With discoveries in cosmology so often couched in mind-boggling timeframes reaching millions and billions of years into the past, it's jarring to think of scientists in the field feting a millisecond phenomenon first observed less than 20 years ago.
And yet, that's exactly what happened today, when the International Center for Relativistic Astrophysics Network (ICRAN) presented its Marcel Grossmann Award to a team of more than 60 scientists for their "innovative detection and comprehensive analysis of a large population of fast radio bursts."
The team includes Physical & Biological Sciences Dean Bryan Gaensler and J. Xavier Prochaska, both professors of astronomy and astrophysics at UC Santa Cruz, as well as several current and former Ph.D. students and a project scientist on staff. They belong to a collaboration using a revolutionary interferometric radio telescope that's over 60 feet wide, and nearly the length of a U.S. football field.
It's called the Canadian Hydrogen Intensity Mapping Experiment (CHIME), and since the first observations in 2018, the FRB team has made several landmark discoveries advancing our understanding of these fleeting extragalactic pulses. The CHIME/FRB project is led by Victoria Kaspi, a physics professor at McGill University who was named to Nature's 2019 list of 10 "people who mattered" in science.
But, just what are fast radio bursts, and why should we care about yet another puzzle presented by our vast universe? We asked Gaensler, Prochaska, and Lordrick Kahinga–an astronomy and astrophysics Ph.D. student at UC Santa Cruz—to break down the mysterious FRB and its fascination among scientists.
Could you please unpack the meaning behind the term “fast radio bursts?”
Gaensler: Fast radio bursts are sudden flashes of radio waves coming from random parts of the sky. Each one is on only for a few milliseconds, but they are extraordinarily bright: In those few milliseconds, they put out more energy than our sun does in an entire year. We also know that they come from objects in distant galaxies, sometimes billions of light years away.
We see a random FRB happening in the sky every minute or two. They are a very frequent and common phenomenon, and we had no idea they were happening until we first found one in 2007.
Among the many cosmic mysteries out there, why are FRBs especially interesting to astronomers and astrophysicist?
Gaensler: FRBs are unbelievably energetic, and so represent extreme conditions of temperature, density, energy, and magnetism—far beyond what we could ever produce in an earthly laboratory. So by studying FRBs, we learn about the properties of matter and physics in a way that we could never otherwise study.
Also, FRB signals are so bright that they “light up” all the material around and in front of them. We thus can use them to probe otherwise invisible gas throughout the universe, at a whole range of distances.
Why is it important to understand the origins of FRBs?
Prochaska: FRBs are a true enigma, with over 50 theories proposed to explain their origin. Indeed, their origin poses one of the current, great mysteries of astronomy. Their very short duration demands that their “progenitors” be small, less than the size of our own Sun, but besides this inference little else is known.
How do they help enable mapping of the universe’s structure and composition?
Prochaska: Encoded in the FRB signal is what astronomers call the “dispersion measure” or DM. This DM value provides a direct measurement of the total number of electrons and therefore ordinary matter that lies between us and the FRB. By discovering FRBs—and measuring their DM—across the sky, we can resolve the total amount and distribution of the matter making up our Periodic Table.
How do we know about the extreme power of FRBs, the incredible distances they travel, and that they bombard Earth about once a minute from all directions?
Kahinga: Astronomers measure the energy of an FRB using its brightness and how far away it is from the Earth. If you can see a light bulb from billions of light-years away, it must be very bright. Once an FRB is detected, astronomers use optical telescopes—like our Shane Telescope at Lick Observatory—to observe the host galaxy and use spectroscopy to estimate the distance. We routinely measure host galaxy distances as a billion light-years away and sometimes much farther.
Regarding the third part of the question, CHIME observes the strip of the sky directly above it and sweeps over about 75% of the sky daily. Using the FRB detection rate of CHIME, which is about 1 FRB per day, the instrument limitations, and the recorded detection rates from other telescopes, astronomers infer that every minute, there is an FRB event somewhere in the sky.
Why do some FRBs repeat while others don’t?
Kahinga: Briefly, we don’t know. This is one of the many fascinating things about FRBs. It is important to note that only a small fraction, about 3% of FRBs, have been observed to repeat. The majority of these repeat sporadically, while a handful are observed to have periodic windows of activity.
This raises some interesting questions: Do all FRBs repeat? Will the one-offs we have observed repeat after some unknown durations? Are repeating FRBs a distinct population from the non-repeating FRBs, and are they produced by different mechanisms?
Kaspi attended ICRAN's 2024 Marcel Grossmann meeting in Pescara, Italy, to receive the award on behalf of the collaboration.
