Today, researchers are announcing the solution to one of the questions that have bothered them over the past decade: What exactly produces the strange phenomena known as fast radio bursts (FRBs)? As their name suggests, FRBs involve a sudden burst of radio-frequency radiation that only lasts a few microseconds. We didn’t even know that FRBs existed until 2007 but we’ve since indexed hundreds of them; Some come from sources that emit frequently, while others seem to just go off at once and be silent.
Obviously, you can produce this kind of sudden burst of energy by destroying something. But the presence of repeated sources indicates that at least some of them were produced by an object that survived the event. This has led to an emphasis on compact objects, such as neutron stars and black holes, with a class of neutron stars called magnetic stars viewed very suspiciously.
These suspicions have now been proven, as astronomers have seen a magnetic star in our galaxy sending out an FRB at the same time that it emits pulses of high-energy gamma rays. This does not answer all of our questions, because we are still not sure how FRBs are produced or why some gamma-ray bursts from this magnetar are related to FRBs. But confirmation will give us a chance to look more carefully at the extreme physics of magnetic stars as we try to understand what is going on.
“Magnetar” is not the latest superhero movie
Magnetic stars are an extreme form of a neutron star, which is a type of object already known to be an extreme. It is the collapsed core of a massive star, dense to the point that the atoms out of existence, leaving a swirling mass of neutrons and protons. This mass is roughly equal to the mass of the Sun, but is compressed into a sphere of about 10 km radius. Neutron stars are known to power pulsars, rapidly repeating bursts of radiation driven by the fact that these massive objects can complete a rotation in a few milliseconds of a second.
Magnetism is a different kind of radical. It tends not to spin quickly but has intense magnetic fields. However, we do not know if these fields were inherited from a star of highly magnetic origin or created by a superconducting material flowing inside the neutron star. Whatever the source, it is about a trillion times stronger than Earth’s magnetic field. This is strong enough to distort the electron orbits of the atoms, effectively canceling out the chemistry of any natural matter that somehow approaches the magnetic star. While the period of high magnetic fields only lasts a few thousand years before the fields dissipate, there are enough neutron stars to maintain a regular supply of magnetism around them.
Their magnetic fields can trigger high-energy events, either by particle acceleration or through magnetic perturbations caused by the transformation of materials inside the neutron star. As a result, magnetic stars have been recognized by their near-uniform production of high-energy X-rays and low-energy gamma rays, giving them the name “soft gamma-ray repeaters”, or SGR. Several of them have been recognized within the Milky Way, including the SGR 1935 + 2154.
In late April of this year, SGR 1935 + 2154 entered an active phase, sending a number of high-energy pulses of photons captured by the Swift Observatory, into orbit around Earth. That was completely normal. What was not normal is that a number of radio observatories picked up the FRB at exactly the same time.
STARE and CHIME
The Canadian Hydrogen Density Mapping Experiment, or CHIME, is a large group of radio antennas that were originally designed for other reasons but turned out to be great for spotting FRBs, as they can continually observe a large strip of sky. The SGR 1935 + 2154 was on the edge of its field of view, which implies some doubts about its identity to the source, but the results were clearly consistent with an association between FRB and gamma-ray output.
And CHIME wasn’t the only thing watching. The Transient Astro Radio Emission Survey 2 (STARE2) also managed to capture the same event, although his team only observed it after discovering that Swift had noticed an energetic star. Therefore, it is evident that the FRB production was somehow related to the gamma ray output of the SGR 1935 + 2154.
But what was noticeable was that both CHIME and STARE2 were able to detect other gamma ray bursts from the SGR 1935 + 2154. he did not do See any FRBs. CHIME reports that she had the opportunity to notice four explosions of the magnet in late 2019 but saw nothing of them. In fact, the set of papers released today includes one devoted entirely to lack of observations made by FAST (the Spherical Radio Telescope with a five hundred-meter aperture, a giant dish in China). This was despite the fact that FAST was intentionally observing the SGR 1935 + 2154 for eight hours in April but was not indicating it when the FRB was observed – although some of these observations occurred during an outbreak of high-energy radiation.
Jules, Ergis and Megatons
These clearly indicate one of two things that happened. Either FRB requires a set of conditions that are seldom present during blast production, or FRBs are sent away from the source, rather than bursting radiating in all directions. In the latter case, we will see only those that, by chance, are directed towards the Earth. We previously detected radio emissions from magnetic stars in our galaxy, but all of them were significantly less powerful.
There’s also the question of whether or not this is actually an FRB of the type that we’ve been exploring all along. Based on its properties and those of other astronomical phenomena, the STARE2 team found the event to be clearly the closest to FRBs. But it is not so far In mass with them, largely because of its energy. Teams calculated that the event was released around 1034 ergs (1027 Joule, or 1011 Megaton). Typical FRBs start out 100 times more powerful and go up exponentially from there, hitting more than 1043 ergs.
While this is compelling and potentially a big step in understanding FRBs, there is just enough uncertainty to keep astrophysicists arguing for longer. However, the fact that a magnetic star could produce something very similar to FRB is likely to have a huge impact on reflection.
how did that happen?
So why should gamma-ray bursts correlate with FRBs at all? Since magnetic stars have been the subject of suspicious looks for nearly the time we knew about FRBs, there is in fact little theoretical modeling of how FRB is produced.
These models are partly informed of the properties of impulsivity. We know that it is common enough that it cannot be produced in an event that destroys its source, something confirmed by the discovery of repeaters. They are also told about the properties of known objects, from pulsars to gamma-ray bursts caused by star destruction.
These models are variations of three basic configurations. One assumes that magnetic fields organize the plasma near the magnetic star in such a way that it forms the radioactive equivalent of the laser, amplifying its energy before it radiates outward. The alternative is that the fields accelerate the charged particles in the plasma and emit radiation when changes in the magnetic field cause these particles to change direction suddenly. The last alternative is relativistic shock, which can occur if a magnet burps some material that has been accelerated by magnetic fields to extremely high speeds, and then collides with the plasma near the object, with the resulting shock occurring.
Now, the only way to know what’s going on is to get more notes. The observatories capturing this FRB will undoubtedly continue to identify those from outside the galaxy, which may be crucial in determining whether all of these events were produced by a single mechanism. But truly understanding this mechanism will likely require close observation of the thirty or so magnetic stars that we know about in the Milky Way. This may not require seeing another locally implanted FRB; Better understanding what is behind gamma-ray eruptions can help determine how these events may also produce radio explosions.
Nature, 2020. Four articles accessed from This is the news story.