2020
March
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Hexaquark d*(2380): a new candidate for dark matter

One of the biggest mysteries of our universe is what is dark matter made of. Its existence is suggested by several astronomical observations, among them peculiarities in the rotation of galaxies. Dark matter would have to make up at least 63% of all matter in the universe and to date, physicists have no idea about its exact nature.

All that is clear is that dark matter interacts with normal matter only via gravity. These could be, among other things, so-called WIMPs (Weakly Interacting Massive Particles), which would be considered cold dark matter. However, researchers are not making very quick progress on their search for these particles. To date, they have only been able to rule out more and more possible candidates, which is gradually making it more and more unlikely that they are actually on the right track.

Now, in an article in the Journal of Physics, researchers have presented a new candidate. This is a so-called hexaquark: a particle consisting of six quarks, the basic building blocks of many elementary particles. Three up and down quarks, its lightest variants, combine to form a d*(2380) hexaquark. For a long time, hexaquarks were considered hypothetical; in 2014, the first was discovered, d*(2380), at the Jülich Research Center. d*(2380) has a mass of 2380 MeV and is thus heavier, but due to its structure, more compact than a proton, the nucleus of a hydrogen atom.

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Cosmic strings and our existence in the universe

The Big Bang was the beginning of this, our universe. Astrophysicists agree on that much at least. Whether it was or will be the only event of this type is a debate for philosophers. But there are still a few unresolved questions involving the Big Bang. The most important of these would probably be: why do we exist at all? Because after all the four fundamental forces finally developed after the Big Bang, matter and antimatter should always be formed in exactly the same amount. The evolution of the universe would thus be relatively boring: matter and antimatter would mutually destroy each other and the universe would remain as empty as if nothing had ever existed. People? That’s an indication something went wrong.

Now, we have to admit that quite objectively we do exist (unless you subscribe to the conjecture that our world is only a simulation). Therefore, the expected sequence of the Big Bang must have been slightly different from what we expected. More matter than antimatter was formed, eventually leading to us. But why should the universe have preferred matter over antimatter? Nobody has come up with a reason yet that has been convincing for all researchers.

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Sleeping monster from the early days of the universe

At first glance, XMM-2599 appears to be a rather boring galaxy (because it’s dying). But an international research team has recently discovered that it’s really a sleeping monster. XMM-2599 formed more than 12 billion years ago, when the universe was still very young, only 1.8 billion years old. At first the galaxy was extremely active. “Even before the universe was 2 billion years old, XMM-2599 had already formed a mass of more than 300 billion suns, making it an ultramassive galaxy,” says Benjamin Forrest, lead author of the study in Astrophysical Journal.

“More remarkably, we show that XMM-2599 formed most of its stars in a huge frenzy when the universe was less than 1 billion years old – and then became inactive,” explains Forrest. The team found that XMM-2599 produced 1000 solar masses in stars per year during its most active period. In contrast, the Milky Way produces only one new star per year.

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