The upcoming Roman space telescope could reveal a new class of ‘feather-light’ black holes, challenging existing theories of black hole formation. If these Earth-sized black holes are found, they could have significant implications for our knowledge of the early universe and the nature of dark matter. Credit: NASA’s Goddard Space Flight Center
NASAby Nancy Grace Roman space telescope could reveal previously unnoticed “feather-light” black holes with masses similar to Earth’s. These primordial black holes, formed in the early universe, could have a significant impact on our understanding of astronomy and particle physics, and could potentially explain some of the dark matter in the universe.
Astronomers have discovered black holes ranging from a few times the mass of the Sun to tens of billions. Now a group of scientists have predicted that NASA’s Nancy Grace Roman Space Telescope could find a class of ‘feather-light’ black holes that have so far escaped detection.
Today, black holes are formed when a massive star collapses or when massive objects merge. However, scientists suspect that smaller “primordial” black holes, including some with masses similar to Earth’s, could have formed during the first chaotic moments of the early universe.
“Detecting a population of primordial Earth-mass black holes would be an incredible step for both astronomy and particle physics, because these objects cannot be formed by any known physical process,” said William DeRocco, a postdoctoral researcher at the University of California Santa. Cruz who led an investigation into how Roman could expose them. An article describing the results has been published in the journal Physical examination D. “If we find them, it will shake up the field of theoretical physics.”
Discovering pristine Earth-mass black holes with NASA’s Roman Space Telescope could transform our understanding of the universe and dark matter. Credit: NASA’s Goddard Space Flight Center
Primordial Black Hole Recipe
The smallest black holes that form today are formed when a massive star runs out of fuel. The external pressure decreases as the fusion decreases, so that the inner gravity wins the tug-of-war. The star contracts and can become so compact that it becomes a black hole.
But a minimum mass is required: at least eight times that of our Sun. Lighter stars will become white dwarfs or neutron stars.
However, conditions in the very early universe may have created much lighter black holes. One that weighs the mass of the Earth would have an event horizon – the point of no return for falling objects – about the width of an American dime.
Just as the universe was born, scientists think it went through a brief but intense phase known as inflation, when space expanded faster than the speed of light. Under these special circumstances, regions more dense than their surroundings may have collapsed, creating primordial low-mass black holes.
Although theory predicts that the smallest particles should evaporate before the universe reaches its current age, those with masses similar to Earth’s could have survived.
Discovering these small objects would have a huge impact on physics and astronomy.
“It would affect everything from the formation of galaxies to the amount of dark matter in the universe and cosmic history,” said Kailash Sahu, an astronomer at the Space Telescope Science Institute in Baltimore who was not involved in the study . “Confirming their identity will be hard work and require a lot of convincing for astronomers, but it would be worth it.”
Stephen Hawking theorized that black holes can slowly shrink as radiation escapes. The slow leak of what is now known as Hawking radiation would, over time, simply cause the black hole to evaporate. This infographic shows the estimated lifetime and event horizon –– the point past which falling objects cannot escape a black hole’s gravity –– diameters for black holes of different small masses. Credit: NASA’s Goddard Space Flight Center
Hints of Hidden Homesteaders
Observations have already provided clues that such objects may be lurking in our Milky Way. Primordial black holes are said to be invisible, but ripples in space-time have helped identify a number of possible suspects.
Microlensing is an observational effect that occurs because the presence of mass distorts the fabric of space-time, such as the imprint a bowling ball makes when placed on a trampoline. Whenever an intermediate object appears to drift near a background star from our vantage point, light from the star must traverse the warped space-time around the object. If the alignment is particularly close, the object can act as a natural lens, focusing and amplifying the light from the background star.
Separate groups of astronomers using data from MOA (Microlensing Observations in Astrophysics) – a collaboration making microlensing observations using New Zealand’s Mount John University Observatory –– and OGLE (the Optical Gravitational Lensing Experiment) have an unexpectedly large population isolated earth found -mass objects.
Planet formation and evolution theories predict certain masses and abundances of rogue planets – worlds that roam the Milky Way, detached from a star. The MOA and OGLE observations suggest that there are more Earth-mass objects floating through the Milky Way than models predict.
This artist’s concept takes a fanciful approach to imagining small primordial black holes. In reality, such small black holes would have difficulty forming the accretion disks they reveal here. Credit: NASA’s Goddard Space Flight Center
“There is no way to distinguish between Earth-mass black holes and rogue planets on a case-by-case basis,” DeRocco says. But scientists expect Roman will find ten times as many objects in this mass range as ground-based telescopes. “Roman will be extremely powerful in statistically distinguishing between the two.”
DeRocco led an effort to determine how many rogue planets should be in that mass range, and how many primordial black holes Roman could distinguish among them.
Finding primordial black holes would reveal new information about the very early universe, and would strongly indicate that an early period of inflation did indeed occur. It could also explain a small percentage of the mysterious dark matter that scientists say makes up most of the mass of our universe but has so far been unable to identify.
“This is an exciting example of something that scientists could do in addition to the data Roman is already getting from his search for planets,” says Sahu. “And the results are interesting regardless of whether scientists find evidence that Earth-mass black holes exist. In either case, it would strengthen our understanding of the universe.”
Reference: “Revealing pristine Earth-mass black holes with the Nancy Grace Roman Space Telescope” by William DeRocco, Evan Frangipane, Nick Hamer, Stefano Profumo and Nolan Smyth, January 8, 2024, Physical examination D.
DOI: 10.1103/PhysRevD.109.023013
The Nancy Grace Roman Space Telescope is operated at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with participation from NASA’s Jet Propulsion Laboratory and Caltech/IPAC in Southern California, the Space Telescope Science Institute in Baltimore, and a science team consisting from scientists from different countries. 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.