"vampire" star system
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Credit: NASA

This 'vampire' star system had an outburst brighter than those sparkly Twilight vamps

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Feb 3, 2020

There is a universe where vampires sparkle — this one. One of these cosmic vampires was recently caught by scientists in data from NASA’s now defunct Kepler spacecraft (RIP). Kepler caught the blinding flash of light generated by one star eating another.

Basically, a double star system consisting of a brown dwarf orbiting a white dwarf went overkill when the white dwarf sucked too much star stuff from its companion. Nobody expected the increase in brightness and super-outburst that followed. What Kepler saw is what happens when the white dwarf consumes too much — a dwarf nova.

“These dwarf nova systems have been studied for decades, so spotting something new is pretty tricky," said research team lead Ryan Ridden-Harper of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. "We see accretion disks all over – from newly forming stars to supermassive black holes – so it's important to understand them."

Vampirism in stars (not a scientific term) is pretty much the sucking of astral blood (also not a scientific term). When one star goes into vampire mode and leeches off the other star’s essence, it accumulates material around it into an accretion disc. You see accretion discs around black holes all the time. Just like a black hole feeds off star stuff and other cosmic debris that falls into its gravitational pull, the white dwarf in the duo accumulates material from the brown dwarf into an accretion disc that keeps growing as the star gorges itself.

Usually, the white dwarf sucks in material from the brown dwarf at a steady rate as the brown dwarf circles it every 83 minutes at a distance close to that between the Earth and the Moon, or about 250,000 miles. The white dwarf’s much stronger gravity eats away at its companion star, and all that material keeps adding on to the accretion disc until there is something of a temper tantrum.

The Disc Instability Model suggests that the point at which a dwarf nova happens is when the system becomes unstable from the white dwarf overindulging. As its accretion disc gathers material more and more rapidly, it gives the star an intense boost in gravitational energy. The nova outburst occurs when it needs to vomit out that extra gravitational energy before it can stabilize again, which explains the flash of light glimpsed by Kepler. This can be a vicious cycle that repeats itself over and over.

What is particularly weird about this dwarf nova is that even “standard theories of accretion disc physics don’t predict this kind of phenomenon,” as NASA explained on their website. These theories can explain the bright bang out of nowhere, but still can’t demystify why the entire process begins so slowly.

Dwarf novae are actually the most common type of novae. They may not get as bright as other novae, but several hundred are already known, and the space agency’s planet hunter TESS may continue to find more as they search space for transients, or objects that pass in front of a star and cause dimming, indicating that something is orbiting that star.

"The detection of this object raises hopes for detecting even more rare events hidden in Kepler data," said co-author Armin Rest, also of STScI.

So yes, vampires that can outshine the darkness do exist, but these have way more luminosity than the entire cast of Twilight drenched in glitter. Sorry Edward.

(via NASA)

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