When a star exhausts its nuclear fuel towards the end of its life, it undergoes a gravitational collapse and throws its outer layers. This results in a magnificent explosion called supernova, which can lead to the creation of a black hole, a pulsar or a white dwarf. And despite decades of observation and research, many scientists are still unaware of this phenomenon.
Fortunately, current observations and improved instruments lead to all sorts of discoveries that offer opportunities for new knowledge. For example, a team of astronomers from the National Radio Astronomy Observatory (NRAO) and NASA recently observed a "cannonball" pulsar quickly moving away from the supernova that could have created it . This discovery already gives insight into how pulsars can pick up speed from a supernova.
The pulsar, designated PSR J0002 + 6216 (J0002), is located about 6,500 light-years from Earth. It was discovered in 2017 by citizen scientists working for a project called [email protected], which relies on volunteers to analyze data from NASA's Fermi Gamma Ray Telescope (FGST). This project has been responsible for the discovery of 23 pulsars up to now.
However, it is this particular discovery that has been particularly significant. Since its discovery, a team led by Frank Schinzel of the National Radio Astronomy Observatory (NRAO) has made follow-up radio observations with the help of the very large Karl G. Jansky network (VLA) in New Mexico . These showed that the pulsar had a tail of shocked particles and magnetic energy extending behind 13 light-years.
Even more interesting was the fact that this tail was pointing to the center of a supernova remnant located 53 light-years behind it (CTB 1). This tail was the result of the rapid movement of the pulsar in the interstellar gas, which resulted in shock waves producing magnetic energy and accelerated particles in its wake. As Shinzel explained in a recent NASA press release:
"With its narrow dart-like tail and fortuitous viewing angle, we can trace this pulsar back to its place of birth. Further study of this object will help us better understand how these explosions are able to "kick" neutron stars at such a high speed. "
Based on Fermi data, the team was able to measure the speed and direction in which the pulsar was moving. This was accomplished through a technique called pulsar timing, in which flashes of gamma rays occurring at each rotation of the pulsar (in the case of J0002, 8.7 times per second) are used to follow the movement.
The team then determined that J0002 was moving at a speed of about 1125 km / s (700 mps) or 4 million km / h (2.5 million mph). In the past, scientists have observed pulsars moving at high speed, but at an average speed five times slower, or 240 km / s (150 mps). As explained by Dale Frail (a NRAO researcher who was part of the discovery team):
"The debris of the explosion in the rest of the supernova had grown faster than the pulsar movement. However, the debris was slowed by its encounter with the tenuous material of interstellar space, which allowed the pulsar to catch up and overtake it. "
The team also determined that the pulsar would eventually catch up with the expanding hull created by the supernova. At first, the expanding debris of the supernova would have moved faster than J0002, but after about 5,000,000 years, the interaction of the envelope with the interstellar gas gradually slowed it down. At 10,000 years, as astronomers currently see it, the pulsar was well outside the shell.
Although astronomers have known for a long time that the supernova explosions that create them can boost pulsars, they still do not know how it goes. One possible explanation is that the instabilities of the collapsed star could have produced a dense and slow region of matter that began to drive the neutron star gradually accelerating it from the center of the explosion.
"This pulsar moves fast enough to escape our Milky Way," said Frail. "Many mechanisms for kicking have been proposed. PSR J0002 + 6216 confirms the idea that hydrodynamic instabilities in the supernova explosion are responsible for the high speed of this pulsar. "
The team plans to make additional observations using the VLA, the very long base network of the National Science Foundation (VLBA) and NASA's Chandra X-ray observatory. I hope that these follow-ups will provide more clues about the speed of this pulsar's acceleration, which could go a long way to solving the mystery that still surrounds supernova explosions.
These results were recently shared at the 17th meeting of the American Astronomical Society (HEAD), which was held March 17-21 in Monterey, California. They are also the subject of a study being published in the last issue of The letters of the astrophysical journal.
Further reading: NRAO, NASA