Our planet, Jupiter and other compact bodies are surrounded by ultra-dense filaments of dark matter called ‘hairs,’ suggests Dr Gary Prézeau of NASA’s Jet Propulsion Laboratory in Pasadena.
This illustration shows Earth surrounded by dark matter hairs. Image credit: NASA / JPL-Caltech.
Dark matter is a hypothetical form of matter that is undetectable by its emitted electromagnetic radiation. In the Universe, dark matter outweighs normal matter by a factor of 6 to 1.
Every galaxy is surrounded by a halo of dark matter that weighs as much as a trillion suns and extends for hundreds of thousands of light-years.
The most interesting thing about dark matter is not simply that astronomers can’t see it, it’s that they know dark matter is not made of the same stuff as normal matter, and only interacts through gravity. This is why they see its effects on the motions of galaxies and stars.
According to recent studies, dark matter forms ‘fine-grained streams’ of particles. “A stream can be much larger than the Solar System itself, and there are many different streams crisscrossing our galactic neighborhood,” said Dr Prézeau, who is an author of a paper accepted for publication in the Astrophysical Journal (arXiv.org preprint).
“When gravity interacts with the cold dark matter gas during galaxy formation, all particles within a stream continue traveling at the same velocity,” he said.
“But what happens when one of these streams approaches a planet such as Earth?”
Dr Prézeau used computer simulations to find out. His analysis finds that when a dark matter stream goes through a planet, the stream particles focus into an ultra-dense ‘hair’ of dark matter.
According to simulations, the hair is densest at a point called the ‘root,’ which has a particle density about a billion times greater than average.
In the case of Earth, the root should be around 600,000 miles (1 million km) away from the planet’s surface, or twice as far as the Moon. The stream particles that graze Earth’s surface will form the tip of the hair, about twice as far from Earth as the hair’s root.
A stream passing through Jupiter’s core would produce even denser roots: almost 1 trillion times denser than the original stream, according to Dr 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 Dr Charles Lawrence, also of NASA’s Jet Propulsion Laboratory.
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Gary Prezeau. 2015. Dense Dark Matter Hairs Spreading Out from Earth, Jupiter and Other Compact Bodies. ApJ, accepted for publication; arXiv: 1507.07009
