Astronomers have previously observed this process—the breaking apart of binary systems because of supernovae— in the Milky Way, but it has not produced the kind of hypervelocity stars that travel millions of kilometers per hour.

This origin story is less extreme, Boubert says. “You’re not talking about the black hole in the center of the Milky Way, the biggest object in our galaxy, and having it catapulting stars off at thousands of kilometers per second,” he said. “You’re talking about a process which is well-documented, which is guaranteed to be happening, and just putting it in a different galaxy.”

Boubert says it helps explain these hypervelocity’s position in the sky. The majority of the 20 known hypervelocity stars are clumped together in two constellations, Leo and Sextans. The black hole theory “can’t explain why we only see the stars in one part of the sky, because you’d expect that particular mechanism, if it’s in the center of the Milky Way, to eject in all directions equally,” he says.

Boubert came to his theory in April last year, when he was reading a research paper that mentioned that the Large Magellanic Cloud orbits around the Milky Way at 400 kilometers per second, or about 1.4 million kilometers per hour. “I put two and two together and realized that if you could eject a star from this dwarf galaxy, it would be very very fast,” he says. The star, already moving at a high velocity because the supernova kicked it out, would get another boost from the fast-moving galaxy. Imagine putting a star into a cannon, and then putting that cannon onto a moving train, Boubert says.

Boubert and his colleagues used data from the Sloan Digital Sky Survey, which has observed millions of cosmic objects in more than one-third of the night sky. They took what they knew, like the rate of star formation in the Large Magellanic Cloud and the prevalence of binary star systems, and input the information into computer models that simulated the evolution of the cloud over 2 billion years. The simulations showed how many binary systems might undergo supernovae and eject runaway stars that could then end up in the Milky Way.

Boubert says his research predicts there may be many more runaway, hypervelocity stars in the Milky Way, as many as 10,000, hiding out of view of telescopes. The stars are traveling so fast that they will likely escape again in a few hundred million years and perhaps, someday, become part of another galaxy. Like their twins, hypervelocity stars may explode too, leaving behind dense cores called neutron stars or matter-gobbling black holes. Some runaways that left the Large Magellanic Cloud as stars may have arrived inside the Milky Way galaxy as neutron stars or black holes.

Boubert suspects this theory will be met with some skepticism after a decade of research based on the leading assumption. He hopes that the European Space Agency’s Gaia mission will provide more data to work with when it releases its first observations next year. The spacecraft, launched in 2013, is monitoring and measuring the position and velocities of about 1 billion stars in the Milky Way.

Until then, hypervelocity stars are a good reminder of the extremes found in the universe. “The fastest thing you typically see in a day is a car, and that’s traveling at 70 kilometers an hour,” Boubert says. “That’s tiny in terms of the vastness and the scale of things that are happening in the sky.”