Fast Radio Bursts Emerge as a New Tool to Probe the Universe's Dark Side

Fast radio bursts (FRBs) — brief, intense blasts of radio waves thought to erupt from magnetars, the rapidly rotating dead stars with the universe's strongest magnetic fields — are emerging as a powerful tool for probing some of the biggest mysteries in cosmology. As FRBs travel billions of light-years to reach Earth, they pass through clouds of gas and dust in galaxies, which subtly change the signal in ways that carry a fingerprint of how matter is distributed across the universe.

A team led by Kritti Sharma, a graduate student working with Caltech astronomy professor Vikram Ravi, analyzed a sample of about 100 FRBs — the first time scientists have used FRBs to directly measure the effect that "feedback" from galaxies, such as energy pumped out by feeding supermassive black holes, has on the clumpiness of matter in the vast regions between galaxies. "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," Sharma said.

Ordinary matter — the atoms that make up stars, planets and everything visible — accounts for only about 5% of the universe's total energy and matter budget; the rest is dark energy (68%) and dark matter (27%). Neutrinos, nicknamed "ghost particles" because roughly 100 trillion pass through a human body every second without leaving a trace, add further complexity. Because feedback from black holes smooths cosmic clumpiness in ways that can look similar to the effects of dark energy, dark matter or massive neutrinos, scientists need to measure it separately to tell these influences apart.

The team found that galactic feedback does smooth surrounding matter, but the effect is weaker than previously measured. "Our analysis of FRBs reveals how gas ejected by astrophysical feedback suppresses cosmic structure. This is amazing considering we only had about 100 FRBs in our sample. It's only the beginning," said co-author Elisabeth Krause of the University of Arizona. The research, published in the journal Nature Astronomy, could get a major boost in 2029, when Caltech's Deep Synoptic Array begins operating in Nevada and is expected to find tens of thousands of FRBs.