What is a primordial black hole made of?

A primordial black hole, surrounded by sheets of gas, dust, and stars (artist's impression).

Image courtesy NASA/ESA/ESO

Primordial black hole could be made of dark matter.

(PhysOrg.com) -- “We know that about 25% of the matter in the universe is dark matter, but we don’t know what it is,” Michael Kesden tells PhysOrg.com. “There are a number of different theories about what dark matter could be, but we think one alternative might be very small primordial black holes.”

When many of us think about black holes, we think of a huge cosmic event, sucking in everything around it. However, there is also the possibility of small black holes. “Einstein’s theory of relativity allows for black holes,” Kesden, a theoretical physicist at New York University, explains, “but doesn’t stipulate a size. It’s very possible that the early universe produced very small black holes. These would gravitate like massive black holes, floating through the universe and clustering.”

Kesden worked with Shravan Hanasoge, from Princeton University and the Max Planck Institute for Solar System Research, to work out method of using solar oscillations to determine whether a small, primordial black hole passed through a star. If the data can show that these small black holes formed near the beginning of the universe do exist, they might make good candidates for dark matter. Their work can be seen in Physical Review Letters: “Transient Solar Oscillations Driven by Primordial Black Holes.”

“Our approach is to consider what happens if you have dark matter made of primordial black holes passing through the sun,” Kesden says. “It’s been thought of before, but no one has actually done the calculations that we have.”

Kesden explains that the sun creates energy from the nuclear fusion at its center: “There is a balance between the outward pressure gradient due to the energy released by fusion and the inward force of gravity. If the sun, or any star, is perturbed it would shake a little.”

“A small, primordial black hole would be the size of an atom but have the mass of an asteroid,” he points out...Keep on reading