/sci/ - Science & Math

>how does it end up with so much more mass

It doesn't.

>Why doesn't a star have that kind of gravity

It does. What it lacks is density, which it will have once it collapses.

>>3528754
not OP but:

if you had this star, it emitted light, then it collapsed into a black hole, now it doesn't produce any light and didn't gain any new mass, how does its gravity get so high as to be able to suck in all that light now?

its gravity related to density or mass>?

>>3528731
Mass doesn't change, density changes.

You could collapse the Earth into a black hole, the schwartzchild radius is something like the size of a hamburger. It wouldn't change the Moon's orbit or anything else though, because the mass is still the same.

Black holes don't behave like they're often portrayed to in popular culture. Unless you're past the event horizon you might not notice the gravitational difference between it and a regular star of the same mass.

>>3528768
then how does it be able to prevent light from escaping?

how is light able to be controlled by gravity, but has no mass?

Gravity is proportional to 1/r^2. An object of uniform spherical shells behaves as a point mass. The gravity around a star is therefore 1/R^2, where R is the radius of the star. If you compress the start to a smaller radius, with the same mass, gravity at the surface increases.

At some point, 1/R^2 becomes so large that it becomes a black hole.

Look up the Schwarzschild radius.

>>3528763

It's escape velocity (the velocity needed to get away from the object permanently) is beyond the speed of light past a point called the event horizon. Light can't escape because it simply isn't fast enough.

as far as i can remember from 3 years ago

Fgravity = (GmM)r^2, so smaller dist means larger force?

>gravity so strong light can't escape

Just a small clarification, the common conception is that gravity is some sort of force that pulls everything inward. When regarding black holes, the space beyond the event horizon is so badly warped by the massive gravitational force that there are no vectors in local space which lead past the event horizon. Space has literally been bent inward.

>>3528763
The gravity didn't get any higher. The fact that it collapses to a tiny as fuck entity means that light can now get close enough to it to get trapped, which it couldn't before because there was a star exterior in the way.

>>3528763

We treat gravity like point masses just because it's simpler that way and works well enough at long distances. Stars are not actually point masses; their mass is distributed throughout their diameter.

Making a star denser lets the light get closer to the center of mass without colliding with it. The closer you can get to the center of mass, the more of the star's gravity you experience.

If you make a star dense enough, you can get close enough to the center of all that mass that the acceleration due to gravity exceeds c and thus not even light can get away again.

>>3528775

See

>>3528789

>>3528789

can't you go back along the same vector you came in by? Surely if there's a connection there's a path to move out?

>>3528787
retard detected
that's the gravitational force between two masses

>>3528806

Don't make /sci/ look like douchebags. Keep the kiddie boasting outta here.

>>3528812
>change direction
>same vector

Vectors don't work that way.

>>3528794
If you had a way to balance the pressure and control the temperature, you could hollow out a little area of a star at its center of mass and just hover there. It's not the distance from the center of mass itself that matters because all spherical shells around you would contribute no net gravitational force.

>>3528829

I guess I don't see how bending space explains why you can't go back (not that I'm doubting it). If a vector can follow a direction into the black hole, why can't another vector go out of the black hole along the same line?

>>3528806
>implying that F != m*a
>implying that we're not talking about the acceleration due to gravity
>calls someone else a retard

Stay classy, my butthurt friend.

>>3528833

The whole of my explanation pointed out that you need to get close to the center of mass while remaining OUTSIDE the mass itself in order to experience greater gravitational forces (if you ran into it, then you have mass pulling in all directions), yet you missed it anyway?

>>3528839
>why can't another vector go out of the black hole along the same line?

Because that line points into the black hole, not out of it. Vectors are directional; you can't decide to follow one backward.

Any vectors leading outside the black hole would have to have a velocity component greater than c, which is impossible.

>>3528857

Ok, think I get ya now. Thanks

>>3528780
Most clear answer.

density. density. density.

>>3528925
Most vague answer.

>>3528847
that's what I meant herp derp

the formula is for two masses, and he's referring the the gravity of ONE mass.

faggot.

>>3528847
>implying his formula had anything to do with the gravity of a black hole