Fastest turn and possibly the latest magnetar known

• Astronomers recently found the fastest turn and possibly the latest magnetar known.
• This object, known as J1818.0-1607, is approximately 21,000 light-years away in the Milky Way galaxy.
• Magnetars are a special class of neutron stars that have extremely powerful magnetic fields.
• Researchers have used Chandra and other telescopes to study the unusual properties of this object.

In 2020, astronomers added a new member to an exclusive family of exotic objects with the discovery of a magnetar. New observations of NASAChandra X-ray Observatory supports the idea that it is also a pulsar, which means that it emits regular light pulses.

Magnetars are a kind neutron star, an incredibly dense object consisting mainly of densely packed neutrons, which form during a supernova from the folded core of a massive star.

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

On March 12, 2020, astronomers detected a new magnetar with NASA’s Neil Gehrels Swift Telescope. It is only the 31st known magnetar, out of the approximately 3000 known neutron stars.

After follow-up observations, researchers determined that this object, named J1818.0-1607, was special for other reasons. First, it may be the latest known magnetar, with an age of about 500 years old. This is based on how fast the rotational speed slows down, and the assumption that it was born much faster. Second, it also rotates faster than any previously discovered magnetar, rotating every 1.4 seconds.

Chandra’s observations of J1818.0-1607 were obtained less than a month after the discovery with Swift, and gave astronomers the first high resolution of this object in X-rays. The Chandra data revealed a point source where the magnetar was located, surrounded by diffuse X-ray emission, probably caused by X-rays reflecting off dust located in its vicinity. (Some of this diffuse X-ray emission may 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 results from the J1818.0-1607 Chandra observations in The astrophysical journal letters.

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

Other astronomers also observed J1818.0-1607 with radio telescopes, such as the Karl Jansky Very Large Array (VLA) of the NSF, and determined that it emitted radio waves. This implies that it also has properties similar to those of a typical ‘rotation-driven pulsar’, a type of neutron star that emits radiation rays that are perceived as repetitive pulses of emission as it rotates and decelerates. Only five magnets, including these, have been recorded to act as pulsars, accounting for less than 0.2% of the known neutron star population.

The Chandra observations may also support this general idea. Safi-Harb and Blumer studied how efficiently J1818.0-1607 converts energy from its decay rate into X-rays. They concluded that this efficiency is lower than that typically found for magnetars, and probably within range for other rotation-driven pulses.

The explosion that created a magnetar of this era would be expected to leave a noticeable rubbish field. To search for this supernova remnant, Safi-Harb and Blumer looked at Chandra’s X-rays, Spitzer’s infrared data, and the VLA’s radio data. Based on the Spitzer and VLA data, they found possible evidence for a remnant, but at a relatively large distance from the magnetar. To cover this distance, the magnetar would have to move at a velocity much higher than that of the fastest known neutron stars, even assuming that it is much older than expected, which would allow more travel time.

Reference: “Chandra Observations of the Newly Discovered Magnetar Swift J1818.0–1607” by Harsha Blumer and Samar Safi-Harb, 26 November 2020, The astrophysical journal letters.
DOI: 10.3847 / 2041-8213 / abc6a2
arXiv: 2011.00324

NASA’s Marshall Space Flight Center manages the Chandra program. The Chandra X-ray Center of the Smithsonian Astrophysical Observatory controls science from Cambridge Massachusetts and flight operations from Burlington, Massachusetts.