(Production Ramiro J. Angulo)
Although two years have passed since the completion of NASA’s Kepler (aka planet hunter) mission, its data continues to unravel new mysteries. Now, a team of astronomers from the US space agency claim to have identified a previously unknown star (a white dwarf) that is feasting on its cosmic companion, a small brown dwarf, cannibalizing the gas until it emits an intense glow. This type of interaction is known as a cataclysmic variable star, although its most popular name is: vampire star.
According to NASA, in this outburst, the star’s brightness increased 1,600 times in less than a day, before starting to fade. Astronomers can explain why the outburst occurred, but the increase in brightness remains a mystery. The disk created around the white dwarf reached a staggering 11,700 ° C at the peak of the outburst, more than twice the surface temperature of Sol (5,506 ° C). It is the same process that occurs, albeit on a much larger scale, around supermassive black holes.
“The two stars are so close that the strong gravity of the white dwarf takes material away from the brown dwarf, absorbing its essence like a vampire,” according to NASA.
Thanks again, Kepler
Kepler / K2: Background Survey is the software used by the experts. It analyzes each pixel in the Kepler file data for sudden jumps in brightness. In essence, he acts as a detective to find clues of very fast and mysterious explosions in the universe.
The system they found includes a white dwarf star with a brown dwarf companion about one-tenth its mass, orbiting the white dwarf every 83 minutes. Recall that a white dwarf is the central remnant of an old dying star with a mass similar to the Sun but with the volume of the Earth. The white dwarf is incredibly dense; its brown counterpart is too big to be classified as a planet, but too small to be considered a star.
Because the star does not constantly feed, it dims and brightens, but the increase in brightness was inconsistent, compared to other dwarf novae, suggesting, according to the researchers, new physics behind these types of outbursts.
Star clusters
Most of the stars that exist in the Milky Way are binary or double stars and this system located 3,000 light years away from Earth, near the constellation Scorpio, is an example of this. They are approximately the same distance as the moon from Earth, and this closeness allows the strong gravity of the white dwarf to separate the material from the brown dwarf, creating an accretion disk and causing a superburst.
When a sun-like star reaches the end of its life and burns all of its fuel, it inflates to form a red giant and explodes about half its mass. Nearby planets and asteroids are consumed by the explosion. Gone will be a fiery white dwarf and the planets and asteroids that survived the event will move further and further away from the white dwarf because the star would no longer have the same gravitational force on them. Finally , white dwarfs slowly cool down as they age.
The researchers say this discovery, made in collaboration with the Space Telescope Science Institute and the US University of Notre Dame, provides new insights into ‘vampire’ star systems and the fate of our own Sun.
“The next steps in this project are to analyze all the Kepler data and extend it to data from the Transiting Exoplanet Survey Satellite, known as TESS,” says Ryan Ridden-Harper, leader of the work. “This will give us a better understanding of the fastest explosions in the universe. And along the way, we might discover some rare events that no other telescope would be able to find.”
Referencia: R Ridden-Harper et al. Discovery of a new WZ Sagittae-type cataclysmic variable in the Kepler/K2 data, Monthly Notices of the Royal Astronomical Society (2019). DOI: 10.1093/mnras/stz2923
NASA illustration of the white dwarf cannibalizing the brown dwarf nova.
