Two dead stars are dancing — and Einstein called the tune

JinLin Han and his colleagues at the Chinese Academy of Sciences spent five years timing radio pulses from PSR J1856-0039 with the FAST telescope — the world's largest single dish, sunk into a natural basin in Guizhou. What they found: two neutron stars whipping around each other every 2.36 hours, with a combined mass of just 2.49 suns — the lightest double neutron star system ever measured. The orbit is shrinking exactly the way Einstein's general relativity says it should. Some 82 million years from now, the two will merge — likely birthing a massive neutron star rather than a black hole, a front-row laboratory for the physics of ultradense matter. Published in Physical Review Letters.