1
$\begingroup$

I'm an amateur to astrophysics but I'm slowly teaching myself things and I have these three doubts.

  1. How does more compression relate to a stronger gravitational pull. Like, when we say that a black hole is a tiny space that has 20-30 suns compressed in it, how does this increase its gravitational pulling power (I'm open to mathematical answers but I prefer a layman type answer for better understanding)

  2. How deep a does a black hole go i.e. what is its depth? And when we say the black hole "sucks" anything "into it", how much can it "suck"? Is there a limit after which the black hole stops consuming anything in its path?

  3. Are there factors which decrease/increase the strength of the gravitational pull of a black hole over time? Or does it remain as it is for eternity?

Apologies for the long question.

$\endgroup$
1
4
$\begingroup$
  1. It doesn't. If the sun were replaced by a black hole of equal mass, the planets would happily keep orbiting just like they are now. The difference is that if we travel towards the sun, the gravitational force it exerts on us would increase, but there would be a limit - eventually we would hit the surface. Black holes have no such surface, so the gravitational force they exert on you will keep going up and up and up as you approach the center.
  2. It sounds like this question comes from the "rubber sheet" analogy. A black hole does not have any notion of depth like the one you describe. A black hole only "sucks" insofar as things are attracted to it gravitationally, and sometimes they fall into it - the same is true of Earth, which captures meteorites all the time.
  3. A black hole gets bigger when things fall into it, though the question of what this process looks like to an outside observer is a very interesting one. Hawking radiation is a theoretical mechanism by which black holes are predicted to decay over time, but this process would be extremely slow for large black holes.
$\endgroup$
4
  • $\begingroup$ When stuff falls into a black hole, how far deep do they travel? On earth, all the meteorites crash into the surface and break apart, but what about a black hole? Do they just keep travelling endlessly towards the centre? $\endgroup$
    – noorav
    Apr 16 '19 at 13:48
  • 1
    $\begingroup$ Yes, it falls in toward the center. What this "looks like" depends on the observer - if you're the one falling in, then you'll get to the center relatively quickly. If you're on the outside, you'll never see anything cross the event horizon. This kind of thing requires a bit of deeper study to understand clearly. $\endgroup$
    – J. Murray
    Apr 16 '19 at 13:54
  • $\begingroup$ is there any point at which I stop falling altogether? $\endgroup$
    – noorav
    Apr 16 '19 at 15:31
  • $\begingroup$ @noorav As J. Murray said, you stop falling when you reach the centre, which for a stellar mass BH happens in a fraction of a millisecond, according to your local measurement of time. But before you reach the centre, you're spaghettified by the tidal force: if you're falling feet first, the gravity at your feet is higher than at your head. As you get closer, even your atoms are ripped apart. With a SMBH, you can cross the EH before that process is noticeable, for a 20-30 M$_\odot$ (solar masses) BH, spaghettification starts before you cross the horizon. $\endgroup$
    – PM 2Ring
    Apr 16 '19 at 16:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.