Can black holes truly be infinite?

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Discussion Overview

The discussion revolves around the nature of black holes, specifically questioning whether they can be considered to have infinite mass and how their mass relates to the stars that formed them. The scope includes conceptual understanding and technical explanations regarding black hole mass and gravitational effects.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that a black hole has an infinite mass in any direction from an observer's perspective.
  • Others argue that a black hole has a finite mass, specifically the mass of the star that collapsed to form it.
  • One participant questions how a black hole can have an event horizon if its mass does not increase over time and is the same as the original star.
  • Another participant clarifies that while a black hole's mass can increase by absorbing objects, it remains finite, and the gravitational attraction is equivalent to that of the original star outside the event horizon.
  • There is a discussion about the difference in gravitational effects between a star and a black hole, particularly regarding the proximity to their centers.

Areas of Agreement / Disagreement

Participants express differing views on the nature of black hole mass, with some asserting it is infinite and others maintaining it is finite. The discussion remains unresolved regarding the implications of these differing perspectives.

Contextual Notes

Participants reference the concept of event horizons and gravitational effects without fully resolving the implications of mass and radius in the context of black holes.

Dan4
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Good morning. Not sure if I am doing this right, but I just wanted to ask a question.
 
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Also, I'm not looking for homework help. Just an understanding.
 
I am assuming that a black hole has an infinite mass in any direction, from a direct line from any observer.
 
Dan4 said:
I am assuming that a black hole has an infinite mass in any direction, from a direct line from any observer.

A black hole has a finite mass. This is generally the mass of the star that collapsed to form it.
 
So the mass doesn't increase over time, and if it's the same mass of the star that created it, how does it have an event horizon or the same gravitational "footprint" as the star that created it?
 
Dan4 said:
So the mass doesn't increase over time, and if it's the same mass of the star that created it, how does it have an event horizon or the same gravitational "footprint" as the star that created it?

It can of course increase in mass over time by objects crashing into it. But, that can happen to a star as well. In any case, the mass remains finite.

The gravitational attraction of a black hole is the same as the star that created it. Except that the star's mass has a physical extent: the Sun is about 1.5 million km across. So, you can only get so close to the centre of the Sun before you crash into the surface. But, if the Sun were a black hole you could get closer than that and the gravity would get stronger the closer you got. And at a certain radius - it would be about 3km for the Sun - you would reach the event horizon.

In other words, the gravitational difference between a star and a black hole is in the region closer than the surface of the star. Outside of that, the gravity is the same for both.
 
Hey thanks! I was focused on the wrong thing and didn't take the radius into account.
 
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