Question

Given that virtually nothing can escape from black holes, explain how black holes are important in producing the enormous luminosities observed from the centers of some galaxies.

Answer 1

As we know that Einstein predict that theory of general relativity, which showed that when a massive star dies, it leaves behind a small, dense remnant core and if that core mass is about 3 times mass of the sun, then gravity with help of other forces produces a Black Hole.  

In general, we assume that Black Hole does not produce radiation (light) itself. So than How we are inferring that luminosities effect?

Here is the reason: We cannot observe directly the presence of Blackhole with help of a telescope (although these telescopes can detect X-rays, Light, EM radiation). However, we can find the effect of Blackhole by studying their effect on other matter nearby.

Suppose Black Hole passes through a cloud of Interstellar matter, it will pull or accrete the matter inward. In that way for example. if a star passes near to the black hole, it will tear apart (due to gravitation pull of black hole). Due to this breaking process the matter will get accelerated and get heats up, thus it emits the X-rays which radiate into space. Hence using the telescope we can detect this emitted energy (x-ray) and from a large distance, this energy is creating a luminescence effect.

Thus in this way, Black Hole can produce enormous luminosities.

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