Many ultra-dense filaments or “hairs” of dark matter may sprout from Earth and the other planets in our solar system. That’s according to new theoretical research from Gary Prézeau of NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. He used computer simulations to find out what happens when a stream of dark matter goes through a planet. The Astrophysical Journal published his research this week, and the JPL published a statement about it on November 23, 2015.
The idea of fine-grained streams of particles of dark matter – all moving at the same velocity and orbiting galaxies such as ours – stems from theoretical calculations done in the 1990s and simulations performed in the last decade.
Prézeau carried the research a step further by simulating what happens to dark matter streams passing through our solar system. He said:
A stream can be much larger than the solar system itself, and there are many different streams crisscrossing our galactic neighborhood.
Dark matter – the invisible, mysterious substance that makes up about one-quarter of all the matter and energy in the universe – doesn’t interact with ordinary matter. So streams of dark matter would pass straight through the planets in our solar system, and come out the other side. But here’s what’s new. According to Prézeau’s simulations, Earth’s gravity would focus and bend a stream of dark matter particles into a narrow, dense filament, which he calls a hair.
He said there should be many such hairs sprouting from Earth, and that Jupiter – largest planet in our solar system – would have more hairs and denser hair roots due to its greater mass.
Prézeau uses the word root to describe the densest part of the dark matter hair. His simulations show that, when particles of a dark matter stream pass through the core of Jupiter, they form a hair whose root has a particle density about a trillion times greater than average. That’s in contrast to the root of a dark matter hair from Earth, whose density would be only about a billion times greater than average. Prézeau said:
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.
The regular matter we can see around us on Earth makes up only 4-5% of the universe, according to modern science. About 24-25% is dark matter, and the rest is dark energy (a strange “pushing” force, associated with the observations that our universe is expanding faster now than in the past).
Neither dark matter nor dark energy has ever been directly detected. So far, we’ve only seen strange gravitational effects in space, which modern scientists attribute to dark matter and dark energy. They’ve now carried their ideas about dark matter and dark energy into theories describing how the universe itself works and came to be. That’s necessary, because dark matter and dark energy are thought to make up such a huge percentage of the universe, a vastly greater percentage than the ordinary matter we see. So, for example, modern theories about the star-filled galaxies we see around us in space suggest that they formed because of fluctuations in the density of dark matter. The JPL statement explained:
Gravity acts as the glue that holds both the ordinary and dark matter together in galaxies.
So you may see that dark matter and dark energy are critical to the thinking of modern astronomers. That’s why many astronomers want to devise and carry out experiments to detect them.
Prézeau’s research suggests that the root of a dark matter hair passing through Earth’s core should be around 600,000 miles (1 million kilometers) away from the surface, or twice as far as the moon. That’s relatively close to us in space, and it would be possible to design and send a space probe to seek out and explore the roots of this dark matter hair … if it exists. Charles Lawrence, chief scientist for JPL’s astronomy, physics and technology directorate, said in the JPL statement:
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.
These scientists said another fascinating finding from Prézeau’s computer simulations is that the changes in density found inside our planet – from the inner core, to the outer core, to the mantle to the crust – would be reflected in the hairs. The hairs would have “kinks” in them that correspond to the transitions between the different layers of Earth. JPL said:
Theoretically, if it were possible to obtain this information, scientists could use hairs of cold dark matter to map out the layers of any planetary body, and even infer the depths of oceans on icy moons.
Needless to say, these ideas are on the frontier of dark matter research, and much more research is needed.
Bottom line: The idea of fine-grained streams of dark matter stems from theoretical calculations done in the 1990s. Now a JPL astronomer, Gary Prézeau, has carried the idea a step further by running computer simulations of what would happen if a dark matter stream encountered Earth or another planet. His work suggests that streams of dark matter – passing through Earth – would emerge as ultra-dense filaments or “hairs” and that there should be many dark matter hairs sprouting from Earth and the other planets in our solar system.
Deborah Byrd created the EarthSky radio series in 1991 and EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.