Scientists believe they have finally discovered what will happen when the sun dies – and it doesn't look good for Earth.

Experts had long been in agreement about when our star will die - in approximately 10 billion years - but were previously unsure as to how it would go.

Now, an international team of astronomers, including Professor Albert Zijlstra from the University of Manchester, believe they have figured it out - and it ends in a blaze of glory known as a planetary nebula.

As the sun burns the last of its hydrogen it will turn into a red giant and expand to 250 times its current size, certainly destroying Earth - although the planet will have long been uninhabitable by the time it comes.

The scientists say this will leave behind a ghostly glowing ring of interstellar gas and dust.


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Image: The Orion Nebula is a diffuse rather than planetary nebula. Pic: ESO/G. Beccari

Planetary nebulae are how 90% of all stars die as they collapse from red giants to white dwarfs - but it was not previously clear if our sun had enough mass to create one.

Using a new data model which predicts the life cycle of stars, the scientists were able to establish what the final status of our sun would be.

Their research, published in the journal Nature Astronomy, has resulted in a model which is used to predict how much gas and dust stars eject into space when they die.

"When a star dies it ejects a mass of gas and dust - known as its envelope - into space," Professor Zijslra said. "The envelope can be as much as half the star's mass.

"This reveals the star's core, which by this point in the star's life is running out of fuel, eventually turning off and before finally dying.

"It is only then the hot core makes the ejected envelope shine brightly for around 10,000 years - a brief period in astronomy.

"This is what makes the planetary nebula visible. Some are so bright that they can be seen from extremely large distances measuring tens of millions of light years, where the star itself would have been much too faint to see."

The image of a planetary nebula above is of a nebula called Abell 39. It is the 39th entry in a catalogue of large nebulae discovered by George Abell in 1966.

It was taken at the Arizona's Kitt Peak National Observatory in 1997 through a blue-green filter that isolates the light emitted by oxygen atoms in the nebula.

Abell 39 has a diameter of about five light years, and the thickness of the spherical shell is about a third of a light year.

The nebula itself is roughly 7,000 light years from Earth, in the constellation Hercules.