Is a young neutron star an oxymoron?
Neutron stars are incredibly dense remnants of stars that collapsed and exploded as supernova, making them spin at immense speeds. By definition, they have lived for millennia, died, and then been reborn as something new.
In any case, a press statement reveals that astronomers discovered one of the youngest known neutron stars while analyzing data from the VLA Sky Survey (VLASS).
This particular example is likely also surrounded by a phenomenon called a pulsar wind nebula, which sees charged particles accelerated to close to the speed of light.
Follow-up observations will allow astronomers to view a neutron star's very early formation and behavior as it interacts with the surrounding nebula, providing new insight into the evolution of dying stars.
Investigating a neutron star and potential pulsar wind nebula
The new images, from the National Science Foundation’s Karl G. Jansky Very Large Array (VLA), show bright radio emissions from the star's magnetic field that have only recently become visible, as they were obscured by a shroud of debris from the supernova explosion that created the fledgling neutron star.
The neutron star, dubbed VT 1137-0337, is located in a dwarf galaxy 395 million lightyears from Earth. It was first spotted by VLASS in 2018 and follow-up observations in 2018, 2019, 2020, and 2022 showed the object in greater detail. Another survey of the same region, VLA's FIRST in 1998, did not detect the neutron star.
The scientists, who reported their findings at the American Astronomical Society's meeting in Pasadena, California, considered several explanations for VT 1137-0337, including a gamma-ray burst and a supernova before settling on a pulsar wind nebula.
"What we're most likely seeing is a pulsar wind nebula," explained Dillon Dong, a Caltech graduate who will begin a Jansky Postdoctoral Fellowship at the National Radio Astronomy Observatory (NRAO) later this year.
Pulsar wind nebulae are created when the powerful magnetic field of a fast-spinning neutron star accelerates its surrounding charged particles — debris from the supernova that created the neutron star — close to the speed of light. All of this causes strong radio emissions, which were detected on Earth.
One of the youngest neutron stars could be an emerging 'super Crab'
The radio emissions picked up by VLASS were initially blocked by the shell of supernova debris surrounding the neutron star. As the shell expanded, it became less dense, allowing the radio waves to pass through.
"Based on its characteristics, this is a very young pulsar — possibly as young as only 14 years, but no older than 60 to 80 years," said Gregg Hallinan, Dong's Ph.D. advisor at Caltech. "This happened between the FIRST observation in 1998 and the VLASS observation in 2018," Hallinan said.
The researchers say the object they discovered is roughly 10,000 times more energetic than the Crab Nebula, one of the best-known examples of a pulsar wind nebula. "It is likely an emerging 'super Crab'," Dong said.
Though the astronomers believe the object is a pulsar wind nebula, they say that it could also be a magnetar, as it has a very strong magnetic field. Magnetars are a strong candidate for the origin of mysterious Fast Radio Bursts (FRBs), which are a focal point for global astronomical researchers. "In that case, this would be the first magnetar caught in the act of appearing, and that, too, is extremely exciting," Dong said.
The team plans to conduct follow-up observations to learn more about the incredibly young VT 1137-0337 by studying how it changes over time. This will provide an impressive and unprecedented window into the early behavior of neutron stars and how they interact with surrounding debris from the explosion that brought them to life.