Have you ever wondered what exactly is the universe made of?
According to the cosmological model, our universe was born 13.7 billions years ago, by a huge e*plosion that gave birth to our space like we know it nowadays:
the Big Bang. Everything that exists was born in that immense e*plosion.
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Science development led us to more and more sophisticated and accurate technology to investigate the cosmos, and little by little astronomers and physicists have learned a lot about the universe, discovering stars, stardust, planets, satellites, asteroids, galaxies, nebulae, clusters of galaxies and so on…Until recently we thought to be well advanced in the comprehension of matter distribution around the universe, nevertheless, starting from the last century,
observations suggest that there is far more to discover!
As a matter of fact, all that exists in the universe seems to be much more than what we can detect. The mass we can see and measure is only a minimum fraction of the whole universe. Yes, because the larger amount of matter is invisible and undetectable by our instruments. It’s like an immense halo that permeates the cosmos without emitting, absorbing and reflecting nor light neither electromagnetic wave.
This is the dark side of the universe.
This is DARK MATTER.
Now physicists assess that only the 15% of the matter in the universe is made of detectable ordinary mass. The overwhelming majority is made up of something that we can’t detect directly, so scientists called it “dark matter”. The name dark is due to the fact that it doesn’t shine, it doesn’t absorb, it doesn’t reflect light or any other electromagnetic radiation, we detect its presence by indirect effects only. It’s like a phantom, we can’t see it, it’s completely invisible.
Wait, what? How is that possible?
Curious to know how? Stick with us and we will tell you how are things in this video!
what is dark matter?
what exactly is made of?
where can we find it?
how can we know that it exists and how we measure it?
How is it arranged in the universe?
How much dark matter?
To answer to all these questions we need to step back
so, let’s rewind a bit the tape and go back in time.
STORY OF DARK MATTER: the 1st evidence in ROTATIONAL VELOCITIES
Since the end of 19th to the beginning of 20th century, many scientists were interested in so-called “obscure stars and dark gases”, little luminous matter that couldn’t be identified with telescopes.
In 1877 Italian priest Angelo Secchi, expert in stellar spectroscopy, in a paper, asked himself questions about the presence of scattered dark masses in space.
In 1933 the swiss physicist Fritz Zwicky was trying to understand the behaviour of clusters of galaxies. In particular, while observing a cluster of a thousand galaxies in the “Coma Berenices”, 150 million light-years far from here, he found some anomalies in their motion. In fact, they were rotating with a speed about 100 time faster than what the theory expected, as if the total mass of the cluster was about 400 times higher than it was.
In other words, the gravity effect of the cluster was too low for such fast orbits.
Nevertheless, so far, this was considered an issue due to a mistake in the process of measurement, because of technical limitation. It was essentially believed that the missing mass was made of faint stars, planets, meteor, scattered gas in interstellar spaces.
2nd evidence of dark matter: THE GRAVITATIONAL LENSE EFFECT
Nowadays we have another instrument to assess the amount of dark matter in the galaxies.
According to Einstein’s general relativity, if we interpose a mass between a distant electromagnetic source and an object that we’re observing, since the mass curves space-time, this mass will act as a lens to bend the light from this source. The more massive an object, the more lensing is observed. By measuring the distortion geometry, the mass of the object can be deduced.
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