Will a Black Hole Ever Hit Earth?

The black hole that is the closest to our solar system has been discovered in our galactic backyard.

The local black hole is roughly 12 times the mass of our sun and is situated about 1,550 light-years away, according to preprint research to be published in The Astrophysical Journal.

While 1,550 light-years is a huge distance in human terms, equal to about 9,000,000,000,000,000 miles, in terms of the size of the universe or even our Milky Way galaxy (which is 100,000 light-years in diameter), this black hole is very near to us.

But what if a black hole was much closer or even drifted through our solar system? Black holes are immense, with gravity so strong that not even light can escape from their pull. They are formed from the heavy cores of dying stars, after the star's entire mass has collapsed under the weight of its gravitational pull.

"To get a better picture of this process, one has to understand that the pressure, due to its mass, of a non-collapsed star causes merging events," Florian Peissker, an astrophysicist at the University of Cologne in Germany, told Newsweek.

He continued: "Hydrogen, the most common building block in the universe, inside of the star merges with each other and creates helium. To fully understand this process, one has to consider relativistic events. Nevertheless, this merging of elements causes outwards-directed radiation which equalizes the inwardly directed pressure. This is called the hydrostatic equilibrium.

"If the hydrogen is used up, there is no outwards-directed radiation that balances the inward-directed pressure. Hence, the star collapses. If the initial mass of the star is high enough, a black hole is created," Peissker said.

Since black holes don't even let light escape, they are more or less invisible and difficult to detect.

"There may well be a handful of closer black holes, a few in binaries and a few single, which are almost impossible to discover except via deflection of background light, which may have recently been done," Roger Romani, a professor of physics at Stanford University, told Newsweek.

He continued: "At 1,500 light-years, this is not quite as close as statistics would suggest for the nearest source, but is not that far off. We are a bit lucky to have such a heavy, easily studied black hole binary nearby."

Black holes can drift across the galaxy rather than orbiting the galactic center, as our sun does. These are known as "rogue" black holes. Some have even theorized that there could be a black hole lurking on the edge of our solar system, silently influencing the orbits of the outer planets with its gravity.

"For the Earth to be destroyed, it would have to have a very close encounter with a large black hole," Steven Tingay, an astrophysicist and executive director of the Curtin Institute of Radio Astronomy at Curtin University, told Newsweek.

He continued: "However, the results of the interaction would be catastrophic well before the Earth is destroyed. The major perturbation of the orbits of the planets could well throw the Earth or another planet out of the solar system, which would be just as bad, possibly worse, than being eaten by a black hole."

But there is very little cause to be worried, he said, as "the chances of a black hole coming through our solar system are tiny."

If a rogue black hole doesn't come very close to the Earth, we might not notice any effects at all. "A very small black hole could possibly travel through the solar system largely unnoticed," Tingay said.

Romani agreed, saying, "Unless one is within a few tens of kilometers, a black hole's gravity acts the same as a star of the same mass. So the effect on the solar system of one passing nearby would be about the same as a star, but less since it is dark—no extra starlight—and much less common.

"The main effect would likely be to perturb comets as it passed through the Oort Cloud. A few might rain down into the inner solar system, giving a bit of a show over the tens of thousands of years that the black hole swept by," Romani said.