Clouds of ancient gas leftover from the birth of the Universe are sweeping down on the centre of our galaxy, say astronomers.
The deuterium - an isotope of hydrogen that has a neutron in its atomic nucleus - is replenishing supplies being "eaten" by the large numbers of stars that inhabit the heart of the Milky Way.
Deuterium studies are a crucial test of Big Bang theories because all of the gas that exists in the cosmos is thought to have been created in the first three minutes after the Universe came into being.
That scientists can now detect more deuterium than expected in the centre of our galaxy makes them think the gas is falling in from outer regions.
Astronomers, led by Don Lubowich, of Hofstra University, New York, US, say there is a 100,000 times more deuterium at the core of the Milky Way than expected.
The team detected radiation from the deuterium using the 12-metre (40-foot) radio telescope at the US National Radio Astronomy Observatory's site on Kitt Peak, Arizona. It was in a gas cloud only about 30 light years from the centre of the Milky Way, about 25,000 light years from Earth.
They found only one part per million of deuterium compared with hydrogen, a million times more deuterium than had been predicted.
The most likely source of the added deuterium, they say, is clouds of primordial matter sweeping in towards our galaxy's centre.
The research is published in the journal Nature.