Want to find dark matter but don’t know where to look? A giant planet could be just the kind of particle detector you need! Fortunately, our solar system happens to have a few available, and the largest and closest is Jupiter. Researchers Rebecca Leane (Stanford) and Tim Linden (Stockholm) published a paper this week describing how the gas giant could hold the key to finding the elusive dark matter.
The nature of dark matter is currently one of the greatest puzzles in physics. It interacts gravitationally – we can see it holding galaxies together that would otherwise fly apart – but it doesn’t seem to interact with normal matter in any other way.
The most popular theories assume that dark matter is a type of particle that is either too small or too weakly interacting to be easily observed. Particle accelerators and collider experiments were set up to collide subatomic particles: the researchers hope that the resulting collision will lack unexpected amounts of energy, which would suggest that unknown particles, possibly dark matter, are escaping from the detector. No luck so far.
However, dark matter should also roam in nature and could be captured by gravity from objects with large sources of gravity such as Earth, Sun and Jupiter. Over time, dark matter could accumulate in a planet or star until there is enough density for one dark matter particle to meet another and annihilate both. Even if we cannot see dark matter for ourselves, we should be able to see the results of such a collision. It would produce high-energy radiation in the form of gamma rays.
The Fermi Gamma-Ray Space Telescope. Photo credit: NASA (Wikimedia Commons).
Step inside NASA’s Fermi Gamma-Ray Space Telescope, launched in 2008 with a Delta II rocket. It has been studying the sky for gamma-ray sources for over a decade. Researchers Leane and Linden used the telescope to study Jupiter and made the first analysis of the giant planet’s gamma-ray activity. They hoped to see evidence of excess gamma rays created by the annihilation of dark matter in Jupiter.
As Leane explains, Jupiter’s size and temperature make it an ideal dark matter detector. “Since Jupiter has a large surface area compared to other planets in the solar system, it can capture more dark matter. You may then wonder why you don’t just use the even bigger (and very close by) sun. Well, the second benefit is that since Jupiter has a cooler core than the Sun, it gives the dark matter particles less of a thermal kick. This can, in part, prevent lighter dark matter from evaporating from Jupiter that would have evaporated from the sun. “
Leane and Linden’s first study of Jupiter did not find dark matter yet. However, there was an enticing excess of gamma rays at low energy levels that requires better tools to study properly. “We’re really pushing the boundaries of Fermi to analyze such low-energy gammas,” said Leane. “Looking ahead, it will be interesting to see if upcoming MeV gamma-ray telescopes like AMEGO and e-ASTROGAM find Jupiter gamma-rays, especially at the lower end of our analysis where Fermi’s performance is suffering. Maybe Jupiter still has some secrets to share … “
At the top left, the gamma ray numbers are shown in a 45 degree range around Jupiter.
The same part of the sky is shown at the top right when Jupiter is absent (background).
The bottom left shows the remaining gamma rays when the background is peeled off.
At the bottom right you can see the size and position of Jupiter from the Fermi telescope. If there was excess gamma rays, the map should illuminate in the lower left corner of Jupiter’s position. At these energy levels it was not, although it was at lower energy levels, necessitating further observation with new telescopes. Photo credit: Rebecca Leane and Tim Linden.
Both the AMEGO and e-ASTROGRAM telescopes are still in the conceptual phase, but they may just be the tools to find dark matter and Jupiter may be the target to find them.
Leane and another colleague, Juri Smirnov (State of Ohio) believe that a similar technique could also be used to search for dark matter in Jupiter-like exoplanets or cool brown dwarf stars.
Exoplanets and brown dwarfs closer to the center of the galaxy, where there are higher densities of dark matter, should appear hotter in the infrared than planets and stars further away, as their nuclei annihilate dark matter more often. The James Webb Space Telescope could potentially provide an infrared survey of enough planets to confirm this theory.
Whether we find evidence of dark matter in an exoplanet or in our own gas giant nearby, such a discovery would represent a huge leap forward in our model of the universe. There’s no guarantee of it, but it’s definitely worth a look and the foundations for finding it are just being laid.
You can find the research here:
Selected image source: NASA / JPL-Caltech / SwRI / MSSS / Kevin M. Gill (Wikimedia Commons).
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