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> That's terrifying. Imagine a rogue supermassive black hole floating in intergalactic space. Why terrifying? It's literally doing nothing, far away from anyth

by tivert 2y ago

> That's terrifying. Imagine a rogue supermassive black hole floating in intergalactic space. Why terrifying? It's literally doing nothing, far away from anything. Seems like the safest place for it to be.

andrewflnr 2y ago
Not doing anything yet. If galaxies can collide, the rogue black hole can collide with your galaxy, and you won't get much warning either. (I mean, realistically you're right, in the same way that our galaxy colliding with Andromeda is scary but has negligible chance of affecting us. But, imagine.)
- yongjik 2y ago
  Galaxies are big, including our own. Unless the rogue black hole is traveling near light speed, you will get at least tens of thousands of years of advance warning. (What you could do with that warning is a different matter, though...)
  - andrewflnr 2y ago
    If you were lucky enough to see the ejection happen, yes. But if one was already on the way?
    - chowells 2y ago
      You would absolutely notice the gravitational distortions a very long time in advance. That's a lot of mass. You can't miss the way it's distorting space for a very long way around it.
    - khafra 2y ago
      There are lots of easily visible stars on the other side of any supermassive black hole that's nearer to you than other galaxies are. When those stars start lensing in ways visible to the naked eye, you're going to know something weird is going on.
    - Iwan-Zotow 2y ago
      You'll see bent light and similar effects.
- The_Colonel 2y ago
  > and you won't get much warning either A supermassive blackhole floating towards you would have very visible effects, it would be impossible to miss for millenias before it gets to you. It's the micro black holes which can hit you without a warning.
  - rompledorph 2y ago
    The article state that small black holes have the size of stars. Micro black holes should be quite big too I guess?
    - The_Colonel 2y ago
      That's likely a mistake in the article. "Small" black holes (i.e. smaller than supermassive) have star/stellar mass, but not size. Micro black holes are only hypothesized so far, but they could get very small - e.g. a black hole with Earth mass would have less than 1 centimeter in diameter. The size itself is not that important for spotting black holes, though. Even if it's as large as a star, all you see staring at the black hole "object" is nothing. What's important are the gravitational effects on the environment, and there the differences are stark. At a distance of 1000 light years, it will be difficult to spot a stellar-mass black hole floating through empty space, because its pull is strong enough only at stellar distances and won't produce enough disturbance in interstellar space for us to notice. OTOH supermassive blackholes will deform whole surrounding star systems because of its immense mass and gravitational pull. A micro black hole (e.g. Earth mass) passing through the solar systems would likely go undetected unless it collides with something (which is improbable). There could be a measurable disturbance, but it would be one-off and difficult to attribute to a black hole.
      - ordu 2y ago
        > A micro black hole (e.g. Earth mass) passing through the solar systems would likely go undetected unless it collides with something (which is improbable). Solar wind? Would it generate some interesting effects when coming too close to a black hole? All these protons accelerated to a near light speed, probably hitting each other and running away into a black hole.
3eb7988a1663 2y ago
I am reminded of a quote from Mass Effect 2. Eventually that black hole could hit something. Damn straight! I dare to assume you ignorant jackasses know that space is empty. Once you fire this hunk of metal, it keeps going till it hits something. That can be a ship, or the planet behind that ship. It might go off into deep space and hit somebody else in ten thousand years. If you pull the trigger on this, you are ruining someone's day, somewhere and sometime. That is why you check your damn targets! That is why you wait for the computer to give you a damn firing solution! That is why, Serviceman Chung, we do not "eyeball it!" This is a weapon of mass destruction. You are not a cowboy shooting from the hip!

by tivert 2y ago

andrewflnr 2y ago

Not doing anything yet. If galaxies can collide, the rogue black hole can collide with your galaxy, and you won't get much warning either. (I mean, realistically you're right, in the same way that our galaxy colliding with Andromeda is scary but has negligible chance of affecting us. But, imagine.)

yongjik 2y ago
Galaxies are big, including our own. Unless the rogue black hole is traveling near light speed, you will get at least tens of thousands of years of advance warning. (What you could do with that warning is a different matter, though...)
- andrewflnr 2y ago
  If you were lucky enough to see the ejection happen, yes. But if one was already on the way?
  - chowells 2y ago
    You would absolutely notice the gravitational distortions a very long time in advance. That's a lot of mass. You can't miss the way it's distorting space for a very long way around it.
  - khafra 2y ago
    There are lots of easily visible stars on the other side of any supermassive black hole that's nearer to you than other galaxies are. When those stars start lensing in ways visible to the naked eye, you're going to know something weird is going on.
  - Iwan-Zotow 2y ago
    You'll see bent light and similar effects.
The_Colonel 2y ago
> and you won't get much warning either A supermassive blackhole floating towards you would have very visible effects, it would be impossible to miss for millenias before it gets to you. It's the micro black holes which can hit you without a warning.
- rompledorph 2y ago
  The article state that small black holes have the size of stars. Micro black holes should be quite big too I guess?
  - The_Colonel 2y ago
    That's likely a mistake in the article. "Small" black holes (i.e. smaller than supermassive) have star/stellar mass, but not size. Micro black holes are only hypothesized so far, but they could get very small - e.g. a black hole with Earth mass would have less than 1 centimeter in diameter. The size itself is not that important for spotting black holes, though. Even if it's as large as a star, all you see staring at the black hole "object" is nothing. What's important are the gravitational effects on the environment, and there the differences are stark. At a distance of 1000 light years, it will be difficult to spot a stellar-mass black hole floating through empty space, because its pull is strong enough only at stellar distances and won't produce enough disturbance in interstellar space for us to notice. OTOH supermassive blackholes will deform whole surrounding star systems because of its immense mass and gravitational pull. A micro black hole (e.g. Earth mass) passing through the solar systems would likely go undetected unless it collides with something (which is improbable). There could be a measurable disturbance, but it would be one-off and difficult to attribute to a black hole.
    - ordu 2y ago
      > A micro black hole (e.g. Earth mass) passing through the solar systems would likely go undetected unless it collides with something (which is improbable). Solar wind? Would it generate some interesting effects when coming too close to a black hole? All these protons accelerated to a near light speed, probably hitting each other and running away into a black hole.

3eb7988a1663 2y ago

I am reminded of a quote from Mass Effect 2. Eventually that black hole could hit something. Damn straight! I dare to assume you ignorant jackasses know that space is empty. Once you fire this hunk of metal, it keeps going till it hits something. That can be a ship, or the planet behind that ship. It might go off into deep space and hit somebody else in ten thousand years. If you pull the trigger on this, you are ruining someone's day, somewhere and sometime. That is why you check your damn targets! That is why you wait for the computer to give you a damn firing solution! That is why, Serviceman Chung, we do not "eyeball it!" This is a weapon of mass destruction. You are not a cowboy shooting from the hip!