Can a material object cross the event horizon of the Black Hole?

[rirakib]

Sure, no problem. Even theoretically a living being.

The event horizon is not a solid sphere, it is simply a region of space, technically the surface of a sphere where the sphere coincides with the place where the escape velocity equals that of light.

Depending on the size of the hole, that surface may be a great distance from the center, so much so that tidal forces do not have a serious effect on anything that crosses it. A different issue is that many black holes, especially those that we can detect, have an environment of very high radiation outside of them due to the gamma rays emitted by the matter that falls inside due to the high temperatures that they reach due to friction, but if the hole is very large and there is no matter in the vicinity technically you could enter without dying in the effort

To enter, to leave nothing of course.

At least theoretically. Despite the fears of some, the closest black hole is at an immense distance, even moving quickly in our direction (which it does not) before "eating" us, life on Earth will have disappeared when the sun enters its red giant phase. On the other hand we cannot observe a black hole like the one I have mentioned at least easily. Black holes are so called because they emit absolutely nothing, they can only be detected by the matter that falls inside, by how they deflect light as it passes by them, or by some other celestial body like a star that somehow rotates with that hole. and let's see its orbit without finding any other celestial body where the companion should be.

[exchemist]

1 hour ago, rirakib said:

Sure, no problem. Even theoretically a living being.

The event horizon is not a solid sphere, it is simply a region of space, technically the surface of a sphere where the sphere coincides with the place where the escape velocity equals that of light.

Depending on the size of the hole, that surface may be a great distance from the center, so much so that tidal forces do not have a serious effect on anything that crosses it. A different issue is that many black holes, especially those that we can detect, have an environment of very high radiation outside of them due to the gamma rays emitted by the matter that falls inside due to the high temperatures that they reach due to friction, but if the hole is very large and there is no matter in the vicinity technically you could enter without dying in the effort

To enter, to leave nothing of course.

At least theoretically. Despite the fears of some, the closest black hole is at an immense distance, even moving quickly in our direction (which it does not) before "eating" us, life on Earth will have disappeared when the sun enters its red giant phase. On the other hand we cannot observe a black hole like the one I have mentioned at least easily. Black holes are so called because they emit absolutely nothing, they can only be detected by the matter that falls inside, by how they deflect light as it passes by them, or by some other celestial body like a star that somehow rotates with that hole. and let's see its orbit without finding any other celestial body where the companion should be.

What point do you wish to discuss? 

Answering a question nobody has asked is a very odd way to start a discussion. 

Or are you just a bot? 

[md65536]

On 2/2/2023 at 2:42 AM, rirakib said:

Despite the fears of some, the closest black hole is at an immense distance, even moving quickly in our direction (which it does not) before "eating" us

Another thing is that its gravitational influence is similar to ordinary matter of the same mass, at a distance, so a black hole of one solar mass wandering into the solar system shouldn't be much more likely or a danger of eating us, as a star of one solar mass doing the same. Similarly a black hole created in the lab would not have enough mass to devour the earth on its own. It would only devour extremely nearby matter (probably closer than atoms are to each other*, depending on its mass of course). A BH made from Earth's matter wouldn't collapse the Earth any easier than the Earth's own mass would collapse on itself, so it would have to eat away at nearby matter until it destroyed the structural integrity of the planet before it would collapse.

That said, Ton 618 has "The largest black hole ever found in the known universe" at 66 billion solar masses. "A black hole of this mass has a Schwarzschild radius of 1,300 AU (about 390 billion km in diameter) which is more than 40 times the distance from Neptune to the Sun." But it's about 18.2 billion light years away, so like you say, it's distance that keeps us safe.

 

* Edit: I vastly overestimated that distance. Atom spacing is on the order of Angstroms (10^-10 m). A black hole with a mass of a million tonnes would have a Schwarzschild radius of about 10^-18 m, a thousandth the size of a proton! Does that mean such a BH might not even collapse a proton even if it passed right through it?

Edited February 4, 2023 by md65536

[joigus]

As usual, I refer to the question on the title when I can't follow the logic that comes below.

Can a material object cross the horizon of the BH?

If the Schwarzschild radius of the BH is much bigger than the size of the material object (2 cases, I'm assuming free fall):

From the outside to the inside of the horizon: Yes, and if the BH is big enough, the material object would be none the wiser that it's crossing a horizon.

From the inside to the outside of the horizon: No, and due to its being in free fall it would be none the wiser that a huge part of space-time is forbidden to them

But,

If the Schwarzchild radius of the BH is comparable to the size of the falling object:

The material object would be squeezed to nuclear spaguetti, according to standard knowledge.

[Genady]

19 minutes ago, joigus said:

If the Schwarzchild radius of the BH is comparable to the size of the falling object

This statement triggered a picture in my mind that I didn't think about before: the Schwarzschild radius of a BH is much smaller than the "falling" object. IOW, a small BH is falling onto a large object. Or even the BH is inside the large object. How does the process look in these cases? Is the latter possible?

[joigus]

BH falling into object or the other way around is a matter of reference frame. The thing about small Schwarzschild radius --in comparison to falling object-- is a question about tidal forces (gradients of gradients or second-order derivatives.) When object is very close to centre of gravitational attraction, it's no longer possible to consider local inertial system as such, due to second-order effects (second order derivatives.)

I'm sure you know about this --from what I can infer. You're either an expert on this or a person so knowledgeable that not even an expert could tell the difference.  

[md65536]

8 hours ago, Genady said:

IOW, a small BH is falling onto a large object. Or even the BH is inside the large object. How does the process look in these cases? Is the latter possible?

Yes of course it's possible and common. Google says 'About 1% of supermassive black holes have an "accretion disk" of gas and dust swirling around them.' So I guess it looks like an object being pulled apart from the inside.

If you want to consider some other object, it should be similar. Some "forces" give the object its shape and keep parts of the object away from the black hole, whether it's the inertia of a spinning accretion disk or chemical bonds of solid matter, and the BH rips away any parts that get too close, regardless of what holds the object together. It would look like spaghettification.

 

The process is just gravitation, not some magical suction that vacuums everything up. For example a human on an extremely massive planet would be crushed by gravity. A black hole with similar gravitation would devour a human from the inside because the latter doesn't have the structural integrity to resist such strong pull. A small enough asteroid would barely have the strength to keep a human stuck to it, let alone damage its shape. A black hole with similar gravitation wouldn't have the strength to rip a human apart or pull more of it in.

Edited February 5, 2023 by md65536