Scientists Finally Confirm A Big Theory About Solar System Formation

By Korey Haynes | February 11, 2019 4:43 pm
a swirling disk of material

Stars, planets, and black holes all grow by consuming material from the center of a spinning disk. Researchers assumed they knew how material fell into the center, but hadn’t tested the theory until now. (Credit: Michael Owen and John Blondin, NCSU)

Planets, stars, and black holes all grow by consuming material from a spinning disk. While these disks may differ in size, they’re all mostly dependent on the mighty force of gravity, which keeps them spinning around the central mass. Gravity lets small clumps grow into bigger clumps. But it’s not enough to pull the whole disk into the middle in one giant clump, because angular momentum is pulling those clumps away from the center as they spin.

That’s a good thing, because it means that the universe is composed of more than just large, lonely clumps of matter — it’s also why the Earth spins around the sun instead of falling in and burning up. But that kind of central accumulation sometimes happens nonetheless, which is why we see things like planets, stars, and active black holes in the universe around us. Something seemed to be missing from the basic angular momentum vs. gravity theory.

Researchers have had an idea for a while now, but no one had ever tested it until now. The key is that these spinning disks of material also carry an electric charge. And since they’re in motion, that means they’re generating a magnetic field. The turbulent motion of many small objects in that magnetic field leads to instabilities, and the objects begin trading angular momentum: some lose it and fall closer into the center, while others gain it and slide farther out.

Researchers at Princeton’s Plasma Physics Laboratory came up with a way to test this basic principle, called magnetorotational instability, or MRI . They published their results January 14 in the journal Communications Physics. Eric Blackman, a co-author on the paper, said the inspiration for their experiment was based on how most textbooks teach the phenomenon of MRI.

Rocks and Springs

People have assumed for a long time that MRI will make disks of material spread out, pushing close material closer to the center, where it can fall into a central star or black hole, and outer material farther away.

Looking for evidence of MRI in space is tricky. Researchers can see the results of material piling into the center of a system – a star is born, or a black hole shoots out active jets. But measuring the flow of material accurately enough to test MRI is beyond our current abilities.

In labs, the closest analog to a giant spinning disk of charged plasma and dust would be a swirling tank of liquid metal, but that’s also difficult to measure – not to mention expensive and occasionally hazardous. So Blackman and his colleagues took the simplest approach, with springs instead of magnetic fields and weights instead of clouds of charged materials. They filled concentric rotating cylinders with water, and attached a weighted ball with a spring to the center. By spinning the cylinders, they could reproduce the effects of MRI.

a water-filled tank

The Princeton experiment used water-filled cylinders, a spring and a ball as an analogy to MRI. (Credit: Eric Edlund and Elle Starkman)

It’s a simple enough analog, but one that no one had bothered trying before. And it turns out that MRI works just as researchers have long predicted, pushing close materials in and farther materials out. “No matter how much we think something is true and how plausible it sounds,” Blackman says, “When you can test it, that makes it more robust.”

This result may not be surprising, and it may not change how astronomers understand star and planet formation. But it is the most fundamental function of science: proving by experiment something that people up until now have only believed to be true.

CATEGORIZED UNDER: Space & Physics, top posts
MORE ABOUT: physics
  • Uncle Al

    When you can test it, that makes it more robust.” You just killed 40 years and some three million published pages of HEP physical theory, the neutrino see-saw mechanism, SUSY; non-classical gravitation, ΛCD, bubbles, foams, strings, the multiverse, the next super dooper pooper scooper BFLHC; grand unification; beauty, naturalness…and made
    Luboš Motl cry.

    • Icarus32Soar

      Isn’t that the fate of all scientific progress? Tears for those superseded by the new?

      • Torbjörn Larsson

        Indeed. Think of atom theory, it took a century after it started to be considered seriously to be well tested. It did not become “killed off” in the process, but it superseded humors or what not. Seems our troll likes his non-progress.

        • Icarus32Soar

          Hi from Australia! Thanx for your thoughtful response. I’ve been on internet forums for years but still don’t understand why people come on them just to be trolls. What satisfaction is there in that?
          In fact even the great Newton said his work was possible because of what others had done before him. “On the shoulders of giants” is how he put it.
          I think the popular media is often to blame, they always present things as breakthroughs, and maybe people who are not scientists or don’t read science just never get the sense of how slow and cumulative a process science actually is. Cheers 😄

      • Uncle Al

        There is only one reality – empirical reality. When theory is not testably predictive it is, at best, only math – that has no requirements other than internal consistency. Elliptic, plane, and hyperbolic geometries each rigorously exclude the other two. Which one is correct? All of them.

        • Icarus32Soar

          Of course. But this is not inconsistent with anything I’ve said.

        • 7eggert

          Were from do you know that this reality does exist?

    • Torbjörn Larsson

      I just saw a similar ludicrous trolling from this handle on another astronomical thread, you seem to have something against science progress. Besides that the article showed an example testing your troll conspiracy – MRI is 60 year old, now lab observed, your “no progress” failed – some of those are well tested: “ΛCD[M]” [sic] is now cores tested in Planck’s 3d data release. Or at least tested recently: the multiverse got a boost by Planck passing inflation as single field slow roll (makes multiverses). And the rest seems a Gish gallop making little sense to astrophysics of star formation.

      Or even relating to high energy particle theory (and who is Luboš Motl) !? To much beer “foam”?


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