Rogue holes: An illustration depicting the gravity waves predicted to form when black holes approach one another. Experts predict that when two black holes of unequal sizes come into close contact in globular clusters, they create asymmetrical gravity waves that can eject them in different directions at extremely high speeds.
Credit: NASA
NEW YORK: Hundreds of undetected black holes, each with a mass thousands of times greater than the Sun, might be stealthily roving our galaxy, ready to devour anything that crosses their paths.
These 'rogue' black holes would be very difficult to spot, said Kelly Holley-Bockelmann, an astronomer at Vanderbilt University in Tennessee, USA.
"Unless it's swallowing a lot of gas, about the only way to detect the approach of such a black hole would be to observe the way in which its super-strength gravitational field bends the light that passes nearby," she added.
Middling mass
Holley-Bockelmann presented the results of her team's supercomputer simulation on Wednesday at the annual meeting of the American Astronomical Society in Texas.
The model predicted the behaviour of a hypothetical class of so-called intermediate-mass black holes, whose origins are still mysterious. These black hole 'middleweights' are thought to have masses mid-way between that of the two classes of most well-known black holes.
Stellar black holes typically have less than 100 solar masses and are produced when ancient, giant stars explode. At the other end of the scale are supermassive black holes with masses equal to millions or even billions of Suns, and which lie nestled at the hearts of many galaxies.
Intermediate-mass black holes are predicted to form in 'packed globular clusters', large huddles of old stars located in the outer regions of galaxies. The computer simulation predicts that when intermediate black holes merge with the stellar variety, they get gravitationally ejected from their clusters at velocities of up to 4,000 kilometers per second.
Gravitational grip
There are roughly 200 globular clusters in the outer halo of the Milky Way. The model predicts that only five to 30 of these clusters are massive enough to retain a gravitational grip on intermediate black holes formed inside them.
The rest would get ejected from their birthplaces, fated to wander through space, and ready to engulf any stars or planets that get in their way. The chances of Earth falling prey to one of these marauding stellar predators is slim, however.
"These rogue black holes are extremely unlikely to do any damage to us in the lifetime of the universe," said Holley-Bockelmann. "Their danger zone ... is really tiny, only a few hundred kilometres. There are far more dangerous things in our neighbourhood."
