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Investigators announced yesterday They have solved a question that has been nagging them for more than a decade: What exactly produces the strange phenomena known as fast radio bursts? As the name implies, FRBs involve a sudden burst of radio frequency radiation that lasts for only a few microseconds. Astronomers didn’t even know they existed until 2007, but have since cataloged hundreds of them; some come from sources that broadcast them repeatedly, while others seem to pop once and go silent.
Obviously, you can produce this kind of sudden energy surge by destroying something. But the existence of repeated sources suggests that at least some of them are produced by an object that survives the event. That has led to a focus on compact objects, like neutron stars and black holes, with a class of neutron stars called magnetars that are very suspicious.
Those suspicions have now been confirmed, as scientists have observed a magnetar in our own galaxy sending out an FRB at the same time as it emitted pulses of high-energy gamma rays. This does not answer all of our questions as we are not yet sure how FRBs are produced or why only some of the gamma ray bursts from this magnetar are associated with FRBs. But confirmation will give us a chance to take a closer look at the extreme physics of magnetars as we try to understand what is going on.
‘Magnetar’ is not the last superhero movie
Magnetars are an extreme form of neutron stars, celestial bodies that already stand out for being extreme. They are the collapsed core of a massive star, so dense that the atoms are squeezed out, leaving a swirling mass of neutrons and protons. That mass is roughly equal to that of the sun, but compressed into a sphere with a radius of about 10 kilometers. Neutron stars are best known for powering pulsars, rapidly repeating bursts of radiation driven by the fact that these massive objects can complete one rotation in a handful of milliseconds.
Magnetars are a different kind of extreme. They tend not to spin that fast but have strong magnetic fields. However, we do not know if those fields are inherited from a highly magnetic host star or if they are generated by superconducting material churning inside the neutron star. Whatever the source, those magnetic fields are roughly a trillion times stronger than Earth’s magnetic field. That’s strong enough to distort the electron orbitals in atoms, effectively removing the chemistry from any normal matter that somehow comes close to a magnetar. While the period of high magnetic fields lasts for only a few thousand years before the fields dissipate, there are enough neutron stars to maintain a regular supply of magnetars.
Its magnetic fields can drive highly energetic events, either by accelerating particles or by magnetic disturbances driven by the displacement of material within the neutron star. As a result, magnetars have been identified by their semi-regular production of high-energy X-rays and low-energy gamma rays, naming them “soft gamma-ray repeaters” or SGRs. Several of them have been identified within the Milky Way, including SGR 1935 + 2154.
At the end of April this year, SGR 1935 + 2154 entered an active phase, sending out a series of high-energy photon pulses that were captured by the Swift Observatory, orbiting the Earth. That was completely normal. What was not normal is that several radio observatories captured an FRB at precisely the same time.
LOOK and a RING
The Canadian Hydrogen Intensity Mapping Experiment, or Chime, is a large variety of radio antennas that was originally designed for other reasons, but which turned out to be excellent at detecting FRBs, as it can constantly observe a large swath of the sky. SGR 1935 + 2154 was at the edge of its field of view, meaning there were some uncertainties in its source identity, but the results were clearly consistent with an association between the FRB and the gamma-ray output.
