Michael Schirber at Space.com:
Two dense stars whipping around each other at breakneck speed may be the strongest known source of Einstein’s space-trembling gravity waves.
The double star – called RX J0806 – was discovered in 1994 in X-rays. Later shown to be blinking on and off every 5.4 minutes, the two-star setup is believed to be a pair of white dwarfs – the dense ashes of burnt-out stars – rotating around each other.
The implied separation is just 50,000 miles – a mere one-fifth the distance between the Earth and the Moon, making this the closest stellar pair ever observed. The tangled duo should be booming out gravity waves – undulations in the fabric of space and time predicted by Einstein’s theory of general relativity.
More here.