What is the Universe made of?

The universe is filled with billions of galaxies and billions of stars, as well as an almost incalculable number of planets, moons, asteroids, comets, and clouds of dust and gas, all swirling in the immensity of space.

But if we zoom in, what are the building blocks of these celestial bodies and where do they come from?

Hydrogen is the most common element found in the universe, followed by helium; together they constitute almost all ordinary matter. But this only represents a tiny slice of the universe – about 5%. Everything else consists of items that can not be seen and can only be detected indirectly.[[[[From the big bang to the present: snapshots of our universe through time]

Mainly hydrogen

It all started with a big Bang, about 13.8 billion years ago, when the extremely hot and dense matter suddenly and rapidly spread in all directions. Milliseconds later, the newborn universe was a huge mass of neutrons, protons, electrons, photons, and other subatomic particles, spinning at about 100 billion degrees Kelvin, according to NASA.

Each fragment of matter constituting all the known elements of the periodic table – and each object of the universe, of black holes Neta Bahcall, a professor of astronomy at the department of astrophysical sciences at Princeton University, New Jersey, said Neta Bahcall.

"We do not even know the laws of physics that would have existed in such a hot and dense environment," Bahcall told Live Science.

About 100 seconds after the Big Bang, the temperature dropped to 1 billion degrees Kelvin. About 380,000 years later, the universe has cooled enough for protons and neutrons to come together to form lithium, helium and hydrogen isotope, deuterium, while free electrons are trapped to form neutral atoms.

Because there were so many zipped protons in the primitive universe, hydrogen – the lighter element, with only a proton and a neutron – became the element the most abundant, constituting nearly 95% of the atoms of the universe. Nearly 5% of the atoms in the universe are helium, according to NASA. Then, about 200 million years after the Big Bang, the first stars were formed and produced the rest of the elements, which make up a fraction of the remaining 1% of all ordinary matter in the universe.

Invisible particles

Something else was created during the Big Bang: dark matter. "But we can not say what shape it took, because we did not detect those particles," Bahcall told Live Science.

Dark matter can not be observed directly – for the moment – but its fingerprints are preserved in the first light of the universe, or in cosmic microwave background radiation (CMB), as tiny fluctuations radiation, said Bahcall. Scientists first proposed the existence of dark matter in the 1930s, starting from the premise that the invisible attraction of dark matter was to be what held together clusters of fast-moving galaxies. Decades later, in the 1970s, the American astronomer Vera Rubin discovered more indirectly black matter evidence in the rotation rates of the stars faster than expected.

Based on Rubin's findings, astrophysicists have calculated that dark matter – even if it can not be seen or measured – should be an important part of the universe. But about 20 years ago, scientists discovered that the universe contained something stranger than dark matter. dark energy, which is supposed to be significantly more abundant than matter or dark matter.[[[[Gallery: Dark Matter Across the Universe]

(Image credit: NASA / ESA)

An irresistible force

The discovery of black energy Scientists wondered if there was enough dark matter in the universe for expansion to spill or spill, causing the universe to collapse towards it. -even.

And of course, when a team of researchers studied the issue in the late '90s, they discovered that not only did the universe not collapse, it was still spreading faster and faster. # 39; outside. The group determined that an unknown force, called dark energy, pushed the universe into the apparent void of space and accelerated its momentum; The results of the scientists earned physicists Adam Riess, Brian Schmidt and Saul Perlmutter the Nobel Prize in Physics in 2011.

The force models needed to explain the accelerated rate of expansion of the universe suggest that dark energy must account for between 70% and 75% of the universe. Dark matter, for its part, accounts for about 20% to 25%, whereas the so-called ordinary matter – what we can actually see – is supposed to constitute Less than 5% from the universe, said Bahcall.

Astrophysicist Mario Livio explained that dark energy represents about three quarters of the universe and understand that this is the biggest challenge facing scientists. She then told Live Science Space.com in 2018.

"Although black energy has not played a huge role in the evolution of the universe in the past, it will play a dominant role in the coming evolution", Livio said. "The fate of the universe depends on the nature of black energy."

Originally published on Science live.