Outcast star

[Sky Pilot]

Does anyone know which star this is?

WASHINGTON: An outcast star is zooming out of the Milky Way, the first ever seen escaping the galaxy, astronomers said on Tuesday.

The star is heading for the emptiness of intergalactic space after being ejected from the heart of the Milky Way following a close encounter with a black hole, said Warren Brown, an astronomer at the Harvard-Smithsonian Center for Astrophysics. The outcast is going so fast, over 1.5 million mph, that astronomers believe it was lobbed out of the galaxy by the tremendous force of a black hole thought to sit at the Milky Way's center.

[andersa]

Does anyone know which star this is?

I haven't seen any coordinates, but Harvard-Smithsonian has issued a press release with a photo.

[Spaceman Spiff]

Over 0.2% the speed of light. Poor thing!

Spiff.

[andersa]

I found some data in an Astrophysics Journal letter: The star's location in the sky is 9h 07m 45.0s, +2?°45'07'' (J2000); that should be in constellation Hydra. Its distance is estimated to 55 kpc. Its radial velocity is given as 853?±12 km/s, more than twice the escape velocity for the Milky Way. Bye, bye!

I wonder if it remembered to bring a towel, or at least some dust to make planets from...

[Sky Pilot]

Is there enough known data to model this in Celestia? It would be interesting to project it's path into the future

[tony873004]

I don't see how the Milky Way's central black hole could eject this star, for the same reason that spacecraft can't use the Sun for a gravity boost. It would have had to receive its escape boost from something else, perhaps another black hole that orbits the central black hole.

[andersa]

It would have had to receive its escape boost from something else, perhaps another black hole that orbits the central black hole.

That's indeed one of the theories presented for the history of this star. Another is that it may have been part of a binary star system in very close formation, the other component of which came too close to a black hole and was swallowed. Having suddenly lost its companion, the remaining component was then sufficiently far away from the black hole not to be swallowed and moving faster than the escape velocity at that point. Knowing the general mass distribution in the Milky Way, it should be possible to work out approximately what was the speed of this star when it was still near the center of the galaxy 80 million years ago.

These theories have already been worked out well in advance of the first observation of what is now believed to be such a star. Anybody curious about the scientific details should probably study the Astrophysics Journal article I mention above (I didn't read it through myself).