Astronomers who studied the motions and radiation characteristics of cosmic microwave background radiation discovered that the vast majority of the matter in our universe was invisible. Around 84 percent is dark matter. This dark matter can be found around galaxies in halos. It is called dark matter because it emits no light. But it is also mysterious, as it is not made up of atoms.
Astronomers have been studying the effects of black hole mergers and recently detected gravitational waves. Black holes usually form in the explosive death massive stars. This can take many hundreds and millions of years, as a star coalesces out of ambient gas, evolves, then dies.
“Deeply Compelling” –Primordial Back Holes as Dark Matter
While some black holes have been inferred to exist in early universes, it is unlikely that enough time exists for the normal formation process. Alternative methods, such as the direct collapse primordial gas or processes associated to cosmic inflation, have been suggested. Many of these primordial black hole could have been created.
“The prospect that the mysterious dark matter might consist of primordial black holes is deeply compelling,” astrophysicist Eric GawiserRutgers University. The Daily Galaxy “We know that dark matter doesn’t emit light and instead interacts only through gravity. And we know that even a few minutes after the Big Bang when the first atomic nuclei were formed, there wasn’t enough normal matter around to make up today’s dark matter, which has led us to imagine that dark matter is made up of a new type of particle that nobody has been able to find yet.
Primordial Black Holes: Ordinary Matter
“The really intriguing aspect,” continues Gawiser, “is that small black holes could actually be made out of normal matter, as long as it collapsed into black holes in the first minute after the Big Bang. These “primordial” black holes would check all of these boxes; they wouldn’t emit light, they would interact through gravity, they would not have acted like normal matter one minute after the Big Bang – and they wouldn’t require the existence of a made-up particle that physicists seem unable to find!
“So why aren’t primordial black holes the preferred theory for the nature of dark matter?” writes Gawiser. “Because we don’t have a good model for what would cause them to form in the first few seconds after the Big Bang. Microlensing is also a term for gravitational lensing that occurs within the Milky Way galaxy due to small black hole types. But, no evidence has been found for the type or planet-mass black hole required. That leaves us without a good current theory for the nature of dark matter, but I wouldn’t bet against the black holes.”
Relics of the Big Bang –Dark Matter is Composed of Primordial Black Holes
Harvard-Smithsonian Center for Astrophysics astronomer Qirong Zhu, who studies the co-evolution of massive black holes and host galaxies from cosmic dawn to present day, led a group of four scientists investigating the possibility that today’s dark matter is composed of primordial black holes, following up on previously published suggestions. Black holes should have a different density distribution to galaxy halos that are made of exotic particles. There are some other differences as well—black hole halos are expected to form earlier in a galaxy’s evolution than do some other kinds of halos.
Scientists suggest that you can look at stars in the halos faint dwarf galaxies to see subtle effects. These galaxies are small and faint, with only a few thousand solar luminosities.
They ran computer simulations to determine if dwarf galaxy halos might reveal primordial black hole presence. Find itThat they might: Interactions between stars and primordial black holes could slightly alter the sizes for the stellar distributions.
The astronomers concluded that these black holes should have masses between two to fourteen solar masses. This is right in line with the expected range of exotic objects.
However, the team stresses that the models are not conclusive and that dark matter’s nature remains mysterious.
LIGO Observations Don’t Exclude the Possibility
“The idea that dark matter is composed of primordial black holes (PBH) is very intriguing,” Distinguished Lecturer in Physics at the University of New Haven, Nikodem Poplawski. In an email, write: The Daily Galaxy. “However, if they existed,” he continued, “they would have been creating binary pairs and merging at rates thousand times larger than the rates observed by LIGO: However, a later research refined those calculations and arguedLIGO observations have not excluded the possibility that all dark matter could be PBH (with the majority of them having mass on average of one solar-mass)
“Also,” Poplawski points out, “Hawking’s evaporation puts a lower limit on the mass of a black hole on the order of 10^11 kg (smaller black holes would have evaporated by now).
“I wrote an article back in 2010,” he continued, “considering the Einstein-Cartan theory of gravity (the simplest extension of general relativity in which quantum-mechanical spin produces spacetime torsion that eliminates singularities and allows black holes to create new nonsingular universes). This theory has a lower limit on black hole mass, at around 1016 kg (the average planetoid’s weight). This could be consistent in a study suggesting that dark matter might be. PBH for asteroid-massPBHs remain hypothetical and have yet to be detected. The smallest discovered black hole is about 3 solar masses (10^30 kg)”
The Daily Galaxy Avi ShporerResearch Scientist, MIT Kavli Institute for Astrophysics and Space Researchvia Harvard-Smithsonian Center for Astrophysics Eric GawiserAnd Nikodem Poplawski.
Image credit NASA/JPL
Avi Shporer Research Scientist, MIT Kavli Institute for Astrophysics and Space Research. A Google ScholarAvi was once a NASA Sagan Fellow at the Jet Propulsion Laboratory (JPL). His motto, not surprisingly, is a quote from Carl Sagan: “Somewhere, something incredible is waiting to be known.”
