# Thread: how can the mass of a black hole be calculated?

I thought the mass is infinite ?
yet i have heard various quantitative results.
Perhaps areas in the black hole are quantifiable?

2.

3. Know the gravity field around it, calculating its mass would be pretty easy. Don't know why you think they're mass is infinite.

4. The mass of a black hole is not infinite, it is equal to the mass of whatever formed the black hole. If a star goes supernova and a part of it collapses into a black hole, the mass of the black hole will be equal to that part of the mass of the star. If more matter falls into the black hole, its mass will increase by the mass of that matter.

5. My apologies,I actually meant mass density.

6. No, it only has to fulfil the criterion of the Scharzschild radius. If a given mass is compressed strong enough so that is not bigger than this radius, it is a Black Hole.
Schwarzschild radius - Wikipedia, the free encyclopedia

7. The mathematical subset called orbital mechanics can determine the mass of an object being orbited.
1. What is the distance between the 2 centers of mass?
2. What is the speed of the object orbiting around the larger object.

Sir Isaac Newton did the math.

8. so in what context can the term infinite density be applied to black holes?

9. IMO neutron star is the most dense material on the universe. It is soo dense such that it wasn't even made of atom (which is always full of space) ,but was made from quark (a basic constituent of matter)! -Everything was soo tightly pack together such that neutron star became the most dense object in the universe and also the most perfect sphere you can find in the universe (and with the smoothest surface)!

I think black hole has singularity... Which is somekind of 'infinite' (not sure what), but isn't infinite density.

10. Your correct Brane Wave there are a few flaws in blackhole theory. Many scientists, such as Hawking, suggest that blackholes probably host a singularity in the center. This singularity consumes a lot of matter and deletes its value (at least that's my understanding of the Hawking's position specifically). Probably the use of the word singularity is not the best to use when discussing a blackhole, because frankly, if there was a singularity at the center of backholes that deleted (consolidated) the value of matter, one would expect, I think, for most blackholes to be about the same size and have the same relative gravity since matter becomes sufficiently compacted at about the same point and then enters theoretically into a singularity where its values are lost. It seems based on astronimcal evidence that some blackholes are much bigger and much more powerful than others which makes it seem unlikely, to me at least, that information is being lost in a singularity. One would think that a singularity would be a pretty efficient drain... Probably the center of a blackhole is just very dense and so dense possibly that matter has no movement and is packed very tightly. I am always amused at how precisely Hawking and other's formulate exact theories on the size and gravitational pull of blackholes and extrapolate that as indicative of a loss of information. Really we have pretty much insufficient astronomical data to know whether matter is being lost in a blackhole.
As to how precisely blackholes are measured on generally looks for distortions in the solar bodies surrounding the black hole. Gamma ray bursts, the wobble of stars, signs of accceleration. A starting point is to look for for wobble in rotation and shifts in the spectral light. You can use Kepler3 to develop a basic understanding of the mass of the black hole. M=w^2*r^3/G There are other considerations as well... but at the end of the day, the reality is, that current calculations are probably not correct if there is more dark matter in the universe than expected. It's hard to say how much of the gravity comes from the blackhole and how much comes from the pinching of dark matter in a large region.

Originally Posted by brane wave
I thought the mass is infinite ?
yet i have heard various quantitative results.
Perhaps areas in the black hole are quantifiable?

11. Actually he's correct in a matter of speaking. It is theorized by some that the center of a blackhole has infinite density. Know that the honest answer to why you've heard conflicting results on the gravity and mass of blackholes is that there is no agreement that the center of a blackhole consists of a singularity. I for one, and others, think, with no disrespect to some brilliant minds, that this is probably not right.

Originally Posted by Lynx_Fox
Know the gravity field around it, calculating its mass would be pretty easy. Don't know why you think they're mass is infinite.

12. Quantative vs Qualative is about the quantity of the whole reason we need to find a qualitive answer. If I was to have millions of friends that'd be the first step towards finding a good answer. Then we need to assist each other to call upon a concrete answer but that's mean an infinity amount of people living through infinity to find the space to understand the masses of blackness. Problem there is we'd have to live forever to get that answer which is for some a nonsense idea. I believe that we could pass on information of Qualitive answers to get a Qualitive review of how far and how huge the masses of space exist in measurement. That would mean passing the information to lots of people through time. probelm again could be example: this information lead to another anwer? In my eyes NO, this is mistrust of information and means that we'll back to square one.

13. Originally Posted by Dishmaster
No, it only has to fulfil the criterion of the Scharzschild radius. If a given mass is compressed strong enough so that is not bigger than this radius, it is a Black Hole.
Schwarzschild radius - Wikipedia, the free encyclopedia
Call me unenlightened but I cannot see how the mass itself can cause the strong gravity associated with a black hole (strong enough that light cannot escape) ...the star before its outer shell went supernova and the core shrunk in size......emitted light and furthermore as the outershell gets thrown off in a supernova the star now collapses into a BH with LESS mass than the original star.

However, gravity is not attributable to density (that I am aware of) - gravity is created by mass. So how can a star with less mass suddenly turn into a sphere from which light cannot escape? (when it could before!)

14. Originally Posted by leohopkins
Originally Posted by Dishmaster
No, it only has to fulfil the criterion of the Scharzschild radius. If a given mass is compressed strong enough so that is not bigger than this radius, it is a Black Hole.
Schwarzschild radius - Wikipedia, the free encyclopedia
Call me unenlightened but I cannot see how the mass itself can cause the strong gravity associated with a black hole (strong enough that light cannot escape) ...the star before its outer shell went supernova and the core shrunk in size......emitted light and furthermore as the outershell gets thrown off in a supernova the star now collapses into a BH with LESS mass than the original star.

However, gravity is not attributable to density (that I am aware of) - gravity is created by mass. So how can a star with less mass suddenly turn into a sphere from which light cannot escape? (when it could before!)
Escape velocity is found by:

And is the speed that something has be be moving if it is and distance r from the center of mass m, and be able to escape completely from mass m, with the requirement that all of mass m is contained within radius r.

You can increase escape velocity by either increasing m or decreasing r (for example. the escape velocity form Earth at a distance of the Moon is only 1.4 km/sec, while at the surface, it is over 11 km/sec).

If the Earth were compacted to 1/2 it present radius while maintaining its present mass, the escape velocity at the surface would increase to 1.414 its present value, to ~15.6 km/sec. (however, if you were to remain at the original distance from the center, the escape velocity would remain the same as before). Meanwhile, the surface gravity would increase by a factor of 4.

If you were to squeeze all the mass of the Earth into a sphere smaller than .885 cm in radius, the escape velocity at its surface would become greater than c and nothing moving at c or less could escape its surface. It becomes a black hole.

Yes it density becomes really high, but that it not directly related to the strength of gravity, the high density is only needed to keep the mass small enough that you can can get close enough to the center for the increase in escape velocity to become high.

And the density need not be that high for large black holes. A super massive black hole with a radius of 10 AU would only have a density of 253 kg/ m³, this is less than that of water!

15. Were you high when you wrote this?
Originally Posted by Jona
Quantative vs Qualative is about the quantity of the whole reason we need to find a qualitive answer. If I was to have millions of friends that'd be the first step towards finding a good answer. Then we need to assist each other to call upon a concrete answer but that's mean an infinity amount of people living through infinity to find the space to understand the masses of blackness. Problem there is we'd have to live forever to get that answer which is for some a nonsense idea. I believe that we could pass on information of Qualitive answers to get a Qualitive review of how far and how huge the masses of space exist in measurement. That would mean passing the information to lots of people through time. probelm again could be example: this information lead to another anwer? In my eyes NO, this is mistrust of information and means that we'll back to square one.

16. All this is explained in my theory i just posted. How can a black hole grow into a super massive if it "deletes" particles of information? Just because we dont know what happens doesnt mean they are deleted from the universe.

17. Brane Wave: Stephen Hawking retracted his paradoxical view that information must be lost when matter falls into a black hole. In place of this idea, his revised mathematics (validated many times by numerous workers) shows that information persists but is confined to the surface or "event horizon" of the black hole. "Hawking radiation" may then be emitted by such a black hole and the information becomes available again. The singularity that is predicted by general relativity (GR) results from extrapolation of GR to the logical extreme. But, it is still logical. The logic cannot be tickered with without destroying the whole ediface. The trouble with singularities is only that one cannot do anything more with them, mathematically. They are a dead end. One can still say that matter therein must be compressed to infinite density, though. But, what does this mean?

If matter is compressed to infinite density, the gravitational field associated with its very existence becomes infinite as well. By GR, this means that as mass falls into a black hole, time itself must slow down whereupon its pace declines toward zero. The only weird thing about black holes is this effect. But, the very same thing is seen when temperature is reduced to near absolute zero when a perfect crystal is studied in the laboratory. One can only extrapolate along a straight line leading toward "zero" degrees Kelvin. One can never reach zero in the lab. The connection to black holes is direct.

What this really means is that matter inside all black holes is still crashing down toward the "center of gravity" but it will never actually get there. But, the center itself exists as the center of gravity as long as an event horizon can be defined. As such, it possesses a gravitational field that has a very unique profile of potential versus radius.

The event horizon surface of a black hole is associated with a certain entropy linked to its surface area. It is also linked to a certain temperature which assures that information is still present and that Hawking radiation may be emitted therefrom. Such radiation may take hundreds of billions of years to significantly affect the mass that is retained in the black hole, however. But, this is just a detail.

Search "Stephen Hawking entropy black hole". There is a class of thermodynamics called "black hole thermodynamics". Hawking and Beckenstein used quantum mechanics and statistical thermodynamics to define SBH, the total entropy of a black hole.

So, the singular nature of a black hole is not just conjecture. It is fact, by general relativity. In order to dispute it, one must also dispute GR.

This has huge implications to the hypothesis of "Dark Matter" and hypothetical "Dark Energy". See the thread "MOND, Prelude to Critique of the Universe" and the thread "Critique of the Universe" .

18. Originally Posted by Janus
Originally Posted by leohopkins
Originally Posted by Dishmaster
No, it only has to fulfil the criterion of the Scharzschild radius. If a given mass is compressed strong enough so that is not bigger than this radius, it is a Black Hole.
Schwarzschild radius - Wikipedia, the free encyclopedia
Call me unenlightened but I cannot see how the mass itself can cause the strong gravity associated with a black hole (strong enough that light cannot escape) ...the star before its outer shell went supernova and the core shrunk in size......emitted light and furthermore as the outershell gets thrown off in a supernova the star now collapses into a BH with LESS mass than the original star.

However, gravity is not attributable to density (that I am aware of) - gravity is created by mass. So how can a star with less mass suddenly turn into a sphere from which light cannot escape? (when it could before!)
Escape velocity is found by:

And is the speed that something has be be moving if it is and distance r from the center of mass m, and be able to escape completely from mass m, with the requirement that all of mass m is contained within radius r.

You can increase escape velocity by either increasing m or decreasing r (for example. the escape velocity form Earth at a distance of the Moon is only 1.4 km/sec, while at the surface, it is over 11 km/sec).

If the Earth were compacted to 1/2 it present radius while maintaining its present mass, the escape velocity at the surface would increase to 1.414 its present value, to ~15.6 km/sec. (however, if you were to remain at the original distance from the center, the escape velocity would remain the same as before). Meanwhile, the surface gravity would increase by a factor of 4.

If you were to squeeze all the mass of the Earth into a sphere smaller than .885 cm in radius, the escape velocity at its surface would become greater than c and nothing moving at c or less could escape its surface. It becomes a black hole.

Yes it density becomes really high, but that it not directly related to the strength of gravity, the high density is only needed to keep the mass small enough that you can can get close enough to the center for the increase in escape velocity to become high.

And the density need not be that high for large black holes. A super massive black hole with a radius of 10 AU would only have a density of 253 kg/ m³, this is less than that of water!
So then, that would indicate that gravity is linked to the "displacement" of space-time; or should I say the more the displacement of space-time in a given region of "space", the stronger the gravity.

19. By "crashing down" I mean that even at this very moment, all the matter that has fallen into a black hole, even if it has already descended to below the event horizon, is still falling. Time is so distorted by the gravity field that the clock virtually stops therein. So all that "stuff" is still dropping into the abyss. It will never actually get to "the center", not in any black hole, anywhere. This is why the hyperbolic gravitational field must be considered to be asymptotic - as a well behaved hyperbola should.

By the way, I am back with my old persona. I was getting nasty e-mail and spam from the misuse of my personal info given in my profile. So I "retired" G.A.K. and registered another persona that I named simply "Kent", with goofy profile info. I also had crippling problems logging-in using G.A.K. So, I had no choice. But, now that these problems are solved - except to respond to Kent's posts that I already made - I will retire him until some other snafu flattens me. Be assured, neither Kent nor G.A.K. are sock-puppets designed to subvert the forum. I will never use them simultaneously or alternately to bust ethics rules.

20. Originally Posted by leohopkins
Originally Posted by Janus
Originally Posted by leohopkins
Originally Posted by Dishmaster
No, it only has to fulfil the criterion of the Scharzschild radius. If a given mass is compressed strong enough so that is not bigger than this radius, it is a Black Hole.
Schwarzschild radius - Wikipedia, the free encyclopedia
Call me unenlightened but I cannot see how the mass itself can cause the strong gravity associated with a black hole (strong enough that light cannot escape) ...the star before its outer shell went supernova and the core shrunk in size......emitted light and furthermore as the outershell gets thrown off in a supernova the star now collapses into a BH with LESS mass than the original star.

However, gravity is not attributable to density (that I am aware of) - gravity is created by mass. So how can a star with less mass suddenly turn into a sphere from which light cannot escape? (when it could before!)
Escape velocity is found by:

And is the speed that something has be be moving if it is and distance r from the center of mass m, and be able to escape completely from mass m, with the requirement that all of mass m is contained within radius r.

You can increase escape velocity by either increasing m or decreasing r (for example. the escape velocity form Earth at a distance of the Moon is only 1.4 km/sec, while at the surface, it is over 11 km/sec).

If the Earth were compacted to 1/2 it present radius while maintaining its present mass, the escape velocity at the surface would increase to 1.414 its present value, to ~15.6 km/sec. (however, if you were to remain at the original distance from the center, the escape velocity would remain the same as before). Meanwhile, the surface gravity would increase by a factor of 4.

If you were to squeeze all the mass of the Earth into a sphere smaller than .885 cm in radius, the escape velocity at its surface would become greater than c and nothing moving at c or less could escape its surface. It becomes a black hole.

Yes it density becomes really high, but that it not directly related to the strength of gravity, the high density is only needed to keep the mass small enough that you can can get close enough to the center for the increase in escape velocity to become high.

And the density need not be that high for large black holes. A super massive black hole with a radius of 10 AU would only have a density of 253 kg/ m³, this is less than that of water!
So then, that would indicate that gravity is linked to the "displacement" of space-time; or should I say the more the displacement of space-time in a given region of "space", the stronger the gravity.

Mathematically, singularities exist, like infinities. They occur in the math at the most inconvenient times. This is why mathematicians hate them. But, there is a "Mathematics of Infinities". So, maybe there should be a few mathematicians specializing in the mathematical properties of "singularities". A singularity would engender infinite displacement, gravity becomes infinitely strong - in the LIMIT - only in the limit of the approach closer and closer to the center of mass. Time is distorted too, so one never gets there. The "center" must actually be "nowhere". That's why it defines an asymptote. This gets almost mystical!

21. Originally Posted by Dishmaster
No, it only has to fulfil the criterion of the Scharzschild radius. If a given mass is compressed strong enough so that is not bigger than this radius, it is a Black Hole.
Schwarzschild radius - Wikipedia, the free encyclopedia

does this mean that the concept of singularity is unnecessary, pointless?. Wouldn't it be more sensible to consider the radius of the black hole as the value just below its SR?

The concepts of infinite and singularity are ok in pure math, but in reality it is extremely dangerous to consider infinite density or infinitely small or...anything.
the laws of physics are meaningless when space and time fall below a certain value or (as a limit), below Planck's units:
They say Coulomb force is meaningless below 10 ^-18m, what happens then at 10^ -36, or 10^ -1000 ? what happens to gravity, radiation, heat etc ?
But even if we limit ourselves to SR, there are some problems which are usually ignored: if time slows down inside a BH , what happens to the laws of physics that are time-dependent? the force of gravity decreases as time slows down and grinds to a halt. What happens to heat , and so on?

22. Originally Posted by ray

But even if we limit ourselves to SR, there are some problems which are usually ignored: if time slows down inside a BH , what happens to the laws of physics that are time-dependent? the force of gravity decreases as time slows down and grinds to a halt. What happens to heat , and so on?
The apparent change of time scales is a result of different reference frames of the observer and the object he observes. Locally, time advances unchanged. You would not recognise any difference, if you would be inside sich a BH (provided you survive the tidal forces).

23. Originally Posted by Dishmaster
The apparent change of time scales is a result of different reference frames of the observer and the object he observes. Locally, time advances unchanged. You would not recognise any difference, if you would be inside sich a BH (provided you survive the tidal forces).
if laws of physics are not affected by time, they are surely affected by space, because space is defined as infinitely small

what happens to forces at a distance od 10^ -100 m? what happens to heat when wavelength can be only ,say, 10^-1000 m?

24. Yeah right .can you proof he black hole dose exist ?just cause 2 man saying it doesn’t mean it is there dose it? .can you put real calculations for a possibility what dose not exist for 100% ?do you want to waist your time with questions what not explainable only in couple of brain? can you proof god doesn’t exist ? no you cannot ,can you ? you only know that much how much your teacher tells you no more, how much you read in book's what could be fake to confuse you , into the big question infinite ,is include everything all question about everything ,science has lot of explanation about materials but no idea about what going on for real, yes they have ,but they teaching u the opposite . the sience just a cover up ,to take your eys away from the real truth , what is really going on !
there is the time comes when you realize everything what you learned it just dose not make sience ,when you realize something just dose not mach up with science ! when you find the mismatch you will find the black hole and its size and your question will be answered but you got to be around 34 years old min, to get youself into that ,when you know your choice ,u'll you have to belive what your teachers tell's you !

25. Grate furst poste!

26. Originally Posted by MeteorWayne
Grate furst poste!
At least I can read and understand what you posted. yogybear's post might as well be in Klingon.

But you know what would make you a better person? Just ignoring the post. But you can't do that can ya?

27. Originally Posted by PumaMan
Originally Posted by MeteorWayne
Grate furst poste!
At least I can read and understand what you posted. yogybear's post might as well be in Klingon.
Aw, c'mon dude's. The kid's got a shiny helmet and ya gotta throw his shoe's up on the wire?

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