Astronomers are finally tuning in on the origin of fast radio bursts
In radio astronomy, fast radio bursts (or frbs, for short) are intense, shortlived (lasting between a fraction of a second to a few seconds) radio pulses in association with extremely intense X-ray flares possibly emanating from what is referred to as a magnetar — a type of neutron star, the supermagnetized remnant of a massive star (typically many times more massive than our Sun) that exploded in a supernova at some point in the past. A magnetar possesses the strongest magnetic field of any known celestial object in the cosmos, up to 1,000 times stronger than a typical neutron star.
Although lasting mere milliseconds to seconds in duration, a single flare from a magnetar releases as much energy during that fraction of a second or seconds as our Sun does in an entire year. As a result of this time-scale brevity, plus the fact that many of them may not reappear, frbs are notoriously difficult to pinpoint in relation to a particular source.
THE FIRST FRB
The very first frb was serendipitously discovered by British-american astronomer Duncan R. Lorimer (b. 1969) in 2007, while going through archival pulsar survey data recorded on July 24, 2001, by the Parkes Radio Telescope at the Parkes Observatory in New South Wales, Australia. This frb, now referred to as the Lorimer Burst FRB 010724, lasted only five milliseconds in duration, and was located near the Small Magellanic Cloud, a dwarf companion galaxy to the Large Magellanic Cloud in the southern celestial hemisphere, both of which, in conjunction with the Milky Way Galaxy and several other dwarf galaxies, constitute the Local Group of galaxies.
As noted, the majority of frbs are one-time performers, meaning they do not reappear — at least on a consistent and predictable schedule. Astronomers estimate that only about 20 per cent of frbs are seen more than once; astronomers refer to the ones that do reappear as “repeaters.” The first “repeater” frb, FRB 121102, was discovered in 2012 near a dwarf galaxy approximately 3.6 Bly away. It was determined that this frb operated on a cycle of approximately 157 to 161 days, wherein it would be active for 90 days, before discharging
a millisecond radio burst, and then going dormant for a period of 67-plus days. On Oct. 13, 2021, Chinese astronomers recorded more than 1,600 frbs from this galaxy. In 2019, the first host galaxy associated with a frb, FRB 180924, was identified. Although eight additional repeating frbs were also discovered in 2019, it wasn’t until January 2020 that the precise location source for one of these repeating frbs (only the second repeater discovered) was identified.
FRBS IN OUR GALAXY
Prior to 2020, frbs were only spotted from extragalactic sources (i.e., outside the Milky Way Galaxy). However, on April 27, 2020, the first frb, FRB 200428, from within our galaxy was discovered, On that date, the magnetar SGR 1935+2154 (SGR 1935), located in the constellation of Vulpecula — the Little Fox at an estimated distance of between 14,000 and 41,000 ly, emitted a series of intense, rapidfire X-ray flares, each lasting less than a second. Fortunately, astrophysicists were observing SGR 1935 at this time, and managed to detect the outbursts. As the series of X-ray bursts atypically lasted for several hours, the astrophysicists were able to observe the SGR 1935 magnetar using NASA’S Neil Gehrels Swift Observatory, NASA’S Fermi Gammaray Space Telescope, and NASA’S Neutron star Interior Composition Explorer (NICER) X-ray telescope aboard the international Space Station (ISS).
POWERFUL FRB
Thirteen hours after the X-ray flare was first detected in SGR 1935, the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a large radio telescope located at the Dominion Radio Astrophysical Observatory in British Columbia (yeah, Canada!), in conjunction with the Nasafunded Survey for Transient Astronomical Radio Emission 2 (STARE2) detectors in California and Utah, detected a burst, lasting only 1/1,000th of a second burst, this one at the frequency of radio waves, the first frb from a source within the Milky Way Galaxy. Although thousands of times less bright than any frb previously recorded, FRB 200428 was classified as the most powerful frb discovered to date.
Astrophysicists studying the SGR 1935 bursts theorized that the X-ray burst originated on the magnetar’s surface, while the frbassociated burst most likely occurred close to the magnetar’s magnetic pole. The association of a radio pulse with the X-ray burst from SGR 1935 strongly suggested that this magnetar produced the Milky Way Galaxy’s equivalent of a frb. Interestingly, in October 2022, SGR 1935 produced another radio burst; this one was studied using the NICER X-ray telescope on the ISS, and NASA’S Nuclear Spectroscopic Telescope Array (NUSTARR) before, during, and after the frb occurred.
GLITCHES
Data from the NICER and NUSTARR telescopes showed that this later burst from SGR 1935 occurred between two glitches, when the magnetar suddenly started spinning faster, and then slowing down to less than its pre-glitch spin rate (calculated to be approximately 11,000 kilometres per hour) in just nine hours; it normally takes a magnetar weeks and sometimes months to revert to its normal spin rate, after speeding up and/or slowing down. As any change in a magnetar’s spin rate involves an enormous amount of energy, astrophysicists theorize that the shorter time scale between the glitches in the spin rates of SGR 1935 may have contributed to the production and intensity of the frb, with the magnetar’s powerful magnetic field a contributing factor, as well.
SPIN RATES
It is believed by some astrophysicists that such glitches may be the result of differences in the magnetar’s interior vs. exterior spin rates. One theory postulates that the surface of a magnetar may be solid, overlying a superfluid core (the result of the magnetar’s extreme density), and that, when the two spin rates get out of sync with one another, there might be a sudden shift in the magnetar’s powerful magnetic field, with an excessive amount of energy then being transferred from the interior to the exterior of the magnetar.
This enormous buildup of energy might intensify to the point that it creates a starquake (a stellar earthquake), cracking the magnetar’s solid crust, through which a short-lived, but extremely intense, burst of X-ray and radio wave radiation escapes into the star’s immediate surroundings.
More recently, in the autumn of 2022, FRB 20220912A flared repeatedly for several months, producing thousands of recorded bursts across different frequency ranges. Within a period of 541 hours of observation by the Allen Telescope Array of the SETI (Search for Extraterrestrial Intelligence), a 42-antenna radio telescope array in northern California, 35 frbs were captured by the radio telescopes, covering 1,344 megahertz of radio bandwidth along the electromagnetic spectrum, primarily centered on 1,572 megahertz.
WHAT’S CAUSING ALL THIS?
While the study of FRB 200428 and FRB 20220912A strongly suggests frbs might be generated by magnetars, and that many of the frbs previously observed in other galaxies outside the Milky Way may, likewise, be produced by magnetars, there are other theories as to the origin of frbs.
Some astronomers think that frbs could be the result of possible collisions between merging black holes or neutron stars, while others postulate that frbs might be associated with gamma-ray bursts, energetic supernovae or the dark matter-induced collapse of pulsars. No doubt, as fast radio bursts are studied in greater detail in the future, and as more precise and accurate data is compiled, astronomers and astrophysicists will come to understand how these elusive and enigmatic phenomena are produced, and the role they play in the great celestial drama of our cosmos.
THIS WEEK’S SKY
Mercury (mag. -1.6, in Aquarius — the Waterbearer), Venus (mag. -3.9, in Capricorn — the Sea Goat), and Mars (mag. +1.3, in Capricorn) are all unobservable this week, sitting, respectively, at 4 degrees, 3 degrees, and 1 degree above the southeast horizon at dawn.
Saturn (mag. +1.0, in Aquarius) and Neptune (mag. +8.0, in Pisces — the Fish) are likewise not observable, sitting 4 degrees and 12 degrees from the Sun at dawn, respectively.
Jupiter (mag. -2.2, in Aries — the Ram) becomes visible around 6:20 p.m., 46 degrees above the southwest horizon as dusk yields to darkness, before sinking toward the horizon, and setting shortly after 11 p.m.
Uranus (mag. +5.8, in Aries) becomes visible to the upper left of Jupiter around 7:15 p.m., before it, too, drops toward the southwest horizon, and sets about 1:45 p.m.
‘SPRING AHEAD’
Don’t forget to put your clocks ahead one hour (“spring ahead”) before you go to bed on the evening of Saturday, March 9, as Atlantic Daylight Saving Time commences on Sunday, March 10, at 2 a.m. As they have since the Winter Solstice in December 2023, the days are slowly getting longer, with sunsets occurring one minute later every evening between now and the Spring/vernal Equinox on March 19, 2024.
Until next week, clear skies.