Chandra’s close-up of the area around the black hole, showing a combined image obtained between 2005 and 2008, when the magnetar was not detected, and in 2013 during the X-ray outburst that led to its discovery Credit: NASA/CXC/INAF/F.Coti Zelati et al
Astronomers are unsure as to why a magnetar close to the supermassive black hole at the centre of the Milky Way is losing its X-ray brightness more slowly than usual and is becoming hotter on its surface.
Magnetars are collapsed stars, called neutron stars, that possess powerful magnetic fields.
SGR 1745-2900 was discovered close to the Milky Way’s supermassive black hole in 2013, using telescopes including the Chandra X-ray Observatory.
At a proximity estimated to be 0.3 lightyears, it is the closest to a supermassive black hole ever discovered.
Astronomers have been keeping an eye on the magnetar with Chandra and ESA’s XMM-Newton since its discovery.
This latest study reveals that its X-ray brightness is dropping more slowly than usual and that its surface is hotter than expected.
One theory is that starquakes could be involved.
These occur when the outer crust of a neutron star cracks, just like on Earth.
However, while this causes a change in brightness and cooling in some magnetars, it is insufficient to explain the slower drop in X-ray brightness and the hot crust seen in SGR 1745-2900.
The researchers have suggested that the heating of the magnetar could be caused by a bombardment of charged particles trapped in twisted bundles of magnetic fields above its surface.
This could also explain the slow drop in X-ray brightness.
The study has also clarified it is not likely this unusual behaviour is caused by the magnetar’s proximity to the supermassive black hole, as it is still too far away to be affected by its magnetic fields or gravity.
Astronomers will continue to study SGR 1745-2900 to learn more about these unusual occurrences as it orbits the black hole at the centre of the Galaxy.