Primordial Black Holes
Click on Image to Enlarge. Image Credit: Sprott Physics
Were vast numbers of black holes spawned during the universe's earliest moments?
So far, there is no hard evidence that such primordial black holes (PBHs) ever existed, but new observations just around the corner could change that.
There are a variety of ways that PBHs might have formed in the early universe. Concentrations of energy associated with exotic energy fields could collapse under their own gravity – according to Einstein's relativity, energy exerts gravity just as matter does – to make black holes. One such energy field is thought to be responsible for the rapid expansion (inflation) of the early universe.
A wide variety of masses for PBHs are possible, depending on the formation scenario. The least massive ones, with less than about the mass of a comet, or 1 trillion kilograms, would quickly evaporate through a quantum process known as Hawking radiation.
More massive PBHs, born with up to 100,000 times the mass of the Sun, could survive to put an imprint on the CMB cosmic microwave background, radiation emitted by warm matter roughly 400,000 years after the big bang.
Normally black holes would emit X-rays as they swallow matter from their surroundings, and these X-rays can escape the vicinity of the black holes to break apart, or ionise, hydrogen atoms. This would subtly affect how matter distributes itself into regions of high and low density - a distribution reflected in the CMB radiation.
This effect might explain a puzzling discrepancy between results of the Wilkinson Microwave Anisotropy Probe (WMAP), which measures the CMB, and studies of how galaxies are clustered.
The two disagree on a parameter called sigma8, which describes how matter clumped together in the early universe. But according to a recent study led by Massimo Ricotti of the University of Maryland in College Park, US, the two measurements agree if PBHs are included in the models.
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