You must look deep into the universe to see the early universe, so why not the Milky Way? No early stars?

2020-01-05 | Theory of Quantum Science original |

Are there no earliest stars in the Milky Way? The simple answer is: Yes! And we have found some early universe relics, which are in our Milky Way.

The universe has a history of 13.8 billion years after its birth. The Big Bang is called the beginning of the universe. It created endless space and time, and brought us original materials composed of all things. Anything we can see now,And starlight comes from light elements synthesized by the Big Bang.

Big Bang Nuclear Synthesis

13.8 billion years ago, about 1 microsecond after the birth of the universe, the space was full of protons, neutrons, neutrinos and photons, as well as electrons and positrons. At this time, the temperature and density were high enough to fully reach nuclear fusion.It is required that protons and neutrons can be combined in this high-temperature, dense furnace, but at this time there are too many high-energy particles photons, and the combination of protons and neutrons cannot exist stably, and will be almost instantlyA high-energy photon explodes. When the universe cools to a certain degree, the first heavy particle combination deuterium of these particles will stabilize. At this time, the universe has been formed for more than three minutes, and the density has dropped by about 1 billion times.

Then protons and neutrons fused violently together to form heavy elements as best they could, but because the expanding universe is now becoming thinner and colder, nuclear synthesis at this time can only form deuterium, helium, lithium, andBeryllium; no other heavier elements can be formed.

This process is called the big bang nuclear synthesis, it is the source of the lightest element in the universe and the ultimate source of all matter today.

Yes, everything comes from the material that was originally formed. Materials like you and I have a common origin. Our bodies are mainly composed of carbon, oxygen, hydrogen, and nitrogen. At the beginning of the formation of the universe, the bodyMost of the elements do not exist. To create these heavier elements, to create almost all the heavy elements on our planet, the universe needs generations of stars to burn their nuclear fuel, fuse light elements into heavy elements, and then combine theseElements are recycled into the interstellar medium to form new, later generations of stars. These heavy elements in the universe are now very common and can be said to be ubiquitous.

looking for early gas clouds

As mentioned above, the universe was initially free of heavy elements, and those gases that originally formed stars far contained only some light elements formed after the Big Bang nuclear synthesis. This is actually one of the greatest predictions of the Big Bang: if we are enoughIf you are lucky, you should find some primitive gases that come directly from the primitive universe. These gases are atoms that have never existed in the stars before. They have never been burned in a nuclear furnace, nor have they been spit back into the universe to form the next generation.Stellar. It can be said to be a pure land existing in the universe.

Of course, it is very difficult to find such a gas cloud, because stars are everywhere in the universe, and the area "uncontaminated by heavy elements" should be extremely rare, and this situation will only increase over time.Less and less.

We currently have a technology that when we observe a very distant universe, we can not only see the light from the object we are looking at, but also the light from a distant object and the absorption line of any object between us.

This makes it possible, at least in principle, to find a cloud of gas that has not collapsed into any stars, as long as the space behind this gas cloud has an area that has collapsed into stars. When starlight passes through this gas cloud, We can judge the composition of this gas through the absorption line it generates.

In an accidental opportunity, scientists found two such gas clouds whose hydrogen and helium contents were exactly the same as predicted by the Big Bang nuclear synthesis, without any heavier elements. In the picture belowThe two clouds marked with green arrows are the most primitive gas clouds we have found, and they have no stars at all.

"Z" on the y-axis is an astronomer's abbreviation for "elements heavier than hydrogen and helium", or more formally, "metal abundance." Why is it so named? Because "X" is hydrogen,"Y" is helium, "Z" is a combination of all other elements but carbon, nitrogen, oxygen, etc. are not metals, but astronomers would not care about these details. So these two original gas clouds are usPrimitive cloud with the least metal content found.

Ancient Universe Relics in the Milky Way

But what about a single star? If we want to measure a single star, we can only be limited to our own galaxy and nearby galaxies such as globular clusters. But we found a very, very metal-deficient star, yesOne of the oldest known stars in the galaxy.

The above-mentioned star with no characteristics, SDSSJ102915 + 172927 Kafuxing, was discovered by the Sloan Digital Sky Survey in the Milky Way. Almost every star we have found before, from rich in metals to lack of metals, Both contain a certain amount of lithium and carbon, and this star is almost all hydrogen and helium.

This is one of the most primitive stars found to date. Its peculiarity is that it is thought that it cannot be formed by normal star formation; because star formation requires the gas cloud to cool first, and people generally think that metal is needed.To cool. If you want to form stars in the way that the earliest stars formed in the universe, you need some special way of cooling, such as through dust.

At present, science does not understand how stars like this are formed, but some stars must be the earliest in the universe. Our best estimate is that if the universe is now 13.73 billion years old, the first stars may be inIt has been formed since 13.68 billion years. Figuring out how it was formed can serve as a window to let us see the earliest era of the universe!

This star has a history of at least 13 billion years and has a mass of about 80% of the sun is a k-type star. The research team that discovered this star hopes to find five to fifty more in the next decade using the same technology.Similar stars! This is our primitive universe, and part of it is in our galaxy!


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