One of the brightest stars in the sky that is visible from Earth will eventually explode and will appear as a full moon during the daytime.
Betelgeuse, about 640,000 light years away, is one of the closest and brightest stars to Earth, and its violent death will be visible from our planet.
Scientists have been curious whether the explosion, called supernova, will happen soon because the star has been dimming significantly over the past few years.
“Betelgeuse is a red supergiant star with a distinctive orange-red hue. Stars in this class are nearing the end of their lives,” Nasa said on its website.
“They are the largest stars in the universe because they puff up and expand out into space in their old age.”
The star is about 10 million years old and is much younger than the Sun in our solar system, which is five billion years old.
However, it is 700 times the size of the Sun and burns through its materials faster, meaning it will have a shorter life than a star like the Sun.
It has a 400-day cycle, as well as a longer cycle that stretches about five years. Our Sun has an 11-year cycle.
A bright, but violent star
This means Betelgeuse has brightness that changes over time, sometimes appearing brighter and then dimmer.
Nasa said that the star took a drastic dip in brightness in 2019, which was unusual.
“Within months, the star had dimmed by about 60 per cent in an event now known as the Great Dimming,” the US space agency said.
“This sudden dimming was so significant that some scientists wondered if Betelgeuse was entering a pre-supernova phase, which precludes a massive star’s explosive ‘death’ in a supernova.
“Talk of a possible explosion sparked intrigue around the world as Betelgeuse would be the closest supernova to be observed and recorded by humans.”
Data from the Hubble Space Telescope showed that Betelgeuse had ejected surface material into space, which temporarily blocked light from the star.
The Sun also ejects material, but this eruption by Betelgeuse was 400 billion times as much mass that is usually emitted during coronal mass ejections.
“The chunk it spewed out into space likely weighed several times as much as our Moon,” Nasa said.
What will the explosion look like from Earth?
Dr Stanimir Metchev, Canada research chair in extrasolar planets at Western University, said that when the explosion happens, the star will appear as a full moon on Earth.
"Betelgeuse is already one of the brightest stars in the sky. However, after an initial explosion, and over the course of the first 2 weeks, Betelgeuse will be come as bright as the full moon, and will in fact be visible during daytime," he said.
"The supernova will then gradually fade over months.
"After tens of years the exploded outer shell of the dead star will have been blown away to a sufficiently large distance from the star, that it will appear as a 'planetary nebula': a ring around the remnant faint core of the dead star."
Will it explode in our lifetime?
Nasa said that the supernova is not likely to happen for about another 100,000 years.
It is predicted that by then the star will become either a neutron star or a black hole.
“The star’s final fate depends on how much material is left after the supernova event,” Nasa said.
Dr Stanimir Metchev also said that it was unlikely that it would happen in our lifetime.
He said the last stages of a star's life can last hundreds of thousands of years.
Will the supernova impact Earth?
Dr Stanimir Metchev said the explosion will not have any negative impact on Earth because of its distance from the planet.
Even at its brightest, it would be about 400,000 times fainter than the Sun.
"The most harmful component to Earth from a supernova explosion would be the x-rays and the gamma rays," he said.
"However, a supernova would have to be less than half of Betelgeuse’s distance to start having an effect on Earth’s atmosphere and life.
"There is no danger of this happening with the nearest stars for hundreds of millions of years.
"Betelgeuse’s explosion as a supernova would offer just a spectacular space show for the lucky Earthlings to witness it."
Stellar views of supernova from Earth
The brightest supernova to appear in Earth's skies was in 1987, when a star exploded 160,000 light years away near the Tarantula Nebula.
Supernova 1987A was so massive that it appeared as a bright star in the sky. Even after dimming, the light could still be observed with telescopes until 2017.
Astronomers predict that flashes from an exploding star that is 10 billion light years away will be visible from Earth in 2037.
This would be the fourth time that light from the same star is visible, after it made its first appearance in 2016 in three different images. The light disappeared in 2019.
The Hubble Space Telescope captured three images of the dying star, called Supernova Requiem (located in the MRG-M0138 galaxy about 10 billion light years from Earth), which appeared as tiny dots.
A study published in the Nature Astronomy journal revealed that a reappearance is expected in 2037.