Gemini North sightings breakthrough in centuries-old effort to unravel astronomical mystery

An international team of astronomers using the GNIRS instrument from Gemini North have discovered that CK Vulpeculae, first seen as a bright new star in 1670, is about five times farther away than previously thought. This makes CK Vulpeculae’s 1670 explosion much more energetic than previously estimated and places it in a mysterious class of objects that are too bright to be members of the well-known type of explosions known as de novae, but too weak to be supernovae.

350 years ago, the French monk Anthelme Voituret saw a shining new star come to life in the constellation Vulpecula. Over the next several months, the star grew almost as bright as Polaris (the North Star) and was watched by some of the top astronomers of the day before it vanished after a year. The new star eventually earned the name CK Vulpeculae and has long been considered the first documented example of a nova – a fleeting astronomical event resulting from an explosion in a nearby binary star system in which one limb is a dwarf. white, the remainder of a Sun-like Star. However, a series of recent results have cast doubt on the long-held classification of CK Vulpeculae as a nova.

In 2015, a team of astronomers suggested that the appearance of CK Vulpeculae in 1670 was the result of two normal stars experiencing a cataclysmic collision. A little over three years later, the same astronomers further proposed that one of the stars was in fact a swollen red giant star, following their discovery of a radioactive isotope of aluminum in the immediate vicinity. from the site of the 1670 explosion. To complicate the picture even further, a separate group of astronomers have come up with a different interpretation. In their article, also published in 2018, they suggested that the sudden brightening in 1670 was the result of the fusion between a brown dwarf – a failed star too small to glow via the thermonuclear fusion that powers the Sun – and a white dwarf. .

Now, adding to the current mystery surrounding the CK Vulpeculae, new observations from the Gemini International Observatory, a program of NSF’s NOIRLab, reveal that this enigmatic astronomical object is much more distant and has ejected gas at much faster speeds. higher than previously reported.

This team, led by Dipankar Banerjee from Physical Research Laboratory Ahmedabad, India, Tom Geballe from Gemini Observatory and Nye Evans from Keele University in the UK, originally planned to use the Gemini Near-Infrared Spectrograph (GNIRS) instrument on Gemini North on Maunakea of ​​Hawaii to confirm the detection in 2018 of radioactive aluminum in the heart of CK Vulpeculae. After realizing that detecting this in the infrared would be much more difficult than they originally thought, astronomers improvised and obtained infrared observations over the full extent of the CK vulpecules, including the two volutes of cloudiness at its outermost edges.

“The key to our discovery was the GNIRS measurements obtained at the outer edges of the nebula,” Geballe explained. “The signature of the red-shifted and blue-shifted iron atoms detected there shows that the nebula is growing much faster than previous observations suggested.”

As lead author and astronomer Banerjee explains, “We didn’t think this was what we were going to find. It was exciting when we found gas traveling at a surprisingly high speed of around 7 million km / hour. This hinted at another story. about CK Vulpeculae than what had been theorized. “

By measuring both the speed of the nebula’s expansion and the momentum of the outermost wicks over the past ten years, and taking into account the tilt of the nebula in the night sky, which had been estimated earlier by others, the team determined that CK Vulpeculae is about 10,000 light years from the Sun – about five times farther away than previously thought. This implies that the explosion of 1670 was much brighter, releasing about 25 times more energy than was previously estimated. This much larger estimate of the amount of energy released means that whatever event caused the sudden appearance of CK Vulpeculae in 1670 was much more violent than a simple nova.

“In terms of the energy released, our discovery places CK Vulpeculae roughly halfway between a nova and a supernova,” Evans commented. “It is one of the few objects in the Milky Way and the cause – or causes – of explosions of this intermediate class of objects remains unknown. I think we all know what CK Vulpeculae isn’t, but nobody knows what it is. “

The visual appearance of the CK Vulpeculae nebula and the high speeds observed by the team could help astronomers recognize relics of similar events – in our Milky Way or in external galaxies – that have occurred in the past.

“It is difficult at this point to offer a definitive or convincing explanation for the origin of the 1670 eruption of CK Vulpeculae,” Banerjee concluded. “Even 350 years after the discovery of Voituret, the nature of the explosion remains a mystery.”

Provided by the Association of Universities for Research in Astronomy (AURA)