Chandra’s observations reveal an extraordinary magnetar

In 2020, astronomers added a new member to an exclusive family of exotic objects with the discovery of a magnetar. New observations from NASA’s Chandra X-ray Observatory support the idea that it is also a pulsar, meaning it emits regular pulses of light.

Magnetars are a type of neutron star, an incredibly dense object mostly made up of tightly packed neutrons, which form from the collapsed core of a massive star during a supernova.

What sets magnetars apart from other neutron stars is that they also have the most powerful known magnetic fields in the universe. For context, the strength of our planet’s magnetic field has a value of about one Gauss, while a fridge magnet is about 100 Gauss. Magnetars, on the other hand, have magnetic fields of around a million billion Gauss. If a magnetar were located one-sixth of the way from the Moon (about 40,000 miles), it would erase all credit card data on Earth.

On March 12, 2020, astronomers detected a new magnetar with NASA’s Neil Gehrels Swift telescope. This is only the 31st known magnetar, out of some 3,000 known neutron stars.

After follow-up observations, the researchers determined that this object, dubbed J1818.0-1607, was special for other reasons. First, it may be the youngest known magnetar, with an estimated age of around 500 years. This is based on the speed at which the rate of rotation slows down and the assumption that it was born rotating much faster. Second, it also spins faster than any previously discovered magnetar, spinning once every 1.4 seconds.

Chandra’s observations of J1818.0-1607 obtained less than a month after the discovery with Swift gave astronomers the first high-resolution x-ray view of this object. Chandra data revealed a point source where the magnetar, which is surrounded by diffuse X-ray emission, possibly caused by X-rays reflecting off nearby dust. (Some of this diffuse x-ray emission can also come from winds blowing away from the neutron star.)

Harsha Blumer of the University of West Virginia and Samar Safi-Harb of the University of Manitoba in Canada recently published the results of Chandra’s observations of J1818.0-1607 in The Letters from the Astrophysical Journal.

This composite image contains a wide field of view in the infrared of two NASA missions, the Spitzer Space Telescope and the Wide-Field Infrared Survey Explorer (WISE), taken before the discovery of the magnetar. Chandra’s x-rays show the magnetar in purple. The magnetar is located near the plane of the Milky Way galaxy at a distance of about 21,000 light years from Earth.

Other astronomers have also observed J1818.0-1607 with radio telescopes, such as the NSF’s Karl Jansky Very Large Array (VLA), and determined that it emits radio waves. This implies that it also has properties similar to those of a typical “spinning pulsar”, a type of neutron star that emits beams of radiation that are detected as repeated pulses of emission as it spins and turns. slows down. Only five magnetars including this one have been recorded to also act as pulsars, constituting less than 0.2% of the known population of neutron stars.

Chandra’s observations may also support this general idea. Safi-Harb and Blumer studied the efficiency with which J1818.0-1607 converts the energy of its decreasing spin speed into X-rays. They concluded that this efficiency is lower than that generally found for magnetars, and probably in the range found for other rotating pulsars.

The explosion that created a magnetar this age would have left a detectable field of debris. To find this supernova remnant, Safi-Harb and Blumer looked at x-rays from Chandra, infrared data from Spitzer, and radio data from the VLA. Based on the Spitzer and VLA data, they found possible evidence of a residue, but at a relatively large distance from the magnetar. In order to cover this distance, the magnetar would have to have traveled at speeds far exceeding those of the fastest known neutron stars, even assuming it is much older than expected, which would allow for a longer travel time.