On Halloween, October 31st, astronomy observes International Dark Matter Day. This day provides scientists worldwide with an opportunity to share information with the public about one of the greatest mysteries of the cosmos.
Since 2017, over 350 events have been organized globally, regionally, and locally by institutions and private individuals. The goal of these events is to engage the public in discussions about what is known about dark matter, as well as the numerous experiments aimed at unraveling its secrets, according to data from Interactions Collaboration, an international community of particle physics communication specialists sponsoring this event.
To try and understand this mystery, imagine a 'box' containing everything that exists in the observable universe: atoms, molecules, planets, stars, black holes, and galaxies. Surprisingly, this 'box' constitutes only 5% of the cosmos. The remaining 95% is divided between dark energy and dark matter; dark energy accounts for 70% of the universe, while dark matter accounts for approximately 25%.
Dark matter was indirectly detected by Vera Rubin in the 1970s, but its nature remains unknown. It does not emit, reflect, or shine, yet it possesses gravity. We know of its existence because it distorts and accelerates entire galaxies. Regardless of whether it is an unknown particle, an exotic property of space, or something entirely new, dark matter could be the missing link in modern cosmology.
The choice of this date is closely linked to the Halloween holiday, which raises themes of mystery and invisibility. This initiative highlights the scientific quest for answers about dark matter, which is one of the universe's main enigmas. Although it has not been directly detected, dark matter is considered necessary to explain astrophysical phenomena such as galaxy rotation.
Since the 1930s, evidence has pointed to the presence of a form of matter that does not emit light, leading to the conclusion of 'hidden' matter whose existence is revealed only through gravitational interaction. Currently, about 40 experiments worldwide are searching for signs of this mysterious substance, hoping for significant progress in the next five to ten years.
Among possible candidates are particles known as WIMPs (Weakly Interacting Massive Particles) and axions. It is hypothesized that dark matter may include various types of particles, forming an unexplored 'dark sector.' In parallel, dark energy continues to be a mystery, possibly related to the 'cosmological constant' proposed by Albert Einstein.
These mysteries motivate scientists worldwide, including Brazilian researchers, to seek answers that could change our understanding of the universe. According to a study published in the journal Physical Review D, a second Big Bang could have given rise to dark matter. According to the most well-known theory, everything in the universe (matter, energy, planets, and stars) originated from a giant cosmic explosion—the Big Bang.
However, scientists now suggest that a similar second event might have occurred shortly after it, giving rise exclusively to so-called dark matter.
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