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Space

Could a Habitable Planet Orbit a Black Hole? (sciencemag.org) 82

Posted by BeauHD from the theoretically-possible dept.
sciencehabit shares a report from Science Magazine: Supermassive black holes have a reputation for consuming everything in their path, from gas clouds to entire solar systems. So is there any way aliens could live on a world that actually orbited one of these cosmic beasts? Surprisingly, the answer is a tentative yes, researchers say, although there are plenty of reasons why life could never take hold in such a place. If it did, living on such a planet would be truly surreal, with the black hole filling nearly half the sky and concentrating leftover photons from the big bang into a pseudosun. It would certainly be no place like home. The deep blackness of the event horizon, looming over nearly half the sky, would be a forbidding presence. And because of the time dilation effects in Albert Einstein's theory of gravity, known as general relativity, 1 year passing on such a planet would see thousands of years go by around an ordinary star. Even if life could take hold on such a world, there's little chance of detecting it. A planet passing in front of a black hole isn't going to make it appear any dimmer when it's black already. An expert says a vast array of radio telescopes, like the one used last year to image a black hole for the first time, might be able to detect such a transit. "Technically it's not so easy, but in theory it's possible." If this idea sounds familiar, it's because it was first published in 2017. The researchers said that in order for a planet to receive strong enough cosmic microwave background (CMB) light, it would need to orbit very close to the black hole's event horizon. However, if it were too close it would get sucked in.

"As the researchers report in The Astrophysical Journal, for their planet to get close enough, the surface of the black hole would have to spin at less than a 100-millionth of a percent shy of the speed of light," reports Science Magazine. "The black hole would also need to be large, the team calculates, at least 163 million times the Sun's mass." It would also need to be "an old galaxy" with "almost empty space" surrounding the black hole. "That's because any other stray matter being sucked into the black hole would emit a blast of radiation during its death spiral powerful enough to kill any life on a nearby planet," the report says.
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Could a Habitable Planet Orbit a Black Hole? More

Could a Habitable Planet Orbit a Black Hole?

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  • Odd Way to Phrase the Headline (Score:4, Insightful)

    by cervesaebraciator ( 2352888 ) on Tuesday February 04, 2020 @10:42PM (#59691992)

    Of course the article and even the summary gets more precise, but this headline can't help but make one immediately think, 'Yeah, duh.' Our planet is habitable, is part of a solar system, which is itself orbiting a super-massive black hole. So, yes, of course. Every verifiably habitable planet orbits a black hole.

    Betteridge is disappointed.

    • Re:Odd Way to Phrase the Headline (Score:5, Interesting)

      by lobiusmoop ( 305328 ) on Tuesday February 04, 2020 @10:52PM (#59692012) Homepage

      I think you are being a pedantic troll here - the article is about planets orbiting black holes, not solar systems.

      Google suggests that stars outnumber black holes 1000:1, so not of great significance anyway,

      • I think you are being a pedantic troll here - the article is about planets orbiting black holes, not solar systems.

        Close, but not quite. A pedantic troll wouldn't acknowledge in the very post that he was focusing on the headline, even though it did not represent the article in the most literal sense. What I said about the headline was true, and I also said it didn't apply to the article.

        But, I have to admit, I did have an ulterior motive in posting. I was curious whether I could elicit any response. I

        • It's like a ghost town here. I always thought this was an interesting, well-curated community. I wonder what's happened.

          Facebook, Twitter, Reddit, and the axiom "checkers sells more than chess".

        • Re: (Score:3)

          by lgw ( 121541 )

          The comments on science articles are really disappointing these days. There used to be a couple of astrophysicists who hung out around here, but they disappeared some years back.

        • Its also a very bad troll.

          If this idea sounds familiar, it's because it was first published in 2017.

          Interstellar [imdb.com] came out in 2014, and the authors even mention it in their abstract. The ideas have been talked about for much longer than 2017.

        • Re: (Score:2)

          by BranMan ( 29917 )

          Have you accounted for the speed of commenting? In the old days there would be several discussion threads going on within an hour or so of posting. Now it seems like a minimum of 1-2 days is needed.

      • Google suggests that stars outnumber black holes 1000:1

        That seems far too low....with 100 billion stars in the Milky Way and one black hole.......

      • Eh, I was kinda thinking along the same lines as the grandparent. Most of unusual circumstances required by the summary are there because the planet needs some source of energy, so why couldn't the planet just be paired with a star and have them both orbiting the black hole? ... Except that's what we're already doing. Sort of.

        I'm not sure how accurate it is to say that we're orbiting a black hole right now, even though there's a black hole at the center of our orbit. We're orbiting the center of mass of

        • I'm not sure how accurate it is to say that we're orbiting a black hole right now, even though there's a black hole at the center of our orbit. We're orbiting the center of mass of the galaxy

          We're not orbiting the Sun, we're orbiting the centre of mass of the Sun-Jupiter system.

          While Sgr A* itself is only a small fraction of the mass of the galaxy, it remains the largest single object measured in the galaxy (TTBOMK, and not counting globular clusters as "single objects", which is at the least an argument t

    • Re: (Score:2)

      by lgw ( 121541 )

      There's a theory that's half-way between the ideas too. Planets could form in the stable region just beyond the accretion disk of a SMBH at the center of a galaxy. In a young galaxy where stuff was still falling in, orbits might only be stable for order of 100 million years, long enough from planets to form, but not cool down. In a very old galaxy, though, you could get a regular planet. More likely to be orbiting a star that orbits the black hole, but still mighty close.

      • Thanks for explaining that--but this also makes me wonder about the time dilation issue. TFS says that one year would pass on this planet when thousands pass around an ordinary star. So if there's an approximate minimum time requirement for a planet to cool down to a point where life (at least the life that we know) could possibly form, then doesn't this mean that such a time requirement would be multiplied by thousands from our point of view? So if it took the earth about a billion years after its formatio

        • Re: (Score:2)

          by lgw ( 121541 )

          I don't know what TFS is talking about. Time dilation at around 5x the radius of the black hole is about 10% - time there is flowing 90% as fast as time here. The only place you see extreme time dilation is far within the smallest stable orbit, during the final moments of falling into the black hole.

    • but this headline can't help but make one immediately think...'Yeah

      One, sure.

    • which doesn't change the fact that i don't fit in my suitcase until someone hammers me down to a foldable version where the same mass is just spread over a lot more x and y than it would be over z and thus it came to pass ! i think 'Van Voght would have like this and could have made some great story from it , true science fiction while this is more like fiction science (but i hear they call it theoretical and it leads to modern-day worldwonders like LHC, even without slavery) ... as for the relevance ... li
  • Comment removed based on user account deletion

  • so I guess it must be possible.

    • Well, they did hire a cosmologist (Kip Thorne) to idiot-check the script before it got to the shooting stage. They didn't always take his advice, but they did listen to it, even if the demands of "drama" trumped those of science.

  • And because of the time dilation effects in Albert Einstein's theory of gravity, known as general relativity, 1 year passing on such a planet would see thousands of years go by around an ordinary star

    I'd imagine the time-passing would be perceptibly different even in the different parts of this hypothetical planet — a planet's diameter away from the black hole would reduce the effect enough to notice...

    • Re: (Score:3)

      by Dunbal ( 464142 ) *
      That would give a whole new meaning to "time zones"...

    • And I thought coding around UTC was a pain in the ass.

    • Re: (Score:3)

      by lgw ( 121541 )

      The planets would have to be orbiting more than about 3.2 times the radius of a black hole The innermost stable circular orbit is a 3 times the radius (for a non-rotating black hole), but that requires a precisely circular orbit. From what I've read, around 3.2R is the closest any realistic orbit can get, and that's for a normal black hole rotating quite fast. Time dilation isn't all that extreme at that distance, though it is there. Supermassive black holes are though to have a stable ring of dust, st

  • Define "habitable", and habitable by WHOM?

    Life forms like our own, made of carbon? ANY matter that fell into the singularity would cause an instantly lethal dose of hard radiation.

    • ANY matter that fell into the singularity would cause an instantly lethal dose of hard radiation.

      That's also true of any star, for useful values of "any matter." Try not to hyperventilate. Don't touch the Sun. In fact, don't even look at the Sun!

  • You have a sun above your head, but you cannot see it.

  • Tidal Force & Time Dilution (Score:3)

    by InfiniteZero ( 587028 ) on Tuesday February 04, 2020 @11:43PM (#59692076)

    Didn't read the article. But if the time dilution effects from gravity are significant, tidal forces will tear the planet apart. See Roche Limit.

    • Didn't read the article. But if the time dilution effects from gravity are significant, tidal forces will tear the planet apart. See Roche Limit.

      They say that it has to be an especially large supermassive black hole. In contrast to stellar-sized black holes, supermassive ones don't have particularly high tidal forces at the event horizon. Supposedly, for a big enough black hole, you could fall through the event horizon and not even notice anything as you cross it.

      • Re: (Score:2)

        by Dunbal ( 464142 ) *

        you could fall through the event horizon and not even notice anything as you cross it.

        Hah. You first...

      • OK that makes sense. Just took a detailed look into the equations. For a given planet, its Roche distance is proportional to the cubic root of the mass of the black hole it's orbiting. The planet must stay outside of that distance so that it won't be torn apart by the tidal forces. On the other hand, the black hole's Schwarzschild radius or event horizon, where time dilution becomes infinite, is proportional to its mass. So obviously, the event horizon grows faster than the Roche distance as the black hole'

      • In fact there is credible theory (i.e. one that cannot be dismissed on present evidence) that the entire Universe is a black hole [wikipedia.org] -- that we are already inside one. When you look at the estimated of the size and mass density of the Universe, they closely match the requirements for being a black hole.

        • There is no density "requirement" on something being a black hole. Small (e.g. stellar mass) BHs have high densities, but larger ones are low density. I make the density of Sgr A* to be about 6g per cubic metre - which is comparable with the density of air near the Earth's surface. (Volume ~1.25E+039 m^3 ; mass ~8.15E+036 kg, density 0.0064kg/m^3)

      • Re: (Score:2)

        by PPH ( 736903 )

        Even with a stellar-sized black hole, the theoretical habitable planet would be orbiting at a considerable distance from the event horizon. So from the planet's point of view, it would be orbiting an object with some low multiple of our Sun's mass, gravitational force, tidal force and time dilation. In other words, nothing unusual. The black hole itself would be invisible. Not just because it is 'black'. But because it is only a few tens of kilometers in diameter. Today, we have telescopes that can resolve

    • Plugged the numbers into the equations. If Planet Earth were orbiting a black hole, in order for Roche Distance = Schwarzschild Radius, the black hole's mass comes out as 2.3 x 10^8 solar mass, which seems to be middle of the pack as far as supermassive black holes are concerned.

      P.S. Yup it should be dilation. I blame autocorrect. :)

      • I blame autocorrect. :)

        auto IN correct

        FTFY For the last several new phones that I've had, one of the first things that I've done is to teach it's "Autocorrect" function the correct spelling of "Bloody AutoIncorrect". Normally I can get it down to 6 screen presses.

  • Of course it's possible (Score:5, Funny)

    by 93 Escort Wagon ( 326346 ) on Wednesday February 05, 2020 @12:30AM (#59692114)

    Soundgarden sang about this almost 30 years ago, for Pete's sake.

  • Slashdot circa 1270:
    How many angels can dance on the head of a pin?

    Slashdot circa 1680:
    How many more epicycles do we need until we've perfectly modeled the heavens?

  • How would it get there? (Score:3)

    by rossdee ( 243626 ) on Wednesday February 05, 2020 @01:06AM (#59692154)

    Stellar mass black holes tend to have a violent past, that would wipe out any life when it collapsed.

    Is somebody proposing that a really advanced civilization could move a habitable planet into orbit around a black hole after it became one?

    Talk to the Magratheans

    • Re: (Score:2)

      by lgw ( 121541 )

      Stellar mass black holes tend to have a violent past, that would wipe out any life when it collapsed.

      Until last year is was assumed that the supernova would wipe out the planet. But then we found exoplanets around white dwarfs, and I think one around a neutron star, but I could be misremembering. There's no good theory yet for why those planets are there. If they are captured long after the supernova, it's possible. I wouldn't have thought that likely either, but it's as good a theory as any right now.

      • There is at least one neutron star known with an entire planetary system - the planets orbiting PSR B1257+12 are named Draugr, Phobetor and Poltergeist. It's believed they were formed in a second round of planet formation following formation of a planetary disk during the merger of two white dwarfs into a neutron star. It's possible a sufficiently large neutron star could gain mass from infalling material and undergo further collapse into a black hole.
    • Comment removed based on user account deletion

  • [Planet would need] "almost empty space" surrounding the black hole. "That's because any other stray matter being sucked into the black hole would emit a blast of radiation during its death spiral powerful enough to kill any life on a nearby planet,"

    What kind of volume are we looking at? For example, suppose a 100km asteroid took the plunge.

  • And because of the time dilation effects in Albert Einstein's theory of gravity, known as general relativity, ...

    Opposed to someone else's theory of gravity, known as General Relativity?

    [ Not picking on the editors, it's in TFA -- of a science magazine. ]

  • Havenâ(TM)t you guys seen the documentary âoeInterstellarâ ? What the heck is wrong with people these days?

  • Of course this idea is not as new as it had been suggested; the physical plausibility of sending observers into Kerr black hole so that they survive the trip have already been thoroughly investigated by other authors in peer reviewed journals (i.e. "Relativistic computers and the Turing barrier" by István Németi and Gyula Dávid, https://doi.org/10.1016/j.amc.... [doi.org] ) in the, I shall say thoroughly sci-fi movie worth, context of general relativistic hypercomputation.

  • I remember that the first extra-solar planets were discovered orbiting a pulsar. The radial velocity method works very well with the precise timing of the pulsar signal.
    https://en.wikipedia.org/wiki/... [wikipedia.org]

    From here to a black hole is only a matter of original star size, with the upper limit at 2.8 solar masses, (I hope I remember correctly) for a neutron star.
    As for a habitable planet, I am sure that the answer is a no.
    Planets tend to remain in orbit around the stars that they formed around. they very rarely m

    • TFS makes it clear that they are talking only about the giant black holes that exist in the center of galaxies "The black hole would also need to be large, the team calculates, at least 163 million times the Sun's mass."

  • It looks like the story of Incandescence, by Greg Egan:

    http://www.gregegan.net/INCAND... [gregegan.net]

  • Probably not habitual to humans, and probably only habitual to simple life. Unfortunately ONE of the biggest reasons there isn't more life in the universe is because there is too much radiation and uncertainty, neither of which are going to improve near a black hole. I think we will eventually realize while simple life is common enough, but complex life almost never happens because the area of space/arrangement of the solar system almost never produces enough long term stability. If Earth wasn't spinning o

    • Unfortunately ONE of the biggest reasons there isn't more life in the universe is because there is too much radiation and uncertainty

      We don't fucking know how much life's in the universe. Speaking of uncertainty.

  • I could have sworn Interstellar was a few years before that. The paper probably had quieter music, though.

  • And it will cause the weather on the planet to change rapidly every few weeks.
  • Can a motorcyclist survive head-on collision with a dump truck travelling at 100 mph? Yes, but the dump truck has to weigh less than 50 pounds.

  • Larry Niven, "The Integral Trees" (1984) has a habitable gas torus around a black hole.

  • 1) While the black hole itself isn't radiating out much (Hawking radiation), any accretion disk would. Radiation being emitted by, even a vestigial accretion disk, would fry the neighborhood. 2) Where is the habitable zone around a black hole? There would not be any, is my guess. So: frozen Earth. 3) Comets and asteroids falling in the black hole (after all, would energize the accretion disk: more frying. 4) Black holes don't "suck" matter/energy. They fall in when matter/energy cross the event horizon. So
  • Imagine a 10^35 years in the future. All the stars have long gone dark and then either been flung out of our galaxy or slowly fallen into the supermassive black hole at the center of our galaxy. Such a huge black hole would have a very low density and a very low rate of gravitational acceleration near the event horizon. No new material would be falling into this black hole. A planet orbiting near(ish) the event horizon would be in a stable orbit and experience almost no tidal forces. The CMB would blu

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