Powerful radio pulses that originate in the depths of the cosmos. Hidden matter around galaxies

Fast Radio Bursts Piercing Gaseous Halos Around Galaxies

This artist’s concept shows fast, distant radio bursts cutting through the gaseous halos around galaxies in the local universe. Radio bursts are depicted traveling from the distant cosmos, through galactic halos and finally reaching telescopes on Earth. The bumps seen in two of the lines represent the radio burst as they travel to Earth. Credit: Courtesy of Charles Carter

Powerful cosmic radio pulses that originate deep in the universe can be used to study the hidden pools of gas that encapsulate nearby galaxies, according to a new study published last month in the journal Science. Astronomy of nature.

So-called 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 detected since then. In 2020, Caltech’s STARE2 instrument (Survey for Transient Astronomical Radio Emission 2) and Canada’s CHIME (Canadian Hydrogen Intensity Mapping Experiment) detected a massive FRB that went off in our own Milky Way galaxy. These earlier findings helped confirm the theory that energetic events likely originate from dead, magnetized stars called magnetars.

As more and more FRBs become available, scientists are now investigating how they can be used to study the gas between us and the flares. Specifically, they would like to use FRBs to investigate haloes of diffuse gas surrounding galaxies. As the radio pulses travel to Earth, the gas surrounding 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 discovered the most FRBs to date. They showed that the subset of two dozen FRBs that passed through galactic haloes slowed down more than FRBs that did not cross.

“Our study shows that FRBs can act as spikes of all the matter between our radio telescopes and the source of the radio waves,” says lead author Liam Connor, Tolman Postdoctoral Scholar Research Associate in Astronomy, who works with assistant professor of astronomy and study co-author Vikram Ravi.

“We used fast radio bursts to shine a light through the halos of nearby galaxies

Milky Way
The Milky Way is the galaxy that contains Earth, and is named after its appearance from Earth. It is a barred spiral galaxy that contains between 100 and 400 billion stars and has a diameter between 150,000 and 200,000 light years.

” 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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