A team of scientists, led by Miguel Santander-García set out to learn why some stars create strangely shaped nebulae late in their lives. What they found was something that has never been seen before, two white dwarves on their way to becoming one star and then exploding in a supernova.

Santander-García of the National Astronomy Observatory, Alcalá de Henares, Spain, wanted to know how some stars produce strangely shaped asymmetric nebulae in their later stages. In conducting this research, one of the objects they observed was the planetary nebulae Henize 2-428.

The team found a close pair of extremely dense white dwarf stars, with a total mass of 1.8 times that of the Sun. It is the most massive pair of such stars found to date. In about 700 million years the stars will merge, causing a massive thermonuclear explosion leading to a Type la supernova.

A white dwarf can have a mass of about 1.4 times that of the sun, anything more than that and it cannot support itself against a gravitational collapse. This is called the Chandrasekhar limit. A Type Ia supernova is what happens when a white dwarf acquires additional mass causing it to exceed the Chandrasekhar limit and explode.

“When we looked at this object’s central star with ESO’s Very Large Telescope, we found not just one but a pair of stars at the heart of this strangely lopsided glowing cloud,” says coauthor Henri Boffin from the European Southern Observatory (ESO) in a statement.

The discovery supports the theory that the odd nebulae shapes that Santander-García was looking for were the result of double central stars. An even bigger discovery, however, was still awaiting the team.

“Further observations made with telescopes in the Canary Islands allowed us to determine the orbit of the two stars and deduce both the masses of the two stars and their separation. This was when the biggest surprise was revealed,” reports Romano Corradi, another of the study’s authors.

The researchers found that each of the stars have a mass slightly less than that of our Sun and that they orbit each other every four hours. They are so close to each other that, according to the Einstein’s theory of general relativity, they will continue to grow closer due to the emission of gravitational waves. Eventually they will emerge into a single star.

That star, however, won’t last long. It will be so massive that it will collapse under its own weight and explode.

“Until now, the formation of supernovae Type Ia by the merging of two white dwarfs was purely theoretical. The pair of stars in Henize 2-428 is the real thing,” explains David Jones, coauthor of the article and ESO Fellow at the time the data were obtained.

The team’s results, reported in the journal Nature and the nebulae Henize 2-428, are sure to draw further attention from other researchers.

“It’s an extremely enigmatic system. It will have important repercussions for the study of supernovae Type Ia, which are widely used to measure astronomical distances and were key to the discovery that the expansion of the Universe is accelerating due to dark energy,” said Santander-García.

Since none of us will be here to see the event in 700 million years, Space Library has put together this artists rendering of what will happen when the two stars merge.