Known as hypervelocity stars, we originally thought just one would be ejected every 100,000 years. The real number is much greater.

KEY TAKEAWAYS

Within our Milky Way galaxy, there are an estimated 200-400 billion stars, largely concentrated in the galactic disk and our central bulge.

Although clouds of gas fall into our galaxy and new stars routinely form in the galactic plane, these stars don’t just die, but many are constantly getting kicked and ejected: far more than early estimates predicted.

Recent data, particularly from the ESA’s Gaia mission, have taught us that these hypervelocity stars are far more common than we realized. It holds dire implications for the ultimate fate of our galaxy, as well as all the others.

Hypervelocity stars

When clusters are torn apart, most of the stars that were once within it do get ejected, but only at speeds of tens of kilometers-per-second. However, beginning in 2005, astronomers have discovered a few stars that have been observed to have not only larger velocities in the range of hundreds of kilometers-per-second, but stars that are moving so fast they are destined to escape from the Milky Way’s gravity, the same way that a fast-enough moving rocket ship can escape from Earth’s gravitational pull.