Where can we best look for dark matter?

It sounds ineffective: searching for dark matter in a place where things are rare. However, these physicists suggest just that.

Every month I send coordinating editor Naomi Vreeburg a list of potential topics for this column — and every month there’s a study connected in some way to the search for dark matter. “once again?” , I can hear Naomi yell into my mind when I hit “send”. But yes, this substance is one of the hottest issues in physics and astronomy.

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This is not strange at all. Five-sixths of the universe seems to be made up of dark matter, in other words: particles that we can’t see, but that influence their environment with their gravity. Well, if your mission is to understand the universe, the fact that the most abundant particles in it leave you completely baffled is a little embarrassing.

Among the recent attempts to get rid of this painful problem, I note a study in which the authors proposed to search for dark matter in the vast expanses of empty space between galaxies. Strange thought: Not only is there a little bit of ordinary matter to be found there, but also a bit of the dark variety. Why are you looking for it in those places? Fortunately, Naomi let me write a little bit about it, which gave me an excuse to dig deeper into it.

particle disappearance

First of all: How do you even search for dark matter particles in the universe? Two processes are important here. First, these dark matter particles can decay into ordinary particles. In addition, this decay process can produce gamma radiation. We can observe this radiation with specialized space telescopes, such as the Fermi Gamma-Ray Telescope of NASA and the US Department of Energy.

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Second, two dark matter particles meeting in space can destroy each other. Both particles disappear, and their mass is converted into radiation. Similarly, this process can also produce a signal that we can see.

But the universe does not consist of dark matter alone. It has many other inhabitants – some of which also produce gamma rays. This makes it very difficult to distinguish gamma rays from dark matter from, for example, gamma rays from supermassive black holes in the hearts of galaxies.

Crowded or empty?

Hence the idea of ​​the Italian astronomers Stefano Accari, Elena Benetti and Nicolao Furengo. They decide to find out where you’d be best off searching for dark matter in the universe.

In densely populated regions with a lot of dark matter, but also many other astronomical objects that make your measurements more difficult? Or in the empty parts of the universe, where there is less dark matter, but also fewer things that emit the same kind of radiation, thus complicating your search?

The latter appears to be the better option, Acari and colleagues show in their article. At least, if you’re talking about gamma rays from dark matter particles that decay into other particles. Encounters between dark matter particles that end in mutual destruction are very rare in the vast voids between galaxies. So you don’t have to rely on this kind of gamma radiation when you’re looking for dark matter in these regions.

Excellent ladder

But we can thus search for decaying dark matter particles in regions where they are, paradoxically, very rare. Unfortunately, that won’t work for our current space telescopes, like the previously mentioned Fermi Space Telescope. So, in their article, Akari and his team imagine a successor that performs better in all sorts of ways, which they call, with Italian flair, Vermissimo: the Fermi supremacy. If you let him study the cosmic voids, he could reveal any dark matter scattered above.

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Just: Before such a thing can be built and running, it will of course be a few years away. So Naomi can look forward to more Far Out proposals in the near future about scientists who think they can advance the search for dark matter. As you wriggle your thumb until a Vermisimo-like viewer can sort it out, physicists and astronomers, gentlemen and ladies, won’t. The whole dark matter story is a little embarrassing for that.

This Far Out is also on KIJK 11/2022, on sale via the button below.

Sources: ArXiv.orgAnd the Scientific American

Image: NASA, ESA, E. Holman (University of Colorado, Boulder)

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