Astronomers discover evidence of the most powerful pulsar in the distant galaxy

As the shell of debris from the supernova explosion expands over a few decades, it becomes less dense and eventually becomes thin enough that radio waves from within can escape. This allowed the VLA Sky Survey observations to detect the bright radio emission created as the rapidly rotating neutron star’s powerful magnetic field sweeps through the surrounding space, accelerating charged particles. This phenomenon is called a pulsar wind nebula. Credit: Melissa Weiss, NRAO/AUI/NSF

Astronomers analyzing data from the VLA Sky Survey (VLASS) have discovered one of the youngest known neutron stars – the superdense remnant of a massive star that exploded as a supernova. Images from the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) indicate that the bright radio emission fueled by the rotation

Most powerful pulsar in the distant galaxy

Top left: A giant blue star, much more massive than our Sun, has consumed, through nuclear fusion at its center, all of its hydrogen, helium and heavier elements down to iron. It now has a small iron core (red dot) at its center. Unlike the early stages of fusion, the fusion of iron atoms absorbs, rather than releases, energy. The energy released by the fusion that held the star against its own weight is now gone, and the star will quickly collapse, triggering a supernova explosion. Top Right: Collapse has begun, producing a superdense neutron star with a strong magnetic field at its center (insert). The neutron star, while containing about 1.5 times the mass of the Sun, is only the size of Manhattan. Bottom Left: The supernova explosion ejected a fast-moving husk of debris into interstellar space. At this stage, the debris shell is dense enough to cover any radio waves coming from the neutron star region. Bottom right: As the debris husk from the explosion expands over the course of a few decades, it becomes less dense and eventually becomes thin enough that radio waves from within can escape. This allowed the VLA Sky Survey observations to detect the bright radio emission created as the rapidly rotating neutron star’s powerful magnetic field sweeps through the surrounding space, accelerating charged particles. This phenomenon is called a pulsar wind nebula. Credit: Melissa Weiss, NRAO/AUI/NSF

“What we’re probably seeing is a pulsar wind nebula,” said Dillon Dong, a graduate student at Caltech who will begin a Jansky postdoctoral fellowship at the National Radio Astronomy Observatory (NRAO) later this year. A pulsar wind nebula is created when the powerful magnetic field of a

The scientists reported their findings at the American Astronomical Society meeting in Pasadena, California.

Giant Blue Star

A giant blue star, much more massive than our Sun, has consumed, through nuclear fusion at its center, all of its hydrogen, helium and heavier elements down to iron. It now has a small iron core (red dot) at its center. Unlike the early stages of fusion, the fusion of iron atoms absorbs, rather than releases, energy. The energy released by the fusion that held the star against its own weight is now gone, and the star will quickly collapse, triggering a supernova explosion. Credit: Melissa Weiss, NRAO/AUI/NSF

Dong and Hallinan discovered the object in data from VLASS, an NRAO project that began in 2017 to survey the entire VLA’s visible sky — about 80% of the sky. Over a period of seven years, VLASS is performing a full sweep of the sky three times, with one goal being to find transient objects. Astronomers found VT 1137-0337 in the first VLASS scan of 2018.

Comparing this VLASS scan with data from an earlier VLA sky survey called FIRST revealed 20 particularly luminous transient objects that may be associated with known galaxies.

“This one stood out because its galaxy is undergoing a burst of star formation and also because of the characteristics of its radio emission,” Dong said. The galaxy, called SDSS J113706.18-033737.1, is a dwarf galaxy containing about 100 million times the mass of the Sun.

The star collapse has begun

The star’s collapse began, producing a superdense neutron star with a strong magnetic field at its center (insert). The neutron star, while containing about 1.5 times the mass of the Sun, is only the size of Manhattan. Credit: Melissa Weiss, NRAO/AUI/NSF

When studying the features of VT 1137-0337, astronomers considered several possible explanations, including a supernova, a gamma-ray burst, or a tidal disruption event in which a star is destroyed by a supermassive one.

Initially, the radio emission was blocked by the shell of debris from the explosion. As this shell expanded, it became progressively less dense until radio waves from the pulsar wind nebula could pass through.

Supernova explosion ejected fast-moving debris shell

The supernova explosion ejected a fast-moving shell of debris into interstellar space. At this stage, the debris shell is dense enough to cover any radio waves coming from the neutron star region. Credit: Melissa Weiss, NRAO/AUI/NSF

“This happened between the FIRST observation in 1998 and the VLASS observation in 2018,” Hallinan said.

Probably the most famous example of a pulsar wind nebula is the Crab Nebula in the constellation Taurus, the result of a supernova that shone brightly in the year 1054. The Crab is easily visible today in small telescopes.

“The object we found appears to be approximately 10,000 times more energetic than the Crab, with a stronger magnetic field,” Dong said. “It’s probably an emerging ‘super crab’,” he added.

VT 1137 0337

VLA images of the location of VT 1137-0337 in 1998 on the left and 2018 on the right. The object became visible to the VLA sometime between these two dates. Credit: Dong & Hallinan, NRAO/AUI/NSF

While Dong and Hallinan consider that VT 1137-0337 is likely to be a pulsar wind nebula, it is also possible that its magnetic field is strong enough for the neutron star to qualify as a magnetar — a class of supermagnetic objects. Magnetars are a leading candidate for the origin of the mysterious Fast Radio Bursts (FRBs) now under intense study.

“In that case, this would be the first magnetar caught in the act of appearing, and that’s also extremely exciting,” Dong said.

In fact, some Fast Radio Bursts have been found to be associated with persistent radio sources, the nature of which is also a mystery. They bear a strong resemblance in their properties to VT 1137-0337, but have not shown evidence of strong variability.

“Our discovery of a very similar bound source suggests that the radio sources associated with FRBs could also be luminous pulsar wind nebulae,” Dong said.

Astronomers plan to carry out more observations to learn more about the object and monitor its behavior over time.

The National Radio Astronomy Observatory is a National Science Foundation facility operated under a cooperative arrangement by Associated Universities, Inc.

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