Cosmic radio pulses probe hidden matter around galaxies

Powerful radio pulses that travel deep into the cosmos could be used to study hidden pools of gas that reside in nearby galaxies, according to a new study appearing in the journal Nature Astronomy.

So-called fast radio bursts, or FRBs, are pulses of radio waves that are typically 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 frequencies). The first FRB was discovered in 2007 and hundreds more have been found since then. In 2020, Caltech’s STARE2 instrument (Survey for Transient Astronomical Radio Emission 2) and Canada’s CHIME (Canadian Hydrogen Intensity Mapping Experiment) discovered a huge FRB that went off in our own Milky Way galaxy† Those earlier results helped confirm the theory that the energetic events most likely originated from dead, magnetized stars called magnetars.

As more and more FRBs come in, researchers are wondering how they could be used to study the gas that lies between us and the bursts. In particular, they would like to use the FRBs to investigate halos of diffuse gas around 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 researchers looked at a sample of 474 distant FRBs detected by CHIME, which is the most FRBs detected to date, and showed that the subset of two dozen FRBs passing through galactic halos were indeed more delayed than not. – intersecting FRBs.

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

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

The study also reports that more matter has been found around the galaxies than expected, about twice as much gas as theoretical models predicted.

All galaxies are surrounded and fed by huge pools of gas from which they were born. However, the gas is very thin and difficult to detect. “These gas reservoirs are huge. If the human eye could see the globular halo that surrounds the nearby Andromeda galaxy, the halo would appear a thousand times larger than the moon,” says Connor.

Researchers have developed several techniques to study the hidden halos. For example, Caltech physics professor Christopher Martin and his team developed an instrument at the WM Keck Observatory, the Keck Cosmic Webb Imager (KCWI), that can exploring the filaments of gas flowing to galaxies from the halos.

This new FRB method will allow astronomers to measure the total amount of material in the halos, which will help build a picture of how galaxies grow and evolve over cosmic time.

“This is just the beginning,” Ravi says. “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.”

Going forward, FRB discoveries are expected to continue rolling in. Caltech’s 110-dish Deep Synoptic Array, or DSA-110, has already detected several FRBs and identified their host systems. 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 larger array, the DSA-2000, which will hold 2,000 dishes and be the most powerful radio observatory ever. 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.

The Nature Astronomy is titled “The Observed Impact of Halogas on Fast Radio Bursts.”

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