Researchers announced yesterday that they have solved a question that has stuck with them for more than a decade: What exactly causes these bizarre phenomena called fast radio explosions? As the name implies, FRB is involved in a sudden burst of radio frequency radiation lasting just a few microseconds. Astronomers didn’t even know they existed until 2007, but they cataloged hundreds of them; some come from sources continuously emitting them, while others seem to burst out once and be silent.
Obviously, you can generate this kind of sudden energy by destroying something. But the existence of repeating sources suggests that at least some of them were created by an object that survived the event. That has resulted in the focus on compact objects, such as neutron stars and black holes, with a class of neutron stars called magnets that are considered highly dubious.
Those doubts are now being raised, as scientists have watched a magnet in our galaxy emit an FRB at the same time it emits high-energy gamma-ray pulses. This does not answer all of our questions, as we are still not sure how the FRB is produced or why only some of these magnetic gamma-ray bursts are linked to the FRB. But validation will give us the opportunity to take a closer look at the extreme physics of a magnet as we try to understand what̵7;s going on.
‘Magnetar’ is not the latest superhero movie
Magnet stars are a polar form of neutron stars, which have been noted as polar. They are the collapsing cores of a large star, so dense that the atoms are squeezed out of existence, leaving behind an eddy mass of neutrons and protons. That mass is close to that of the sun – but compressed into a sphere about 10 kilometers in radius. Neutron stars are best known for supplying energy to pulsars, rapidly repeating radiation bursts due to the fact that these giant objects can complete a rotation in a few milliseconds.
Magnets are another type of pole. They tend not to rotate quickly but have a strong magnetic field. However, we do not know whether those fields were inherited from a very magnetic parent star or produced by the superconducting material surrounding the inside of the neutron star. Either way, those fields are about a trillion times stronger than Earth’s. That is powerful enough to distort the electron orbitals in the atom, eliminating the chemical effect for any ordinary matter that would somehow get close to a magnet. While the period of high magnetic fields lasted only a few thousand years before these fields dissipated, there are still enough neutron stars to hold a steady supply of magnetic fields around.
Their magnetic fields can energize high-energy events, either by accelerating particles or through magnetic disturbances caused by matter shifting inside neutron stars. As a result, the magnets have been identified by producing high-energy X-rays and low-energy gamma rays, giving them the name “soft gamma ray repeater” or SGR. Some of them have been identified in the Milky Way, including SGR 1935 + 2154.
At the end of April this year, SGR 1935 + 2154 entered the active phase, emitting a number of high-energy photon pulses picked up by Swift Observatory in orbit around the Earth. That is completely normal. It is unusual for several radio observatories to acquire an exact FRB at the same time.
STARE and a CHIME
Canada’s hydrogen intensity mapping experiment, also known as Chime, is a series of large radio antennas that were originally designed for other reasons but have become great for detecting FRB, as it has can continuously observe a large band in the sky. The SGR 1935 + 2154 is located at the edge of its field of view, which means there is some uncertainty in the identity of the emitter, but the results are clearly consistent with the relationship between FRB and gamma ray output.