The galaxy known as M87 has thrown a globular cluster made of thousands of stars hurling through space at two million miles per hour (3.2 million km/h). Scientists have named the globular cluster HVGC-1, which stands for hypervelocity globular cluster. The recently discovered star cluster is now on a super speed journey to the middle of nowhere. HVGC-1 is now destined to drift through the void between the galaxies for eternity.
"Astronomers have found runaway stars before, but this is the first time we've found a runaway star cluster," said Nelson Caldwell of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
Globular clusters, like HVGC-1, are ancient relics of the early universe. According to National Geographic, "Globular clusters such as HVGC-1 are considered cosmic fossils because they contain some of the oldest known stars in the universe." Globular clusters usually contain thousands of stars densely packed into a ball just a few dozen light-years across. The giant elliptical galaxy M87 contains thousands of globular clusters. The Milky Way Galaxy, in contrast, is home to about 150 globular clusters.
Scientists discovered HVGC-1 with a little luck. A team of researchers has spent years studying the space around M87. The first step was to sort target objects by color. This separates the globular clusters around M87 from other galaxies. Next, they used something called the Hectospec tool on the MMT Telescope in Arizona. Using this tool they examined hundreds of globular clusters in detail.
The data was collected and automatically analyzed by a computer which calculated the speed of every cluster. Anything out of the ordinary was examined manually and most turned out to be errors or glitches. However, HVGC-1 was not a glitch. Its surprisingly high velocity was real.
"We didn't expect to find anything moving that fast," said Jay Strader of Michigan State University.
Astronomers aren't sure why HVGC-1 got ejected from its parent galaxy. One hypothesis states that it could have been caused by a pair of supermassive black holes at the galaxy's core. The star cluster may have floated too close to those black holes. Its outer stars would have been pulled into the black holes, but the dense core of the cluster remained intact. The two black holes possibly acted like a stellar slingshot, firing the globular cluster away at incredible speed.
M87 is a supergiant elliptical galaxy that has six trillion times the mass of our own sun. M87 is located about 5.3 million light years away from Earth and is one of the most massive galaxies in the nearby universe.
The discovery of HVGC-1 suggests that the core of M87 holds two supermassive black holes. This could be the result of a collision between two galaxies long ago, which combined to form a single super massive galaxy. The same thing will happen to our own galaxy, The Milky Way. Our galaxy is on a collision course with the Andromeda Galaxy. In a few billion years the two galaxies will collide and spend the next few million years in a cosmic gravitational dance until they create a new elliptical galaxy that astronomers have dubbed Milkomeda.