A pulsar wind nebula is created when the powerful magnetic field of a rapidly spinning neutron star accelerates surrounding charged particles to nearly the speed of light. Probably the most famous example of this type of nebula is the Crab Nebula in the constellation of Taurus — the result of a supernova that shone brightly in 1054 CE.
Top left: a giant blue star, much more massive than our Sun, has consumed, through nuclear fusion at its center, all its hydrogen, helium, and heavier elements up to iron. It now has a small iron core (red dot) at its center. Unlike the earlier stages of fusion, the fusion of iron atoms absorbs, rather than releases, energy. The fusion-released energy that has held up the star against its own weight now is gone, and the star will quickly collapse, triggering a supernova explosion. Top right: the collapse has begun, producing a superdense neutron star with a strong magnetic field at its center (inset). The neutron star, though containing about 1.5 times the mass of the Sun, is only about the size of Manhattan. Bottom left: the supernova explosion has ejected a fast-moving shell of debris outward into interstellar space. At this stage, the debris shell is dense enough to shroud from view any radio waves coming from the region of the neutron star. Bottom right: As the shell of explosion debris expands over a few decades, it becomes less dense and eventually becomes thin enough that radio waves from inside can escape. This allowed observations by the VLA Sky Survey to detect bright radio emission created as the rapidly spinning neutron star’s powerful magnetic field sweeps through the surrounding space, accelerating charged particles. This phenomenon is called a pulsar wind nebula. Image credit: Melissa Weiss, NRAO / AUI / NSF.
The newly-discovered pulsar wind nebula resides in SDSS J113706.18-033737.1, a dwarf galaxy some 395 million light-years away from Earth in the constellation of Leo.
Designated VT 1137-0337, the object was spotted in data from the VLA Sky Survey (VLASS), an NRAO project that began in 2017 to survey the entire sky visible from NSF’s Karl G. Jansky Very Large Array (VLA).
Over a period of seven years, VLASS is conducting a complete scan of the sky three times, with one of the objectives to find transient objects.
The astronomers found VT 1137-0337 in the first VLASS scan from 2018.
Comparing that VLASS scan to data from an earlier VLA sky survey called FIRST revealed 20 particularly luminous transient objects that could be associated with known galaxies.
“This one stood out because its galaxy is experiencing a burst of star formation, and also because of the characteristics of its radio emission,” said Dr. Dillon Dong, an astronomer at the National Radio Astronomy Observatory.
In studying the characteristics of VT 1137-0337, Dr. Dong and his colleagues considered several possible explanations, including a supernova, gamma ray burst, or tidal disruption event in which a star is shredded by a supermassive black hole.
The astronomers concluded that the best explanation is a pulsar wind nebula.
“In this scenario, a star much more massive than the Sun exploded as a supernova, leaving behind a neutron star,” they said.
“Most of the original star’s mass was blown outward as a shell of debris.”
“The neutron star spins rapidly, and as its powerful magnetic field sweeps through the surrounding space it accelerates charged particles, causing strong radio emission.”
“Initially, the radio emission was blocked from view by the shell of explosion debris. As that shell expanded, it became progressively less dense until eventually the radio waves from the pulsar wind nebula could pass through.”
The researchers consider VT 1137-0337 to most likely be a pulsar wind nebula, it also is possible that its magnetic field may be strong enough for the neutron star to qualify as a magnetar.
“In that case, this would be the first magnetar caught in the act of appearing, and that, too, is extremely exciting,” Dr. Dong said.
Source link: https://www.sci.news/astronomy/pulsar-wind-nebula-distant-dwarf-galaxy-10907.html
