Hubble/European Space Agency and NASA

Disk galaxies rotate once every billion years, no matter their size

If you sat at the edge of a spinning disk galaxy it would take 1 billion years to go the entire way around, no matter how big it was, reports. Researchers examined the velocity of neutral hydrogen in a range of galaxies from small dwarfs to massive spirals and used these measurements to calculate how long the galaxy took to rotate. They found that all the galaxies spun like clockwork, completing a single rotation at their outermost edge in about 1 billion years, regardless of their size. The scientists also discovered that disk galaxies had sharp edges containing more older stars than expected, which will help astronomers define where a galaxy ends in future observations.

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