Primordial Black Holes

  • Released Tuesday, May 7, 2024
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This artist's concept takes a fanciful approach to imagining small primordial black holes. In reality, such tiny black holes would have a difficult time forming the accretion disks that make them visible here.Credit: NASA's Goddard Space Flight Center

This artist's concept takes a fanciful approach to imagining small primordial black holes. In reality, such tiny black holes would have a difficult time forming the accretion disks that make them visible here.

Credit: NASA's Goddard Space Flight Center

Astronomers have discovered black holes ranging from a few times the Sun’s mass to tens of billions. Now a group of scientists has predicted that NASA’s Nancy Grace Roman Space Telescope could find a class of “featherweight” black holes that has so far eluded detection.

Today, black holes form either when a massive star collapses or when heavy objects merge. However, scientists suspect that smaller “primordial” black holes, including some with masses similar to Earth’s, could have formed in the first chaotic moments of the early universe.

The smallest black holes that form nowadays are born when a massive star runs out of fuel. Its outward pressure wanes as nuclear fusion dies down, so inward gravitational pull wins the tug-of-war. The star contracts and may get so dense it becomes a black hole.

But there’s a minimum mass required: at least eight times that of our Sun. Lighter stars will either become white dwarfs or neutron stars.

Conditions in the very early universe, however, may have allowed far lighter black holes to form. One weighing the mass of Earth would have an event horizon –– the point of no return for infalling objects –– about as wide as a U.S. dime coin.

Just as the universe was being born, scientists think it experienced a brief but intense phase known as inflation when space expanded faster than the speed of light. In these special conditions, areas that were denser than their surroundings may have collapsed to form low-mass primordial black holes.

While theory predicts the smallest ones should evaporate before the universe has reached its current age, those with masses similar to Earth could have survived.

Animated version of the above.

Credit: NASA's Goddard Space Flight Center

This artist's concept takes a fanciful approach to imagining small primordial black holes. In reality, such tiny black holes would have a difficult time forming the accretion disks that make them visible here. Brief, animated GIF.Credit: NASA's Goddard Space Flight Center

This artist's concept takes a fanciful approach to imagining small primordial black holes. In reality, such tiny black holes would have a difficult time forming the accretion disks that make them visible here. Brief, animated GIF.

Credit: NASA's Goddard Space Flight Center

Stephen Hawking theorized that black holes can slowly shrink as radiation escapes. The slow leak of what’s now known as Hawking radiation would, over time, cause the black hole to simply evaporate. This infographic shows the estimated lifetimes and event horizon –– the point past which infalling objects can’t escape a black hole’s gravitational grip –– diameters for black holes of various small masses.

Credit: NASA's Goddard Space Flight Center

For More Information

See https://www.nasa.gov/missions/roman-space-telescope/how-nasas-roman-mission-will-hunt-for-primordial-black-holes/

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NASA's Goddard Space Flight Center. However, individual items should be credited as indicated above.

This page was originally published on Tuesday, May 7, 2024.
This page was last updated on Tuesday, May 7, 2024 at 9:23 AM EDT.

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