September 30, 2022

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Powerful radio pulses originate deep in the universe’s probe material hidden around galaxies

Fast Radio Bursts Piercing Gaseous Halos Around Galaxies

This artist’s concept shows fast, distant radio bursts penetrating gaseous halos around galaxies in the local universe. The radio bursts were photographed traveling from the distant universe, through galactic halos, and finally reaching telescopes on Earth. The bumps seen in two of the lines represent the radio burst as it travels toward Earth. Credit: Courtesy of Charles Carter

Powerful cosmic radio pulses originating in the depths of the universe can be used to study hidden pools of gas in nearby galaxies, according to a new study published last month in the journal. natural astronomy.

What’s called fast radio blasts, or FRBs, are pulses of radio waves that usually originate from millions to billions of light years away. (Radio waves are electromagnetic radiation like the light we see with our eyes but have longer wavelengths and lower frequencies.) The first FRB was discovered in 2007, and since then, hundreds more have been discovered. In 2020, the California Institute of Technology’s STARE2 instrument (Survey of Transient Astronomy Radio Emissions 2) and Canada’s CHIME (Canadian Hydrogen Intensity Mapping Experiment) Massive FRB Discovered In Our Milky Way Galaxy. These previous findings helped confirm the theory that energetic events most likely originate from dead magnetars called magnetars.

As more and more FRBs enter, scientists are now looking into how they can be used to study the gas between us and the eruptions. Specifically, they would like to use FRBs to probe the diffuse halos of gas that surround galaxies. As the radio pulses travel toward Earth, the gas enveloping the galaxies is expected to slow the waves and scatter the radio frequencies. In the new study, the research team looked at a sample of 474 remote FRBs detected by CHIME, which has detected the most FRBs to date. They showed that the subset of twenty FRBs that passed through the galactic halos actually slowed down more than the non-crossing FRBs.

“Our study shows that FRBs can serve as skewers for all material between radio telescopes and a radio wave source,” says lead author Liam Connor, a Tolman postdoctoral researcher in astronomy, who works with an assistant professor of astronomy and a co-author on the study, Vikram Ravi.

“We used fast radio bursts to shine light through the halos of galaxies near[{” attribute=””>Milky Way and measure their hidden material,” Connor says.

The study also reports finding more matter around the galaxies than expected. Specifically, about twice as much gas was found as theoretical models predicted.

All galaxies are surrounded and fed by massive pools of gas out of which they were born. However, the gas is very thin and hard to detect. “These gaseous reservoirs are enormous. If the human eye could see the spherical halo that surrounds the nearby Andromeda galaxy, the halo would appear one thousand times larger than the moon in area,” Connor says.

Researchers have developed different techniques to study these hidden halos. For example, Caltech professor of physics Christopher Martin and his team developed an instrument at the W. M. Keck Observatory called the Keck Cosmic Webb Imager (KCWI) that can probe the filaments of gas that stream into galaxies from the halos.

This new FRB method allows astronomers to measure the total amount of material in the halos. This can be used to help piece together a picture of how galaxies grow and evolve over cosmic time.

“This is just the start,” says Ravi. “As we discover more FRBs, our techniques can be applied to study individual halos of different sizes and in different environments, addressing the unsolved problem of how matter is distributed in the universe.”

In the future, the FRB discoveries are expected to continue streaming in. Caltech’s 110-dish Deep Synoptic Array, or DSA-110, has already detected several FRBs and identified their host galaxies. Funded by the National Science Foundation (NSF), this project is located at Caltech’s Owen Valley Radio Observatory near Bishop, California. In the coming years, Caltech researchers have plans to build an even bigger array, the DSA-2000, which will include 2,000 dishes and be the most powerful radio observatory ever built. The DSA-2000, currently being designed with funding from Schmidt Futures and the NSF, will detect and identify the source of thousands of FRBs per year.

Reference: “The observed impact of galaxy halo gas on fast radio bursts” by Liam Connor and Vikram Ravi, 4 July 2022, Nature Astronomy.
DOI: 10.1038/s41550-022-01719-7

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