A pendulum swings on its own, but sometimes it suddenly starts swinging so violently that it nearly breaks free from its mount. That's roughly how the white dwarf GD 1212 behaves — a star the size of Earth but with a mass almost like the Sun's. Normally, it pulsates with a period of about 1100 seconds, as if breathing: its brightness changes rhythmically due to waves traveling through its interior.
On the 61st day of observations, the Kepler telescope caught something unusual: in half a day, the star brightened by 17.5%, and its surface heated up by about 850 degrees. A room lamp suddenly blazed like a spotlight, even though no one touched the switch. The pulsations during the flare sped up and intensified — the pendulum swung faster and with a wider arc.
The cause of such flares lies in the nonlinear interaction of waves — a process physicists call parametric instability. Energy stored in the main pulsations (parent modes) suddenly transfers to secondary oscillations (daughter modes), which quickly damp out near the star's surface, heating it. This is like a swing set where one swing suddenly transfers its energy to the neighboring swing, making it jerk and creak.
The scientists also noticed a "failed" flare — a tiny brightness increase of just 0.35%, which nevertheless changed the pulsation frequency. These observations offer a glimpse into the mechanics of stellar interiors and help understand how energy is redistributed under extreme conditions, where matter is compressed a million times more strongly than on Earth. Thus, a pendulum that breaks free from its mount reveals the workings of the entire mechanism.
White dwarfs are so dense that a teaspoon of their material would weigh as much as several elephants — about 5 tons.
In Isaac Asimov's novel "The Gods Themselves," energy is transferred between universes — a similar principle works in white dwarf pulsations, just on the scale of a single star.