Question

Why black whole have most gravitational force

Answer 1

Because thee are many objects of extreme density objects with such strong gravitational attractions...

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Answer 2

Why does a black hole have such an incredible gravitational pull?

In order to physically appreciate this question, it is necessary to have an idea about the notion of “Compactness” and “Surface Gravitational Redshift” of a compact object (z):

1+z=(1−2GM/Rc2)−1/2

Suppose a compact star has z=0.1. Then the photons emitted from its surface will lose energy by working out its gravitational attraction and when they would reach extremely far [math] R \to \infty [\math], their energy would be reduced by a factor of (1+z = 1 +0.1 =1.1).

And we may define “z” as the gravitational compactness of the compact star. For

GMRc2≪1, it turns out that

z≈GMRc2

For Sun, z∼2×10−6

For a compact White Dwarf, z could be more than one order larger. And the Neutron Stars, which are the most compact objects known with certainty, z~0.1.

Now recall, the Event Horizon of a Black Hole is refined as

R=Rs=2GMc2

Then one can see that for the EH:

1+zEH=∞

This is the physical reason that gravitational pull of a BH appears to be infinite at the EH, and nothing can escape it. Also even if a photon with energy say 100 billion eV would leave from the vicinity of the EH, its far away energy would be zero.

This answer can be further sharpened:

In Newtonian gravity, the Acceleration Due to Gravity is given by

gNew=GMR2

In GR, one can form a suitable Acceleration Scalar by considering the norm of 4-acceleration of a free falling particle. This gives the equivalent of GR Acceleration Due to Gravity:

gGR=GMR21−2GM/Rc2√

This may be also written as

gGR=gNew(1+z)

And for R≪Rs; gGR≈gNew

But as R→Rs; gGR→∞

This is the precise reason why a BH has such an “incredible pull”. It is just not “incredible”, but it is INFINITE at the Event Horizon.

In GR, no physically measurable quantity (SCALAR) can blow up at place which is regular or non-singular. And the fact that we are now talking about SCALARs, means such a physical divergence cannot be wished away or hidden by means of any coordinate transformations which are invoked to claim that “Event Horizon is No Physical Singularity”.

On the other hand, this simple result, first clarified in 1981:

American Journal of Physics 49, 412 (1981), shows that Event Horizon is indeed a physical singularity, and hence should not form in real gravitational collapse.

Hope this helps you❤