Scientists believe they have found out why the universe’s biggest black holes have been growing more slowly over the last 10 billion years. The issue has long stumped astronomers but a new study believes the reason could be because they are starved of gas.
Supermassive blackholes, or SMBHs, are at the centre of almost every large galaxy, although scientists are still not sure how they emerged. Their huge gravity can cause stars to orbit around them in a particular way, however they are not ‘wormholes’ providing shortcuts through space or to other universes or dimensions, neither do they suck in other matter, according to NASA. The space experts explain that “from far enough away, their gravitational effects are just like those of other objects of the same mass”.
SMBHs can have up to hundreds of thousands to billions of times the Sun’s mass.
According to Live Science, these huge cosmic objects have been growing at a significantly slower rate since the ‘cosmic noon’, a period when the universe was less than a quarter of the age it is today.
A new study, published in The Astrophysical Journal, suggested this could be because there is less gas for them to consume.
Study co-author Fan Zou, an astronomer at the University of Michigan, told Live Science: “We knew black holes were growing more slowly, but not why — and it turned out to be that individual black holes are consuming material much less rapidly, rather than there simply being fewer growing black holes or smaller ones.”
The researchers, who studied 1.3 million galaxies, reportedly found consumption by SMBHs has reduced because cold gas levels have fallen since the cosmic noon.
Speaking to Live Science, Mr Zou added: “What surprised me most was that we could actually isolate the main reason, and there is indeed a dominating reason instead of a messy mix.”
Sagittarius A*, the SMBH at the centre of the Milky Way, is four million times the mass of the Sun.
NASA says despite this, it is still reasonably small when compared to SMBHs found in other galaxies.
It noted a black hole in the Holmberg 15A galaxy as holding “at least 40 billion solar masses”.