It's a doomsday scenario on a slightly-less-than galactic scale: A star cluster has been ejected from a galaxy (designated M87) relatively near our own and is hurtling toward our small planet at two million miles per hour as you read. That's pretty fast and sounds rather unavoidable. But there is good news to go with this seeming intergalactic catastrophe: The scientists that discovered the runaway star cluster noted that the likelihood of it actually getting near our solar system and endangering the home planet is rather slim.
The Independent reported May 1 that the castaway star cluster, a globular cluster consisting of thousands of gravitationally bound stars, is more likely to “drift through the void between the galaxies for all time,” or that is what the astronomers at Harvard-Smithsonian Center for Astrophysics say.
Relatively speaking, the star cluster, although headed toward the Earth at present, might still pass in the general vicinity of where the Earth is now -- but by the time it actually gets to this point in space, the Earth and all its Milky Way companions will have traveled far away and into another part of the expanding universe.
Nelson Caldwell at the Harvard-Smithsonian Center for Astrophysics stated: "Astronomers have found runaway stars before, but this is the first time we've found a runaway star cluster."
Those runaway stars, called "hypervelocity stars," are usually flung out by black holes at a galaxy's center. (Side note: Hypervelocity planets also exist, being shot out or galactic cores at escape velocity.) The astronomers that discovered the runaway cluster -- labeled HVGC-1, or Hypervelocity Globular Cluster-1 -- don't know for certain but believe that the cluster was ejected by two supermassive black holes whose gravitational pull acted as a slingshot on the star grouping. The two black holes are believed to have been formed via the collision of two galaxies.
Star clusters themselves are fairly large, many reaching dimensions dozens of light-years across.
It is estimated that, for every billion stars, there is at least one runaway star. With the newly found existence of runaway star clusters, the estimation just might have to be adjusted.
According to Fox News, HVGC-1 was found using the MMT Telescope in Arizona after the team of astronomers had spent years studying the space around the M87 galazy. The speed of the cluster was calculated by computer.
The intense rate of speed -- in this case, 2 million miles per hour -- is what allows the star cluster to attain escape velocity from its parent galaxy's gravitational clutch.
Study co-author Jay Strader of Michigan State University noted about the surprise find, "We didn't expect to find anything moving that fast."
The study is scheduled for publication in The Astrophysical Journal.