Space news: Astronomers left puzzled by 350-year mystery of unexplained stellar explosion

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The stellar explosion of a star dubbed CK Vulpeculae was first spotted by the French monk Anthelme Voituret in 1670. In the months following its discovery, the event grew in brightness until it almost matched Polaris, the Northern Star. CK Vulpeculae faded from view after about a year, leading astronomers to believe it was a nova – a type of stellar explosion that occurs in systems bearing a Sun-like star and white dwarf

But a team of international astronomers using the Gemini North GNIRS instruments has now dismantled theory, offering new insight into the explosion.

Originally spotted in the constellation of Vulpecula, the astronomers found the explosion happened fives times further away than previous estimates.

Even more surprisingly, this puts the 1670 event into a class of much more energetic astronomical phenomena.

These events are too bright to be regular novas but are also too faint to be even bigger supernovas – explosions caused by the death of supermassive stars.

Five years ago, a team of astronomers suggested CK Vulpeculae appeared in our night skies after the head-on collision of two stars.

And just three years later, the same astronomers tweaked their theory, suggesting one of these stars was a red dwarf – an example of the most numerous stars in the Milky Way galaxy.

The new theory came to light after isotopes of aluminium were detected around the explosion.

But the theory was further complicated when in 2018 a separate team of astronomers proposed the 1670 event was produced by a brown dwarf and white dwarf colliding.

Now, researchers have found CK Vulpeculae is farther away and spewing gasses more violently than previous records show, at speeds of nearly seven million kilometres per hour

The new team was led by astronomers from the UK, India and the Gemini Observatory in Maunakea, Hawaii.

The team obtained infrared observations across CK Vulpeculae and detected two nebulas – wisps of stellar gas – near its outermost edges.

Tom Geballe of the Gemini Observatory said: “The key to our discovery was the GNIRS measurements obtained at the outer edges of the nebula.

“The signature of redshifted and blueshifted iron atoms detected there shows that the nebula is expanding much more rapidly than previous observations had suggested.”

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Lead author Dipankar Banerjee of the Physical Research Laboratory Ahmedabad, India, added: “We did not suspect that this is what we would find.

“It was exciting when we found some gas travelling at the unexpectedly high speed of about seven million km/hour.

“This hinted at a different story about CK Vulpeculae than what had been theorized.”

By calculating the speed at which the nebula was expanding, as well as how much the wisps had moved in the last 10 years, the researchers found CK Vulpeculae sits about 10,000 light-year or 58,786,254,000,000,000 miles from the Sun.

The finding shows the object is located about five times further than previous estimates.

The researchers also found the 1670 explosion erupted about 25 times more energy than previously estimated, meaning whatever triggered the event was much more violent than a nova.

Nye Evans of Keele University in the UK said: “In terms of energy released, our finding places CK Vulpeculae roughly midway between a nova and a supernova.

“It is one of a very few such objects in the Milky Way and the cause — or causes – of the outbursts of this intermediate class of objects remain unknown. I think we all know what CK Vulpeculae isn’t, but no one knows what it is.”

Professor Banerjee added: “It is difficult at this stage to offer a definitive or compelling explanation for the origin of the 1670 eruption of CK Vulpeculae.

“Even 350 years after Voituret’s discovery, the nature of the explosion remains a mystery.”

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