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In the Universe there are scattered materials, inside and outside the galaxies. We talk about interstellar matter, light, background radiation and dark matter.
It is formed gases and dust particles between the stars and galaxies. Most of it is not visible, but it can be detected through its gravitational effects and electromagnetic emissions.
It is formed, above all, by hydrogen, but there are also small amounts of helium, nitrogen, oxygen, carbon and simple molecules of water, alcohols and ammonia.
A hydrogen atom and an oxygen atom can combine to form a very active OH (hydroxyl) group, capable of bonding with almost any material. If it encounters a hydrogen atom, it forms a water molecule.
Since the 1970s, increasingly complex molecules have been located, consisting of dozens of atoms.
Some could, under favorable conditions, form organic matter, which is the basis of living organisms.
The light, waves or particles?
Light waves, like those from X-rays, cannot be emitted one at a time, but only in packages called "quanta". The science that studies it is quantum mechanics.
These types of high frequency radiation, depending on how they are observed, behave as particles and, at the same time, as waves. The particles of light are photons. They have no mass and travel at about 300,000 km / s.
Background cosmic radiation
In 1965 the "tangible" evidence of the Big Bang was found. Checking a very sensitive microwave detector, two scientists discovered a strange radiation that came equally from all points of space.
Other theorists had already predicted that a "glow" testimony of the Big Bang would have to be observed, coming from the entire universe, and that this light, due to the expansion of the Universe, would be presented in the form of a microwave.
It is believed that dark matter is a material that does not emit any electromagnetic radiation. Its existence is based on theoretical considerations and is, for now, one of the main problems that astrophysics has.
By studying the forces in the Universe, it is estimated that the total matter is much more than that detected by our instruments. Since we know nothing about her, we call her dark matter.
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