Supernova 2020eyj: first radio signal and massive explosion of dying white dwarf

Astronomers have made a groundbreaking discovery by detecting a radio signal from a dying white dwarf star that experienced a massive explosion. Typically, stars like our sun end their lives in a quiet manner, but in binary star systems, they can result in powerful supernova explosions. 

This marks the first time that scientists have observed the radio signature of such an event in a galaxy over 400 million light-years away. The findings provide intriguing insights into the nature of the companion star involved.

When stars weighing up to eight times the mass of our sun consume their nuclear fuel, they shed their outer layers and form planetary nebulae, leaving behind a dense, hot core called a white dwarf.

However, if a white dwarf gains additional mass and exceeds about 1.4 times the mass of our Sun, it triggers a self-destruct mechanism, leading to a Type Ia supernova explosion.

The origin of the extra mass required for such an explosion has long puzzled scientists. It was previously thought that the gas stripped off a larger companion star in close orbit could contribute to the explosion.

However, this theory was challenged because stars tend to scatter gas, making it difficult to observe a radio signal from the supernova. As a result, scientists began considering the possibility that Type Ia supernovae are the result of two white dwarfs spiraling inward and merging, leaving no gas to generate a radio signal.

Supernova 2020eyj, discovered in March 2020, initially behaved like a typical Type Ia supernova but exhibited peculiar characteristics after seven weeks.

It stopped fading in brightness and displayed features indicating an abundance of helium-rich gas. This led scientists to suspect that Supernova 2020eyj belonged to a rare subclass of Type Ia supernovae, in which the blast wave interacts with gas that was stripped from the outer layers of a surviving companion star.

To confirm their hypothesis, the researchers aimed to detect enough shocked gas to produce a radio signal. An array of radio telescopes across the United Kingdom was employed to observe the supernova about 20 months after the explosion. 

Surprisingly, they successfully detected the radio signature of an "infant" Type Ia supernova for the first time, providing evidence that not all Type Ia supernovae are caused by the merger of two white dwarfs.