Zombie white dwarf fed on neighbor star until exploding in a thermonuclear blast

It is obvious that this supernova is a Type Ia.

The first supernova in radio waves has been discovered by astronomers, who discovered that a white dwarf star that was about to explode was feeding on a partner star like a cosmic vampire before it burst. This zombie star was avidly eating on helium-rich material from its stellar victim, which ultimately resulted to its own destruction, as opposed to consuming blood like the vampires of mythology.

This Type Ia supernova, designated supernova SN 2020eyj, was found by the Zwicky Transient Facility camera on Palomar mountain. The Nordic Optical telescope on La Palma and the huge Keck telescope in Hawaii were used to further investigate this discovery. These investigations showed that the supernova was distinct from earlier Type Ia supernovas in that the material surrounding it was abnormally dominated by helium-rich materials.

Erik Kool, a postdoctoral researcher in the department of astronomy at Stockholm University, is the study's primary author. "Once we saw the signatures of strong interaction with the material from the companion, we tried to also detect it in radio emission," he said in a release. The first Type Ia supernova has been discovered in radio waves, which scientists have been attempting to achieve for decades.

The researchers hypothesized that the companion star being drained by the fatal white dwarf is rich in helium after detecting strong signs of the element in the light from the exploding system. The research team also discovered that the companion donor star had mostly been depleted of material prior to the explosion.

When material ejected by an exploding star collides with nearby matter, known as circumstellar material, electrons are accelerated to near-light speeds and emit what are known as synchrotron emissions, which can include radio waves. This is how radio waves like the ones used to detect this supernova are produced.

These radio waves wouldn't be there if the supernova took place in a so-called "clean" environment devoid of circumstellar material. This is the first time that astronomers have found these radio emissions emanating from a Type Ia supernova.

Astronomers refer to Type Ia supernovas as "standard candles" because they produce a standard amount of light that is consistent from event to event. They may be used as a cosmic yardstick to measure the distance between Earth and supernovae as well as the pace of the universe's expansion. Both of these measurements can be made using the light they release.

Despite its usefulness, scientists still don't fully understand the causes of Type Ia supernovas. According to the widely accepted hypothesis, sort Ia supernovas are caused when a compact white dwarf star consumes too much mass from a partner star, which can be any sort of star, from a big star to another white dwarf. However, this new research demonstrates that there are other possible scenarios.

However, it is still connected to the ones we use to study the expansion of the universe, according to co-author and researcher Joel Johansson from the Department of Physics at Stockholm University. "This supernova tells us that there are many different pathways to a white dwarf star explosion," says the author, "whereas normal Type Ia supernovae appear to always explode with the same brightness."

How dead stars emerge from the tomb suddenly

White dwarfs, like the one that formerly existed in the system under study, are stellar leftovers that develop when stars with masses comparable to the sun run out of nuclear fusion fuel and die.

The outward radiation pressure that protects stars from the inward pressure of gravity ends when the hydrogen needed to turn into helium in the cores of sun-like stars runs out. During what is known as the red giant phase, this results in the star's core collapsing and its outer layers expanding to as much as 100 to 1,000 times the star's initial diameter. In around 5 billion years, the sun will transition into this red giant phase, expanding and engulfing the inner planets, including Earth. This will leave a dead white dwarf star with a cooling stellar core that is surrounded by shed stellar material.

Solo stars like the sun will eventually go extinct, but white dwarfs in binary systems may resurge if material from a partner star flows to their surface. These dead stars may undergo further nuclear fusion on their surfaces as a result, but if they take in too much material, it may drive them above the Chandrasekhar limit, which has catastrophic consequences.

The Chandrasekhar limit, which is 1.4 times the mass of the sun, is the threshold beyond which a star cannot go supernova. Accordingly, overfeeding might lead a white dwarf that is below that limit to accumulate enough material to undergo a supernova. It is unclear exactly how this overfeeding takes place. This kind of radio wave observations could be able to provide some light on the process.

A thorough examination of the radio waves from SN 2020eyj and comparable Type Ia supernovas, according to the study team, might help identify the properties of the star systems that give rise to them.

The team's research was published on Wednesday (May 17) in the journal Nature