For the first time, NASA’s Neutron Star Interior Composition Explorer (NICER) has detected merging X-ray patches of millions of temperatures on the surface of a magnetar.
“The biggest spot eventually merged with a smaller spot, something we’ve never seen before,” said George Younes, a researcher at George Washington University and NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
This unique set of observations, published Jan. 13 in The Astrophysical Journal Letters, will help guide scientists to a more complete understanding of the interaction between the crust and the magnetic field of these extreme objects.
A magnetar is a type of isolated neutron star characterized by a strong magnetic field, the fractured core that a massive star leaves behind when it explodes.
By compressing a mass greater than that of the Sun into a sphere regarding 12 miles (20 km) in diameter, the neutron star is made of matter so dense that a teaspoon weighs like a mountain on Earth.
What distinguishes neutron stars is that they have the strongest magnetic fields known, which are a thousand times stronger than a typical neutron star magnet.
The magnetic field represents an enormous store of energy that, when perturbed, can lead to a burst of enhanced X-ray activity that lasts from months to years.
On October 10, 2020, NASA’s Neil Girls Swift Observatory detected such a sudden outburst of a new magnetar, called SGR 1830-0645 (or SGR 1830 for short), in the constellation Gear. Although the exact distance is not known, astronomers estimate the object is regarding 13,000 light-years away.
According to NASA, the Swift observatory monitored with X-rays the repetitive pulses that revealed that the body rotates every 10.4 seconds.
Measurements by NICER, an X-ray telescope installed aboard the International Space Station, show that the X-ray emission showed three nearby peaks with each rotation, which occurred when three individual surface patches hotter than their surroundings merged in and out of our view.
The NICER telescope monitored the magnetic star SGR 1830 almost daily, from its discovery on October 10 until November 17, 2020, following which the sun was very close to the field of view for safe observation. During this period, the emission peaks gradually changed, occurring at slightly different times in the magnetar’s rotation.
And NASA explained that the spots form and move as a result of the movement of the crust, just like the movement of tectonic plates on Earth that drives seismic activity.
Astronomers believe that the three moving hot spots likely represent the locations where the coronal rings, which are often seen on the Sun, connect to the surface.
“Understanding this process is a huge challenge for theorists, and now both NICER and SGR 1830 have given us a more direct look at how the crust behaves under extreme stress,” said Sam Lander, an astrophysicist at the University of East Anglia in Norwich, UK, and one of the study’s authors.
The team believes that these observations reveal a single active region in which the crust has become partially molten, slowly deforming under magnetic stress. The three moving hot spots likely represent the sites where coronal rings, similar to the bright, glowing arcs of plasma visible on the Sun, contact the surface. The interaction between epitopes and cortical motion leads to drift and fusion behaviour.
“Changes in pulse shape, including decreasing numbers of peaks, had previously only been seen in a few rapid observations, which were widely separated in time, so there were no way to track its development.
