Entire Star Cluster Thrown Out of Its Galaxy at Two Million Miles Per Hour
Posted on April 30, 2014
p class="first">An entire star cluster has been thrown out of its galaxy at two million miles per hour. The star cluster, HVGC-1, was thrown out of the galaxy known as M87. HVGC stands for hypervelocity globular cluster. The Harvard-Smithsonian Center for Astrophysics (CfA) says these clusters "usually contain thousands of stars crammed into a ball a few dozen light-years across."Nelson Caldwell of the CfA says, "Astronomers have found runaway stars before, but this is the first time we've found a runaway star cluster."
Caldwell is the lead author of the study published here in The Astrophysical Journal Letters. The researchers have been studying the space around M87 for years. They first sorted targets by color to separate stars and galaxies from globular clusters. Then they used the Hectospec instrument on the MMT Telescope in Arizona to examine hundreds of globular clusters. A computer analyzed the data and calculated the speed of each cluster. Any oddities were examined by hand. Most of those turned out to be glitches, but HVGC-1 was different. Its surprisingly high velocity was real.
Jay Strader of Michigan State University, a co-author on the study, says, "We didn't expect to find anything moving that fast."
Astronomers aren't sure how HVGC-1 got ejected from the galaxy at such a high velocity. One scenario involves M87 having a pair of supermassive black holes at its core. These two black holes could have acted like a slingshot sending the cluster hurtling out of the galaxy.