An ancient and “nearly naked” black hole that astronomers believe may have been created in the first fraction of a second after the big bang has been spotted by the James Webb space telescope.
If confirmed as a so-called primordial black hole, a theoretical class of object predicted to exist by Stephen Hawking but never before seen, the discovery would upend prevailing theories of the universe.
Until now, the mainstream view has been that stars and galaxies appeared first and that black holes were created only when the earliest stars ran out of fuel and collapsed under their own gravity.
But the latest observations by the space telescope, which reveal a gargantuan black hole with only a sparse halo of surrounding material dating back to the dawn of the cosmos, appear incompatible with this sequence of events.
“This black hole is nearly naked,” said Prof Roberto Maiolino, a cosmologist at the University of Cambridge who is one of the team behind the observations. “This is really challenging for the theories. It seems that this black hole has formed without being preceded by a galaxy around it.”
Primordial black holes are hypothesised to have been formed in the first fraction of a second after the big bang by denser and hotter regions collapsing in on themselves. In this scenario, black holes of varying sizes were stitched into the fabric of the cosmos from almost the beginning and acted as gravitational pockets around which the dust and gas that formed the first galaxies began to cluster. Hawking pioneered the theory in the 1970s, but with no observational proof in the decades since they have come to be viewed as speculative or “exotic”.
The latest observations focus on a “little red dot” known as QSO1 dating back more than 13bn years to when the universe was just 700m years old. It is one of a scattering of such dots found by the JWST that are so red, so compact and so bright that astronomers have concluded they must be ancient supermassive black holes.
Given that black holes are typically assumed to start small and snowball over time by gobbling up stars, scientists have been puzzled about how these black holes got so big so early in the universe’s history.
Despite QSO1’s extreme distance, astronomers were able to track the orbital speed of the swirling halo of gas and dust. This measurement gave the mass of the central black hole as 50m solar masses, with the total mass of the surrounding material being less than half of this value, according to the findings posted on the preprint Arxiv website.
“This is in stark contrast with what we observe in our local universe, where the black holes at the centre of galaxies [like the Milky Way] are about a thousand times less massive than their host galaxy,” said Maiolino.
In a separate analysis, the glowing material around the black hole was found to be chemically “pristine”, comprising almost exclusively of hydrogen and helium, the two elements left over after the big bang. The absence of heavier elements, which are forged in stars, adds to evidence that there is no significant star formation in the black hole’s vicinity.
“These results are a paradigm change,” said Maiolino. “Here we’re witnessing a massive black hole formed without much of a galaxy, as far as we can say from the data.”
Another way this could have occurred is through a vast cloud of gas and dust in the early universe collapsing directly into a black hole rather than fragmenting and forming stars. But “direct collapse” is predicted to require very specific environmental conditions that are not evident in the observations, leading the scientists to have a slight preference for the primordial black hole scenario.
Prof Andrew Pontzen, a cosmologist at University of Durham who was not involved in the research, said: “A confirmed primordial origin for black holes would have profound implications for fundamental laws of physics.
“The researchers behind this study use new JWST observations to strengthen the case for primordial origins, but it’s an indirect argument and it will take time for the debate to be settled. A decade from now the next generation of gravitational wave detectors, perfect for sniffing out black holes across the entire universe, will settle the matter.”
Source link
