Black holes spit out mighty high-speed jets of matter that include heavy atoms, a study published in Nature said on Wednesday.

Astronomers have been intrigued for decades by narrow beams of matter spewed out from black holes, the most powerful phenomena in the Universe.

The jets are known to contain electrons, which are a negatively-charged particle.

But the enigma is that the jets are not negatively-charged overall, which implies there should be something positively-charged in there to balance things out.

That "something" appears to be atoms of iron and nickel, according to astronomers using Europe's XMM-Newton space telescope and the Compact Array facility in eastern Australia.

Lines of atoms were seen in emissions streaming out of a small black hole called 4U1630-47 at two-thirds the speed of light.

The jets' source appears to be the accretion disk, a belt of hot gas that swirls around the hole's maw.

The finding is important because black holes, in addition to being destroyers, are creators, too.

They recycle matter and energy back into space, and the jets help to shape when and where a galaxy forms stars.

"Jets from supermassive black holes help determine a galaxy's fate," said Tasso Tzioumis of Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) in a press release.

"So we want to understand better the impact jets have on their environment."

An iron atom is about 100,000 times more massive than an electron, which means it carries a far more energy relative to a lighter particle travelling at the same speed.

Collisions with matter in interstellar space could generate gamma rays and electrons, the authors suggested.