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ohwilleke
Gold Member
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Conceptually, at least, this is a simple question, although I recognize that it might be hard to calculate in practice from available data.
The matter-energy budget of the universe is measured (in a model dependent way) to consist of a certain percentage of dark energy, a certain percentage of dark matter, and a certain percentage of ordinary matter.
Most of the ordinary matter is made up of stars and interstellar gas with a smidgen of planets, asteroids, comets, and neutrinos thrown in for good measure. Some of that ordinary matter is in the form of black holes. Photons also contribute slightly to the total.
(Black holes also gobble up dark matter like everything else and also dark energy if it is "stuff" rather than a default curvature of space or something. In truth, I don't really know in the Standard Model of Cosmology which part of the matter-energy budget for the universe black holes are assigned to. I have assumed that they are part of the ordinary matter budget, but feel free to correct me if this assumption is wrong.)
What estimates exist of the proportion of ordinary matter (or all matter or all matter-energy in the universe) that is in the form of black holes at this moment in time?
As I understand the matter, there is reasonably reliable estimates of how many galaxies of various types there are in the universe, and galaxies of each type of characteristic sized central supermassive black holes. So, estimating the share of the mass of the universe that is in the form of supermassive black holes shouldn't be an overwhelming task and surely someone has done that.
Stellar sized black holes have also been observed, and those observations ought to be capable of being converted into estimates of the number of stellar sized black holes in the universe, although probably with bigger error bars. I have no idea how the estimated mass of stellar black holes in the aggregate compares to the aggregate mass of supermassive black holes. I would think that someone has also estimated this in the scholarly literature.
This source suggests that the proportion of ordinary matter than is in the form of supermassive black holes or stellar sized black holes is about 11/10,000, but I have a hard time evaluating its credibility, and it doesn't consider two other possible kinds of black holes.
Even if the estimate for supermassive black hole mass (1/10,000th of the total galaxy mass) is order of magnitude correct (and that estimate really needs to be confirmed with better data), the estimate for the mass of stellar black holes must be too low.
This is true first, because even if 1/1000th of star mass is fated to end up as a stellar black hole based upon the size and type of the star, every stellar black hole will gobble up some mass including mass from other stars that were not on track to collapse into stellar black holes.
This is also true because some stars that are not fated to collapse into stellar black holes will nova, and some of the ejected material will either go directly into a black hole or will go into a star that is the right size and type to collapse into a stellar black hole eventually.
LIGO has shown us that there are also intermediate sized black holes out there, which hadn't been observed before even though almost all theories said that they had to exist. The error bars on how many of those there are in the universe is probably going to get much smaller as LIGO accumulates data, but surely there must be some theoretical estimates that exist already to get from stellar black holes to supermassive ones, and some of those theoretical estimates must be consistent with LIGO measurements to date even though that is a quite small data set so far.
If you make the assumption that supermassive black holes star as stellar black holes that merge until they become supermassive black holes, that alone bounds the potential aggregate mass of intermediate sized black holes, and we have decent estimates at both ends.
Some theorists think that there are sub-stellar sized primordial black holes as well. And, the theories that suppose that they exist seem very well suited to estimating their aggregate mass at any particular time in the history of the universe. Efforts to determine in primordial black holes could be dark matter from various kinds of observations have put some serious bounds on how much mass in the universe can be in that form.
BONUS: Has anyone estimated the change in the proportion of ordinary matter that is in the form of black holes over the history of the universe? And, if so what are those findings?
With very weak assumptions, the proportion of ordinary matter in the form of black holes will always rise over time. One need only assume that the aggregate mass of black hole matter due to existing black holes absorbing matter, and due to stars collapsing into black holes, is greater than the amount of new matter condensed out of radiation or other forms of energy, and this is almost surely true for the vast majority of the history of the universe (although the amount of primordial black hole mass could fall and balance that out somewhat due to Hawking radiation).
But, beyond that assumption it gets tricky. If lots of stars are formed at around the same time, there should be peaks and valleys in black hole formation from star collapse since stars that can collapse into black holes tend to have similar lifetimes.
Also, as the universe expands, matter is more spread out, so the average amount of matter near black holes that they can swallow up should fall over time. But, the fall shouldn't be as fast as in an analog to the ideal gas formula, because matter has clumped up as the universe has evolved with filaments of matter causing average distance from a black hole to other matter to fall much more slowly than the average mass per volume of space in the universe. Likewise, average distance from a black hole to other matter falls much more slowly in the core of a galaxy than in its periphery.
But, a black holes eat up the closest matter to them, the stream of matter into them should slow down because the "low hanging fruit" has already been eaten up.
The matter-energy budget of the universe is measured (in a model dependent way) to consist of a certain percentage of dark energy, a certain percentage of dark matter, and a certain percentage of ordinary matter.
Most of the ordinary matter is made up of stars and interstellar gas with a smidgen of planets, asteroids, comets, and neutrinos thrown in for good measure. Some of that ordinary matter is in the form of black holes. Photons also contribute slightly to the total.
(Black holes also gobble up dark matter like everything else and also dark energy if it is "stuff" rather than a default curvature of space or something. In truth, I don't really know in the Standard Model of Cosmology which part of the matter-energy budget for the universe black holes are assigned to. I have assumed that they are part of the ordinary matter budget, but feel free to correct me if this assumption is wrong.)
What estimates exist of the proportion of ordinary matter (or all matter or all matter-energy in the universe) that is in the form of black holes at this moment in time?
As I understand the matter, there is reasonably reliable estimates of how many galaxies of various types there are in the universe, and galaxies of each type of characteristic sized central supermassive black holes. So, estimating the share of the mass of the universe that is in the form of supermassive black holes shouldn't be an overwhelming task and surely someone has done that.
Stellar sized black holes have also been observed, and those observations ought to be capable of being converted into estimates of the number of stellar sized black holes in the universe, although probably with bigger error bars. I have no idea how the estimated mass of stellar black holes in the aggregate compares to the aggregate mass of supermassive black holes. I would think that someone has also estimated this in the scholarly literature.
This source suggests that the proportion of ordinary matter than is in the form of supermassive black holes or stellar sized black holes is about 11/10,000, but I have a hard time evaluating its credibility, and it doesn't consider two other possible kinds of black holes.
Even if the estimate for supermassive black hole mass (1/10,000th of the total galaxy mass) is order of magnitude correct (and that estimate really needs to be confirmed with better data), the estimate for the mass of stellar black holes must be too low.
This is true first, because even if 1/1000th of star mass is fated to end up as a stellar black hole based upon the size and type of the star, every stellar black hole will gobble up some mass including mass from other stars that were not on track to collapse into stellar black holes.
This is also true because some stars that are not fated to collapse into stellar black holes will nova, and some of the ejected material will either go directly into a black hole or will go into a star that is the right size and type to collapse into a stellar black hole eventually.
LIGO has shown us that there are also intermediate sized black holes out there, which hadn't been observed before even though almost all theories said that they had to exist. The error bars on how many of those there are in the universe is probably going to get much smaller as LIGO accumulates data, but surely there must be some theoretical estimates that exist already to get from stellar black holes to supermassive ones, and some of those theoretical estimates must be consistent with LIGO measurements to date even though that is a quite small data set so far.
If you make the assumption that supermassive black holes star as stellar black holes that merge until they become supermassive black holes, that alone bounds the potential aggregate mass of intermediate sized black holes, and we have decent estimates at both ends.
Some theorists think that there are sub-stellar sized primordial black holes as well. And, the theories that suppose that they exist seem very well suited to estimating their aggregate mass at any particular time in the history of the universe. Efforts to determine in primordial black holes could be dark matter from various kinds of observations have put some serious bounds on how much mass in the universe can be in that form.
BONUS: Has anyone estimated the change in the proportion of ordinary matter that is in the form of black holes over the history of the universe? And, if so what are those findings?
With very weak assumptions, the proportion of ordinary matter in the form of black holes will always rise over time. One need only assume that the aggregate mass of black hole matter due to existing black holes absorbing matter, and due to stars collapsing into black holes, is greater than the amount of new matter condensed out of radiation or other forms of energy, and this is almost surely true for the vast majority of the history of the universe (although the amount of primordial black hole mass could fall and balance that out somewhat due to Hawking radiation).
But, beyond that assumption it gets tricky. If lots of stars are formed at around the same time, there should be peaks and valleys in black hole formation from star collapse since stars that can collapse into black holes tend to have similar lifetimes.
Also, as the universe expands, matter is more spread out, so the average amount of matter near black holes that they can swallow up should fall over time. But, the fall shouldn't be as fast as in an analog to the ideal gas formula, because matter has clumped up as the universe has evolved with filaments of matter causing average distance from a black hole to other matter to fall much more slowly than the average mass per volume of space in the universe. Likewise, average distance from a black hole to other matter falls much more slowly in the core of a galaxy than in its periphery.
But, a black holes eat up the closest matter to them, the stream of matter into them should slow down because the "low hanging fruit" has already been eaten up.
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