Signals From Space: Five Theories On What They Are

Mysterious cosmic signals have been picked up. What are they and where do they come from?

A nebula of stars

Mysterious signals have been picked up from distant galaxies.

When fast radio bursts or FRBs, as they are called, reach Earth's telescopes they shine brightly for a few milliseconds, then disappear.

Astronomers have detected dozens over the past decade - and have just announced they've found more of them, including a rare repeating signal.