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# Landing on a black hole!!

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Hi I was reading about how putting nuclear waste into the sun would be pointless, due to orbital mechanics, and needing more energy than it take to leave the solar system, but what about black holes? does that mean it would actually be a lot more difficult to get into a black hole than people realise, my head says no but surely the same principle applys?, does it apply to spinning black holes only. Confused, please help.

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What did you have in mind...

Every city would have its own geosynchronous orbiting, artificial  miniature Black Hole to be used as a garbage dump ?
They'd have to put up a tall fence around it.
Anyone falls in; there's no getting them out.

As for 'landing' on a Black Hole, what would you land on ?
There's nothing there.
Our best theory says the event horizon is a mathematical construct, and the central singularity is a dimensionless point.

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Sorry poor explanation, I was reading a thread which explained why it would be difficult and pointless to dump nuclear waste into the sun, basically the sun would just cause you too orbit around super fast the only way to counter this would require so much energy it would be pointless. I was wondering would a black hole have the same effect, so if you flew near one it would more likely cause you to orbit around. I know it sounds dumb but why is it hard to "land" on the sun but not a black hole, is it because it's so massive. Thanx for reply btw.

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Your questions are unclear. If you want to throw waste into a BH, why do you need to land? And because of the nature of a BH, there's no way you could leave if you did. Past the event horizon, no amount of energy will ever let you escape.

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Ok bad word, not land but use the sun as a nuclear waste dump, overcoming the gravity ( I think) would make it so difficult it would be pointless, but then why doesn't the same principle apply to a black hole, I don't actually want to throw waste into a black hole that was just an example. I thought that this meant that a rotating black hole would be like trying to dump nuclear waste into the sun but a non rotating black hole would just suck you straight in.

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9 minutes ago, Curious layman said:

Ok bad word, not land but use the sun as a nuclear waste dump, overcoming the gravity ( I think) would make it so difficult it would be pointless, but then why doesn't the same principle apply to a black hole, I don't actually want to throw waste into a black hole that was just an example. I thought that this meant that a rotating black hole would be like trying to dump nuclear waste into the sun but a non rotating black hole would just suck you straight in.

OK you need to learn what escape velocity actually means.

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20 minutes ago, Curious layman said:

﻿﻿I w﻿﻿as reading a﻿ threa﻿﻿d﻿ which explained why it would be difficult and pointless to dump nuclear waste into the sun

Was it a thread here on  https://www.scienceforums.net/  ? Can you Link to it?

We may be able to assist you if we know the principle that is being applied

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It was a thread I'll look for it, I know a black hole is inescapable but why isn't it easy to get something to the surface of the sun using the same principles as a black hole, why doesn't the sun just pull you straight in, albeit a lot slower, like a black hole does. Thanx for link. Will read.

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13 minutes ago, et pet said:

We may be able to assist you if we know the principle that is being applied

We might, but probably not you or I...

8 minutes ago, Curious layman said:

why doesn't the sun just pull you straight in,

Because we're trying to escape, but we can't run fast enough.

Edited by dimreepr
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I thought if you fired off a probe towards the sun it wouldn't just into to it, it wouldn't get anywhere near it, but if you fired a probe into a black hole obviously it would go straight into it, why the difference?

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3 minutes ago, Curious layman said:

I thought if you fired off a probe towards the sun it wouldn't just into to it, it wouldn't get anywhere near it, but if you fired a probe into a black hole obviously it would go straight into it, why the difference?

There is no difference.

If you can't run fast enough...

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If it doesn't have enough velocity to continue on past, matter ends up in orbit. Eventually via losing/gaining energy via collisions it either passes the event horizon or is ejected.

Black holes are basically normal outside of their event horizon. You can treat them like any other star gravitationally. Still a monstrous amount of mass in a relatively small volume though.

You're velocity causes you to orbit around the sun. If you could slow down, via a force in the opposite direction, you would fall into it.

Edited by Endy0816
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Let's say you fill a sink with water. You place a toy boat into the water and it floats on top.

What happens when you remove the drain plug and the water begins to flow out?

Does the boat immediately fall down the drain, or does it follow the whirlpool path and circle around the drain for a while until it finally gets close enough to drop down.

The waste into a star (whether our sun or one that's collapsed into a BH) follows roughly the same pattern. It WILL eventually fall in, but it will first orbit for a really long time before it does. This is only a problem if you want it to fall in immediately like an arrow driving itself into a target.

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A radial trajectory WILL take you straight in.
Its like an orbit through the center of the Sun.
You're NOT coming out the other side.

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Trying to rocket our waste off-planet is too dangerous, even if we could justify the costs (roughly US$20K/kg, or about US$5-6T). One Challenger-level incident and we've got a bunch of nasty in the upper atmosphere.

24 minutes ago, MigL said:

A radial trajectory WILL take you straight in.
Its like an orbit through the center of the Sun.
You're NOT coming out the other side.

So if you had a facility in space that produced hazardous waste, and it was near enough to a BH that you could safely and cheaply put a capsule full of it on a radial trajectory, you could use the BH as a dump, right?. A minute out, the capsule might still have enough energy to change course, but once past the EH, spacetime is so heavily curved by the gravity that there is only one path to follow, for anything, no matter how much energy it has available to escape. The path in both space and time leads to the dimensionless point at the center.

We can't know what happens, but it sounds more like a trash compactor than a dump.

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9 hours ago, Curious layman said:

Hi I was reading about how putting nuclear waste into the sun would be pointless, due to orbital mechanics, and needing more energy than it take to leave the solar system, but what about black holes? does that mean it would actually be a lot more difficult to get into a black hole than people realise, my head says no but surely the same principle applys?, does it apply to spinning black holes only. Confused, please help.

If a trash can of nuclear waste is motionless relative to the sun, it would be simple to push it toward the sun. The same would be true of a trash can motionless relative to a black hole.

But any trash can on earth is not motionless relative to the sun; it is orbiting the sun at 67,000 mph. Imagine you were at the end of a rope and I was swinging you around at 67,000 mph. Think of how hard it would be to climb up that rope to me.

In order for the trash can to become motionless relative to the sun, we would have to launch it in the opposite direction of the earth's orbit at 67,000 mph. It is this amount of energy needed that people refer to when they say it is not worth sending the waste to the sun.

On a related topic, this same principle is one of the reasons we tend to launch missions to planets further from the sun than us (Mars, Jupiter, etc.) rather than those closer to the sun than us (Mercury, Venus)

Edited by zapatos
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8 hours ago, Curious layman said:

It was a thread I'll look for it, I know a black hole is inescapable but why isn't it easy to get something to the surface of the sun using the same principles as a black hole, why doesn't the sun just pull you straight in, albeit a lot slower, like a black hole does. Thanx for link. Will read.

9 hours ago, Curious layman said:

Ok bad word, not land but use the sun as a nuclear waste dump, overcoming the gravity ( I think) would make it so difficult it would be pointless, but then why doesn't the same principle apply to a black hole, I don't actually want to throw waste into a black hole that was just an example. I thought that this meant that a rotating black hole would be like trying to dump nuclear waste into the sun but a non rotating black hole would just suck you straight in.

All BH's would at the very least be Kerr type metric, or rotating BH's, due to conservation of energy and momentum from the star from whence it was formed. A Kerr BH also has a sphere called an "ergosphere" as detailed here.....https://www.google.com/search?q=kerr+black+hole+diagram&tbm=isch&source=iu&ictx=1&fir=lSxu1ufLsf-szM%3A%2CY1UiMFOQlWaGkM%2C_&vet=1&usg=AI4_-kSWYrAlQsVhp9bRKjMsZ1Ynpz2HuA&sa=X&ved=2ahUKEwiAo7CV_eniAhXKXCsKHXTYDmIQ9QEwCHoECAMQDg#imgrc=lSxu1ufLsf-szM:

It would be theoretically possible to extract energy from the ergopshere region. Also, all BH's have what we call a "photon sphere" a distance at 1.5 Schwarzchild radius at which light/photons would orbit. We, astronomers that is, use the Schwarzchild metric BH, for ease of calculation. The Kerr BH actually has two photon spheres rotating in different directions. As you can probably see, things do get messy with calculations etc. Suffice to say anything that ventures inside the photon sphere will spiral into the BH and be lost.

The EH of a BH can be summed up as where the escape velocity equals the speed of light "c", much as the escape velocity of Earth is around 11kms/sec. The other point is that approaching a BH, one would spiral in, following the curvature of spacetime.

A BH of course has no surface to speak of and is formed when any mass is squeezed to beyond its Schwarzchild radius...for the Sun, that would be around 3 kms radius or 6 km diameter, noting of course that the Sun can never become a BH. From that point GR tells us that further collapse is compulsory, at least up to the quantum/Planck level where GR even fails us. So in effect a BH is nothing other then critically curved spacetime with a singularity  as defined by the failure of GR at the core, where a surface of sorts may exist at or below the quantum/Planck level.

A good site for info on BH's of all types can be found at https://jila.colorado.edu/~ajsh/

Edited by beecee
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2 hours ago, zapatos said:

On a related topic, this same principle is one of the reasons we tend to launch missions to planets further from the sun than us (Mars, Jupiter, etc.) rather than those closer to the sun than us (Mercury, Venus)

I would agree in the case of Mercury, but Venus has only slightly higher delta-v requirements compared to Mars and quite a bit lower than Jupiter. Check out this handy Solar System Delta-v Map

Also Venus has a significantly more sizable atmosphere which can assist with aerobraking and if you decided to land on it, doesn't require retrorockets or space cranes etc. The biggest downside is that Venus missions require a boatload of protection for the spacecraft if landing is planned.

Edited by pavelcherepan
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Ok good, thanx for that, I get it now, it would fly into the sun eventually, and it could orbit around a black hole, it depends on its trajectory. Those links were really great too. Zapatos really nailed it for me though.

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2 hours ago, Curious layman said:

Ok good, thanx for that, I get it now, it would fly into the sun eventually, and it could orbit around a black hole, it depends on its trajectory. Those links were really great too. Zapatos really nailed it for me though.

Just to add a bit to what Zapatos said.    You wouldn't have to kill quite all of the Earth's orbital speed in order to drop something into the Sun.  Using the Earth's mean circular velocity of 29.9 km/sec,   You would need to drop that to ~2.9 km/sec, meaning you need to kill "just" 27 km/sec of the Earth's velocity.  Essentially, what you are doing is putting a object into an elliptical orbit that just grazes the surface of the Sun at perihelion.

The same works for a black hole.  However, a black hole makes for a smaller "target". A solar mass black hole only has an event horizon radius of ~3 km ( vs. 695000 km for the Sun)

This means you would have to shed even more of the Earth's orbital velocity in order to "drop" an object into it, because you need to drive the periapis lower. For all intents and purposes, you would have to kill all of the Earth's orbital velocity in order to score a hit.   So it would be easier to hit the Sun from the Earth than it would to hit a solar mass BH from the same orbit.

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Easier to hit the sun than a black hole!! Well that's even more interesting, but does make sense. Cheers

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• 1 year later...

found it!

Completely pointless now of course. Thought I'd put a link anyway.

On 6/14/2019 at 2:31 PM, et pet said:

Was it a thread here on  https://www.scienceforums.net/  ? Can you Link to it?

We may be able to assist you if we know the principle that is being applied

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On 6/14/2019 at 4:01 PM, Phi for All said:

Trying to rocket our waste off-planet is too dangerous, even if we could justify the costs (roughly US$20K/kg, or about US$5-6T). One Challenger-level incident and we've got a bunch of nasty in the upper atmosphere.

So if you had a facility in space that produced hazardous waste, and it was near enough to a BH that you could safely and cheaply put a capsule full of it on a radial trajectory, you could use the BH as a dump, right?. A minute out, the capsule might still have enough energy to change course, but once past the EH, spacetime is so heavily curved by the gravity that there is only one path to follow, for anything, no matter how much energy it has available to escape. The path in both space and time leads to the dimensionless point at the center.

We can't know what happens, but it sounds more like a trash compactor than a dump.

Still many paths available at that point...but all end up at the center as you pointed out. All must have an inward radial component.

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• 4 months later...
On 6/14/2019 at 2:38 PM, Curious layman said:

Hi I was reading about how putting nuclear waste into the sun would be pointless, due to orbital mechanics, and needing more energy than it take to leave the solar system, but what about black holes? does that mean it would actually be a lot more difficult to get into a black hole than people realise, my head says no but surely the same principle applys?, does it apply to spinning black holes only. Confused, please help.

So, I think it's very expensive to transport nuclear waste to a black hole. 😹😹

Can we just learn how to neutralize nuclear waste with some field or electromagnetic effect for example? 😉

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6 minutes ago, Maxim Bronevsky said:

Can we just learn how to neutralize nuclear waste with some field or electromagnetic effect for example? 😉

No, there’s no reason to think this is possible with known physics.

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