Supernova: star dies from the eyes of scientists

Astronomical premiere
On the cosmic deathbed: Scientists observe the death of a giant star – in real time

by Yannik Schüller
January 7th, 2022, 4:16 pm

Stars are born, live and die – in this they are not so dissimilar to us. However, “the last breath” of a star is much more spectacular. For the first time, scientists have succeeded in observing the explosive agony of one of these giant gas spheres – and that in real time.

Led by researchers from Northwestern University and the University of California, the team has followed the last 130 days in the life of a distant celestial body – to the bitter and visually stunning end. The astronomers published their observations on Thursday in the renowned “Astrophysical Journal”.

Stellar death: when the star engine runs out of fuel

A star, like our sun, is basically nothing more than a huge nuclear reactor. During its entire lifetime, hydrogen atom nuclei fuse in the star’s interior, producing helium. A huge amount of energy is released in the process.

The dying process begins when the star has used up all the hydrogen available to it. At this point, the central core fire of the celestial body goes out, as the US magazine “Astronomy” explains. Since the core, which only consists of the remaining helium, is no longer supported by the fusion energy, it shrinks. At the same time, however, the star’s core is surrounded by a thin shell of fusing hydrogen. The result: The pressure of gravity continues to heat the core, and the outer shell of the star expands enormously. When it has reached a temperature of around 100 million degrees Celsius, however, the nuclear fusion continues under the unrestrained pressure – only this time carbon and oxygen are produced. And the whole thing starts from the beginning – whereby the star continues to expand and takes on the luminosity of sometimes thousands of suns. In the end, the core is made of iron, that’s all you can get at first.

But at some point that will end. Particularly heavy stars (at least five times the mass of our sun) experience a particularly brilliant ending. When the inward pressure of gravity finally wins the upper hand, the giant will collapse. This collapse happens so quickly that the outer parts of the star are thrown into space in huge shock waves – a supernova.

“Like watching a ticking time bomb”

Scientists observed precisely such a dying star shortly before its departure. The object in question is 120 million light-years away from our earth and is located in the galaxy NGC 5731. For comparison: The closest star (Proxima Centauri) as seen from our sun is “only” 4.2 light-years away .

When it died, the star we were now observing was ten times more massive than our sun and thus belonged to the stellar class of red supergiants. According to the scientists, observing this stellar farewell contradicts previous ideas about what would happen to such a huge celestial body shortly before its death. Until now, it was assumed that such stars would behave relatively “quietly” before their end – that there would be no violent eruptions or extremely luminous emissions.

In this case, however, the astronomers were able to watch the star ejecting hot gas beforehand and tearing itself apart before it finally exploded in a Type II supernova. “This is a breakthrough in our understanding of what massive stars do just before they die,” the study’s lead author Wynn Jacobson-Galán said in a statement. It was the first time ever that the death of a red supergiant was recorded.

The researchers became aware of the dying star thanks to the STARR telescope from the University of Hawai, which captured the bright radiation in the summer of 2020. 130 days later, the astronomers could have witnessed the final end in the form of the supernova at the same point.

“It’s like watching a ticking time bomb,” said the study’s lead author Raffaella Margutti. Researchers have never before observed such violent activity in a star of this size.

This is what the end of the star could have looked like:

What kind of death is our sun facing?

Basically, the more massive a star, the shorter it lives. Our sun belongs to the category of “yellow dwarfs” – a term that is of course to be understood in astronomical terms. Because our sun already has a diameter of around 1.4 million kilometers and a life expectancy of around 10 billion years.

When the time comes, our star will inevitably inflate itself. The fluffed sun is then likely to devour Venus and Mercury, like Matt Caplan, assistant professor at Illinois State University, all rolled into one Contribution to “Astronomy” predicts. The earth would not necessarily be swallowed up directly, but it would probably perish into a lifeless, scorched rock. Later the sun turns into a planet-sized white, then finally into a black dwarf. With that the light in our solar system would have gone out for good.

But don’t worry: there is still plenty of time until the Grand Final. Scientists assume that our star has just finished half of its life.

sources: “The Astrophysical Journal“;”CNN“;”Science Daily“;”Astronomy“; NASA