New NASA research suggests that their upcoming space telescope, the Nancy Grace Roman, will be able to look for primordial black holes, which can be smaller than regular black holes, with masses even smaller than a planet like ours. Well, as long as these objects exist, that is. But you might be wondering: what are primordial black holes?
Black holes need extreme compression to form. At least, that’s how the stellar black holes come to be. A massive star goes supernova and its core is compacted so tightly under the gravitational collapse that an object with incredible density is born. An object from which nothing, not even light, can escape.
Black holes go from masses of a few times that of the Sun, to billions of times our little star. The formation of the supermassive black holes is more complex. Maybe they were seeded by black holes from very massive stars, or maybe gas clouds just collapsed on themselves under gravitational forces.
But since all the way back in 1966, researchers have suggested the possibility of a completely different class of black holes. These are the primordial black holes. They formed within the first microseconds after the Big Bang, at a time when the universe was a hot dense plasma of particles.
Now making a black hole back then was not extremely difficult. The universe experienced a period of extraordinary expansion called cosmic inflation. And even right after, the universe was still hot enough for a black hole to form. You just need a difference in the density of a region of the universe of 10 percent for the collapse to form and the black hole to pop into existence.
Given that you don’t need stellar conditions, it is possible to create much smaller black holes than what you get with supernovae. In fact, you could get primordial black holes with the mass of an asteroid compressed into the size of a molecule. Such an object could be in the Solar System right now. These objects could either be like a parasite, falling into stars and beginning to eat them from the inside, or they might also be the seed of all supermassive black holes, including the one at the center of the Milky Way.
Primordial black holes remain completely theoretical and this is why Roman’s observations could be revolutionary. This work won’t require any unplanned observations. The telescope will look for rogue planets, planets that float freely in space unbound from the stars from which they formed, and that quest might reveal the existence of primordial black holes over time. The telescope could find a large number of them.
“There’s no way to tell between Earth-mass black holes and rogue planets on a case-by-case basis,” lead author William DeRocco, a postdoctoral researcher at the University of California Santa Cruz, said in a statement. “Roman will be extremely powerful in differentiating between the two statistically.”
“This is an exciting example of something extra scientists could do with data Roman is already going to get as it searches for planets,” added Kailash Sahu, an astronomer at the Space Telescope Science Institute in Baltimore, who was not involved in the study. “And the results are interesting whether or not scientists find evidence that Earth-mass black holes exist. It would strengthen our understanding of the universe in either case.”
The study is published in the journal Physical Review D.
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