Hi everyone,

wondering if anyone can answer what probably seems like a silly question. If at the centre of a black hole is a singularity (infinatley small and massive) How can we have different size black holes (super massive and microscopic). Isn't a singularity a singularity, does there mass increase or does there size increase.

cheers

Black holes are mostly mathematical theory, with very little observation, except computer models. More conservative researchers say, we don't know what is inside the event horizon and likely never will know for sure.
Some have recently calculated that the singularity is small, but not infinitely small. If so, the singularity can range in mass from a gram to the mass of a large galaxy.The radius of the singularity may be inversely proportional to the 4th or 5th power of the mass with much higher singularity density for very massive black holes. In my opinion, most of the mass will be inside the event horizon, but not yet in the singularity. I picture a traffic jam of mass trying to get inside the very small singularity, but that may not agree with the math. In any case, galaxy mass black holes are different in many ways from the low mass black holes which may soon be made at the new collider in Switzerland. The solar mass black holes are also quite different, so we should likely specify the mass range we are thinking before making assumptions. Neil

To answer this properly i see a need for explanations of terminologies used.
I am of the view that small sub atomic black holes are short lived. So the Large Hadron Collider might produce a BH but it will be gone in a short while. So the size of a black hole is measured how? we can not see it can we... So it is measured by calculating it's gravity force. As objects orbit clues are given as to the mass of the object being orbited. We have noted that super massive short lived stars are prime targets of becoming BH's. While at the core of the Galactic mass lies a super massive BH., or a group of them...
Radio and in-fared astronomy are important tools as we 'see' very little of a BH. We see whats effected by it.
I have, when talking to students. Often used the following by Carl Sagen..
'The size of the black hole is directly proportional to its mass. Which has become part of it.'

thanks that helps a little, so does this mean the more matter/energy that falls into a black hole the larger the mass of the singularity, hence the larger the gravitational effect of the black hole.

You keep using that word 'singularity'... Its not actually prov en that inside the event horizon of a black hole is a singularity. Its a probability. Its a place we can not look into. The state of mater inside a black hole is alien to our understanding. Its dense hot and dense... oh ya its dense too. Did I tell you how dence it is... very.glad to have helped mark.

Blackholes appear to have a upper size limit in the 10 to the 10 solar mass range, I think the largest found so far is 18 Billion times the mass of our sun, according to some articles I recently read.

http://www.newscientist.com/article/dn13166 talks about the 18 Billion Solar Mass black hole recently discovered.

If we don't know whats going on inside the event horizon, then I think you'll find an even spread of the mass would result in Black Holes that would float on water ... not very dense at all. :-)

I'd be interested to see some references for these two statements.
There doesn't seem to be any particular reason to cut off allowable black hole masses above the Planck mass, which is about 100,000 times smaller than a gram.
And the "radius of the singularity", if one is offered, is usually just the radius at which we know we'll need new physical theory: the Planck length, on the order of 10^-35 metres.

Grant Hutchison

http://xxx.lanl.gov/abs/0808.2813 discusses upper size limits.

One; Where did you get this idea...?

Two; Your understanding of the black hole is not as mine... ?

The understanding of the density of matter in a black hole would not fit your description.

Light... No.
Very heavy. Yes.

All that mass in a space smaller than a star... Remembering that computer models and mathematics seem to support the observations made.
Have a look at yesterdays 'picture of the day' and its explanation of movment...
I would not say we know so much as to argue the inside of a black hole's state. mark

If you calculate the "volume" of the event horizon based on a sphere of the Schwarzschild radius, you find that the apparent density varies with the inverse square of mass. For supermassive black holes, you can indeed get densities less than water, if you calculate this way. The threshold is around 130 million solar masses, which is rather large.
And I confess I'm not convinced of the physical validity of the calculation.

Grant Hutchison

Nor would they float on water. They'd suck up the water, the planet, the entire solar system, in very rapid order.

__________________
If I set the budget, we'd have Ares and more. Unfortunately, I don't set the budget, and Ares is just too expensive and too far out for us to accomplish our goals within the budget we were given.

If we halt the ISS, all versions of Ares, and transport Orion and Altair aboard DIRECTv3's Jupiter family of Shuttle-Derived Launch Vehicles, we just might make it back to the Moon by 2020.

patsta,

The more mass falls into a black hole, the stronger its gravitational field
and the larger its event horizon. That is true nomatter what is going on
inside the event horizon. Whether or not there is a "singularity", and
whatever the volume occupied by the matter within the black hole, the
gravitational effects on the surrounding region are identical.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves