New York, Oct 22 (IANS): Massive black holes spewing out radio-frequency-emitting particles at near-light speed can block formation of new stars in ageing galaxies, a study has found.

The research provides crucial new evidence that it is these jets of radio-frequency feedback streaming from mature galaxies' central black holes that prevent hot free gas from cooling and collapsing into baby stars.

When someone looks into the past history of the universe, he sees these galaxies building stars.

"At some point, they stop forming stars and the question is: Why? Basically, these active black holes give a reason for why stars stop forming in the universe," said Tobias Marriage, assistant professor of physics and astronomy at the Johns Hopkins University in the US.

In space, hot gas drawn into a galaxy can cool and condense, forming stars.

Some gas also funnels down into the galaxy's black hole, which grows together with the stellar population.

This cycle can repeat continuously; more gas is pulled in to cool and condense, leading to increased star formation and consequent enlargement of the already massive central black hole.

But in nearly all mature galaxies - the big galaxies called elliptical because of their shape - that gas does not cool any more.

"If gas is kept hot, it cannot collapse. When that happens, it means no new stars," added, Johns Hopkins postdoctoral fellow, Megan Gralla.

The findings were published in the journal Monthly Notices of the Royal Astronomical Society.