White dwarfs are the final fate of Sun-like stars. They are very dense, with a mass similar to the Sun but a size similar to Earth.
As a white dwarf forms, it spins down rapidly due to magnetic braking. This means that by the time a white dwarf is a few billion years old, it is rotating very slowly, completing one rotation in several days or even weeks.
However, some white dwarfs are observed to be rotating much faster, completing one rotation in just a few hours.
The team of astronomers, led by Associate Professor Simone Scaringi from Monash University, used theoretical models and computer simulations to show that the sudden increase in rotation rate is caused by a process known as the "spin-up" of the white dwarf's magnetic field.
The spin-up process occurs when the white dwarf's magnetic field becomes twisted and tangled, causing it to store energy. This energy can then be released suddenly, causing the white dwarf to rotate much faster.
The astronomers found that the spin-up process is most likely to occur in white dwarfs that have a strong magnetic field and are surrounded by a dense cloud of gas and dust.
The team's findings are published in the journal Nature Astronomy.
"This is a significant breakthrough in our understanding of white dwarfs," said Associate Professor Scaringi.
"We have finally solved the mystery of how these stars can suddenly increase their rotation rate."
The team's findings will help astronomers to better understand the evolution of white dwarfs and how they interact with their surroundings.
