Black holes have to be the universe's most mysterious phenomena.
For one, they defy our conventional understanding of physics, especially around gravity and spacetime. Plus, there is just so little we truly know about them.
In our galaxy, the Milky Way, it's believed there could be anywhere from 10 million to 1 billion stellar mass black holes.
These gravitational enigmas are notoriously difficult to detect, mainly because they don't emit any light. So far, we've identified about 20 of them, with the nearest known black hole being around 1,565 light-years away from Earth.
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However, all has been turned on its head.
Recent astronomical studies have suggested that these enigmatic occurrences might lurk much closer to Earth than previously thought.
While it sounds like the plot of a new sci-fi thriller, research conducted by a team of astronomers at the University of Padua, led by Stefano Torniamenti, is challenging our understanding of these cosmic neighbors.
The findings, published in the Monthly Notices of the Royal Astronomical Society, were uncovered when the astronomers turned their attention to the Hyades cluster - a group of stars in the constellation of Taurus, located only 150 light-years away. Through detailed analysis and modeling, the researchers suggested the existence of two or three stellar mass black holes within this cluster.
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The revelation comes from combining observational data from the Gaia satellite with sophisticated simulations, pointing towards the hidden presence of these black holes.
The Hyades cluster is an open cluster, a kind of stellar family born from the same molecular cloud, moving together through space. As it ages – it's currently about 625 million years old – its stars begin to drift apart. The center of the cluster, densely packed with stars, is where black holes are most likely to be found, born from the remnants of massive stars.
Detecting these black holes is a complex task. Black holes are essentially invisible unless they're actively consuming material from a nearby star - a pretty rare phenomenon. So, the team had to rely on indirect methods, studying the cluster's dynamics to uncover their existence.
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"Our simulations can only simultaneously match the mass and size of the Hyades if some black holes are present at the center of the cluster today, or until recently,” explained Torniamenti.
And if you're worried about being swallowed up by a black hole - don’t be. The astronomers have reassured us that the discovery of these nearby black holes doesn't pose any threat to Earth. Even the fastest-moving of these black holes is only traveling at three kilometers per second.
Instead of fear-mongering, the research was conducted to merely help us understand more about the nature of black holes and our galaxy as a whole.
As astrophysicist Mark Gieles of the University of Barcelona explains:
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"This observation helps us understand how the presence of black holes affects the evolution of star clusters and how star clusters in turn contribute to gravitational wave sources.
"These results also give us insight into how these mysterious objects are distributed across the galaxy."