Tikalon Blog by Dev Gualtieri

Fast Radio Bursts

December 11, 2023

The measurement of physical properties to greater accuracy is an important part of physics. Deviation of measured values of physical properties from expected results demonstrates that a particular model is in error; and, there might be some new physics lurking in the shadows. Often the deviation is very small; so, there's always an impetus to improve measurement precision. I wrote about a current example of this in a recent article (Fifth Force,October 2, 2023), the Muon g-2 Experiment at the Fermi National Accelerator Laboratory (Fermilab).[1] This experiment found a significant deviation of the gyromagnetic ratio of the muon at the 12th decimal place.[1]

James Clerk Maxwell and his thermodynamic equations.

James Clerk Maxwell (1831-1879) is best known for his electrodynamic equations. He also deduced a set of thermodynamic equations, known as his relations to avoid confusion, as shown here. (Left image, an engraving of Maxwell by George J. Stodart from Wikimedia Commons. The equations were rendered using Inkscape. Click for larger image.)

Preeminent Scottish physicist, James Clerk Maxwell (1831-1879), published an 1860 paper on the kinetic theory of gases, entitled "Illustrations of the dynamical theory of gases," in which he calculates from first principles the properties on an ideal gas.[2] In this paper, Maxwell remarks that his result for the specific heat of diatomic gases at low temperature differed from the measured values. The root of this problem was a quantum mechanical effect not understood until fifty years later, and it underscores the importance of measurement in physics. As Maxwell wrote in his paper,

"In order to lay the foundation of such investigations on strict mechanical principles, I shall demonstrate the laws of motion of an indefinite number of small, hard, and perfectly elastic spheres acting on one another only during impact."[2]

and,

"This mathematical result appears to be in conflict with known experimental values for the specific heats of gases."[2]

Until recently, astronomical observations were something done during the few hours of darkness available at night. In the really early days of astrophotography, when chemical imaging was all that was available, some images were created over the course of many nights by storing the photographic plate in darkness during the day between multiple exposures. The emergence of radio astronomy in the mid-20th century allowed observation of regions of space whenever they were over the horizon, day or night.

The earliest realization that some astronomical phenomena happened on very short time scales was the discovery of pulsars in 1967 by Jocelyn Bell (b. 1943), with the discovery's being credited to her thesis advisor, Antony Hewish (1924-2021).[3] The first observed pulsar, PSR B1919+21, has a period of 1.3373 seconds, and a pulse width of just 40 milliseconds.[3]

Fast radio bursts (FRBs) are another transient astronomical radio wave with pulse width as low as a fraction of a millisecond. It's estimated that a typical FRB releases as much energy in a millisecond as the energy output of our Sun over several days. The first FRB was discovered in 2007 in a search through archival pulsar survey data. Fewer than a thousand FRBs have been detected to date, and the locations of just 5% of these has been determined, although it's estimated that there are as many as 10,000 unobserved fast radio bursts per day.[4]

The data record of fast radio burst FRB 140514 detected at Parkes Observatory, New South Wales, Australia, on May, 14, 2014.

(Swinburne Astronomy Productions image, via Niels Bohr Institute.)

A recently discovered FRB demonstrates the ubiquity of these events in the universe. In 2022, the Australian Square Kilometre Array Pathfinder radio telescope in Western Australia had detected a radio burst from a source more than halfway back to the Big Bang. This FRB, designated FRB 20220610A, was traced back to a morphologically unusual group of galaxies at redshift 1.016 ± 0.002.[6-9]

The discovery was by a huge international research team from Macquarie University (Sydney, Australia), the Australia Telescope National Facility (Epping, Australia), the Netherlands Institute for Radio Astronomy (Dwingeloo, Netherlands), Swinburne University of Technology (Hawthorn, Australia), Curtin University (Perth, Australia), Northwestern University (Evanston, Illinois), the University of California (Berkeley, California), the University of California (Santa Cruz, California), the Kavli Institute for the Physics and Mathematics of the Universe (Kashiwa, Japan), the Square Kilometre Array Observatory (Jodrell Bank, United Kingdom), the University of Sydney (Sydney, Australia), and the Pontificia Universidad Católica de Valparaíso (Casilla, Chile)

The Australian Square Kilometre Array Pathfinder Radio Telescope

The Australian Square Kilometre Array Pathfinder.

This radio telescope is located at the Murchison Radio-astronomy Observatory in Western Australia, which is in the Australian Radio Quiet Zone WA (ARQZWA), established to isolate the radio astronomy receivers from potential interference.[10] (CSIRO image.)

The location of FRB 20220610A was (standard equinox J2000) right ascension, 23h 24m 17.569s ± 0.040s, and declination, -33° 300' 49.3700'' ± 0.5000. The radio burst was detected at 1271.5 MHz, and the detector time resolution of 1.18 ms indicated a pulse shorter than that.[6] The pulse energy was (6.4 ± 0.7) x 10³² erg/hertz, for a total burst energy of about 2x10⁴² erg, which is three-and-a-half times as energetic as all unambiguously localized FRBs.[6,9] This energy is equivalent to the total emission of the Sun over the course of 30 years.[8]

The Australian Square Kilometre Array Pathfinder was able to give an accurate location for FRB 20220610A, and this allowed the European Southern Observatory's Very Large Telescope in Chile to pinpoint the source.[8] This was a peculiar galaxy that looked as if it was merging with one or two other galaxies.[7] It was determined that the probability of correct association was greater than 99.99%.[6] This galaxy is eight billion light years distant.[8] The previous FRB record distance is 5 billion light years.[9]

Fast radio bursts have a potential application in the measurement of the density of matter of the universe. That's because charged particles such as electrons in the path from source to the Earth cause dispersion, so it's possible to determine the matter density along the path.[6,9] This would give insight into the fact that more than half of normal matter is missing, possibly contained within thin filaments connecting galaxies.[7-8] While the origin of fast radio bursts is presently unknown, most astronomers think that they are magnetars, highly magnetic neutron stars.[7] This research was funded by the U.S. National Science Foundation, the Australian Research Council, the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (Dutch Research Council), and the Fondo Nacional de Desarrollo Científico y Tecnológico.[6]

Locations of some fast radio bursts. (screenshot of a NASA Science Visualization Studio animation.[11] Click for larger image.)

Fast Radio Bursts

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