When stars between 10 and 25 times the mass of the Sun go supernova, they leave behind a neutron star. They are the smallest and densest stellar object, packing into a sphere with a diameter of 20 kilometers (12.4 miles) and a mass of just over twice of our Sun. Magnetars are a very special class of highly magnetic neutron star – the extremely dense core of a star that has gone supernova, with the most powerful magnetic fields in the universe. Pulsars are another class of neutron star, known for their regular pulsation of sometimes hundreds of times a second.
Last year astronomers discovered J1818.0-1607, the youngest known magnetar. It is also the one rotating the fastest, completing a full spin in less than 1.4 seconds. The latest observations revise distance and suggest that this very special stellar object is even more special. The findings are reported in The Astrophysical Journal Letters.
Out of 3,000 known neutron stars, there are 2,000 known pulsars, with 31 classified as magnetars. Only five are both pulsars and magnetars. NASA’s Chandra observations have placed J1818.0-1607 among those five.
When fast-rotating neutron stars form, their spin is very high and slows down with time. As the rotation speed declines, some of the energy from this decrease is converted into X-rays, and these were observed by Chandra. The data shows that this object is less efficient than other magnetars at producing X-rays – its efficiency levels are on par with what has been seen from rotation-powered pulsars.
Indications of the double nature of this magnetar also came from a different group of astronomers. The radio emission detected from this star using the NSF’s Karl Jansky Very Large Array (VLA) is alike what is usually seen from rotation-powered pulsars.
The new work has also started a bit of a mystery. Neutron stars are often found surrounded by the debris of the supernova explosion that created them. There was the expectation to find a considerable amount of stuff around J1818.0-1607, but it was far from obvious.
The authors of this study used data from Chandra, the VLA, and retired infrared telescope Spitzer to zero in on the supernova remnant. They found a possible candidate for it, but it is quite far from the magnetar. Even if this object is much older than what has been estimated, the material must have traveled faster than any other known supernova remnant related to a neutron star. More observations will be necessary to try and unravel this mystery. The object is located close to the plane of the Milky Way at a distance of about 21,000 light-years from our planet.