Cartwheel Galaxy

[monmarfori]

That is a picture of a galaxy

[witold]

Center should be smaller

[monmarfori]

You are wrong.
But it is from the merger.

[atomic7732]

the blackhole would be much smaller either way.

[bessy]

in fact a black hole is massive in 3d space if you removed the 4th dimension

for eg the black hole in the center of our galaxy if it was only in 3d all the stars and dust that orbit it would apear as a extremely thin ring around it
it lookes small in real life because space changes size depending on gravity the bigger the gravity field the bigger space becomes and in turn time stretches as well as they are intertwined

see if you stretch space you create a gravity field
for eg the earth is bigger on the inside than it looks from the out side because it bends space as well

it sounds stupid i know

[Alex_Ian_Hamilton]

Hi bessy,
I’m not totally sure on the theory behind this, I know there is length contraction within a gravitational field, but I think to suggest “if you removed the 4th dimension”, which in this situation is basically saying (if there was no gravity) doesn’t really have any meaning.

With respects to a black hole, the size is determined by the “Schwarzschild radius” or event horizon (assuming the black hole isn’t rotating, then it’s tweaked a bit), this is the radial distance (from the singularity) that represents the area where the gravitational acceleration is so fast that even light can’t escape. Basically, it’s not a solid object with actual volume, it’s merely the places where gravity is so strong as to trap light.

The actual size of the mass within the black whole isn’t known (and won’t be until we have a theory of quantum gravity), but many theories suggest that the entire mass will be condensed into a volume-less and infinitely massive point of space and time, in which case no removing of any dimensions will make that object any bigger.

Using the Schwarzschild radius, we can calculate the rough radius of a black whole as:



Which, assuming a 1 billion solar mass black hole (which is middleweight):



Or in easier units:



This is about the radius of the orbit of Uranus, in other words, smaller then our solar system.
I checked this by searching online for the size of a quasar, which they suggest is about the size of a solar system.
Which when you considering the whole galaxy is about 150000 light-years across, means that the black hole should be pretty small:



Personally, I think it’s amazing how small these things are, especially when you think of Quasars (active galaxies that are throwing out masses of energy), the jets from a quasar can be many thousands of times more energetic then all the stars in the galaxy combined; and yet all that energy is being released by an area the size of a solar system.

OK, now my head hurts, if anyone sees an issue with my calculations (or anything) please say, there were lots of numbers I had to throw around and I could have easily made a error somewhere...

[monmarfori]

You may have epilepsy seizures from using that one.

[Alex_Ian_Hamilton]

Yup, I was almost having seizures the second I tried to work it out in AU... lol

Tho you can't believe how happy I was when I plugged in the numbers and the answer was pretty much what I expected (such a relief).

I never dad say, I line your galaxy tho, it looks cool; sorry I got caught up in the math. (how sad)