A star survived its own death and is coming back to life. It gets weirder

A star that returned from the brink of death is doing something unexpected. Sakurai’s Object went supernova in 1181 and was visible as a bright object in the Cassiopeia constellation for at least 185 days. Astronomers who lived in the early years of the samurai in Japan at the time observed the remnants of a star that exploded and still survived.

Now, NOIRLab’s Gemini North telescope, comprising two powerful telescopes in Hawaii and Chile, has captured the debris field in great detail. Dubbed Pa 30, the region has ionised gases in perfectly symmetrical knots, revealing a bizarre occurrence. So while we can see that something chaotic happened, the surviving progenitor star continued to remain right at the centre and has not moved from its place at all.

Ilaria Caiazzo, co-author of the new paper published in The Astrophysical Journal, said that Pa 30 is located around 7,500 light-years from Earth, which makes it "uniquely valuable for study." While that might seem like a long distance, the star is only about one-fourth of the distance to the centre of the Milky Way.

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The new observations resolve enormous strands of red ionised sulfur and blue-green ionised oxygen. Caiazzo said this object is so huge that “the planetary region of our solar system could fit in each knot about ten times with room to spare.”

What happened to Sakurai’s Object

In 1996, the star was seen flaring back to life even after all its nuclear fuel was over. It swelled and released clouds of gas and dust. A typical star ends up as a white dwarf, and Sakurai’s Object was also moving towards the same destiny. But then a layer of helium deep inside it suddenly reignited and threw up large amounts of material into space. It became huge once again, thus also known as a born-again star.

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Not hotter, but colder

In 2005, a model predicted the star would reach about 161,500°F (90,000 K) by 2020. However, that hasn't happened. Instead, the latest observations show that the star’s surface is about 54,500°F (30,500 K) hot right now. Even though it is still roughly five times hotter than the surface of the Sun, the figure is way below the prediction made 21 years ago.

“Our measurements show that the star is reheating more gradually than some earlier models predicted," Albert Zijlstra of the University of Manchester said.

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The star itself is not visible. The dust and gas it had thrown out shrouded it completely. The team detected a powerful, steady wind blowing off the star's surface rich in carbon and helium with speeds of about 310 miles per second. This revealed that its surface composition has shifted significantly to roughly 43 per cent helium and 51 per cent carbon. The material thrown out in the 1990s has also spread about 300 times farther.

Fate of the star

Current astronomical understanding and comparisons, similar to stars like V605 Aquilae, show that Sakurai's Object will eventually finish its life as a white dwarf.