The upcoming Roman Space Telescope may discover a new kind of “ultralight” black hole that challenges existing theories of black hole formation. The discovery of an Earth-mass black hole could have important implications for our knowledge of the early universe and the nature of dark matter. Photo courtesy of NASA’s Goddard Space Flight Center.
National Aeronautics and Space Administration (NASA)Nancy Grace Roman Space Telescope A previously undiscovered “ultracompact” black hole with a mass similar to that of Earth may be discovered. These primordial black holes, which formed in the early universe, could explain some of the dark matter in the universe and have major implications for our understanding of astronomy and particle physics.
Astronomers have discovered black holes ranging in mass from a few times the sun to tens of billions of times the mass of the sun, and now a group of scientists predicts that NASA’s Nancy Grace Roman Space Telescope may discover a previously unseen “ultralight” black hole.
Currently, black holes form when massive stars collapse or heavy objects merge, but scientists think that smaller, “primordial” black holes, including some with masses similar to Earth, may have formed in the first chaotic moments of the early universe.
“The discovery of Earth-mass primordial black holes would be an astonishing step for both astronomy and particle physics, because these objects cannot form through any known physical process,” said William DeRocco, a postdoctoral researcher at the University of California, Santa Cruz, who led the study of how Roman could find them. A paper describing the results Published in the journal Physics Review D“If discovered, it would have a major impact on the field of theoretical physics.”
![NASA Roman Space Telescope art illustration](https://scitechdaily.com/images/NASA-Roman-Space-Telescope-Art-Illustration-777x518.jpg)
Discovery of an Earth-mass primordial black hole by NASA’s Roman Space Telescope could transform our understanding of the universe and dark matter. Photo courtesy of NASA’s Goddard Space Flight Center
Recipe for a primordial black hole
The tiniest black holes that form today are born when a massive star runs out of fuel. As nuclear fusion fades, the outward pressure weakens and the inward gravity wins the tug of war. The star contracts, becomes too dense, and collapses. Black Hole.
But the minimum mass required is at least eight times that of the Sun: any star less than that would become a white dwarf or a neutron star.
But in the early universe, much lighter black holes could have formed: for a black hole with a mass similar to that of Earth, the event horizon (the point of no return) would be roughly the width of a US dime.
Scientists believe that very early in the universe, space expanded faster than the speed of light during a brief but violent phase known as inflation. During this unique period, a denser region could have collapsed to form a low-mass primordial black hole.
Theory predicts that the smallest of these would evaporate before the universe reached its current age, but some with masses similar to Earth’s may have survived.
The discovery of these tiny objects will have a huge impact on physics and astronomy.
“It will have implications on everything from galaxy formation to the dark matter content of the universe to the history of the universe,” says Kailash Sahu, an astronomer at the Space Telescope Science Institute in Baltimore, who was not involved in the study. “It will be a lot of work to confirm what it is, and it will take a lot of time to convince astronomers, but it will be well worth it.”
![Primordial black hole lifespan infographic](https://scitechdaily.com/images/Primordial-Black-Hole-Lifetimes-Infographic-777x437.jpg)
Stephen Hawking theorized that black holes slowly get smaller as radiation escapes them. This slow leakage, now known as Hawking radiation, causes the black hole to evaporate over time. This infographic shows the estimated lifetimes and event horizon (the point at which no escape from the black hole’s gravity) diameters of black holes of various small masses. Credit: NASA Goddard Space Flight Center
Hidden Pioneer Tips
Observations have already revealed clues that such objects may be lurking within our galaxy: primordial black holes are invisible, but wrinkles in space-time have helped to identify some possible objects.
Microlensing is an observational effect that occurs because the fabric of space-time is distorted by the presence of mass, similar to the mark left by a bowling ball on a trampoline. Whenever, from our perspective, an intervening object appears to be drifting close to a background star, the starlight must traverse the warped space-time around the object. If particularly close, the object acts like a natural lens, concentrating and amplifying the light of the background star.
Separate groups of astronomers used data from MOA (Microlensing Observations in Astrophysics) and OGLE (Optical Gravitational Lensing Experiment), which are microlensing observations at the Mount John University Observatory in New Zealand. An unexpectedly large population of isolated Earth-mass objects.
Theories of planetary formation and evolution predict a certain amount of mass and abundance for planets that are not bound to stars and that roam the galaxy, and the MOA and OGLE observations suggest that there are many more Earth-mass objects floating around in the galaxy than models predict.
This artist’s concept takes a fanciful approach to imagining a tiny primordial black hole. In reality, such a small black hole would have a hard time forming the accretion disk we see here. Credit: NASA Goddard Space Flight Center
“There’s no way to distinguish between Earth-mass black holes and rogue planets on a case-by-case basis,” DeRocco says. But scientists expect Roman to find 10 times more objects in this mass range than ground-based telescopes. “It’s going to be extremely powerful at statistically distinguishing between the two.”
DeRocco led the effort to determine how many rogue planets exist in that mass range, and how many of them might be primordial black holes that Roman could identify.
The discovery of primordial black holes would reveal new information about the very early universe, strongly suggesting that early inflation did occur, and could explain a tiny fraction of the mysterious dark matter that scientists say makes up most of the universe’s mass but has so far not been able to identify.
“This is an exciting example of what scientists can do with the data Roman is already getting in its search for planets,” Sahu said. “The results will be fascinating whether or not scientists find evidence of the existence of Earth-mass black holes. Either way, they should improve our understanding of the universe.”
References: William DeRocco, Evan Frangipane, Nick Hammer, Stefano Profumo, and Nolan Smith, “Nancy Grace Roman Space Telescope Reveals Earth-Mass Primordial Black Hole,” January 8, 2024; Physics Review D.
DOI: 10.1103/PhysRevD.109.023013
The Nancy Grace Roman Space Telescope is managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with participation from a science team consisting of scientists from NASA’s Jet Propulsion Laboratory and Caltech/IPAC in Southern California, the Space Telescope Science Institute in Baltimore, and various research institutions. Key industrial partners are BAE Systems, Inc. in Boulder, Colorado, L3Harris Technologies in Rochester, New York, and Teledyne Scientific & Imaging in Thousand Oaks, California.