NASA’s Neutron Star Interior Composition Explorer (NICER) has detected the merger of multimillion-degree X-ray spots on the surface of a magnetar, a supermagnetized stellar core the size of a metropolis, for the first time.
“NICER watched how three brilliant, X-ray-emitting hot spots steadily roamed around the object’s surface while also reducing in size,” said George Younes, a researcher at George Washington University in Washington and NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The larger spot finally merged with a smaller one, something we’ve never seen before.”
This one-of-a-kind combination of data, presented in a research lead by Younes and published on Jan. 13 in The Astrophysical Journal Letters, will help scientists get a better understanding of the interaction between the crust and magnetic field of these extreme objects.
A magnetar is a sort of solitary neutron star formed by the crushed core of a massive star after it bursts. A neutron star is formed of stuff so dense that a teaspoonful would weigh as much as a mountain on Earth, compressing more mass than the Sun into a ball approximately 12 miles (20 kilometers) wide.
Magnetars have the greatest magnetic fields known, up to 10 trillion times stronger than a refrigerator magnet and a thousand times stronger than a normal neutron star. The magnetic field is a massive reservoir of energy that, when disrupted, may cause an explosion of heightened X-ray activity that can last months or years.
On October 10, 2020, NASA’s Neil Gehrels Swift Observatory detected a new magnetar, SGR 1830-0645, that produced such an outburst (SGR 1830 for short). It’s in the constellation Scutum, and although the exact distance is unknown, scientists think that it’s around 13,000 light-years distant. Swift pointed its X-Ray Telescope to the source and detected repeated pulses that suggested the object rotated every 10.4 seconds.
According to NICER observations from the same day, the X-ray emission had three near peaks with each revolution. They were created by three separate surface patches that were significantly hotter than their surroundings and swirled into and out of our vision.
SGR 1830 was seen virtually daily by NICER from its discovery until November 17, when the Sun became too close to the field of view for safe observation. The emission peaks progressively moved throughout this time, occurring at slightly different moments in the magnetar’s spin. The findings support a scenario in which the spots develop and travel as a consequence of crustal motion, similar to how tectonic plate motion generates seismic activity on Earth.
“The crust of a neutron star is very strong, but the tremendous magnetic field of a magnetar may stretch it past its limits,” said Sam Lander, an astronomer at the University of East Anglia in Norwich, UK, and a co-author of the work. “Understanding this mechanism has long been a source of consternation for theorists, but NICER and SGR 1830 have provided us with a far more direct view at how the crust reacts under severe stress.”
The team believes that these data point to a single active location in which the crust has become partly molten and is steadily deforming due to magnetic stress. The three moving hot areas are most likely where coronal loops, which resemble the brilliant, incandescent arcs of plasma seen on the Sun, link to the surface. The drifting and merging behavior is driven by the interaction of the loops and crustal motion.
“Changes in pulse form, including decreased number of peaks, were previously noticed only in a few’snapshot’ observations far separated in time, thus there was no method to trace their development,” stated Zaven Arzoumanian, Goddard’s NICER research lead. “Such shifts might have happened abruptly, which is more compatible with a lurching magnetic field than with roaming hot patches.”
NICER is a NASA Explorers Program Astrophysics Mission of Opportunity that offers regular flight chances for world-class scientific studies from space using novel, streamlined, and efficient management techniques in the heliophysics and astrophysics research domains. The SEXTANT component of the project, which demonstrates pulsar-based spacecraft navigation, is supported by NASA’s Space Technology Mission Directorate.