Hubble captures Supersonic Star ejected from Milky Way

This Hubble Space Telescope photo shows the superfast star HE 0437-5439 (with arrow) as it is being booted from the MIlky Way galaxy. Credit: NASA/ESA/Z. Levay (STScI)/O. Gnedin/W.Brown

A super-hot blue star hurtling through space has been shot completely out of the Milky Way, new Hubble Space Telescope photos reveal.

The star is streaking across space at a blistering speed of 1.6 million mph (2.5 million kph) – three times faster than our sun's orbital velocity in the Milky Way. Hubble observations confirm that the stellar speedster hails from the Milky Way's core, settling some confusion over where it originally called home.

Astronomers think the star is a survivor from a triple-star system that traveled through the bustling center of our Milky Way galaxy 100 million years ago, but made the perilous mistake of wandering too close to the galaxy's giant black hole, which captured one of the stars and flung the other two out of the Milky Way. The two ejected stars then merged to form a super-hot, blue star.

While it may seem a little farfetched, astronomers using NASA's Hubble Space Telescope say it is the most likely scenario for the so-called hypervelocity star, known as HE 0437-5439, one of the fastest ever detected.

"Using Hubble, we can for the first time trace back to where the star comes from by measuring the star's direction of motion on the sky," said astronomer Warren Brown of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., lead author of the study and a member of the Hubble team that observed the star.

"Its motion points directly from the Milky Way center. These exiled stars are rare in the Milky Way's population of 100 billion stars. For every 100 million stars in the galaxy lurks one hypervelocity star."

This illustration shows one possible mechanism for how the star HE 0437-5439 acquired enough energy to be ejected from our Milky Way galaxy. Credit: NASA/ESA/A. Feild (STScI)/O. Gnedin/W. Brown