Researchers from Keele University in the UK have worked with an international team of astronomers to uncover that a "nova", which was witnessed from Earth more than 300 years ago, was in fact a white dwarf and a brown dwarf star colliding.
Using the Atacama Large Millimeter/submillimeter Array (ALMA), an astronomical interferometer of 66 radio telescopes in the Atacama Desert of northern Chile, the team of astronomers found evidence that the stars collided in a short-lived blaze of glory that was witnessed on Earth in July 1670 - an event that was to be named Nova Cygni.
A white dwarf refers to the remains of a star like the Sun at the end of its life, and a brown dwarf is a "failed" star without sufficient mass to sustain thermonuclear fusion.
In July of 1670, observers on Earth witnessed the new star, or nova, in the constellation Cygnus - the Swan. Where previously there was no obvious star, there abruptly appeared a star as bright as those in the Plough, that gradually faded, reappeared, and finally disappeared from view.
Modern astronomers studying the remains of this cosmic event initially thought it was triggered by the merging of two main-sequence stars - those on the same evolutionary path as our Sun. This so-called new star was long referred to as 'Nova Vulpeculae 1670', and later became known as CK Vulpeculae.
However, we now know that CK Vulpeculae was not what we would today describe as a nova, but is in fact the merger of two stars: a white dwarf and a brown dwarf.
By studying the debris from this explosion - which takes the form of dual rings of dust and gas, resembling an hourglass with a compact central object - the research team concluded that it was a merger.
Professor Nye Evans, Professor of Astrophysics at Keele University and co-author on the paper, said:
"CK Vulpeculae has in the past been regarded as the oldest 'old nova'. However, the observations of CK Vulpeculae I have made over the years, using telescopes on the ground and in space, convinced me more and more that this was no nova.
"Everyone knew what it wasn't - but nobody knew what it was! But a stellar merger of some sort seemed the best bet."
With ALMA, the team's observations of the dusty hourglass and the warped disc, plus the presence of lithium and peculiar isotope abundances, meant the jigsaw all fitted together.
"In 1670 a brown dwarf star was 'shredded' and dumped on the surface of a white dwarf star, leading to the 1670 eruption and the hourglass we see today," he added.
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