Magnetars are stars with highly effective magnetic fields, some trillion occasions stronger than the Earth’s. They’re a sort of neutron star. That’s, they as soon as exploded as a supernova, on the identical time imploding to turn into the quickly rotating dense corpses of now-dead stars. Extraordinarily quick rotation is a key attribute of neutron stars generally, and of magnetars specifically. And that’s why, on October 5, 2020, astronomers had been shocked to see a magnetar out of the blue decelerate. It started emitting radio waves a couple of days later. What brought about this? In late January 2023, a global group of astrophysicists and astronomers suggested a solution: a volcano-like eruption on the floor of the magnetar that spewed a “wind” of huge particles into space.
The researchers published their peer-reviewed findings in January 2023 in Nature Astronomy. There’s additionally a preprint of the paper available on arXiv.
Magnetar slow-downs are uncommon
Usually, magnetars rotate as soon as each few seconds. And their rotation slows down solely very slowly. Slowing down by a single rotation per second can take tens of hundreds of years for a magnetar. But – in uncommon instances, as with the sudden slowdown in 2020 of magnetar SGR 1935+2154 – magnetars can apparently decelerate very abruptly.
However astronomers say these abrupt slowdowns of magnetars – which they name anti-glitches – are uncommon. They usually haven’t been certain what causes them. Astrophysicist Matthew Baring at Rice College, one of many lead authors of the paper, examined a brand new idea alongside along with his colleagues. They used X-ray information from the European House Company’s X-ray Multi-Mirror Mission (XMM-Newton) and NASA’s Neutron Star Inside Composition Explorer (NICER) to check SGR 1935+2154’s 2020 slowdown.
The outcomes counsel an attention-grabbing situation: a volcano-like eruption or rupture that may have brought about the slowdown. It might have performed so by spewing a “wind” of huge particles out into space. And this “wind” might need altered the magnetar’s magnetic fields. This, in flip, might have brought about the magnetar to decelerate out of the blue, and to start out producing radio waves. Baring said:
Folks have speculated that neutron stars might have the equal of volcanoes on their floor. Our findings counsel that may very well be the case and that on this event, the rupture was probably at or close to the star’s magnetic pole.
Glitches and anti-glitches
Magnetars don’t simply decelerate. They will additionally pace up. Scientists name an abrupt enhance in rotational pace in a magnetar a glitch. That’s why sudden slowdowns are referred to as anti-glitches. Glitches are often attributable to sudden shifts throughout the magnetar itself. As Baring defined:
In most glitches, the pulsation interval will get shorter, that means the star spins a bit quicker than it had been. The textbook clarification is that over time, the outer, magnetized layers of the star decelerate, however the interior, non-magnetized core doesn’t. This results in a buildup of stress on the boundary between these two areas, and a glitch indicators a sudden switch of rotational power from the quicker spinning core to the slower spinning crust.
2020 magnetar slowdown was distinctive
Certainly, the sudden slowdown of magnetar SGR 1935+215 in October 2020 was a novel occasion, the researchers say. As Baring defined:
A robust, huge particle wind emanating from the star for a couple of hours might set up the circumstances for the drop in rotational interval. Our calculations confirmed such a wind would even have the ability to vary the geometry of the magnetic subject outdoors the neutron star. The overall properties of the X-ray pulsation possible require the wind to be launched from a localized area on the floor.
What makes the October 2020 occasion distinctive is that there was a quick radio burst from the magnetar just some days after the anti-glitch, in addition to a switch-on of pulsed, ephemeral radio emission shortly thereafter. We’ve seen solely a handful of transient pulsed radio magnetars, and that is the primary time we’ve seen a radio switch-on of a magnetar virtually contemporaneous with an anti-glitch.
Therefore, the timing means that the identical occasion brought about each the slowdown and radio emissions. Baring added:
The wind interpretation supplies a path to understanding why the radio emission switches on. It supplies new perception we’ve not had earlier than.
Excessive objects
Magnetars are excessive in lots of different methods, too, not simply due to their robust magnetic fields. For instance, they launch huge quantities of power within the type of flares, X-rays and gamma-ray bursts.
They will even have an effect on Earth’s magnetic subject. In 2004, a flare on the floor of a magnetar compressed the magnetic subject of the Earth from a distance of fifty,000 light-years!
A neutron star’s inside changing into a superconducting fluid would possibly create the magnetic subject of a magnetar. Astronomers say the inside is made up of neutrons, quarks and unique states of matter resembling Bose-Einstein condensates.
Just a few magnetars are additionally identified to be each magnetars and pulsars, these “cosmic lighthouses” of the universe.
They’re fascinating! And this examine could also be a stepping stone to understanding them higher.
Backside line: Astronomers say they suppose they know why a quickly spinning magnetar slowed down out of the blue in 2020. They are saying a strong volcano-like eruption on the magnetar’s floor is responsible.
Source: Magnetar spin-down glitch clearing the way for FRB-like bursts and a pulsed radio episode
