It takes a long time for supermassive black holes, like the one at the center of our Milky Way galaxy, to form.
Even so, at only about 10 solar masses, the resulting black hole is a far cry from the 4 million-solar-masses black hole, Sagittarius A*, found in our Milky Way galaxy, or the billion-solar-mass supermassive black holes found in other galaxies.
Such gigantic black holes can form from smaller black holes by accretion of gas and stars, and by mergers with other black holes, which take billions of years.
Why, then, is the James Webb Space Telescope discovering supermassive black holes near the beginning of time itself, eons before they should have been able to form?
UCLA astrophysicists have an answer as mysterious as the black holes themselves: Dark matter kept hydrogen from cooling long enough for gravity to condense it into clouds big and dense enough to turn into black holes instead of stars.
Hydrogen clouds in the early universe had too much molecular hydrogen, and the gas cooled quickly and formed small halos instead of large clouds.”
The forms and properties of dark matter are therefore a mystery that remains to be solved.
While we don’t know what dark matter is, particle theorists have long speculated that it could contain unstable particles which can decay into photons, the particles of light.
Dark matter could be made of particles that slowly decay, or it could be made of more than one particle species: some stable and some that decay at early times.
Even very mild decay of dark matter yielded enough radiation to prevent cooling, forming large clouds and, eventually, supermassive black holes.
Supermassive black holes, such as the one at the center of our galaxy, take a very long time to form. A massive star with the mass of at least 50 suns must burn out and collapse in on itself, which can take up to a billion years, in order for a black hole to form.
The resulting black hole is still very different from the 4 million solar mass black hole, Sagittarius A*, in our Milky Way galaxy, or the billion solar mass supermassive black holes in other galaxies, even at only about 10 solar masses. These enormous black holes can develop from smaller ones through mergers with other black holes, which take billions of years, and the accretion of gas and stars.
Astrophysicists at UCLA have an explanation as mysterious as the black holes themselves for why the James Webb Space Telescope is finding supermassive black holes close to the beginning of time, eons before they should have been able to form: dark matter prevented hydrogen from cooling long enough for gravity to condense it into clouds large and dense enough to become black holes instead of stars. The research is documented in the Physical Review Letters journal.
Senior author Alexander Kusenko, a UCLA professor of physics and astronomy, remarked, “How surprising it has been to find a supermassive black hole with a billion solar mass when the universe itself is only half a billion years old.”. It’s similar to wondering who built a modern car when dinosaur bones are discovered. “. .
A massive cloud of gas may collapse directly into a supermassive black hole, avoiding the protracted process of stellar burning, accretion, and mergers, according to some astrophysicists. The problem is that while a big cloud of gas will be drawn together by gravity, it won’t merge into a single cloud. Rather, it condenses portions of the gas into tiny halos that float close to one another without creating a black hole.
The gas cloud cools down too quickly, which is the cause. The pressure of a hot gas can overcome gravity. Before gravity has a chance to gather the entire cloud into a single black hole, it can, however, prevail in numerous tiny regions of cooler gas and decreased pressure. These regions then collapse into dense objects.
First author and doctoral student Yifan Lu stated, “The amount of molecular hydrogen has a lot to do with how quickly the gas cools.”. When a molecule’s bound hydrogen atoms come into contact with a loose hydrogen atom, their energy is released. As the hydrogen molecules absorb heat energy and radiate it out, they act as cooling agents. Too much molecular hydrogen was present in the early universe’s hydrogen clouds, which caused the gas to cool quickly and form tiny halos rather than massive clouds. “. .
Lu and Zachary Picker, a postdoctoral researcher, developed code to simulate every scenario that could arise. They found that extra radiation could heat the gas and cause the hydrogen molecules to split, changing the way the gas cools.
“The addition of radiation within a specific energy range prevents the fragmentation of large clouds by destroying molecular hydrogen,” explained Lu.
But from what source is the radiation coming?
Matter that is visible to us, such as our bodies, planet, stars, and everything else, makes up a very small percentage of the universe’s total mass. The bulk of matter is composed of some new particles that science has not yet been able to identify. This is evidenced by the gravitational pull that matter has on celestial objects and by the bending of light rays from far-off sources.
For this reason, the composition and characteristics of dark matter are still a mystery. Though the nature of dark matter remains unknown, particle theorists have long conjectured that it might contain unstable particles that have the ability to decay into photons, or light particles. For the gas to stay in a big cloud during its collapse into a black hole, the simulations required to include such dark matter.
It is possible that dark matter is composed of both slowly decaying particles and multiple particle species, some of which are stable and some of which decay quickly. In either scenario, radiation in the form of photons, which disintegrate molecular hydrogen and slow down the cooling of hydrogen clouds, may be the end result of decay. Large clouds and eventually supermassive black holes were formed when dark matter decayed, even at very mild levels because the radiation produced was sufficient to prevent cooling.
