- 3409 - - HAWKING’S - blackholes to explain the Universe? We may soon be able to test one of Stephen Hawking's most controversial theories. In the 1970s, Hawking proposed that dark matter, the invisible substance that makes up most matter in the cosmos, may be made of blackholes formed in the earliest moments of the Big Bang.
--------------- 3409 - HAWKING’S - blackholes to explain the Universe?
- We may soon be able to test one of Stephen Hawking's most controversial theories. In the 1970s, Hawking proposed that dark matter, the invisible substance that makes up most matter in the cosmos, may be made of blackholes formed in the earliest moments of the Big Bang.
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- One of the biggest mysteries in astronomy remains the nature of “dark matter” and the formation and growth of blackholes. Dark matter makes up over 80% of all the matter in the universe, but it doesn't directly interact with light in any way. It just floats around being massive, affecting the gravity within galaxies but not light.
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- Blackholes might be responsible for this elusive stuff. After all, blackholes are famously dark, so filling a galaxy with blackholes could theoretically explain all the observations of dark matter.
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- In the modern universe, blackholes form only after massive stars die, then collapse under the weight of their own gravity. So making blackholes requires many stars, which requires a bunch of normal matter.
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- Scientists know how much normal matter is in the universe from calculations of the early universe, where the first hydrogen and helium formed. And there simply isn't enough “normal matter” to make all the dark matter astronomers have observed, even in blackholes.
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- Then in 1971, Stephen Hawking suggested that blackholes formed in the chaotic environment of the earliest moments of the Big Bang. There, pockets of matter could spontaneously reach the densities needed to make blackholes, flooding the cosmos with them well before the first stars existed.
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- Hawking suggested that these "primordial" blackholes might be responsible for dark matter. While the idea was interesting, most astrophysicists focused instead on finding a new subatomic particle to explain dark matter.
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- Models of primordial blackhole formation ran into observational issues. If too many formed in the early universe, they changed the picture of the leftover radiation from the early universe, known as the “cosmic microwave background” (CMB). That meant the theory only worked when the number and size of ancient blackholes were fairly limited, or it would conflict with measurements of the CMB. .
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- The idea was revived in 2015 when the “Laser Interferometer Gravitational-Wave Observatory” found its first pair of colliding blackholes. The two blackholes were much larger than expected, and one way to explain their large mass was to say they formed in the early universe, not in the hearts of dying stars.
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- To pass current observational tests, primordial blackholes have to be within a certain mass range. The “primordial blackholes” had a mass of around 1.4 times the mass of the sun. They constructed a model of the universe that replaced all the dark matter with these fairly light blackholes, and then they looked for observational clues that could validate this model.
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- They found that primordial black holes could play a major role in the universe by seeding the first stars, the first galaxies and the first supermassive blackholes. Observations indicate that stars, galaxies and supermassive blackholes appear very quickly in cosmological history, perhaps too quickly to be accounted for by the processes of formation and growth that we observe in the present-day universe.
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- Primordial blackholes could well be the seeds from which all supermassive black holes form, including the one at the center of the Milky Way. The theory is simple and doesn't require a zoo of new particles to explain dark matter.
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- The James Webb Space Telescope, which launched Christmas Day, 2020, is specifically designed to answer questions about the origins of stars and galaxies. And the next generation of gravitational wave detectors, especially the “Laser Interferometer Space Antenna” (LISA), is poised to reveal much more about blackholes, including primordial ones if they exist.
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- Together, the two observatories should give astronomers enough information to piece together the story of the first stars and potentially the origins of dark matter.
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- Hawking radiation, sometimes also called Bekenstein-Hawking radiation, is a theoretical prediction from British physicist Stephen Hawking which explains thermal properties relating to blackholes.
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- A blackhole was considered to draw all matter and energy in the surrounding region into it, as a result of the intense gravitational fields; however, in 1972 the Israeli physicist Jacob Bekenstein suggested that blackholes should have a well-defined entropy, and initiated the development of blackhole thermodynamics, including the emission of energy, and in 1974, Hawking worked out the exact theoretical model for how a blackhole could emit black body radiation.
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- “Hawking radiation” was one of the first theoretical predictions which provided insight into how gravity can relate to other forms of energy, which is a necessary part of any theory of “quantum gravity“.
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- In a simplified version of the explanation, Hawking predicted that energy fluctuations from the vacuum cause the generation of particle-antiparticle pairs of virtual particles near the event horizon of the blackhole.
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- One of the particles falls into the blackhole while the other escapes before they have an opportunity to annihilate each other. The net result is that, to someone viewing the blackhole, it would appear that a particle had been emitted.
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- Since the particle that is emitted has positive energy, the particle that gets absorbed by the blackhole has negative energy relative to the outside universe. This results in the blackhole losing energy, and thus mass ,because E = mc^2.
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- Smaller primordial blackholes can actually emit more energy than they absorb, which results in them losing net mass. Larger blackholes, such as those that are one solar mass, absorb more cosmic radiation than they emit through Hawking radiation.
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- There are some concerns that it ultimately results in information being lost, which challenges the belief that information cannot be created or destroyed.
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- Physicists challenged Hawking's original calculations in what became known as the trans-Planckian problem on the grounds that quantum particles near the gravitational horizon behave peculiarly and cannot be observed or calculated based off of space-time differentiation between the coordinates of observation and that which is being observed.
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- Like most elements of quantum physics, observable and testable experiments relating to the Hawking Radiation theory are almost impossible to conduct.
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- Additionally, this effect is too minute to be observed under experimentally achievable conditions of modern science, so the results of such experiments are still inconclusive to proving this theory. We may have to wait a long time to find the answer.
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January 13, 2022 HAWKING’S - blackholes to explain the Universe? 3409
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