Scientists Discover Shrinkage In Star Spinning Like Space Ballerina

Scientists may have found a star that is contracting as it spins faster and faster in outer space, representing the first time experts have observed this theorized shrinkage of a white dwarf actually happening.

Young white dwarfs are believed to go through a period of contraction, but it has been difficult to see that in action because most of the white dwarfs astronomers have observed have been older, and measuring small differences in a radius can be tricky on such faraway objects. But according to a study in the Monthly Notices of the Royal Astronomical Society, a team has discovered a white dwarf about 2,000 light years away that could be contracting for the last two decades.

That idea comes from the fact that the object’s spin has been steadily speeding up over those 20 years, and now only takes several seconds to make one rotation. The study authors say that a contracting white dwarf would explain why that increased rotation is occurring, and puts the star’s age at about 2 million years.

The relationship between contracting and spinning faster is a matter of physics. The object’s angular momentum, a function of mass, radius and velocity, remains constant in this scenario. Because the mass of the white dwarf is also not changing, a decrease in radius leads to an increase in velocity.

It has often been explained by pointing out how ballerinas or ice skaters will twirl around more quickly when their arms are pulled into their chests instead of reaching out — the dancers are making themselves more compact, which affects their speed.

“If correct, this is the first direct evidence for a white dwarf contraction on early evolutionary stages,” the authors wrote.

White dwarfs are essentially shells of their former selves — they are the super-dense remains of a small or average-sized star like our sun that got old and ran out of gas. First the star expands outward into a red giant, then eventually its core collapses and the star blows off all its outer layers. What’s left is the white dwarf, which can pack the mass of the sun into a space as small as Earth.

The white dwarf that the astronomers have focused on in this study is part of a binary system with the complicated name HD49798/RX J0648.0-4418, in which two stars orbit the same point in space, located in the Puppis constellation. According to the study, it completes a spin on its axis every 13.2 seconds.

Lomonosov Moscow State University said that is the fastest spin of any known white dwarf, and it is only getting faster. The rotation is estimated to pick up by about 7 nanoseconds every year.

“This might seem a very small change, but it is actually a very large effect for a body weighing more than our sun but with a radius as small as about [3,100 miles],” the university said. “Indeed, such a large spin-up rate could not be easily explained in standard ways.”

Scientists have projected that in the first several million years of a white dwarf’s existence, its radius could shrink a few hundred miles. This particular white dwarf is estimated to be contracting about a centimeter each year, based on its velocity changes.

If that contraction rate was constant through its first 2 million years of life, its radius would shrink a little more than 12 miles during that time.

“For decades it has been theoretically clear that that young white dwarfs are contracting,” researcher Sergei Popov said in the statement. “Yet, that very phase of contraction has never been observed ‘in real time.’”

According to the astrophysicist, his team got help seeing the contracting white dwarf because of the light being reflected off of a matter that was building up around a neighboring star, a process known as accretion.

“Thanks to this discovery, astrophysicists will be able to study and evaluate the evolution patterns of young white dwarfs — and successfully look for similar systems in the galaxy,” Popov said.