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Weird 'gravitational molecules' could orbit black holes like electrons swirling around atoms

This computer simulation shows supermassive black holes only 40 orbits from merging.
This computer simulation shows supermassive black holes only 40 orbits from merging.
(Image: © NASA's Goddard Space Flight Center)

Black holes are notable for many things, especially their simplicity. They're just … holes. That are "black." This simplicity allows us to draw surprising parallels between black holes and other branches of physics. For example, a team of researchers has shown that a special kind of particle can exist around a pair of black holes in a similar way as an electron can exist around a pair of hydrogen atoms — the first example of a "gravitational molecule." This strange object may give us hints to the identity of dark matter and the ultimate nature of space-time.

Ploughing the field

To understand how the new research, which was published in September to the preprint database arXiv, explains the existence of a gravitational molecule, we first need to explore one of the most fundamental –- and yet sadly almost never talked about –- aspects of modern physics: the field.

Related: The 12 strangest objects in the universe

A field is a mathematical tool that tells you what you might expect to find as you travel from place to place in the universe. For example, if you've ever seen a TV weather report of temperatures in your local area, you're looking at a viewer-friendly representation of a field: As you travel around your town or state, you'll know what kind of temperatures you're likely to find, and where (and whether you need to bring a jacket).

This kind of field is known as a "scalar" field, because "scalar" is the fancy mathematical way of saying "just a single number." There are other kinds of fields out there in physics-land, like "vector" fields and "tensor" fields, which provide more than one number for every location in space-time. (For example, if you see a map of wind speed and direction splashed on your screen, you're looking at a vector field.) But for the purposes of this research paper, we only need to know about the scalar kind.

The atomic power couple

In the heydays of the mid-20th century, physicists took the concept of the field — which had been around for centuries at that point, and was absolutely old-hat to the mathematicians — and went to town with it.

They realized that fields aren't just handy mathematical gimmicks — they actually describe something super-fundamental about the inner workings of reality. They discovered, basically, that everything in the universe is really a field.

Related: The 11 most beautiful mathematical equations

Take the humble electron. We know from quantum mechanics that it's pretty tough to pin down exactly where an electron is at any given moment . When quantum mechanics first emerged, this was a pretty nasty mess to understand and untangle, until the field came along.

In modern physics, we represent the electron as a field — a mathematical object that tells us where we're likely to spot the electron the next time we look. This field reacts to the world around it — say, because of the electric influence of a nearby atomic nucleus — and modifies itself to change where we ought to see the electron.

The end result is that electrons can appear only in certain regions around an atomic nucleus, giving rise to the entire field of chemistry (I'm simplifying a bit, but you get my point). 

Black hole buddies

And now the black hole part. In atomic physics, you can completely describe an elementary particle (like an electron) in terms of three numbers: its mass, its spin and its electric charge. And in gravitational physics, you can completely describe a black hole in terms of three numbers: its mass, its spin and its electron charge.

Coincidence? The jury's out on that one, but for the time being we can exploit that similarity to better understand black holes.

In the jargon-filled language of particle physics that we just explored, you can describe an atom as a tiny nucleus surrounded by the electron field. That electron field responds to the presence of the nucleus, and allows the electron to appear only in certain regions. The same is true for electrons around two nuclei, for example in a diatomic molecule like hydrogen (H2.)

You can describe the environment of a black hole similarly. Imagine the tiny singularity at a black heart somewhat akin to the nucleus of an atom, while the surrounding environment — a generic scalar field — is similar to the one that describes a subatomic particle. That scalar field responds to the presence of the black hole, and allows its corresponding particle to appear only in certain regions. And just as in diatomic molecules, you can also describe scalar fields around two black holes, like in a binary black hole system.

The authors of the study found that scalar fields can indeed exist around binary black holes. What's more, they can form themselves into certain patterns that resemble how electron fields arrange themselves in molecules. So, the behavior of scalar fields in that scenario mimics how electrons behave in diatomic molecules, hence the moniker "gravitational molecules."

Why the interest in scalar fields? Well for one, we don't understand the nature of dark matter or dark energy, and it's possible both dark energy and dark matter could be made up of one or more scalar fields), just like electrons are made up of the electron field.

If dark matter is indeed composed of some sort of scalar field, then this result means that dark matter would exist in a very strange state around binary black holes — the mysterious dark particles would have to exist in very specific orbits, just like electrons do in atoms. But binary black holes don't last forever; they emit gravitational radiation and eventually collide and coalesce into a single black hole. These dark matter scalar fields would affect any gravitational waves emitted during such collisions, because they would filter, deflect and reshape any waves passing through regions of increased dark matter density. This means we might be able to detect this kind of dark matter with enough sensitivity in existing gravitational wave detectors.

In short: We soon might be able to confirm the existence of gravitational molecules, and through that open a window into the hidden dark sector of our cosmos.

Originally published on Live Science.

  • danr2222
    Fields, as they might be defined operationally, were not used for 'centuries' before the mid-twentieth century; perhaps a little over one century. They were properly qualified (by Dedekind) less than a century before.
    Reply
  • TorbjornLarsson
    Interesting, since scalar field particles seems to be the remaining possibility with the exclusion of WIMPs (in LHC, ACME and Fermi-LAT to the Griest-Kamionkowski bound). Axions were proposed to solve matter/antimatter symmetry and already neutrinos promise (at a measly 2 sigma, but still) to solve that. The paper notes that:

    Light scalar fields are interesting solutions to some of the most pressing problems in physics. One example is the dark matter problem.



    It is tempting to introduce fields with a scale (the Compton wavelength) similar to the size of galactic cores. One would thus be dealing with fields of mass 10^−21 eV or similar, in what is known as fuzzy dark matter models .

    More massive and clumpy CDM dark matter is observed, and the cusp-core problem that fuzzy dark matter was supposed to solve has been better solved by CDM and baryon physics since 2015 https://astrobites.org/2015/06/12/the-labor-of-outflows-against-dark-matter-halo/ ].]
    The authors don't seem to say why they look at binaries, but I assume they wanted to look for imprints in gravitational wave behavior during mergers. The field variation is amplitude modulated by the binary rotation but essentially and for isolated or well separated black holes is resonating at the scalar mass. We'll see - they do think

    compact binaries are a fertile ground to new phenomenology.

    👹:

    electrons can appear only in certain regions around an atomic nucleus

    There is a non-zero likelihood for an lower-most energy s orbital electron to be located at the nucleus center - but I get your point.
    Reply
  • TorbjornLarsson
    danr2222 said:
    Fields, as they might be defined operationally, were not used for 'centuries' before the mid-twentieth century; perhaps a little over one century. They were properly qualified (by Dedekind) less than a century before.

    Aren't you describing the unrelated mathematical "field" concept, where Dedekind (1831 – 1916) worked on ring theory especially?

    The physical field was introduced by Faraday (starting in 1831 as a fact!), made explicit 1845 and formalized by Maxwell 1864 https://en.wikipedia.org/wiki/Michael_Faraday#Electricity_and_magnetism , https://en.wikipedia.org/wiki/Faraday%27s_law_of_induction , https://en.wikipedia.org/wiki/Quantum_field_theory ]. Modern quantum field theory had to await Einstein's relativity and quantum discoveries, of course - it was developed starting in 1925.
    Reply
  • TorbjornLarsson
    In atomic physics, you can completely describe an elementary particle (like an electron) in terms of three numbers: its mass, its spin and its electric charge. And in gravitational physics, you can completely describe a black hole in terms of three numbers: its mass, its spin and its electron charge.

    Coincidence? The jury's out on that one,

    I don't get that implication!?

    Black holes have thermodynamics (temperature and entropy) so are systems with microstates and notably continuous mass, spin and electric charge, elementary particles are microstates and have discrete (internal) mass, spin and electric charge - for gravity you should have gravitons with zero mass and electric charge but spin=2.

    Aren't black holes more analogous with critical points of phases, where the mean field theory of an nearly ideal gas breaks down?
    Reply
  • Mike Grant
    Is it possible that the hydrogen atoms are so compressed in the gravitational field of black holes that it actually achieves metallic form, holds that form long enough create the conditions for the metallic form to grow and thicken to a point where the existence of the so-called "worm hole" effect actually achieves sustainability? Noting the X Rays emitted from the center of the Milky Way as by products of the churn and spin in the center of the hole, what other explanations for the phenomena indicate the possibility? As nothing seems to be able to be detected from a lateral view of a black hole, an incredibly thick and dense wall of metallic hydrogen, not usually seen elsewhere, could be a source of inquiry into the nature of their gravitational being.
    Reply