Radio Flashes from Deep Space Provide Caltech Scientists a New Way to Map the Universe

Intense, brief flashes of radio light that travel across billions of light-years to reach Earth can be used to measure how ordinary matter is spread through the universe, according to a new study that researchers say could help solve some of the biggest questions in cosmology.

The study, published in the journal Nature Astronomy, analyzed a sample of about 100 of the flashes, known as fast radio bursts, or FRBs. It is the first to directly measure the impact of galactic feedback — the gas and energy that galaxies push out into space — on clumpy matter in the large-scale regions around and between galaxies.

The measurement matters because feedback processes inside galaxies have been muddying researchers’ ability to precisely measure the cosmological effects they are actually trying to study: dark matter, dark energy and the mass of neutrinos.

“We’ve established that FRBs are a leading probe of the distribution of matter in the universe,” said Kritti Sharma, lead author of the new study and a graduate student who works with Vikram Ravi, a professor of astronomy at Caltech and a coauthor of the paper. “These FRB data can be used to enhance cosmology experiments that are trying to answer questions about dark matter, dark energy, and the mass of neutrinos.”

How a radio flash becomes a measuring stick

Fast radio bursts travel across billions of light-years to reach Earth, passing through a fog of matter along the way. Their origins are unclear, but they are thought to possibly come from highly magnetized dead stars called magnetars.

The key is what happens to the signal in transit. The denser the fog the bursts travel through, the more their signals become dispersed — similar to the way a prism splits white light into a rainbow of colors.

Thanks to that dispersing trait, the bursts make excellent tracers of how ordinary matter is distributed in the universe. Ordinary matter is the same stuff that makes up people, planets and stars, and anything made of subatomic particles called baryons. As the radio beams pass through that matter, they can essentially map out how much is present and how clumpy it is.

Untangling the galaxies from the cosmos

Many questions persist about the nature of dark energy, a repulsive force or substance that is causing the universe to fly apart at increasing speeds, and about dark matter, a substance that far outweighs matter in the universe but cannot be seen.

Mysteries about neutrinos also endure. The ghostly particles pass freely through ordinary matter, and their mass remains unmeasured — a figure that could help reveal how large-scale galactic structures in the universe formed.

Dark energy, dark matter and neutrinos are all predicted to influence how matter clumps together, so scientists use sky surveys to map that clumping and gain clues to the nature of these cosmological phenomena. The problem is that feedback processes inside galaxies can also affect how smooth or clumpy matter is, muddying the researchers’ ability to precisely measure the cosmological effects.

All galaxies harbor supermassive black holes at their centers, which voraciously feed on nearby matter while also ejecting winds of hot, ionized — or charged — gas into their surroundings. Exploding stars can also expel energy into the galactic neighborhoods. This feedback has a role in smoothing out the material outside the galaxies, making it less clumpy.

“The feedback process thins the gas around the galaxies, redistributing matter across vast distances. It smooths out clumps of matter in a way that looks astonishingly similar to what massive neutrinos do, or what dark energy or dark matter theories predict,” Ravi said. “Unless scientists can independently measure this contribution from feedback, they can’t tell these effects apart.”

What the bursts showed

The results show that galactic feedback does indeed smooth surrounding material, making it less clumpy. But it does so less than what has been measured previously by state-of-the-art surveys, including the eROSITA X-ray telescope and the former microwave-based Atacama Cosmology Telescope in Chile, which ended in 2022.

“Our analysis of FRBs reveals how gas ejected by astrophysical feedback suppresses cosmic structure, delivering constraints competitive with X-ray and microwave surveys,” said coauthor Elisabeth Krause, a professor of astronomy and physics at the University of Arizona. “This is amazing considering we only had about 100 FRBs in our sample. It’s only the beginning.”

Tens of thousands more on the way

Caltech’s Deep Synoptic Array, or DSA, a powerful radio telescope scheduled to be built by 2029 in a remote valley in Nevada, is expected to find tens of thousands of fast radio bursts, vastly enhancing the cosmic events’ power to improve cosmology measurements.

Data from the DSA, which is funded by Schmidt Sciences, will work synergistically with several cosmology experiments. They include the European Euclid mission, in which NASA’s Jet Propulsion Laboratory and Caltech’s IPAC astronomy center play key roles; the Dark Energy Spectroscopic Instrument, or DESI, in Arizona; the Vera Rubin Observatory in Chile; and NASA’s newly launched Nancy Grace Roman Telescope, in which JPL and IPAC also play roles.

Caltech manages JPL for NASA.

“The DSA will be a game changer for the field,” said Ravi, who is the co-principal investigator on the DSA project.