Passing the Test

The more scientists try to break down Albert Einstein’s theory of gravity, the stronger it looks. An experiment that kept an eye on a pair of extreme dead stars, for example, confirmed several of its predictions.
The theory is General Relativity. Einstein presented it in 1915, and it’s withstood every test since then. Yet scientists know that it must break down at the tiniest scales, or inside objects like black holes. They’re pushing to find its limits.
The new experiment spent 16 years watching the Double Pulsar — two dead stars in a tight orbit around each other. A pulsar is the crushed core of a once giant star. It spins rapidly, beaming energy into space like a lighthouse. Telescopes on Earth record each “pulse” of energy.
The Double Pulsar is about 2400 light-years away. Each of its stars is heavier than the Sun, but only the size of a city. One of them spins about three times per second, the other about 45 times per second.
Astronomers used radio telescopes all across Earth to w