NASA’s Kepler Space Telescope is very good at detecting subtle traces of distant exoplanets by detecting faint changes in star brightness. Kepler has successfully discovered many new worlds during the mission, but recent discoveries are perhaps one of the most interesting to date.
As the researchers describe in a new paper in the Monthly Journal of the Royal Astronomical Society, Kepler has discovered an unprecedented “super-outburst”. It comes from a previously unknown dwarf star system. In less than 24 hours, the dwarf star suddenly increased its brightness by 1,600 times, and then slowly weakened and disappeared.
The dwarf star system being studied consists of a white dwarf star and a brown dwarf star, about one-tenth the mass of a white dwarf. A white dwarf is the remains of an aging solar star that contains about the size of the earth in a sphere of the Earth’s size. A brown dwarf is an object of mass between 10 and 80 times that of Jupiter because it is too small to perform nuclear fusion. The brown dwarf orbits the white dwarf every 83 minutes, just 250,000 miles (about 400,000 kilometers), about the distance from Earth to the moon.
They are so close that the powerful gravitational pull of the white dwarf strips the brown dwarf’s material and sucks away its essence like a vampire. The peeled material forms a disk (called a accretion disk) input as it rotates toward the white dwarf. When the dwarf star system experiences a superburst, the brightness increases by more than 1,000 times.
The Kepler Space Telescope captured the entire event, observing a slow rise in brightness and then rapidly increasing it. Although sudden changes in brightness are theoretically predicted, the reason for the slow start remains a mystery. The standard theory of accretion disk physics could not predict this phenomenon, which was subsequently observed in two other dwarf superflares.
Observations show that the temperature of the disk has risen from about 5000-10000 degrees F (2700-5300 degrees C) in normal conditions to 17,000-21000 degrees F (9700-11700 degrees C) at the peak of the super-explosion. This type of dwarf nova system is relatively rare, with only about 100 known.
The object’s detection offers hope for detecting more rare events hidden in Kepler data. The team plans to continue digging up Kepler data, as well as data from another exoplanet hunter, the Exoplanet Survey Satellite Tess (TESS) mission, to look for other transients.