White Dwarf Stars to Collide in Catastrophic Supernova

A pair of white dwarf stars located deep inside the planetary nebula Henize 2-428 are slowly moving closer and closer towards each other, destined to collide in a catastrophic supernova explosion.

Reported in the journal Nature, the European Southern Observatory's (ESO) Very Large Telescope (VLT) in Chile was originally studying how some stars produce strangely shaped, asymmetric nebula. They focused on Henize 2-428 and found something they did not expect - not just one star, but two.

"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," co-author Romano Corradi, a researcher at the Instituto de Astrofísica de Canarias, said in a press release.

The next shocker was that the two stars were white dwarfs - tiny, extremely dense stars with a total mass about 1.8 times that of the Sun. The fact that there are two stars supports the theory that double central stars may explain the odd shapes of some of these nebulae.

They've also found that the stars orbit every 4 hours and due to the emission of gravitational waves, they are slowly spiraling into one another. Within the next 700 million years, these stars will merge and under the stress of their combined mass, explode in a giant supernova.

"Until now, the formation of supernovae Type Ia by the merging of two white dwarfs was purely theoretical," said co-author David Jones, an ESO Fellow at the time the data were obtained. "The pair of stars in Henize 2-428 is the real thing!"

"It's an extremely enigmatic system," added lead researcher Santander-García. "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."

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