5 basic unanswered dark matter questions

Since at least the 1920s, one hypothesis has permeated the world of astronomy: the universe contains more matter than can be seen with the naked eye. In the 1930s, Swiss astronomer Fritz Zwicky noticed that galaxies in a distant cluster orbited each other at a faster rate than would be expected given their visible masses. He proposed that an invisible substance, which he called dark matter, could be gravitationally pulling these galaxies together.

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This idea was harder to prove than support as there was no evidence of this mysterious matter yet. Even with powerful telescopes such as Hubble and Kepler, it has not yet been detected, but its existence has always been more than a probability, but a strong possibility. About 85% of the mass of the universe is made up of material that scientists cannot see - dark matter, to complicate matters, does not emit light or energy. So would it matter to the study of the universe?

"Star movements tell how much it matters, " said Yale University researcher Pieter van Dokkum, who led the team that identified the Dragonfly 44 galaxy, which is composed almost entirely of dark matter.

1. What is dark matter?

No one knows for sure. Some scientists have even conjectured that it would be made up of small weak stars and black holes, but detailed observations have not revealed enough objects to explain the influence dark matter has on other celestial bodies.

The most widely accepted hypothesis is that it is formed by a hypothetical element called the Low Interaction Mass Particle (or WIMP) that would behave like a neutron - except that it is between 10 and 100 times heavier.

2. Can we detect dark matter?

If dark matter is made of WIMPs, they would be everywhere, invisible and almost imperceptible. Although they do not usually interact with ordinary matter, it is hypothetically possible for a dark matter particle to hit a proton or electron as it travels through space. So for decades, researchers have experimented to study a large number of common underground particles, where they are protected from interfering radiation that can mimic a collision between dark matter and particles. No reliable discoveries have been made.

In early 2019, the Chinese PandaX experiment reported the latest non-detection of WIMP.

3. Does dark matter consist of more than one particle?

Everyone has heard of protons, electrons and neutrons, and some know neutrinos, muons and pions. Researchers then wonder if dark matter is complicated as well. "There's no reason to suppose that all dark matter in the universe is made of just one kind of particle, " said Harvard University physicist Andrey Katz. According to him, dark protons can combine with dark electrons to form dark atoms, producing configurations as diverse and interesting as those found in the visible world. The sky is literally the limit.

4. What are the properties of dark matter?

According to some theories, dark matter particles must have their own antiparticles, and both would annihilate each other. The Alpha Magnetic Spectrometer (AMS) experiment at the International Space Station (ISS) has been looking for signs of this annihilation since 2011 and has detected hundreds of thousands of events. Even so, scientists are still not sure if they come from dark matter, because they don't even know exactly what dark matter is.

5. Does dark matter exist throughout the galaxy?

It seemed to be the force that unites large structures, such as galaxies and galactic clusters; but by early 2019 astronomers announced they had found the galaxy NGC 1052-DF2, with almost no dark matter at all. "Apparently, it is not a requirement for a galaxy to form, " Pieter van Dokkum said at the time. However, another group of astronomers published an analysis suggesting that the new galaxy had more dark matter than previously suggested.