If you follow astronomy much, you’ve probably heard of the idea that our galaxy has an enormous black hole at the center of it. Sort of like a donut, if the hole in the middle swallowed up all light and deformed spacetime in the vicinity. (Come to think of it, I actually have eaten a few donuts like that…) Our galaxy isn’t alone in this feature, either; scientists believe that many galaxies sport one of these interstellar road hazards at their center. Aside from rendering the plot of Star Trek V even more nonsensical, this raises the question of how these supermassive black holes are formed. Now a new discovery by NASA’s Hubble space telescope may help scientists understand this process, as well as providing a snapshot of the development in action.
The subject in question is a mid-sized black hole residing near “the edge of the galaxy ESO 243-49, 290 million light-years from Earth.” This is one of the first medium-sized black holes ever discovered, and scientists believe that it may have once served as the core of a small dwarf galaxy, one which has since slammed into ESO 243-49 (pictured above). That collision would have shredded and cannibalized the dwarf galaxy, stripping away its stars and leaving the black hole trapped on its outer edge. The idea is that the supermassive black holes are formed from collisions like this one, when smaller black holes impact and merge with each other.
The idea of this galactic fender-bender is supported by the observation of a cluster of young, blue stars, possibly less than 200 million years old, near the mid-sized black hole. These baby stars would have been formed by the impact of the two galaxies. Sean Farrell, of the Sydney Institute for Astronomy in Australia, explains:
Before this latest discovery we suspected that intermediate-mass black holes could exist, but now we understand where they may have come from. The fact that there seems to be a very young cluster of stars indicates that the intermediate-mass black hole may have originated as the central black hole in a very-low-mass dwarf galaxy. The dwarf galaxy might then have been swallowed by the more massive galaxy, just as happens in our Milky Way.
To give you a sense of scale, this “mid-sized” black hole “has an estimated weight of about 20,000 solar masses.” That’s 20,000 times the mass of our own sun. To make your head swim even more, the black hole at the center of our galaxy is believed to have a mass of more than 4 million solar masses.