Astronomers continue to find that black holes, once thought to be rare anomalies in the Universe, can be found just about anywhere. The most recent discovery, detailed in a study published today by the Royal Astronomical Society, provides strong evidence that there are hundreds of black holes hiding in the globular cluster NGC 6101, which sits about 50,000 light years across the galaxy from Earth.
A globular cluster is a group of stars gravitationally bound to one another that orbit the center of the galaxy as a single unit. We have observed many of these clusters. British astronomers from the University of Surrey decided to take a closer look at NGC 6101 because it has a bizarre structure. Specifically, the individual stars in NGC 6101 are much older than researchers would assume given how young the cluster itself is. Also, there are surprisingly few stars in the center of the cluster, making it seem "inflated."
The answer to this mystery? Hundreds of black holes a few times larger than the Sun are inside the cluster, something that was previously thought to be impossible.
"Due to their nature, black holes are impossible to see with a telescope, because no photons can escape," explains Miklos Peuten of the University of Surrey in a press release. "In order to find them we look for their gravitational effect on their surroundings. Using observations and simulations we are able to spot the distinctive clues to their whereabouts and therefore effectively 'see' the un-seeable."
A computer simulation that modeled the formation of NGC 6101 over billions of years revealed that the presence of a large number of black holes could explain the strange structure of the cluster. The find calls into question some of the existing theories regarding how black holes form after the supernova of a massive star. It also suggests that a number of other globular clusters around the galaxy could be hiding large numbers of black holes, which would add a new piece to the puzzle of how the entire Milky Way formed.
Another globular cluster was recently revealed to be a "fossil" from the time of galactic formation—a ball of gas and dust that should have been absorbed by the violent center of the Milky Way, but escaped and is preserved to this day. With more discoveries like these, we might eventually unravel the mystery of how galaxies form across the Universe.
