Have we already seen our first “lightning snatch”? – Ars Technica

By combing through a trove of data, researchers may have discovered evidence that we did indeed observe our first “glitter,” a strange astronomical event caused by the sudden collapse of an extremely massive neutron star. This event was triggered by a previous merger of two neutron stars; This creates an unstable intermediate neutron star, which is prevented from collapsing immediately due to its rapid rotation. In a blitzkrieg, the neutron star’s strong magnetic fields slow its rotation, causing it to collapse into a black hole several hours after merging.

This collapse abruptly deletes the dynamo that powers the magnetic fields, releasing their energy in the form of a fast radio burst. The researchers who conducted the analysis suggested that this phenomenon could explain the non-recurring forms of these events.

Too big to live

How big can a neutron star get before it collapses into a black hole? We don’t have a good answer, in part because we’re not sure what happens to the strange forms of matter inside one of these massive objects. We don’t even know if the neutrons that give the star its name linger or collapse into their constituent quarks. It’s one of those pesky questions where the answer includes “it depends.”

The big thing it depends on is how fast the neutron star is spinning. A fast enough spin can negate the gravitational pull on the neutron star’s outer layers, keeping something too heavy to stay a bit. If the spin slows down, everything will quickly be crushed into a single state. The simplest way to slow down one of these stars is through its magnetic field, which will interact with charged particles in the environment, pulling the object’s rotation.

These are the conditions required for a neutron star to merge and create a lightning wave. If neutron stars are heavy enough, their merger would create an object above the mass limit that should cause it to collapse into a black hole. But the collision is also likely to cause the object to spin fast enough that it can’t collapse. Their superfluid interiors could host a dynamo that supports an intense magnetic field, which would likely make the object a magnetar but certainly slow its spin. The dynamics of this equilibrium must occur by lightning within hours of the neutron star merger.

Once collapse occurs, the dynamo that created the magnetic fields disappears along with the rest of the neutron star. There’s a lot of energy swirling around in this field, and losing a neutron star releases it in a process the new paper refers to as “magnetosphere shedding.” This rush of energy is something we can potentially detect.

Waves and bursts

Or make that “already detected”. For some time now, we have been observing bursts of energy originating from a region of intense magnetic fields. These fast radio bursts (FRBs) occasionally recur, and have been associated with highly magnetic neutron stars called magnetars. But there were also a number of FRBs that didn’t seem to replicate at all, suggesting that the conditions that produced them may have destroyed their source. This is consistent with lightning storm.

For the new work, a team of researchers made use of data from two types of observatories. One is the LIGO/VIRGO Gravitational Wave Detection Collaboration, which can identify gravitational signals produced when massive objects, including neutron stars, merge. The second is the Canadian Hydrogen Density Mapping Experiment, an observatory built for something else that has turned out to be exceptionally good at locating FRBs.

The search was relatively simple: the researchers looked for events captured by both observatories that occurred at about the same time and in the same region of the sky, with the FRB arriving less than a day after the gravitational waves. Of the 21 neutron star mergers detected by gravitational waves, only one has been matched to an FRB, with FRB 20190425A about 2.5 hours after GW190425.

Until we get more detectors online, gravitational wave events can only be located within a wide strip of sky, so all we can say for sure is that the FRB occurred within an area that has a 70 percent chance of the neutron star being present. merger occurred. But it was also the right distance, and we haven’t detected many neutron star mergers. As a result, the researchers estimated the probability of this chance co-localization to be only 0.004.

Blitz Limits

If this research is correct, the events we’ve been grouping together as FRBs are actually the product of two different events. Recurring events occur in the environment around a magnetar. Single shot events are caused by the death of a highly magnetized neutron star within a few hours of its formation.

If FRB 20190425A4 / GW190425 is a blitzkrieg, we already have a good idea of ​​what the physics of the event should look like, since astrophysics has spent a fair amount of computer time modeling it. As a result, even this single event can place some restrictions on the processes involved. Gravitational wave detectors indicate that pre-merger neutron stars likely weigh between 1.35 and 2.0 times the mass of the Sun, with the post-merger object being just over 3.2 solar masses. Based on this information, the researchers determined the maximum mass of a neutron star to be somewhere between 2.6 and 3.0 times the mass of the Sun. Any greater than that collapses.

The more of these events we see, the better constraints we’ll put on the physics of these things. Since both events are highly unpredictable, we’ve put together a number of observatories that are constantly collecting data to make sure we catch one as it happens. So if blitz attacks are a regular occurrence, it won’t take long until we see more of them.

natural astronomy2023. DOI: 10.1038 / s41550-023-01917-x (about DOIs).