back to article Planets may lurk in harshest environments. Not that Novell NetWare server you can't unplug – black holes

Giant planets up to ten times the mass of the Earth can form around violent supermassive black holes without the need for stars, according to research accepted into The Astrophysical Journal. "With the right conditions, planets could be formed even in harsh environments, such as around a black hole," Keiichi Wada, first author …

  1. Pascal Monett Silver badge

    Okay, planets. Why not ?

    But Life ? Even planets are likely going to have a hard time not smashing into each other. I really don't see that kind of environment as being anywhere near a place where Life could take hold.

    On the other hand, with all the stuff that's in the area, water is likely to be there as well, so those planets could very well have water. If they are massive rocky planets, there could be water deep down, shielded by dozens of meters of rock, where some form of bacterial life could subsist.

    Since the idea is that planets form in the accretion disk, they will orbit the black hole and not get sucked in. That means that they'll be around for the next wave of matter that falls in. Except that, if that next wave is in the form of an incoming star, then all bets are off as to the stability of the planets' orbits. They'll either get ejected from the system (at high velocity), or they'll be dragged into the singularity, ripping apart along the way.

    Either outcome means the death of any life that may have taken hold.

    Not a nice place to be born, to say the least.

    1. MonkeyBob

      Re: Okay, planets. Why not ?

      Life as we know it can't exist on these planets. We depend on our star for a source of energy, which radiates outwards from it. Black holes suck in everything, including any energy that might be around.

      1. Julz Silver badge

        Re: Okay, planets. Why not ?

        You could have gravitational squeezing of the planet as a source of energy and I'm sure there would be plenty of high frequency radiation being emitted from the accretion disc amongst others. Might make for some interesting forms of life.

        Mines the one with a Dweller book in the pocket.

        1. Anonymous Coward
          Anonymous Coward

          Re: Okay, planets. Why not ?

          But that would on no way be in the ball park of the energy we get from the sun. Orders or magnatude off.

          If you are going to reach..

          You end up throwing any sense and science out. "Life coykd be anywhere in any type." Is a valid statement but has no scientific data to back it up. Currently we have one type of life... even if theoretical crystal creatures could live on titan or clockwork cockroaches in a subterranean gravity wobble warmed superearth.

          1. Brewster's Angle Grinder Silver badge

            Winter is coming.

            "But that would on no way be in the ball park of the energy we get from the sun. Orders or magnatude off."

            I'm not sure what you're saying here. The problem is there is too much energy around a black hole. (The paper says 1010-12L - with planet formation inside 106 AU.) The authors' problem is finding a region cold enough for planet formation to take place, given observational evidence of warm dust. They do that. But it's not inconvertible that the planet could migrate to somewhere slightly warmer - it's a turbulent environment.

            I still don't think there'd be life there, but.

      2. Rich 11 Silver badge

        Re: Okay, planets. Why not ?

        Black holes suck in everything, including any energy that might be around.

        But only at the event horizon. Imagine a photon generated at a point somewhere in the accretion disk. If it happens to be emitted directly towards the black hole it will end up being sucked in (assuming it doesn't strike anything else first). If it is emitted in a direction that will just miss the event horizon it will swing around the black hole and maybe even head back almost towards the point where it was generated. If it is emitted off to one side it could pass round the black hole and head out into space, possibly even appearing to a distant observer as if it had passed through the black hole. But if it is emitted directly away from the black hole then it will escape quite comfortably, even though to an observer higher up the gravity well it will appear to take longer than a simple distance-over-velocity calculation would suggest. So a gamma ray emitted from the accretion disc could end up striking a planet in the outer disc, generating a particle shower and ultimately heat.

        (All of the above is a simplistic treatment; the photon's path would also be affected by the frame-dragging effect caused by a spinning black hole.)

      3. Anonymous Coward
        Anonymous Coward

        Black holes aren't magic

        They won't "suck in" anything that an object of equivalent mass would suck in. If they sucked in "everything, including all energy that might be around" they would be truly be black and we would have no chance of seeing any evidence that they exist.

        Any black hole with enough "stuff" around it to form planets would emit (not the black hole itself, but the stuff orbiting it being heated up) enormous amounts of energy/radiation. Besides, life doesn't necessary need energy from the outside. If a massive planet 10x the size of Earth had Earth or Moon sized moons orbiting it closely, it could be like Jupiter/Europa, which has liquid water in its oceans due to the heat from the tidal forces. Life is just as possible on that black hole moon as it is on Europa, without any sunlight being necessary.

      4. tfb Silver badge

        Re: Okay, planets. Why not ?

        Black holes suck in everything, including any energy that might be around.

        Black holes, or rather their accretion disks, are among the most luminous objects we know. The most luminous ones are thousands of times brighter than entire galaxies such as ours. Lack of energy is not the problem here: too much energy at too short a wavelength probably is (life, as we understand it, doesn't do very well in hard-x-ray environments).

  2. Spherical Cow Bronze badge

    If it looks like a planet and quacks like a planet...

    This is yet another example of planets which don't fit the official definition of a planet.

  3. 0laf Silver badge

    Did I read this right that a supermassive black hole could have planets with orbits 10ly out?

    If that right my mind is indeed boggled.

    I look forward to this being modelled in Elite :-D

    1. Anonymous Coward
      Anonymous Coward

      Orbits can be at any distance eventually*. But formationat that distance. But yeah could look fun in elite.

      Rochet.... richocette.... rocheee... "dangerous" distances exempt.

    2. MyffyW Silver badge

      'twas rumoured that Frontier:Elite2 had a black hole at the centre of the galaxy. Never found it though, given how hard the actual centre of the galaxy was to locate.

      Get's back in her heavily-hacked Viper. The one with the type 7 hyperdrive.

  4. Venerable and Fragrant Wind of Change

    Seems intuitively reasonable. Lots of matter swirling around: some of it might look like planets.

    But .. why "up to 10 times the mass of Earth"? That's not a giant: Jupiter is just next door and over 300 times the mass of Earth!

  5. Anonymous Coward
    Anonymous Coward

    I wonder where they got that idea from?

    Not so strange I suppose that someone from Kagoshima comes up with this when the city of Kagoshima itself has formed around a violent massive volcano.

  6. swm Silver badge

    Stable orbits around a black hole?

    I thought that there were no stable orbits near a black hole. Maybe an orbit 10 light years out would be stable for a while (more than 10 years).

    1. tfb Silver badge

      Re: Stable orbits around a black hole?

      There are no stable circular orbits sufficiently close to a black hole. For a Schwarzschild (non-spinning) BH the critical radius is 6GM/c^2, where M is the mass of the object.

      The objects they consider in the paper have masses in the range 10^6-10^9 solar masses. A 10^6 solar mass black hole has an innermost stable circular orbit radius of about 0.06au (ie about 1/16th of the Earth's orbital radius, and about 1/7 of the orbital radius of Mercury), while a 10^9 one is about 60au, which is outside the orbit of Pluto by a bit. A light year (ly) is about 63,000au.

      The planets which might form around these objects have orbital radii of about 10ly: stable orbits very definitely exist at such radii.

  7. Sleep deprived

    "Planets can only form if parts of the disk is shielded from the hostile radiation"

    Is this hostile radiation breaking up structures, heating up the dust or ?

    1. tfb Silver badge

      Re: "Planets can only form if parts of the disk is shielded from the hostile radiation"

      Yes, heating it. You need somewhere which is shaded from the horrors going on further in. Active accretion disks involve extremely energetic phenomena.

  8. JCitizen Bronze badge

    Stuff planets are made of..

    I watched a time lapse film of several stars orbiting a black hole - the orbit was highly elliptic though. If this can happen why not planets? I'd imagine black holes could rob planets from star systems and probably gobble a lot of them up as well. Who would really know if those stars were formed from being close to a black hole or not - many questions here. I know it is realistic to assume no stars and only planets can form around a black hole orbit, but who is to say they couldn't get so massive they'd graduate to star size?

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