This artist’s concept depicts distant, fast-moving radio bursts penetrating the gaseous halos around galaxies in the local universe. The radio bursts are shown traveling from the distant cosmos through the galactic halos and eventually reaching telescopes on Earth. The bumps seen in two of the lines represent the radio burst itself as it approaches earth. Photo credit: Courtesy of Charles Carter
Powerful cosmic radio pulses originating deep in the Universe can be used to probe hidden gas pools cocooning nearby galaxies, according to a new study published in the Journal last month natural astronomy.
Fast radio bursts, or FRBs, are pulses of radio waves that typically originate 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 hundreds more have been discovered since then. In 2020, Caltech’s STARE2 (Survey for Transient Astronomical Radio Emission 2) instrument and Canada’s CHIME (Canadian Hydrogen Intensity Mapping Experiment) discovered a massive FRB going off in our own Milky Way. These earlier results helped confirm the theory that the energetic events most likely originated from dead, magnetized stars called magnetars.
As more FRBs roll in, scientists are now studying how they can be used to study the gas that lies between us and the blasts. In particular, they plan to use the FRBs to study halos of diffuse gas surrounding galaxies. As the radio pulses propagate 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 examined a sample of 474 distant FRBs detected by CHIME, which has detected the most FRBs to date. They showed that the subset of two dozen FRBs that passed galactic halos were actually slowed down more than non-overlapping FRBs.
“Our study shows that FRBs can act as skewers of all matter between our radio telescopes and the source of the radio waves,” says lead author Liam Connor, the Tolman Postdoctoral Scholar Research Associate in Astronomy, who works with the assistant professor of astronomy and is a co-author of the Study, Vikram Ravi.
“We used fast radio bursts to cast a light through the halos of nearby galaxies
” data-gt-translate-attributes=”[{” 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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