Mysterious fast radio bursts could reveal hidden matter around galaxies

artist's depiction
An artist's illustration of a fast radio burst (Image credit: ESO/M. Kornmesser)

Rapid bursts of radio waves that originate millions to billions of light-years away from Earth could be used as probes to investigate halos of difficult-to-see diffuse gas surrounding nearby galaxies.

New research shows that these pulses called fast radio bursts (FRBs), slow as they pass through the gas enveloping the galaxies between their source and Earth. This also has the effect of dispersing their radio frequencies. 

Using this to investigate galactic gas haloes, researchers from the California Institute of Technology (Caltech) found twice as much material as previously believed in these envelopes that enshroud galaxies. This has implications for how these collections of stars and planets evolve over great periods of time.

Related: Discovery of second repeating fast radio burst raises new questions

The astronomers looked at a sample of 474 distant FRBs with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) confirming that 24 FRBs intercepted by galactic halos were indeed slowed down compared to others that traveled to Earth unimpeded. Thus, this effect can be used to probe the material through which the FRB passes. 

"Our study shows that FRBs can act as skewers of all the matter between our radio telescopes and the source of the radio waves," Tolman Postdoctoral Scholar Research Associate in Astronomy at Caltech, Liam Connor, said in a statement. "We have used fast radio bursts to shine a light through the halos of galaxies near the Milky Way and measure their hidden material."

The use of more distant FRBs from outside our galaxy to investigate the massive pools of gas which surround other galaxies has already revealed a surprise. The astronomers found that there is more matter in gas haloes than previously believed, around twice as much as predicted by theoretical models. 

"These gaseous reservoirs are enormous," Connor said. "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."

Because these gas halos are the remains of the same material that is used to form the stars and planets a deeper investigation of them could lead to a better understanding of how galaxies evolve over periods of billions of years.

Related: Scientists detect strange 'fast radio burst' from within our own Milky Way

An artist's illustration shows the 300,000 light-year wide gas halo that surrounds the Milky Way.   (Image credit: NASA/CXC/M.Weiss; NASA/CXC/Ohio State/A.Gupta et al.)

Though researchers aren't currently certain of the origins of FRBs, first detected in 2007, they believe that these pulses of electromagnetic radiation lasting from a fraction of a millisecond to a few milliseconds are emitted by rapidly rotating magnetic dead stars called magnetars.

Evidence of this connection was provided in 2020 when Caltech's Survey for Transient Astronomical Radio Emission 2 (STARE2) instrument was teamed with CHIME to detect a massive FRB erupting in the Milky Way

Since their discovery in 2007, hundreds of FRBs have been observed and these revelations are expected to continue rolling in thanks, in part, to Caltech's 110-dish Deep Synoptic Array, or DSA-110. 

The project has already identified several FRBs and traced them back to the galaxies from which they originated. Caltech scientists have plans to build an even larger telescope array over coming years which will consist of 2,000 dishes. Named DSA-2000, the project will be the most powerful radio observatory ever built and could detect and identify thousands of FRBs and their sources each year.

"This is just the start," assistant professor of astronomy at Caltech, Vikram Ravi, said. "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."

The team's research was published in the journal Nature Astronomy.

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Robert Lea
Senior Writer

Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.