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mfb- t1_j4u4r33 wrote

What do you mean by "virtual object"?

Black holes are real objects in space.

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peacefultoker420 OP t1_j4uopga wrote

But we they physical objects? If they are a mathematical expression of space time and the singularity itself is not made of matter, just the warping of source time, surely they can't be classed as a physical item like a chair or a star

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mfb- t1_j4utpg8 wrote

A black hole has a mass and deforms spacetime, a chair has a mass and deforms spacetime. The chair might have a more complex internal structure (we are not sure, because we can't check for black holes), but why would that be relevant to call it a physical object? A black hole is obviously there in space, so it's a physical object.

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Dead_Shaman_ t1_j4vhjbh wrote

I think you mix the two concepts of "the singularity is not physical" (which is true, as it is only a mathematical construct) with "black holes are not physical". We use different mathematical constructs to approximate physics effects. Using the notion of a singularity works if you are beyond the event horizon, but if you are close this would be a different and more complicated affair. Nevertheless, a black hole is real, wether or not we can fully describe it in every regime of space-time.

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matteogeniaccio t1_j4ucyvr wrote

Yes and no. A black hole is defined as the volume behind the event horizon, the "point of no return".
The event horizon is not a physical surface, you only have its definition: you wouldn't know it's a point of no return unless you waited for an infinite amount of time. A good approximation of the event horizon is the surface where the escape velocity is the speed of light.

Nevertheless, black holes are real objects. Their gravity has effects on the outside world. They are created by a stellar collapse. They can orbit around another massive astronomical object.

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