9 ms·

Not really. A black hole isn't any more dangerous than any other object with the same mass. A black hole with the mass of Earth, for instance, would behave exac

by c3534l 7y ago

Not really. A black hole isn't any more dangerous than any other object with the same mass. A black hole with the mass of Earth, for instance, would behave exactly as Earth does, except when an object collides with it, it continues on down into the center where it would hit Earth's crust if it were a planet.

fooker 7y ago
>continues on down into the center You'll get a Nobel prize or two if you could prove that..
- saagarjha 7y ago
  Not really, it’s pretty simple that an object that dense would just pass through the ground.
  - mlnj 7y ago
    The ground or the entire planet cannot remain in its current form anywhere near a black hole. There would be no ground for the black hole to sink to. Besides wouldn't the 'ground' gravitate towards the black hole than the other way around?
    - zaarn 7y ago
      For the black hole the ground is merely more dense vacuum, the ground has barely enough time to move if it comes in at interplanetary velocities (50km/s+), so by the time the ground will begin to react to the intense gravity, the black hole will have passed through with the force of a few hundred nuclear explosions.
      - sliken 7y ago
        At 6000 km away the gravity at the nearest surface of earth is zero. 1 minute (at 50km/sec) later it would be 3000 km the acceleration 4.5G or so. 1.5 minutes later it would 1500 km away the acceleration would be 17G or higher. 2 minutes later it would be on the surface, and everything ripped up (including buildings, soil, bedrock, crust, and the magma below would go from being accelerated up at incredible velocities to an even more intense acceleration down. Over that 2 minutes the black hole is going to chew the hell out of the earth for 1000s of km in all directions and that's just the start of the fun. As it hits the surface everything within 1000km will be experiencing 40G. The pressure waves will go from negative (as the black hole pulls the atmosphere away from the earth) to a HUGE over pressure as magma, bedrock, and water get slammed back down into the earth at 40G. Said over pressure wave of intense heat and pressure will expand outward from the point of impact and create problems world wide. Worse on the opposite side it will just take a large chunk with it (approximately the volume of which the black hole has significantly more than 1G of gravity) which could easily take a continent with it, or say most of the pacific ocean. I could see ocean levels and air pressure lowering significantly. After all why would the air stick around a 1G planet instead of a more than 1G black hole? The area from which the air is removed is likely to be somewhere around 12,000 km wide (the area of which the black hole applies more than 1G). So I'm not sure I believe the "barely enough time to move" thing when for minutes the accelerations will be crazy.
  - fooker 7y ago
    What do you think the density of a black hole is? :)
    - cthalupa 7y ago
      Almost certainly not actually infinite in reality :) We treat it that way because, despite it showing that our model of physics is breaking down at that point, it works really well for most real purposes. But look at string theory, loop quantum gravity, etc., and you will find plenty of the variants within those umbrellas do not have a singularity at the heart of black holes.
  - sliken 7y ago
    Not to mention that anything with 9mm would accelerate at the speed of light to the singularity. So while moving through the earth it wouldn't meet any resistance at all.
hailk 7y ago
A layman here. Wouldn't a Black Hole with a mass equal to Earth's be significantly smaller than Earth? Won't the Gravitational range (Schwarzschild radius?) be significantly less than Earth's?
- tempay 7y ago
  No at a distance it would be exactly the same. You would only start to notice the difference gravitationally once you get to be around 1 earth radius away.
- deleted 7y ago
  [deleted]
- cthalupa 7y ago
  The Schwarzschild radius is determined by the mass of the object, not the volume. Radius = (2 * Gravitational Constant * Mass)/(Speed of Light^2)
  - ttul 7y ago
    In other words, 9mm
    - kijin 7y ago
      The entire mass of Earth, compressed down to the size of a bullet. That's actually a very vivid illustration, unlike most of the other large numbers that get thrown around in astronomy.
      - everyone 7y ago
        Its actually compressed down to a point. A singularity. The 9mm is just the radius from the point from which nothing can return.
        chopin 7y ago
        To be fair, we don't know what is behind those 9mm. Einstein's equations predict a singularity but afaik there is consensus that those don't hold there.
sliken 7y ago
If a black hole has the mass of the earth it's Schwarzschild radius would be about 9mm. If it was disturbed from an orbit well past pluto it would have quite a velocity when it hit earth. The good news is it would pass effortlessly through the earth and not go to the earth's core and stay there. After all where is the resistance going to come from? Now if the blackhole was brought to rest at the earth surface it wouldn't reach escape velocity (11.2 km/sec), but anything coming from way past pluto would likely have a much larger velocity. The bad news is that having an earth skewer the earth at high speed is going to cause some pretty crazy gravitational interactions. Also some of the matter falling into the black hole from earth would be consumed, but some of it would radiated out, no idea if that would be worse than the physical disruptions or not.
- ehsanu1 7y ago
  The collision case is screaming for a "What If"-style exposition, as in https://what-if.xkcd.com/ https://what-if.xkcd.com/
- IvyMike 7y ago
  To paraphrase Neal Stephenson, "The earth blew up without warning and for no apparent reason."
- Zardoz84 7y ago
  and wildy change Earth orbit
- KiwiJohnno 7y ago
  >crazy gravitational interactions Thats putting it very mildly. Its actually quite an interesting thought exercise - As this black hole approached earth its gravity would counteract earth's gravity, meaning everything near where it "touched down" would experience near zero-g as it approached. The opposite side of the earth would experience greatly increased gravitational pull... Then while the black hole was inside the earth, everything would be experiencing close to 2G, then zero G for a bit for the poor souls on the side of the earth where it exited. Because of the fantastic amount of momentum it would have, and it would certainly be travelling at well over earth escape velocity I would expect it would travel straight through earth and keep going, not even coming close to stopping inside earth. The affects on earth would be very... bad. I'd imagine it would trigger devastating global earthquakes, as well as epic rock slides from the changing gravitational forces. Not to mention the tsunamis from the oceans sloshing around like water in a giant bath, as well as all the rockslides both above and below water. It would be a mess. Assuming this object would be travelling at 100km/sec, and the gravity would maybe begin to badly affect us when it was 50,000 km out from the surface of the earth (?) then it would take about 16 hours to travel from this distance, impact the earth and then reach this distance out the other side. I'm not sure how much energy would be released by the matter being consumed by the black hole - It might not be very much, after all its total gravitational pull wouldn't be very high, but would be travelling at probably at least 50+ km/second - certainly more than 11km/sec (earth escape velocity) The matter in front of the black hole might simply be swallowed up without much fuss, or if there is any "resistance" to this matter falling down past the event horizon I'd imagine it would be like a continuous series of nuclear bombs going off as matter was flash heated to the point of spontaneous nuclear fusion before it passed the event horizon. The one good point to note in all of this is it would be extraordinarily difficult to disturb this object from its object so it fell into the inner solar system. After all, it has the same mass as earth, and we don't have to be worried about random stuff disturbing earth's orbit.
mongol 7y ago
I think a black hole with earth mass would be much more dangerous than earth itself.
- spacehome 7y ago
  Humans might be plenty dangerous to the rest of the galaxy. It remains to be seen.
stevula 7y ago
To the parent comment’s point though, would that really be any worse than an earth-sized planet colliding with the earth? If anything it sounds like it might be less destructive.
deleted 7y ago
[deleted]

by c3534l 7y ago

fooker 7y ago

>continues on down into the center You'll get a Nobel prize or two if you could prove that..

saagarjha 7y ago
Not really, it’s pretty simple that an object that dense would just pass through the ground.
- mlnj 7y ago
  The ground or the entire planet cannot remain in its current form anywhere near a black hole. There would be no ground for the black hole to sink to. Besides wouldn't the 'ground' gravitate towards the black hole than the other way around?
  - zaarn 7y ago
    For the black hole the ground is merely more dense vacuum, the ground has barely enough time to move if it comes in at interplanetary velocities (50km/s+), so by the time the ground will begin to react to the intense gravity, the black hole will have passed through with the force of a few hundred nuclear explosions.
    - sliken 7y ago
      At 6000 km away the gravity at the nearest surface of earth is zero. 1 minute (at 50km/sec) later it would be 3000 km the acceleration 4.5G or so. 1.5 minutes later it would 1500 km away the acceleration would be 17G or higher. 2 minutes later it would be on the surface, and everything ripped up (including buildings, soil, bedrock, crust, and the magma below would go from being accelerated up at incredible velocities to an even more intense acceleration down. Over that 2 minutes the black hole is going to chew the hell out of the earth for 1000s of km in all directions and that's just the start of the fun. As it hits the surface everything within 1000km will be experiencing 40G. The pressure waves will go from negative (as the black hole pulls the atmosphere away from the earth) to a HUGE over pressure as magma, bedrock, and water get slammed back down into the earth at 40G. Said over pressure wave of intense heat and pressure will expand outward from the point of impact and create problems world wide. Worse on the opposite side it will just take a large chunk with it (approximately the volume of which the black hole has significantly more than 1G of gravity) which could easily take a continent with it, or say most of the pacific ocean. I could see ocean levels and air pressure lowering significantly. After all why would the air stick around a 1G planet instead of a more than 1G black hole? The area from which the air is removed is likely to be somewhere around 12,000 km wide (the area of which the black hole applies more than 1G). So I'm not sure I believe the "barely enough time to move" thing when for minutes the accelerations will be crazy.
- fooker 7y ago
  What do you think the density of a black hole is? :)
  - cthalupa 7y ago
    Almost certainly not actually infinite in reality :) We treat it that way because, despite it showing that our model of physics is breaking down at that point, it works really well for most real purposes. But look at string theory, loop quantum gravity, etc., and you will find plenty of the variants within those umbrellas do not have a singularity at the heart of black holes.
- sliken 7y ago
  Not to mention that anything with 9mm would accelerate at the speed of light to the singularity. So while moving through the earth it wouldn't meet any resistance at all.

hailk 7y ago

A layman here. Wouldn't a Black Hole with a mass equal to Earth's be significantly smaller than Earth? Won't the Gravitational range (Schwarzschild radius?) be significantly less than Earth's?

tempay 7y ago
No at a distance it would be exactly the same. You would only start to notice the difference gravitationally once you get to be around 1 earth radius away.
deleted 7y ago
[deleted]
cthalupa 7y ago
The Schwarzschild radius is determined by the mass of the object, not the volume. Radius = (2 * Gravitational Constant * Mass)/(Speed of Light^2)
- ttul 7y ago
  In other words, 9mm
  - kijin 7y ago
    The entire mass of Earth, compressed down to the size of a bullet. That's actually a very vivid illustration, unlike most of the other large numbers that get thrown around in astronomy.
    - everyone 7y ago
      Its actually compressed down to a point. A singularity. The 9mm is just the radius from the point from which nothing can return.
      - chopin 7y ago
        To be fair, we don't know what is behind those 9mm. Einstein's equations predict a singularity but afaik there is consensus that those don't hold there.

sliken 7y ago

If a black hole has the mass of the earth it's Schwarzschild radius would be about 9mm. If it was disturbed from an orbit well past pluto it would have quite a velocity when it hit earth. The good news is it would pass effortlessly through the earth and not go to the earth's core and stay there. After all where is the resistance going to come from? Now if the blackhole was brought to rest at the earth surface it wouldn't reach escape velocity (11.2 km/sec), but anything coming from way past pluto would likely have a much larger velocity. The bad news is that having an earth skewer the earth at high speed is going to cause some pretty crazy gravitational interactions. Also some of the matter falling into the black hole from earth would be consumed, but some of it would radiated out, no idea if that would be worse than the physical disruptions or not.

ehsanu1 7y ago
The collision case is screaming for a "What If"-style exposition, as in https://what-if.xkcd.com/ https://what-if.xkcd.com/
IvyMike 7y ago
To paraphrase Neal Stephenson, "The earth blew up without warning and for no apparent reason."
Zardoz84 7y ago
and wildy change Earth orbit
KiwiJohnno 7y ago
>crazy gravitational interactions Thats putting it very mildly. Its actually quite an interesting thought exercise - As this black hole approached earth its gravity would counteract earth's gravity, meaning everything near where it "touched down" would experience near zero-g as it approached. The opposite side of the earth would experience greatly increased gravitational pull... Then while the black hole was inside the earth, everything would be experiencing close to 2G, then zero G for a bit for the poor souls on the side of the earth where it exited. Because of the fantastic amount of momentum it would have, and it would certainly be travelling at well over earth escape velocity I would expect it would travel straight through earth and keep going, not even coming close to stopping inside earth. The affects on earth would be very... bad. I'd imagine it would trigger devastating global earthquakes, as well as epic rock slides from the changing gravitational forces. Not to mention the tsunamis from the oceans sloshing around like water in a giant bath, as well as all the rockslides both above and below water. It would be a mess. Assuming this object would be travelling at 100km/sec, and the gravity would maybe begin to badly affect us when it was 50,000 km out from the surface of the earth (?) then it would take about 16 hours to travel from this distance, impact the earth and then reach this distance out the other side. I'm not sure how much energy would be released by the matter being consumed by the black hole - It might not be very much, after all its total gravitational pull wouldn't be very high, but would be travelling at probably at least 50+ km/second - certainly more than 11km/sec (earth escape velocity) The matter in front of the black hole might simply be swallowed up without much fuss, or if there is any "resistance" to this matter falling down past the event horizon I'd imagine it would be like a continuous series of nuclear bombs going off as matter was flash heated to the point of spontaneous nuclear fusion before it passed the event horizon. The one good point to note in all of this is it would be extraordinarily difficult to disturb this object from its object so it fell into the inner solar system. After all, it has the same mass as earth, and we don't have to be worried about random stuff disturbing earth's orbit.

mongol 7y ago

I think a black hole with earth mass would be much more dangerous than earth itself.

spacehome 7y ago
Humans might be plenty dangerous to the rest of the galaxy. It remains to be seen.

stevula 7y ago

To the parent comment’s point though, would that really be any worse than an earth-sized planet colliding with the earth? If anything it sounds like it might be less destructive.

deleted 7y ago

[deleted]