As the shell of explosive debris from the supernova expands over several decades, it becomes less dense and eventually becomes thin enough that the radio waves inside can escape. This allowed observations from the VLA Sky Survey to detect bright radio radiation created when the powerful magnetic field of a rapidly rotating neutron star passes through the surrounding space, accelerating charged particles. This phenomenon is called 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 Karl G. Jansky National Science Foundation Very Large Array (VLA) show that bright radio radiation powered by the rotating pulsar’s magnetic field has only recently emerged behind a dense shell of debris from a supernova explosion.
The object, called VT 1137-0337, is located in a dwarf galaxy 395 million light-years from Earth. It first appeared in an image of VLASS made in January 2018. It did not appear in an image of the same region made by the FIRST VLA study in 1998. It continued to appear in later observations of VLASS in 2018, 2019 , 2020 and 2022.
Top left: A giant blue star, much more massive than our Sun, has absorbed, through fusion at its center, all its hydrogen, helium and heavier elements to iron. It now has a small iron core (red dot) in its center. Unlike the earlier stages of synthesis, the fusion of iron atoms absorbs rather than releases energy. The fusion energy that has held the star against its own weight is now gone, and the star will quickly collapse, causing a supernova explosion. Top right: The crash began, producing a superdense neutron star with a strong magnetic field in the center (inserted). The neutron star, although about 1.5 times the mass of the Sun, is only the size of Manhattan. Bottom left: A supernova explosion has thrown a rapidly moving shell of debris out into interstellar space. At this stage, the shell of debris is dense enough to obscure any radio waves coming from the neutron star region. Bottom right: As the shell of explosive debris expands over several decades, it becomes less dense and eventually becomes thin enough that the radio waves inside can come out. This allowed observations from the VLA Sky Survey to detect bright radio radiation created when the powerful magnetic field of a rapidly rotating neutron star passes through the surrounding space, accelerating charged particles. This phenomenon is called pulsar wind nebula. Credit: Melissa Weiss, NRAO / AUI / NSF
“What we’re probably seeing is a pulsating wind nebula,” said Dylan Dong, a Caltech student who will begin a postdoctoral fellowship with Jansky at the National Radio Astronomical Observatory (NRAO) later this year. A pulsar wind nebula is created when the powerful magnetic field of a rapidly rotating neutron star accelerates the surrounding charged particles to almost the speed of light.
“Based on its characteristics, it’s a very young pulsar – probably only 14 years old, but not older than 60 to 80,” said Greg Halinan, a doctoral student at Dong at Caltech.
The scientists announced their findings at a meeting of the American Astronomical Society in Pasadena, California.
A giant blue star, much more massive than our Sun, has absorbed, through fusion at its center, all its hydrogen, helium and heavier elements to iron. It now has a small iron core (red dot) in its center. Unlike the earlier stages of synthesis, the fusion of iron atoms absorbs rather than releases energy. The fusion energy that has held the star against its own weight is now gone, and the star will quickly collapse, causing a supernova explosion. Credit: Melissa Weiss, NRAO / AUI / NSF
Dong and Halinan discovered the object in data from VLASS, an NRAO project that began in 2017 to study the entire sky visible to the VLA – about 80 percent of the sky. For a period of seven years, VLASS performed a full scan of the sky three times, one of the goals being to find transient objects. Astronomers discovered VT 1137-0337 during the first VLASS scan of 2018.
A comparison of this VLASS scan with data from an earlier study of the VLA sky, called FIRST, revealed 20 particularly luminous transient objects that could be associated with known galaxies.
“This one stood out because its galaxy was experiencing an explosion of star formation, and also because of the characteristics of its radio broadcast,” 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 collapse of the star began, producing a superdense neutron star with a strong magnetic field in the center (insertion). The neutron star, although about 1.5 times the mass of the Sun, is only the size of Manhattan. Credit: Melissa Weiss, NRAO / AUI / NSF
In studying the characteristics of VT 1137-0337, astronomers considered several possible explanations, including a supernova, a gamma-ray burst, or a tidal destruction event in which a star is shattered by a supermassive black hole. They concluded that the best explanation was the pulsar wind nebula.
In this scenario, a star much more massive than the Sun exploded like a supernova, leaving behind a neutron star. Most of the original star’s mass was blown out like a shell. The neutron star rotates rapidly, and as its powerful magnetic field passes through the surrounding space, it accelerates charged particles, causing strong radio emissions.
Initially, the radio emission was blocked from view by the shell of explosive debris. As this shell expands, it becomes less and less dense, until finally the radio waves from the pulsar wind nebula can pass through it.
The supernova explosion threw a rapidly moving shell of debris out into interstellar space. At this stage, the shell of debris is dense enough to obscure 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,” Halinan said.
Probably the most famous example of a pulsar wind nebula is the Cancer Nebula in the constellation Taurus, the result of a supernova that shone brightly in 1054. Cancer is easily seen today in small telescopes.
“The object we found appears to be approximately 10,000 times more energetic than Cancer, with a stronger magnetic field,” Dong said. “It’s probably an emerging ‘super cancer,'” he added.
VLA images of the location of VT 1137-0337 in 1998, left and 2018, right. The object became visible to the VLA somewhere between these two dates. Credit: Dong & Hallinan, NRAO / AUI / NSF
While Dong and Halinan believe that VT 1137-0337 is most likely a pulsar wind nebula, it is also possible that its magnetic field is strong enough for a neutron star to qualify as a magnetar – a class of supermagnetic objects. Magnetars are a leading candidate for the origins of the mysterious rapid radio bursts (FRB), which are now being intensively studied.
“In this case, this will be the first magnetar caught in the act of appearing, and it’s also extremely exciting,” Dong said.
Indeed, it has been found that some rapid radio bursts are associated with constant radio sources, the nature of which is also a mystery. They have strong similarities in their properties with VT 1137-0337, but have shown no evidence of strong variability.
“Our discovery of including a very similar source suggests that FRB-linked radio sources may also be glowing pulsar wind nebulae,” Dong said.
Astronomers plan to conduct additional observations to learn more about the object and to observe its behavior over time.
The National Radio Astronomical Observatory is a facility of the National Science Foundation managed under a collaborative agreement by Associated Universities, Inc.
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