A distant galaxy has thrown a cosmic fastball, astronomers say, ejecting an entire cluster of stars that's moving in our general direction at above two million mph.
Thrown out of the galaxy known as M87, the star cluster astronomers have dubbed HVGC-1 will likely drift through open space between galaxies for eternity, scientists say.
"Astronomers have found runaway stars before, but this is the first time we've found a runaway star cluster," says Nelson Caldwell of the Harvard-Smithsonian Center for Astrophysics.
The HVGC tag stands for a hypervelocity globular cluster; such clusters -- thousands of individual stars jammed into a tight ball spreading over just a few light years -- are left-over relics from the early epoch of the universe.
Around 150 such clusters have been found in our own Milky Way galaxy.
In comparison, the M87 galaxy is inhabited by thousands of the globular clusters, but astrophysicists are at a loss to explain how a particular one could be thrown out at such high velocities.
One theory holds that M87 possesses two supermassive examples of black holes in its central region, which could have acted like a slingshot to hurl HVCG-1 out of the galaxy if it had the misfortune to wander to close to the black hole pair.
The discovery of HVGC-1 came after years of studying the cosmic reaches inside M87, analyzing hundreds of clusters and using computers to calculate the speed of each of them.
Odd results were usually the result of computer glitches, the researchers say, but the unexpected velocity of HVGC-1 was real, as confirmed by the MMT Telescope in Arizona.
"We didn't expect to find anything moving that fast," study co-author Jay Strader at Michigan State University says.
Its speed is so high it has probably completely left the limits of M87 and is now moving through interstellar space, the researchers say.
That's not easy, since the giant elliptical M87 is one of the largest galaxies known in the universe, containing the mass of six trillion suns.
If HVGC-1 has escaped the confines of M87 and moved out to wander through empty space, that's likely its permanent fate, the researchers emphasized.
