Artists love to anthropomorphize stars as lovely ladies, but truth be told, stars can be very violent. Astronomers have found a particularly bloodthirsty example in a binary star 3,000 light-years away, in which a small dead star slowly and periodically strips its companion of gas.
This type of interaction is known as a catastrophic variable star, but you may know it by its more popular name, the vampire star.
These are binary systems in which a smaller star, usually a white dwarf (the compact core of a dead star with the mass of the Sun), passes through material ejections from its larger companion.
But in the case of this system, the dynamics are even stranger: the binary companion is a brown dwarf, an object that began to form in the same way as a star, but cannot build up enough mass to trigger hydrogen fusion in the core. Such objects are sometimes referred to as 'sunken stars', with mass between the planets as gas giants and small stars.
This particular brown dwarf was 10 times less massive than the white dwarf in the binary.
The event was discovered in archived data collected by the Kepler Space Telescope in 2016. The space telescope captured a star that grew brighter, but the data was archived without detecting an event.
But recently, an automated program began analyzing data looking for changes in stars – called transient events – and found it.
“The rare event we found was a super-burst of brightness from a new dwarf star that could be considered a vampire star system,” explained astronomer Ryan Ridden-Harper of the Australian National University.
'Kepler's incredible data shows a 30-day period during which the dwarf nova quickly became 1,600 times brighter, then dims and gradually returns to its normal brightness.'
This brightness was created by material orbiting a white dwarf in an accretion disk – the same process that occurs on a much larger scale around supermassive black holes. The vortex disk generates such intense heat through friction that it becomes incandescent.
In turn, this produces star transient events. Since the star is not constantly fed, it dims and brightens.
But there was something else strange. The rise in brightness has been inconsistent, as has been observed in other super-outbursts of dwarf vampires, suggesting that the researchers say new physics is behind these outbreaks.
“The next steps for this project are to comb through all of the Kepler data and compare it with the data from the Transiting Exoplanet Survey Satellite, which is known as TESS,” said Ridden-Harper.
'This will give us an understanding of the fastest explosions in the universe. We might find some rare events that no other telescope could find. '
The study was published in the Royal Astronomical Society's Monthly Notices.
