Arrakhis: The tiny satellite aiming to reveal what dark matter is made of

The European House Company (ESA) lately introduced a brand new mission of its science program: a small telescope orbiting the Earth dubbed Arrakhis. However though its identify is impressed by the sci-fi novel Dune, it is not going to be in search of sandworms or “spice” on a desert planet.

As a substitute, this nimble satellite will punch massively above its weight and attempt to observe down one of the crucial elusive and mysterious substances within the universe: darkish matter. That is the time period given to the hypothetical invisible matter that’s considered extra ample than regular matter and have an analogous gravitational impact on its environment.

The mission is classed as quick (F), which implies it’s smaller, extra centered and has a faster turnaround (lower than ten years to launch) than different forms of ESA missions. The company’s earlier F-mission, chosen in 2019, known as the Comet Interceptor. Already parked at a steady level within the Photo voltaic System, this probe is ready for a comet to point out up and fly by it, one thing that is as a result of occur across the time that Arrakhis launches within the early 2030s.

Observe the sunshine

Since dark matter nonetheless eludes detection, the mission will goal sources of sunshine which can be delicate to it. We count on regular matter—the stuff that truly emits gentle, equivalent to stars in galaxies—to maneuver primarily underneath the affect of dark matter, which is extra ample.

We consider total galaxies are moved backward and forward by the underlying dark matter, like beacons unfold throughout an invisible ocean. Their crusing is bumpy although, as dark matter is considered distributed erratically throughout the universe, forming a “cosmic net” over huge distances, and having a extra clumpy look on galaxy scales. A few of these clumps must be populated with small galaxies known as dwarf galaxies, whereas others could be made up fully of dark matter.

There’s additionally particles left over from these dwarf galaxies that enterprise too near the host galaxies they orbit. As the encompassing dark matter rips these galaxies aside via gravitational tides, they begin to unravel into lengthy streams of stars that wrap round huge swathes of space. These skinny veils of sunshine are one other reference to the unseen. By counting and measuring their shapes, we will infer what kind of particle dark matter is fabricated from—and in the end which cosmological model is probably the most correct.

The clumpiness in space is a sturdy prediction of our cosmological fashions, because it merely represents the end result of gravity performing on matter. Nonetheless, our fashions give conflicting predictions in regards to the variety of these clumps, which may very well be increased or decrease relying on what type of particle or particles we assume dark matter to be made up of.

Within the “customary” mannequin of cosmology, dark matter particles are assumed to be “cold”, that means they’re heavy and sluggish shifting (an instance could be “weakly interacting huge particles”, or Wimps). This means that our Milky Way will comprise lots of of dark matter clumps, a few of which can comprise dwarf galaxies. However the issue is that we solely see a number of dozen dwarf galaxies round us, which could be very puzzling. It might imply that the majority of those clumps are fabricated from dark matter.

Cosmologists produce other viable concepts although. For instance, if dark matter is “warm”—that means that particles are a lot lighter and quicker, equivalent to sterile neutrinos—there could be far fewer clumps to start with. Observations can provide us the ultimate clue as to which mannequin is true, however to get there, we first want an correct census of dwarf galaxies orbiting the Milky Way.

The tip of the iceberg

There are sturdy indications that the dwarf galaxies found thus far close to the Milky Way or different massive galaxies are simply the tip of the iceberg, and that many more remain hidden behind the sunshine of their hosts. Arrakhis will be capable of uncover this lacking inhabitants even at massive distances from us.

Observing this faint starlight has confirmed to be difficult even for the most important telescopes on Earth, because it requires very deep imaging and surveying of huge parts of the sky. Moreover, the Earth’s ambiance is a hindrance. Arrakhis will observe from space, with an progressive digicam that probes deeper in each the optical and near-infrared a part of the spectrum, and with a a lot wider discipline of view. (By the way, the sort of digicam can even look back at Earth with wonderful decision.)

The hundred or so Milky Way-like methods that can be noticed are about 100 million light-years away, the place only a few dwarf galaxies have been found thus far, and no stellar streams but. Once we know the variety of soon-to-be found dwarf galaxies and the way they are going to be seen distributed in space, we must always be capable of pin down the right cosmological mannequin.

Arrakhis will discover most of the lacking items within the puzzle that dark matter supplies, complementing what we already know from the close by universe and what we are going to be taught sooner or later from different upcoming telescopes, equivalent to Euclid or the Vera Rubin Observatory.

The hope is that these detailed, mixed observations will lastly reveal the dark matter thriller, and assist us perceive what makes up nearly all of matter within the cosmos.

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