THE FAST RADIO BURST ENIGMA
A mysterious and very large population of astrophysical objects is firing single, energetic, millisecond, bursts of radio wave emission throughout the cosmos. We have detected these Fast Radio Bursts, but their source population remains a giant enigma.
Let’s review the basic properties of FRBs and constraints on the sources.
Ubiquitous: If we could observe the entire sky in the appropriate wavelength range, astrophysicists estimate that 3,000–10,000 FRBs per day would be observed.
Very Compact: Given the discrete millisecond timescale of the FRBs, the objects must have sizes that are equal to or less than 10 km.
Single and Short: Of the 35 that have been detected so far, only one candidate repeats. The other 34 are one-off bursts with millisecond scale durations.
Energetic: The energy output of FRBs is prodigious. The FRBs energies have been estimated in the 10³⁹ ergs to 10⁴² ergs range, which is very energetic, and clearly astrophysical.
Just Radio Waves: So far no other form of radiation at gamma-ray, X-ray or optical wavelengths is observed in the case of FRBs, nor are gravitational waves linked to them.
Large Dispersion Measures: The shorter wavelengths are observed first, followed by the longer wavelengths. This stretching of the arrival times of the different wavelengths indicates that the bursts have traveled a long way through the cold plasma of space. Therefore the FRBS are not local; they come from cosmological distances.
Frequency Range: So far the observed FRBs have frequencies primarily in the 580 MHz to 1.4 GHz range.
Polarization: Some of the FRBs have circular polarization, and possible connection to magnetic fields.
Now that the reality of FRBs has been accepted by the astrophysical community, their nature represents a huge astrophysical mystery story and many research teams are racing to observe more FRB events. Identifying the source population and emission mechanism will require a much larger set of observed FRBs. The new CHIME observatory should soon detect multiple FRBs per day. Other research teams are gearing up for detections, and the possibility that we might have 1,000s of FRB observations in the near future is almost guaranteed.
Since a very compact astrophysical object seem to required in order to explain FRBs, the most common guesses for their sources are pulsars, magnetars and black holes. Discrete Scale Relativity offers a unique and natural model for FRBs based on its prediction that the dark matter is composed of stellar-mass primordial black holes that have mass, spin and charge. This means that they are Kerr-Newman black hole solutions of General Relativity, using the Einstein-Maxwell field equations.
In the previous writing linked below, I have argued that DSR implies that an analogue of the bremsstrahlung radiation that is well-known on the Atomic Scale of nature’s self-similar hierarchy has an exact or nearly exact analogue on the Stellar Scale. I would recommend that the reader take the 3 minutes required to read this piece as background for what comes below.
I have subsequently learned that there is a form of bremsstrahlung radiation, called magneto-bremstrahlung radiation, which has some properties that seem uniquely applicable to the FRB enigma. The radiation on the Atomic Scale is called synchroton radiation and it is generated when a relativistic charged particle is deflected by a magnetic field. Synchroton radiation can have a wide range of possible wavelengths, high flux, and high brilliance. It requires an external magnetic field and it can involve both circular and linear polarization of the radiation.
What really intrigues me about magneto-bremsstrahlung radiation is that highly relativistic sources can radiate in narrowly beamed “pencil rays”. For a fixed external observer, these beams are only lined up for a very short time. This would explain the “Nothing-Blast of Radio Waves-Nothing” nature of FRBs.
The other key property of bremsstrahlung is the fact that only discrete frequency/wavelength bands are emitted and this might explain why FRBs do not radiate at other than radio frequencies. This is something that is almost never observed for other highly energetic astrophysical phenomena.
What is needed now is a factor of about 100 increase in the number of observed FRBS. This large set of observations is crucial to identifying the full ranges of the properties characterizing FRBs, and to learning whether they have additional properties not observed yet. Happily, in a year or two this crucial data set should be in hand. Some very exciting science is on the horizon.