Dark matter is thought to be everywhere, literally, but we can't see it; we can only detect its gravitational presence over large cosmic scales. Now, theoretical physicists are theorizing what configuration the dark stuff may take around Earth. And it's becoming a bit of a hairy subject.
If we are to take the findings of a recent computer simulation to heart, it looks as if the planets in our solar system are growing rather trendy dark matter "beards," an idea that not only reveals previously unknown interplanetary fashion trend, it could also provide a guide as to where to seek out direct evidence of the invisible matter that is thought to make up 85 percent of the mass of the entire universe.
ANALYSIS: Is Earth Surrounded by Dark Matter?
Currently, direct evidence for dark matter is maddeningly tough to track down. But indirect evidence for dark matter can be found throughout the cosmos. Galactic clusters, for example, contain vast reservoirs of mass that we can't see, but for any light passing through these reservoirs, its presence is revealed. Although dark matter - also known as "non-baryonic matter" - cannot interact via the electromagnetic force (in other words it cannot scatter, reflect, emit or refract light, light normal - or "baryonic" - matter can), as predicted by Einstein's general relativity, its powerful gravitational field can warp spacetime. Telescopes can detect this spacetime curvature and, after measuring how much warping is going on, and calculating how much visible matter is contributing, we find that the vast majority of the gravity needed is not being produced by the matter we can see (stars and galaxies), but by stuff that we can't (dark matter).
Over the years, astrophysicists have been coming up with ideas as to how dark matter interacts gravitationally with normal matter and how the two types of matter interrelate. Observations of the motions of stars in galaxies, for instance, shows that there needs to be a lot more matter contained within galaxies to explain star motions. This indirect observation has led to the hypothesis that all galaxies are embedded in a dark matter halo. Over much larger scales, dark matter should form vast filaments along which normal matter (galaxies) are threaded. On smaller scales, within galaxies, it is thought that "fine-grained streams" of dark matter flow throughout interstellar space, evolving with the galaxies.
ANALYSIS: How Low Can a Dark Matter Halo Go?
But how does dark matter interact with individual planets?
In a new study published by the Astrophysical Journal, Gary Prézeau of NASA's Jet Propulsion Laboratory in Pasadena, Calif., describes the results of his theoretical model that goes some way to explain how streams of dark matter particles may interact with our planet's gravitational field.
"A (dark matter) stream can be much larger than the solar system itself, and there are many different streams crisscrossing our galactic neighborhood," said Prézeau in a JPL press release. "When gravity interacts with the cold dark matter gas during galaxy formation, all particles within a stream continue traveling at the same velocity."
As these streams begin to interact with a planet, according to results from his computer simulation, the streams pass straight through, focusing as an "ultra-dense filament," producing many dark matter "hairs" that seem to sprout well above Earth's surface. This stream will not interact with our planet's normal matter, it will pass through as if nothing were there, but channeled by the intensity of Earth's gravity.
However, it's not just Earth; all gravitational fields, and therefore all the planets of the solar system, should experience an intense concentration of dark matter, projecting strands of dark matter far into interplanetary space. For Earth, the dark matter streams will emerge from the planet, concentrating as "roots" of the dark matter hairs around 600,000 miles above the surface (approximately twice the Earth-moon distance) - the roots will be concentrated masses of dark matter. The "tips" of the hairs should be located over twice as far away from the planet's surface as the hairs' roots (the diagram above does a good job of visualizing this configuration).
ANALYSIS: Dark Matter Matters, Especially When You Can't Find It
Although this hypothesis is based purely in theoretical simulations of equations for how we think dark matter behaves, it could act as a template for future exploration of dark matter.
"If we could pinpoint the location of the root of these hairs, we could potentially send a probe there and get a bonanza of data about dark matter," said Prézeau.
"Dark matter has eluded all attempts at direct detection for over 30 years. The roots of dark matter hairs would be an attractive place to look, given how dense they are thought to be," said Charles Lawrence, chief scientist for JPL's astronomy, physics and technology directorate.
Interestingly, according to Prézeau's model, the hairs should retain information about the insides of the planets the dark matter stream is passing through, creating a planetary "fingerprint" of sorts that could be used to remotely explore any planet's interior.
Obviously, this research comes with some huge caveats, the key one being that, even though we have yet to directly measure dark matter particles, they interact with planetary gravitational fields as expected by current theoretical models. Also, to test this "dark matter hair" theory, we'll need to develop a way to detect concentrations of dark matter in the vicinity of Earth. Have the presence of the roots of these dark matter hairs already been detected? Could their presence explain some as-yet to be explained mysteries (such as the infamous "flyby anomaly")?
Who knows, but it's interesting to think that what we see in our solar system is only a fraction of the story; dark matter "beards" could be all the rage.