Seeing the light: The HST WFPC2 image of gravitational lensing in the galaxy cluster Abell 2218, indicating the presence of large amount of dark matter.
Credit: Andrew Fruchter at STScI
SYDNEY: Dark gulping, whereby clumps of dark matter collapse, may solve the mystery of how supermassive black holes formed in the first billion years of the universe’s existence, much earlier than current models predict.
Supermassive black holes were thought to have formed when smaller black holes merged, or when a giant star collapsed and swallowed up vast amounts of matter.
But these processes should take up to a billion years, says the theory, so the presence of supermassive holes early on in the universe’s history has so far been a dilemma.
Dark matter interactions
To find an answer, astrophysicists Curtis Saxton and Kinwah Wu from University College London, In England, developed a model that looks at the interactions between dark matter and gas in forming galaxies.
They say clumps of dark matter may form in the galactic core and rapidly collapse when galaxies merge. Because the collapse involves dark matter, this dark gulping would happen without a trace of electro-magnetic radiation being emitted.
The theory was presented at the European Week of Astronomy and Space Science at the University of Hertfordshire, in England, last week.
“In the usual picture, a black hole forms by accumulating gas or stars from its surroundings, and this infalling material inevitably becomes hot and luminous on its way in. It's a puzzle that billion-solar-mass black holes existed in the earliest quasars, because their accretion luminosity ...should have been more conspicuous,” Saxton told Cosmos Online.
Violent disturbance
“Dark matter is completely uninhibited by radiation. In principle a black hole could devour [dark matter] at any rate, if external conditions set up a sufficient supply” he said.
The gulping would probably occur whenever the centre of the galaxy cluster suffers a violent disturbance, such as a major merger of galaxies, Saxton said. “Between major mergers, the inner structure of the dark halo gently settles into an equilibrium that's poised for collapse. Like an avalanche waiting to happen.”
Commenting on the research, astrophysicist Scott Croom from the University of Sydney, in Australia, said that while the theory was intriguing, it relied on a particular type of model where dark matter is strongly ‘self-interacting’. Classical models of dark matter describe them as weakly interacting particles.
“Most models assume [dark matter] doesn’t interact because that’s the simplest assumption. Other weakly interacting particles we know of, such as neutrinos, don’t interact strongly with themselves,” said Croom.
If dark matter did strongly self-interact within the galactic core it would cause a ‘cooling catastrophe’ where radiation cools down and collapses very quickly.
“It’s an interesting idea, [but] whether it bears any relationship to reality only time will tell,” Croom said. “What it really points to is the fundamental need to understand what dark matter particles are.”
The results will be published in the British journal, the Monthly Notices of the Royal Astronomical Society.
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