When a star consumes its nuclear fuel towards the end of its life, it undergoes a gravitational breakdown and discards its outer layers. This leads to a great explosion, known as the supernova, which can lead to the creation of a black hole, a pulsar, or a white dwarf. And despite decades of observation and research, there are still not many scientists who know about this phenomenon.
Luckily, ongoing observations and improved instruments are leading to discoveries of all kinds that enable new insights. For example, a team of astronomers using the National Radio Astronomy Observatory (NRAO) and NASA recently observed that a "cannonball" pulsar is being thrown off the supernova, which is believed to have created it. This finding already provides information about how pulsars can record speed from a supernova.
The pulsar, referred to as PSR J0002 + 6216 (J0002), is located about 6,500 light-years from Earth. It was originally discovered in 2017 by citizen scientists working on a project called [email protected] where volunteers analyze data from NASA's Fermi Gamma Ray Space Telescope (FGST). This project was previously responsible for the discovery of 23 pulsars.
This particular discovery, however, was particularly important. Since its first discovery, a team led by Frank Schinzel of the National Radio Astronomy Observatory (NRAO) has conducted subsequent radio observations using the Very Large Array of Karl G. Jansky (VLA) of New Mexico. These showed that the pulsar had a tail of shocked particles and magnetic energy that stretched 13 light-years beyond.
More interesting was the fact that this tail pointed to the center of a supernova remnant 53 light years behind (CTB 1). This tail was the result of the interstellar gas's rapid movement of the pulsar, resulting in shock waves that generate magnetic energy and accelerate particles. Shinzel recently said in a NASA press release:
"Thanks to its narrow, arrow-like tail and random view, we can trace this pulsar right back to its birthplace. Further investigations of this object will help us to understand how these explosions "let" neutron stars "kick" at such a high speed.
Based on the Fermi data, the team was able to measure how fast and in which direction the pulsar was moving. This was achieved by a technique known as "pulsar timing" in which gamma-ray flashes that occur at each rotation of the pulsar (in the case of J0002, 8.7 times per second) are used for motion tracking.
The team found that J0002 was traveling at a speed of about 1125 km / s (700 mps) or 4 million km / h (2.5 million miles per hour). In the past, scientists have observed that pulsars travel at high speed, but at an average speed that is about five times slower – 240 km / s (150 mps). Dale Frail (a NRAO researcher who was part of the discovery team) said:
"The explosive debris in the supernova remnant originally expanded faster than the pulsar's motion. However, the debris was slowed down by the encounter with the tough material in interstellar space, allowing the pulsar to catch up and overtake it.
The team also noted that the pulsar would eventually catch up with the pulsar expanding shell created by the supernova. First, the expanding debris of the supernova would have moved outward faster than J0002, but after about 5,000 thousand years, interstellar gas shell interaction gradually slowed the atmosphere down. After 10,000 years, as the astronomers now see, the pulsar was far outside the grenade.
While astronomers have long known that pulsars can get kicked out by the supernova explosions they produce, they remain unclear as to what happens. One possible explanation is that instabilities in the collapsing star are a dense, slowly moving area of matter who had pulled the neutron star with it and accelerated it gradually away from the explosion center.
"This pulsar moves fast enough to finally escape our Milky Way," said Frail. "Numerous mechanisms for making the kick have been proposed. What we see in PSR J0002 + 6216 supports the assumption that hydrodynamic instabilities in the supernova explosion are responsible for the high velocity of this pulsar. "
Looking to the future, the team plans to conduct additional observations using VLA, the National Science Foundation's Very Long Baseline Array (VLBA) and NASA's Chandra X-ray Observatory. This follow-up will hopefully provide further clues as to how this pulsar has gained so much speed that could help solve some of the secrets that still surrounds supernova explosions.
These findings were recently shared at the 17th High Energy Astrophysics Division (HEAD) of the American Astronomical Society, held March 17-21 in Monterey, California. They are also the subject of a study published for publication in the latest issue of The Astrophysical Journal Letters
. Further references: NRAO NASA