Are dormant black holes the same thing as dark matter? If not, why not?
It's been bugging me for a long time that dark matter and dormant black holes seem to be the same thing. I'm not a scientist, I'm just a science buff, and I'd never really studied either subject in school. But, I keep asking myself: why would there be two different mysterious substances (dark matter and whatever is at the centers of dormant black holes) that so closely resemble one another?
So, a few days ago, I started doing some focused research. Over the years I've found that whenever I have a science question, it usually has already been asked and answered somewhere on the Internet.
I soon found a web site called "Ask Ethan," which has the exact question I was asking: "Are black holes made of dark matter?" The page does a very good job of explaining how black holes are thought to be created. However, it also contains arguable statements like this:
So initially, when they’re first formed, black holes are pretty much 100% normal (baryonic) matter, and just about 0% dark matter. Remember that dark matter interacts only gravitationally, unlike normal matter, which interacts via the gravitational, weak, electromagnetic and strong forces. All of this is a fancy way to say that when normal matter comes into contact with other normal matter, it goes “splat,” meaning that it can stick together, clump, exchange momentum and accrue even more normal matter when this occurs. Dark matter, on the other hand, doesn’t “splat” either with normal matter or with other dark matter. This is why, when we look at galaxies and clusters of galaxies, we picture spiral or elliptical galaxies where the normal matter is confined to a relatively small region of space, but they are embedded within dark matter halos that extend for maybe thousands of times the volume of the normal matter.To me, the first sentence in the quoted paragraph above is highly questionable. I would assume just the opposite. I would assume that when a black hole is created, it is 100% dark matter, i.e., the normal matter that was ultra-compressed by the imploding supernova. The supernova turns normal matter into the dark matter that is at the center of a black hole.
The second sentence in the quoted paragraph does a good job of explaining what happens when a supernova creates a black hole consisting of dark matter. It turns normal matter into a form of matter that is somehow stripped of all the properties which give it the weak, electromagnetic and strong forces. That would explain how the matter that is at the center of a black hole can be so highly compressed without causing nuclear fusion.
The last paragraph in the article contains this conclusion:
And there you have it: a quantitative answer to the question of whether black holes are made of dark matter or not. At most they can only be made of about 0.004% dark matter, and that’s the most optimistic number that applies only to the most massive ones!That might be so, but it's definitely not how I see things. So, I looked for more information.
This article attracted my eye: "NASA simulation suggests black holes may make ideal dark matter labs." It seemed to say what I've been thinking, that black holes are "factories" that create more dark matter. They take in normal matter, strip normal matter of its weak, electromagnetic and strong forces, perhaps spewing out those forces in the form of X-rays, and leaving only dark matter behind at the center of the black hole.
Unfortunately, the article begins this way:
While we don’t yet know what dark matter is, we do know it interacts with the rest of the universe through gravity, which means it must accumulate around supermassive black holes.Huh? Reading the article, I found that it suggests that supermassive black holes concentrate dark matter that was created elsewhere and cause the dark matter particles to collide. That has nothing to do with what I'd been thinking. And there's nothing conclusive in the article, except for another description of some properties of dark matter that I consider to be very important:
dark matter [is] an elusive substance accounting for most of the mass of the universe that neither reflects, absorbs, nor emits light.That description of dark matter should be compared to this description of dormant black holes I found elsewhere:
Roughly 90 percent of the biggest black holes in the known universe are dormant, meaning that they are not actively devouring matter and, consequently, not giving off any light or other radiation.The source is this article: "Dormant Black Hole Eats Star, Becomes X-ray Flashlight."
Think about it. A dormant black hole doesn't reflect light, nor does it emit light, and it doesn't absorb light, it bends the path of light - a process called "gravitational lensing." What need is there to have two different things - dark matter and black holes - if they have the same physical properties?
Searching further, I soon found a web page where someone asked the question I've been asking, but just phrased in a different way: "Could the Universe's dark matter be made up of black holes?"
However, the answer was (in part):
What's important to realize about this is that our studies of dark matter don't just tell us that "it's out there somewhere"; when we study a galaxy, we learn something about the total distribution of matter within it. This means that we know the dark matter surrounds galaxies and is not a central object, like a black hole, within galaxies.Who says black holes are "centralized in the middle of the galaxy"? I'd seen an article which said there could be millions of black holes within our galaxy. And who says "black holes are nothing that special, gravitationally"? Just the opposite would seem to be true if a black hole can be dormant and yet be a massive gravitational source with no real explanation for what is inside the black hole.
The problem with your idea is that black holes are nothing that special, gravitationally: they're just accretions of matter. They are centralized in the middle of the galaxy, and according to the laws of gravity, they can't pull very hard on stuff far out at the edge of a galaxy.
A June 27, 2016, article on Astowatch.net web site titled "Clandestine Black Hole May Represent New Population" states:
Astronomers have combined data from NASA’s Chandra X-ray Observatory, the Hubble Space Telescope and the National Science Foundation's Karl G. Jansky Very Large Array (VLA) to conclude that a peculiar source of radio waves thought to be a distant galaxy is actually a nearby binary star system containing a low-mass star and a black hole. This identification suggests there may be a vast number of black holes in our Galaxy that have gone unnoticed until now.The article also says,
Because this study only covered a very small patch of sky, the implication is that there should be many of these quiet black holes around the Milky Way. The estimates are that tens of thousands to millions of these black holes could exist within our Galaxy, about three to thousands of times as many as previous studies have suggested.But nowhere in the article does it mention "dark matter." It's just about "millions" of black holes which could be in the same places where dark matter is believed to be.
It should seem "obvious" that dormant black holes and dark matter could be the same thing. It seems so "obvious" that the question seems to be, What facts about dark matter show that it cannot possibly be dormant black holes?
I then found an article titled "Is Dark Matter Made of Tiny Black Holes?" It's from November 14, 2013 and says,
A planet-hunting NASA spacecraft has detected no sign of moon-size black holes yet in the Milky Way galaxy, limiting the chances that such objects could make up most of the "dark matter" that has mystified scientists for decades.
Dark matter is one of the greatest scientific mysteries known — an invisible substance thought to constitute up five-sixths of all matter in the universe. It remains so mysterious that scientists are still uncertain as to whether dark matter is made of microscopic particles or far larger objects.and
Over four years, Kepler monitored the brightness of more than 150,000 stars in the Milky Way to detect regular dimming caused by planets crossing in front of them. If a primordial black hole passed in front of one of these stars, the star would become temporarily brighter instead. That's because black holes warp light around them with their gravitational fields, a phenomenon known as gravitational lensing.and
Until now, researchers had eliminated the chances that black holes that are approximately the mass of the moon could make up dark matter. Kepler's data show no evidence of black holes between 5 and 80 percent of the moon's mass, suggesting these black holes could not constitute most dark matter.
However, even smaller primordial black holes, ones less than 0.0001 percent the mass of Earth's moon, could still make up the entirety of dark matter, Griest said. Future missions — such as the European Space Agency's Euclid spacecraft or NASA's proposed WFIRST satellite — could look for smaller black holes than those identified by the Kepler data.
"We've ruled out a range of primordial black holes as dark matter, but have not ruled them out completely," Griest told SPACE.com. "They're still a viable candidate for dark matter."Hmm. That definitely fits with the way I envision things. Most dark matter is supposed to be like a cloud surrounding the Milky Way galaxy. Small black holes wouldn't produce any substantial gravitational lensing effect on distant stars and galaxies.
It's quite possible that I'm totally misunderstanding everything. But, if I'm understanding things correctly, there's also a key to "The Theory of Everything" in this. The key is figuring out how you can strip a particle of normal matter of all of its electromagnetic, weak and strong forces, and produce a particle of dark matter that only possesses gravitational force, and thus can be packed like grains of wet sand into a spherical ball of dark matter that is so small that mathematicians can misinterpret it to be a single, dimensionless point of infinite density.
This "Theory of Everything" might also explain "The Big Bang." A gigantic mass of dark matter encountered something that restored electromagnetism, weak and strong forces to the dormant dark matter - like a bowl of nitroglycerin being hit by a bullet. And there could be lots of left-over "unexploded" dark matter floating around.
Of course, I could be wrong about all this.