Speeding star might escape the Milky Way: A cosmic mystery

A simulation of a possible explanation for an L subdwarf named CWISE J124909+362116.0's speed shows it as a part of a white dwarf binary pair that ended with the white dwarf exploding into a supernova. Credit: Adam Makarenko / W.M. Keck Observatory.

While it may seem like the sun is stationary with the planets moving around it, the sun is actually orbiting the Milky Way galaxy at a speed of about 220 kilometers per second—almost half a million miles per hour.

This seems fast, but a recently discovered faint red star is moving even faster, catching the attention of scientists.

A citizen science project called Backyard Worlds: Planet 9 and a team of astronomers found a rare hypervelocity L subdwarf star racing through the Milky Way.

This star, named CWISE J124909+362116.0 (“J1249+36”), is moving so quickly that it might leave the Milky Way altogether.

The research, led by Professor Adam Burgasser from the University of California San Diego, was presented at a national astronomy meeting in Madison, Wisconsin.

The star was first noticed by volunteers from the Backyard Worlds: Planet 9 project. These volunteers look through huge amounts of data collected by NASA’s Wide-field Infrared Survey Explorer (WISE) mission.

They tag moving objects in the data, and when enough people tag the same object, astronomers investigate. J1249+36 stood out because it was moving at about 600 kilometers per second (1.3 million miles per hour).

This speed is fast enough for the star to escape the Milky Way’s gravity, making it a potential “hypervelocity” star.

To learn more about J1249+36, Burgasser used the W.M. Keck Observatory in Hawaii to measure its infrared spectrum.

The data showed that J1249+36 is a rare L subdwarf, a type of star with very low mass and temperature. These subdwarfs are some of the oldest stars in the Milky Way.

The discovery was made possible by new atmosphere models created by Roman Gerasimov and Efrain Alvarado III from UC San Diego. Their models matched the observed spectrum of J1249+36 accurately.

The team used this data and images from other telescopes to measure J1249+36’s position and speed in space. They found that the star’s speed and path could allow it to escape the Milky Way. But what caused this star to move so fast?

Scientists have two main theories. In the first scenario, J1249+36 was once the companion of a white dwarf. White dwarfs are the remnants of stars that have used up their nuclear fuel.

If a white dwarf gains too much mass from a companion star, it can explode as a supernova. This explosion could have given J1249+36 a “kick,” sending it flying through space at high speed.

In the second scenario, J1249+36 was part of a globular cluster, which is a group of stars bound together by gravity.

These clusters can have black holes at their centers. If a star gets too close to a black hole binary (two black holes orbiting each other), the interaction can fling the star out of the cluster at high speed.

To find out which scenario is correct, Burgasser’s team plans to study J1249+36’s elemental composition. If the star was near a supernova, it might have elements from the explosion in its atmosphere. If it came from a globular cluster, it might have a different set of elements.

By studying J1249+36, astronomers hope to learn more about the history and dynamics of the Milky Way.

Whether the star was sped up by a supernova or a black hole, its discovery is an exciting opportunity to understand our galaxy better.