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Ancient Galaxy Collision Created Enormous Stellar Swirls

New simulations suggest that enormous swirls of stars surrounding a distant galaxy formed when two equal-sized galaxies collided. The galaxy, named NGC 5907, is located 50 million light-years away in the constellation Draco.

Its loops and currents, containing stars, gas and dust, are 150,000 light-years across. Researchers studying these swirls previously thought they were formed when a relatively small galaxy hit a larger one, getting torn apart in the process.

But in the new study, a massive computer simulation shows that it would have been impossible for a very small galaxy to produce the observed streams. More likely, two roughly equal-sized galaxies crashed into each other 8 or 9 billion years ago. The simulation also showed that the galaxies must have been very gas-rich in order to produce the swirls surrounding NGC 5907.

Most large spiral galaxies are thought to have formed from similar processes. Over the history of the universe, smaller galaxies have collided with one another and merged, producing ever-larger galaxies. Our own Milky Way galaxy is headed on a crash course with the neighboring Andromeda galaxy in 4.5 billion years.

Above: (1) Visible light image of NGC 5907. (2) Simulation of the collisions that produced NGC 5907 (1 Gyr = 1 billion years).