm it.

"Only the powerful gravity of a very massive black hole could propel a star with enough force to exit our galaxy," explained Brown.

While the star's speed offers one clue to its origin, its path offers another. By measuring its line-of-sight velocity, it suggests that the star is moving almost directly away from the galactic center. "It's like standing curbside watching a baseball fly out of the park," said Brown.

Its composition and age provide additional proof of the star's history. The fastest star contains many elements heavier than hydrogen and helium, which astronomers collectively call metals. "Because this is a metal-rich star, we believe that it recently came from a star-forming region like that in the galactic center," said Brown. Less than 80 million years were needed for the star to reach its current location, which is consistent with its estimated age.

The star is traveling twice as fast as galactic escape velocity, meaning that the Milky Way's gravity will not be able to hold onto it. Like a space probe launched from Earth, this star was launched from the galactic center onto a never-ending outward journey. It faces a lonely future as it leaves our galaxy, never to return.

Brown's co-authors on the paper announcing this find are Margaret J. Geller, Scott J. Kenyon and Michael J. Kurtz (Smithsonian Astrophysical Observatory). This study will be published in an upcoming issue of The Astrophysical Journal.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Explore further: Team develops cognitive test battery for spaceflight

add to favorites email to friend print save as pdf

Related Stories

Transiting exoplanet with longest known year

Jul 21, 2014

Astronomers have discovered a transiting exoplanet with the longest known year. Kepler-421b circles its star once every 704 days. In comparison, Mars orbits our Sun once every 780 days. Most of the 1,800-plus ...

Sun-like stars reveal their ages

Jul 10, 2014

(Phys.org) —Defining what makes a star "Sun-like" is as difficult as defining what makes a planet "Earth-like." A solar twin should have a temperature, mass, and spectral type similar to our Sun. We also ...

Mysterious X-ray signal intrigues astronomers

Jun 24, 2014

(Phys.org) —A mysterious X-ray signal has been found in a detailed study of galaxy clusters using NASA's Chandra X-ray Observatory and ESA's XMM-Newton. One intriguing possibility is that the X-rays are ...

Recommended for you

Rosetta's comet: In the shadow of the coma

39 minutes ago

This NAVCAM mosaic comprises four individual images taken on 20 November from a distance of 30.8 km from the centre of Comet 67P/C-G. The image resolution is 2.6 m/pixel, so each original 1024 x 1024 pixel ...

DNA survives critical entry into Earth's atmosphere

21 hours ago

The genetic material DNA can survive a flight through space and re-entry into the earth's atmosphere—and still pass on genetic information. A team of scientists from UZH obtained these astonishing results ...

Team develops cognitive test battery for spaceflight

22 hours ago

Space is one of the most demanding and unforgiving environments. Human exploration of space requires astronauts to maintain consistently high levels of cognitive performance to ensure mission safety and success, and prevent ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.