Cosmic detectives are investigating a case of mistaken stellar identity: An exploding star that was once thought to be the oldest recorded nova a nuclear explosion on the surface of a dead star was more likely caused by the merger of two stars.

In 1670, a bright new star appeared in the constellation Cygnus, the Swan, and stayed there for two years you cansee the location of the new stars in this video. The short-lived star was grouped into the "nova" category, but over the last 30 years, astronomers have been questioning its identity.

A new research paper that examines the chemical makeup of the crime scene may be the final nail in the coffin. The researchers suggest that the so-called nova is instead the oldest example of another type of stellar explosion sometimes called a "red nova" a somewhat newly-discovered phenomenon that scientists are still working to understand. [Photos ofSupernova StarExplosions]

In 1670, a new star appeared just above the head of the swan that makes up the constellation Cygnus. Many astronomers took note of this newcomer, so its appearance and life span are well documented. It was dubbed Nova Vul 1670 at the time, "nova" referred simply to any new star.

In the last 300 years, however, the word "nova" has taken on a much more specific and scientific meaning.

By today's definition, a classic nova is an explosion that takes place on the surface of a white dwarf the small, dense, nugget of leftover material from a star that has stopped burning. The white dwarf syphons material away from another nearby star, the pressure builds up on its surface and a nuclear reaction releases an incredible burst of energy. (Unlike Type Ia supernovas, which start in a similar fashion, the white dwarf in a nova is expected to survive through the explosion.)

Many things about CK Vulpeculae's identity as a nova just don't line up, said Tomasz Kaminski, a postdoctoral fellow at the European Southern Observatory.

For example, novas tend to burn in the sky for days not years, as CK Vulpeculae did. Plus, the new star of 1670 didn't disappear right away. After two years, it faded, then reappeared, then faded for good which is very unusual for a nova, Kaminski said. And observations have shown that CK Vulpeculae's temperature is much lower than that of a nova, where the radiation from the nuclear reaction continues to generate heat after the explosion is done, Kaminski said.

The new study, which is detailed in the March 23 edition of the journal Nature, may finally strip CK Vulpeculae of its "nova" title. Kaminski and his co-authors looked at the different molecules present in the wreckage of CK Vulpeculae, and found a profile that they say cannot be created by a classical nova.

But if CK Vulpeculae isn't a nova, then what is it?

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Astronomy's Oldest Known 'Nova' a Cosmic Case of Mistaken Identity