For the first time ever, astronomers have found evidence for a white dwarf and brown dwarf colliding – and the event may have been seen on Earth back in 1670.
Reported in the Monthly Notices of the Royal Astronomical Society, an international team of scientists used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe the remnants of the suspected explosion, more than 2,000 light-years from Earth.
In 1670, this event in the night sky – known as Nova Vulpeculae or CK Vulpeculae – flared to be one of the 100 brightest stars in the sky. It disappeared from view soon after, leading astronomers to later suspect it was an explosion called a nova.
Previous studies have suggested the event was the result of two stars like our Sun colliding. But this latest study suggests it is something more unusual: a collision between a dead star (a white dwarf) and a failed star (a brown dwarf).
“The type we believe that happened here is a new one, not previously considered or ever seen before,” Professor Albert Zijlstra from the University of Manchester said in a statement. “This is an extremely exciting discovery."
The event left behind an hourglass shape, which has been difficult to explain. Studying this debris, however, the researchers found that a white dwarf-brown dwarf merger could be the answer.
It’s thought the hourglass shape was the result of the brown dwarf, which is a failed star that was unable to ignite nuclear fusion at its core, being shredded apart and dumped on the surface of the white dwarf.
As a result, the brown dwarf disintegrated, burning up in thermonuclear explosions that were triggered on the white dwarf. Surrounding the white dwarf would have been a rotating disk of shredded material from the brown dwarf that was firing out jets into space.
The researchers came to this conclusion by watching the light from two more distant stars pass through the debris of the merger. This showed the presence of lithium, something that’s normally destroyed in the interiors of stars (but not in brown dwarfs), suggesting one was involved in the collision.
"The white dwarf would have been about 10 times more massive than the brown dwarf, so as the brown dwarf spiralled into the white dwarf it would have been ripped apart by the intense tidal forces exerted by the white dwarf,” the aptly named Professor Sumner Starrfield said in the statement.
Back in 1670, the event produced a bright light that was seen by the Carthusian monk Anthelme and the astronomer Hevelius. Today, it leaves us with an intriguing first glance at an event we’ve never seen before.