Pulsars are one of the most extreme objects in the universe, packing the mass of the Sun into a tiny radius – an average of around 20 kilometers (12 miles) – and can spin on their axis hundreds of times per second.
Well, that’s what they usually do. But astronomers have now confirmed the discovery of the slowest pulsar yet, which leisurely rotates once every 6.67 hours.
This pulsar, known as 1E 161348–5055, or 1E 1613 for short, is the compact object at the center of RCW 103, a supernova remnant about 10,000 light-years from the Solar System. Astronomers are certain that the object is indeed a pulsar, a spinning neutron star that emits radio waves in pulses, but its long and unusual rotation period is an unexplained mystery.
Researchers have put forward two solutions. Either 1E 1613 is orbiting around a companion star and we are seeing a combined effect, or there are some mechanisms that are slowing it down faster than expected. Astronomers estimate that the supernova went off about 2,000 years ago and that’s not enough time for a pulsar to slow down this much simply by losing energy.
A potential clue to solving this mystery came in June when the pulsar emitted a short X-ray burst detected by NASA’s Swift observatory. The source appeared to be very similar to a magnetar, a type of pulsar with a magnetic field hundreds of million of times stronger than Earth’s, making 1E 1613 the 30th magnetar ever discovered.
Magnetars rotate around their axis in about 10 seconds so this doesn’t really solve the mystery. But in the paper, published in the Astrophysical Journal Letters, the researchers lead by Nanda Rea from the University of Amsterdam argue that the slowing down mechanism could be caused by material from the supernova being captured by the strong magnetic field and falling back onto the pulsar.
Another group has confirmed the findings of Rea’s team in a paper available online and accepted for publication in the Monthly Notices of the Royal Astronomical Society. More observations are necessary, but researchers are confident that we can find out why 1E 1613 is so slow.
"We will keep monitoring the source in the X-rays to pin down the exact spin-down," Rea told IFLScience.
"We'll keep observing it in the infrared band to search for any sign of this material still around and possibly in the millimeter band in the near future with the same aim."