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Runaway star spotted trying to escape the Milky Way galaxy

Our Sun may seem like the center of the universe to us, but it’s actually on the move, orbiting the Milky Way galaxy at a speed of nearly half a million miles per hour. That’s fast, but it’s nothing compared to a recently discovered star runaway that’s blazing a trail across the cosmos.

This stellar speedster, known as CWISE J124909+362116.0 (J1249+36 for short), is a low-mass star, or L subdwarf, that’s not only hypervelocity but potentially on a trajectory to escape the Milky Way altogether.

Runaway stars

A runaway star is a star moving through space at an unusually high velocity, often exceeding 30 km/s.

These stars are ejected from their original location, typically a star cluster, due to gravitational interactions or supernova explosions. In gravitational interactions, close encounters with other massive stars can sling a star out of its cluster.

Alternatively, if a star in a binary system explodes as a supernova, the remaining star may be propelled away at high speed. Runaway stars can travel vast distances, sometimes leaving their galaxies.

Runaway star J1249+36 going nova. Credit: UCSD
Runaway star J1249+36 going nova. Credit: UCSD

Their high speeds and trajectories can provide insights into the dynamics and past events of their regions of origin.

Studying runaway stars helps astronomers understand star formation, stellar evolution, and the gravitational forces within star clusters.

Their movement through the interstellar medium can also create shock waves, affecting the surrounding gas and dust.

Citizen science

The discovery of J1249+36 is a testament to the power of citizen science. It was first spotted by volunteers participating in the Backyard Worlds: Planet 9 project, a collaborative effort between scientists and the public.

These citizen scientists sift through massive amounts of data collected by NASA’s Wide-field Infrared Survey Explorer (WISE) mission, looking for moving objects in the sky.

The human eye’s knack for pattern recognition makes it an invaluable tool for spotting anomalies that computer algorithms might miss.

Runaway star J1249+36

J1249+36 caught the attention of volunteers due to its remarkable speed. Initial estimates pegged it at a mind-boggling 1.3 million miles per hour, fast enough to break free from the Milky Way’s gravitational grip.

To learn more about this speedy star, astronomers turned to the W.M. Keck Observatory in Hawaii, where they used its powerful instruments to analyze the star’s light.

The findings revealed that the runaway star J1249+36 is an L subdwarf, a type of star that’s both small and cool, representing some of the oldest stars in our galaxy.

What’s the origin story?

The question that intrigued scientists most was: What gave this star such a tremendous kick? Two leading theories emerged.

One possibility is that J1249+36 was once part of a binary star system with a white dwarf, the dense remnant of a dead star.

If the white dwarf siphoned off too much material from its companion, it could have triggered a supernova explosion, flinging J1249+36 into space at high velocity.

The second theory involves a close encounter with a black hole. Globular clusters, dense swarms of stars, are thought to harbor black holes at their centers.

If J1249+36 strayed too close to a black hole binary (two black holes orbiting each other), the gravitational chaos could have ejected it from the cluster at an incredible speed.

“This is where the source became very interesting, as its speed and trajectory showed that it was moving fast enough to potentially escape the Milky Way,” explained Adam Burgasser, a professor of astronomy and astrophysics at the University of California San Diego and the lead researcher on the project.

Chemical fingerprint of runaway star

To determine which scenario is more likely, scientists are looking for clues in the runaway star’s chemical composition.

If J1249+36 was launched by a supernova, its atmosphere might contain traces of heavy elements created in the explosion. Alternatively, the star’s chemical makeup could reveal whether it originated in a globular cluster.

“We’re essentially looking for a chemical fingerprint that would pinpoint what system this star is from,” said Roman Gerasimov, a UC San Diego alumnus who developed new models to study L subdwarfs.

Milky Way’s mysteries

Whether J1249+36’s incredible journey was triggered by a supernova, a close encounter with a black hole, or some other cosmic event, its discovery offers valuable insights into the Milky Way’s history and dynamics.

This runaway star, hurtling through space at unimaginable speeds, serves as a reminder of the vastness and complexity of our universe.

The research on J1249+36 was presented at the 244th national meeting of the American Astronomical Society (AAS) in Madison, Wisconsin.

This ongoing study, fueled by the combined efforts of citizen scientists and professional astronomers, is a shining example of how collaboration can lead to remarkable discoveries.

As we continue to explore the cosmos, who knows what other stellar surprises await us in the vast expanse of the Milky Way.


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