Rice physicists: Volcano-like rupture triggered distant star's slowdown

A Rice University study suggests that a volcano-like rupture triggered a magnetar slowdown.

In a captivating celestial event, a distant neutron star approximately 30,000 light years from Earth surprised astronomers with a sudden change in its rotation Oct. 5, 2020. This unprecedented phenomenon offered scientists an opportunity to investigate an extraordinary event known as an "anti-glitch" in SGR 1935+2154, an immensely magnetic neutron star referred to as a magnetar. 

With the aid of advanced orbiting telescopes, astrophysicist Matthew Baring and his team from Rice University embarked on an exploration of this rare occurrence. Their findings, published in Nature Astronomy, present an intriguing theory explaining the cause behind this enigmatic slowdown.

The team began by analyzing the rotation of the cosmic phenomenom. 

Equipped with X-ray data obtained from the European Space Agency's X-ray Multi-Mirror Mission (XMM-Newton) and NASA's Neutron Star Interior Composition Explorer (NICER), Baring and his co-authors meticulously scrutinized the rotation of the distant magnetar.

Their research proposes that the sudden slowdown might have been triggered by a volcano-like rupture on the star's surface, expelling an outflow of massive particles into space. This remarkable particle wind was then identified as the catalyst for subsequent radio emissions detected by China's Five-Hundred-meter Aperture Spherical Telescope (FAST).

The Rice University researchers then validated the volcanic hypothesis.

While the concept of volcanoes on the surface of neutron stars has long been the source of speculation, Baring's findings provide substantial credibility to this hypothesis. The anti-glitch-causing rupture is believed to have occurred near or at the star's magnetic pole, as determined by the research team. 

Magnetars, including SGR 1935+2154, represent a distinct type of neutron star that emerges from the remnants of a collapsed star, compacted under immense gravitational forces. These incredibly dense objects, measuring only a few dozen miles wide, rotate every few seconds and possess the most intense magnetic fields observed in the universe. The emission of powerful radiation, such as X-rays and sporadic radio waves, and gamma rays, enables astronomers to gain invaluable insights into these peculiar celestial bodies.

In order to understand glitches and anti-glitches, Baring noted the star's shifts.

Glitches, sudden increases in rotational speed, are commonly attributed to internal shifts deep within the star. According to Baring, the conventional explanation suggests that the star's outer magnetized layers gradually decelerate while the non-magnetized core remains unaffected. 

This discrepancy creates stress at the boundary between the two regions, resulting in a glitch where rotational energy is rapidly transferred from the faster-spinning core to the slower-spinning crust. 

Conversely, anti-glitches, abrupt rotational slowdowns of magnetars, are exceptionally rare and challenging to explain. Although glitches can be understood as changes occurring within the star, anti-glitches are more likely caused by external factors affecting the star's surface and its surrounding space.

In addition, insights on radio emissions are a key part of the study.

What sets the October 2020 event apart is the occurrence of a fast radio burst from the magnetar shortly after the anti-glitch, accompanied by the activation of pulsed, ephemeral radio emissions. 

Ultimately, the study, which arrived from the hypothesis, is the volcano-driven wind model.

Baring's study introduces a novel model, suggesting that the anti-glitch observed in October 2020 was triggered by a powerful wind carrying massive particles, originating from a volcano-like rupture on the star's surface. This wind persisted for several hours, establishing the conditions necessary for the drop in the rotational period. 

Furthermore, the event had the potential to alter the magnetic field's geometry beyond the neutron star itself. The localized region required for the observed X-ray pulsation properties led scientists to postulate a volcano-like formation responsible for the anti-glitch.