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Theories of dark matter exotic. Gravitational waves. Observatories in the space. Giant black holes. Collision of galaxies. Lasers If you are a fan of all that is great in the universe, this article is for you.
Most of the contents of our universe have a totally unknown form of physics. It's just a crude fact that we'll all have to get used to. If you are tempted to think that it's just some sort of cosmological problem, a problem that only arises on very large scales, so I have bad news for you. One of these mysterious components of the cosmos is – to our knowledge – a form of matter.
But not any matter, otherwise we would have seen it before. No, we think it's kind of dark material; matter that simply does not interact with light. No show. No absorption. No dispersion. Nothing. And the fact that dark matter exists should not be this surprising, should he? After all, who dictated that everything in the universe must interact with light?
Nobody did it and so here we are. If you look at a random galaxy, objects that light up – stars, nebulae, etc. – represent only a small fraction of the total mass quantity of this galaxy. The exact relationship between "normal" matter and dark matter depends on many factors, such as the history of galaxy formation. But in general, the smaller the galaxy, the more it is dominated by dark matter.
Smaller galaxies, called dwarf galaxies, could be a practical laboratory for studying dark matter. In these galaxies, dark matter is free to do what it does without any of these light-interacting materials to really complicate things. If dark matter does something strange (much stranger than simply exist), as if it interacted with itself through the weak nuclear force or if it was composed of several types of exotic particles, then all the effects would occur in a dwarf galaxy. the Milky Way.
That's fine, apart from the little warning that despite all these interesting physical activities, it's hard for us to see it. Because it's dark.
One of the many things we do not understand about dark matter is its behavior in the nuclei of galaxies. Simple simulations of the evolution of galaxies predict what is called a "cusp", a hard core of incredibly high density sitting in the otherwise creamy center of a galaxy. But the observations do not show this: there should be many stars that follow the gravitational influence of all this dark matter. And of course, there are a lot of stars in the center of a galaxy, but not this a lot.
Something must smooth the central dark matter. It could be exotic interactions in dark matter itself. These could be more commonplace causes, such as supernovae winds releasing gas. It could be both, or neither.
Astronomers are very interested in the hearts of galaxies, especially dwarf galaxies, because that's where they can potentially learn a lot about dark matter. And despite their complicated and messy physics, we still need stars and gases to observe, probe and study dwarf galaxies, hoping to track the behavior of the underlying dark matter. But dwarf galaxies are distant, dark and small – and their core even more so.
How could we look in them?
Fortunately, galaxies have more than stellar citizens. They also have black holes. Supermassive giants in their nuclei and millions of smaller ones floating within them. And the fact that giant black holes tend to congregate in the nuclei of host galaxies could be useful. So maybe – work with me here – if we could somehow study the behavior of black holes inside dwarf galaxies, we could get clues about the nature of dark matter.
But black holes are also black and hard to see. And small. And in the distance. Fortunately, we do not have to see black holes, we can hear them.
When black holes meet, they shake and deform the fabric of space-time to the point of causing waves, like ripples extending from a heavy stone fallen into the water. These gravity waves propagate in space at the speed of light, extending slightly and compressing any intermediate material when they wash. In fact, your body is, as you read, being pulled and squeezed like a piece of mastic from the countless gravitational waves that cross the Earth.
These gravimetric waves are incredibly difficult to detect. That is why the first people to measure them have received Nobel Prizes for their efforts, which have lasted for decades, to use interfering light beams to capture the subtle signal.
But our three gravitational wave observatories on the surface of the Earth can not help us solve our black hole problem in the dwarf galaxy to study dark matter. These black holes – known as black holes of intermediate mass – are too small to create a signal detectable by the Milky Way when they merge.
But an observatory of gravitational waves in space could. The proposed LISA mission (which means, as you might have guessed, a laser interferometer space antenna) could have the good sensitivity to see the signal of merging medium-sized black holes, just like those found in the heart of dwarf galaxies.
And according to a new article recently accepted by the journal Astrophysical Letters led by Tomas Tomfal of the University of Zurich, different models of dark matter (and its possible interactions with the light-loving material type) can influence the frequency and the speed of the black holes of the dwarf galaxies are confused, which LISA can possibly distinguish.
It's a devious way to understand dark matter, but in a problem as thorny as this one, it is promising.
Read more: "LISA Black Hole binaries formation in the fusion of dwarf galaxies: the imprint of dark matter"
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