When did the first light appear in the universe?
The speed of light gives us a wonderful tool for studying the universe. As the light travels at a speed of only about 300,000 km / s, looking at distant objects, we look into the past.
We see the Sun not directly, but the Sun 8 minutes old. We see Betelgeuse 642 years ago. Andromeda 2.5 million years ago. And so you can continue further, looking further in space and deeper into the past. As the universe expands, distant objects used to be closer.
If you start the clock in the opposite direction, and bring it to the beginning, then you will arrive at a place that was hotter and denser than today's Universe. It was so dense that the entire Universe immediately after the Big Bang was a soup of protons, neutrons and electrons that nothing held together.
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After it expanded slightly and cooled, its density and temperature began to resemble what happens in the center of a star like our Sun. It became cold enough for ionized hydrogen atoms to begin to appear.
Since the conditions in the Universe corresponded to what is happening in the core of the star, the temperature and pressure were enough to synthesize helium and other heavier elements from hydrogen. Based on the proportions of the presence of elements in the universe today: 74% of hydrogen, 25% of helium and 1% of all different, we know how long the universe has been in this “star” state.
It lasted about 17 minutes. From 3 minutes elapsed since the Big Bang, to 20 minutes elapsed since that moment. And in these moments, the clowns collected so much helium that it should be enough for a lifetime of their pursuit of people with the help of animals twisted from balls.
The synthesis process creates photons of gamma radiation. In the core of the Sun, these photons jump from atom to atom, erupt from the nucleus to the outside, through the emitting zone of the Sun, and eventually fly into space. This process can take tens of thousands of years. But in the early universe this initial photon of gamma radiation had nowhere to go. Everywhere there was a hot and dense universe.
The universe continued to expand, and as a result, just a few hundred thousand years after the Big Bang, it cooled enough so that these hydrogen and helium atoms began to attract free electrons and turn into neutral atoms.
This was the moment when the first light appeared in the Universe, between 240,000 and 300,000 years after the Big Bang, known as the epoch of recombination. For the first time photons could take a break, being tied to atoms by electrons. At that moment, the universe turned from opaque to transparent.
This is the earliest light, in principle, available to astronomers for observation. Let's say in chorus: Cosmic Microwave Background Radiation [or relic radiation - approx. trans.]. Since the Universe has been expanding for 13.8 billion years, the very first photons stretched out, having experienced a redshift, and, after passing ultraviolet and the visible part, moved into the microwave part of the spectrum.
If we could see the Universe with microwave eyes, this first blast of radiation would be visible in any direction. The universe celebrates its existence.
After the first explosion of light, everything was dark, there were no stars and galaxies, only a huge number of original elements. At the beginning of the dark ages, the temperature of the entire universe was about 4000 K. Compare this with the current figure of 2.7 K. By the end of the dark ages, 150 million years later, the temperature dropped to a more reasonable 60 K.
In the next 850 million years, these elements gathered in huge stars of pure hydrogen and helium. Without heavier elements, stars could form, tens and even hundreds of times larger than our Sun. This is the star population of III, the first stars for the observation of which we do not yet have sufficiently powerful telescopes. Astronomers suggest that they formed approximately 560 million years after the Big Bang.
Then the first stars exploded like supernovae, more massive stars formed, and also exploded. It is very difficult to imagine how it all looked when the stars exploded like fireworks. But we know that these events were so frequent and so powerful that they illuminated the entire Universe in the era of reionization. Most of the universe was occupied by hot plasma.
The early universe was hot and terrible, and there were not enough heavy elements on which the known life rests. Oxygen cannot be obtained without synthesis in a star, even in several generations of stars. Our solar system arose as a result of many generations of supernovae that exploded and sowed our region of space with more and more heavy elements.
I have already mentioned that the Universe cooled from 4000 K to 60 K. But after about 10 million years since the Big Bang, the temperature of the Universe was still about 100 C, that is, the boiling point of water. And after another 7 million years, it cooled to 0 ° C, the temperature of freezing water.
What led astronomers to the idea that for about 7 million years everywhere in the universe could find liquid water. And on Earth, wherever we find liquid water, life also occurs there.
It is possible that primitive life could have been formed when the universe was only 10 million years old. Physicist Avi Loeb [Avi Loeb] calls this time the era of the inhabited universe. There is no evidence of this possibility, but the idea is very cool.
I am always struck by the thought that around us in any direction there is the first light emitted by the Universe. It took him 13.8 billion years to reach us, and although we need microwave eyes to observe it, it exists and is ubiquitous.
We see the Sun not directly, but the Sun 8 minutes old. We see Betelgeuse 642 years ago. Andromeda 2.5 million years ago. And so you can continue further, looking further in space and deeper into the past. As the universe expands, distant objects used to be closer.
If you start the clock in the opposite direction, and bring it to the beginning, then you will arrive at a place that was hotter and denser than today's Universe. It was so dense that the entire Universe immediately after the Big Bang was a soup of protons, neutrons and electrons that nothing held together.
')
After it expanded slightly and cooled, its density and temperature began to resemble what happens in the center of a star like our Sun. It became cold enough for ionized hydrogen atoms to begin to appear.
Since the conditions in the Universe corresponded to what is happening in the core of the star, the temperature and pressure were enough to synthesize helium and other heavier elements from hydrogen. Based on the proportions of the presence of elements in the universe today: 74% of hydrogen, 25% of helium and 1% of all different, we know how long the universe has been in this “star” state.
It lasted about 17 minutes. From 3 minutes elapsed since the Big Bang, to 20 minutes elapsed since that moment. And in these moments, the clowns collected so much helium that it should be enough for a lifetime of their pursuit of people with the help of animals twisted from balls.
The synthesis process creates photons of gamma radiation. In the core of the Sun, these photons jump from atom to atom, erupt from the nucleus to the outside, through the emitting zone of the Sun, and eventually fly into space. This process can take tens of thousands of years. But in the early universe this initial photon of gamma radiation had nowhere to go. Everywhere there was a hot and dense universe.
The universe continued to expand, and as a result, just a few hundred thousand years after the Big Bang, it cooled enough so that these hydrogen and helium atoms began to attract free electrons and turn into neutral atoms.
This was the moment when the first light appeared in the Universe, between 240,000 and 300,000 years after the Big Bang, known as the epoch of recombination. For the first time photons could take a break, being tied to atoms by electrons. At that moment, the universe turned from opaque to transparent.
This is the earliest light, in principle, available to astronomers for observation. Let's say in chorus: Cosmic Microwave Background Radiation [or relic radiation - approx. trans.]. Since the Universe has been expanding for 13.8 billion years, the very first photons stretched out, having experienced a redshift, and, after passing ultraviolet and the visible part, moved into the microwave part of the spectrum.
If we could see the Universe with microwave eyes, this first blast of radiation would be visible in any direction. The universe celebrates its existence.
After the first explosion of light, everything was dark, there were no stars and galaxies, only a huge number of original elements. At the beginning of the dark ages, the temperature of the entire universe was about 4000 K. Compare this with the current figure of 2.7 K. By the end of the dark ages, 150 million years later, the temperature dropped to a more reasonable 60 K.
In the next 850 million years, these elements gathered in huge stars of pure hydrogen and helium. Without heavier elements, stars could form, tens and even hundreds of times larger than our Sun. This is the star population of III, the first stars for the observation of which we do not yet have sufficiently powerful telescopes. Astronomers suggest that they formed approximately 560 million years after the Big Bang.
Then the first stars exploded like supernovae, more massive stars formed, and also exploded. It is very difficult to imagine how it all looked when the stars exploded like fireworks. But we know that these events were so frequent and so powerful that they illuminated the entire Universe in the era of reionization. Most of the universe was occupied by hot plasma.
The early universe was hot and terrible, and there were not enough heavy elements on which the known life rests. Oxygen cannot be obtained without synthesis in a star, even in several generations of stars. Our solar system arose as a result of many generations of supernovae that exploded and sowed our region of space with more and more heavy elements.
I have already mentioned that the Universe cooled from 4000 K to 60 K. But after about 10 million years since the Big Bang, the temperature of the Universe was still about 100 C, that is, the boiling point of water. And after another 7 million years, it cooled to 0 ° C, the temperature of freezing water.
What led astronomers to the idea that for about 7 million years everywhere in the universe could find liquid water. And on Earth, wherever we find liquid water, life also occurs there.
It is possible that primitive life could have been formed when the universe was only 10 million years old. Physicist Avi Loeb [Avi Loeb] calls this time the era of the inhabited universe. There is no evidence of this possibility, but the idea is very cool.
I am always struck by the thought that around us in any direction there is the first light emitted by the Universe. It took him 13.8 billion years to reach us, and although we need microwave eyes to observe it, it exists and is ubiquitous.
Source: https://habr.com/ru/post/399207/
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