Since ancient times, stars have been the representatives of eternity and perseverance in people's minds. In our limited life, it is difficult for us to see that the stars in the night sky will change greatly! But now we know that stars also have ages, and they will live and die. In the galaxies of the universe, some stars are newborn babies, while others are ancient stars that have been formed since the birth of the universe. They are equivalent to the age of the universe. So what is the oldest star in the universe that we know at present? Will we have a chance to find the first stars formed after the birth of the universe in the future?
First, we found the oldest cluster according to Herodotus.
Looking up at the night sky, there are tens of thousands of stars visible to the naked eye scattered in the dark night. They look different in shape and color, some are very dazzling, while others are dull. Some stars are blue, some are white, and some are yellow, orange or even red. Different colors represent stars of different sizes and masses. Some of these stars are constantly flashing and their luminosity is constantly changing, while others are stable light sources. All this shows that stars, like us, are rich in diversity.
However, what we see is not necessarily true, and vision sometimes makes us illusion because of the interference of some external factors! For example, the crazy twinkling stars in the night sky (such as Sirius) are related to the turbulence of the earth's atmosphere, but have nothing to do with the inherent properties of the stars themselves! The next time we see a star blink, it's not actually that the luminosity of the star itself is changing, but that the atmosphere disturbs the starlight when the star passes through the atmosphere.
Similarly, some stars themselves are brighter or darker than others. But because the stars farther away from us look darker, the stars closer to us look brighter. So the apparent brightness of a star (which looks like how bright) cannot represent the intrinsic brightness of a star (which actually has how bright). But the color of the stars is another matter.
A blue star and a red star, their colors will not change because of distance and atmosphere. Stars are protons, neutrons and electrons. They are normal substances and are heated to extremely high temperatures by internal nuclear fusion. Because of the temperature difference, there will be color difference. When we see Betelgeuse on the right and Betelgeuse on the left, we see that the color difference they show is real.
If we can know how far a star is from us (by parallax method, variable star and 1A supernova), and then calculate its intrinsic brightness according to its apparent brightness, we will find that there is a universal and important relationship between the color of a star and its magnitude, or its intrinsic brightness.
This relationship is called hertzsprung-Russell diagram, which enables us to determine which stage of the life cycle of a star is at present. For a sun-like star (a star with a mass of 40% to 400% of the sun), it will start as a main sequence star until the core hydrogen fuel is exhausted and nuclear fusion stops. Then the star will brighten, expand and cool slightly, and in the process, the star will become a brighter subgiant (subgiant). Eventually, the star will begin to fuse helium in the core and become a real red giant (ⅲ giant), and the color of the star may oscillate at different points between red and yellow. When the helium in the core is exhausted, the outer layer will be blown into interstellar space, and the core will shrink into a hotter but significantly darker white dwarf.
When we observe the cluster (cluster) formed at the same time, because the brightest and bluest main sequence stars consume the fastest fuel, we can observe the main sequence stars with different masses in the cluster. Disappear? , or the beginning of a sub-giant, can determine the age of a cluster.
For an open cluster, its age ranges from about/kloc-0.0 million years to some very old examples, such as NGC 188, which is about 5 billion years old, even older than our sun! But in many places, we can see clusters older than NGC 188.
Globular cluster is one of the oldest objects in the universe, such as messier 56 in the above picture. Their age is usually over 65.438+02 billion years, and some globular clusters are over 65.438+03 billion years, which is close to the age of the universe itself. They are indeed relics of different times in the universe.
According to the abundance of heavy elements in stars, we found the oldest known star.
Studying globular clusters is very useful for reviewing and understanding the earliest stage of the universe, because older celestial bodies were formed closer to the Big Bang! As time goes on, generations of stars survive and die, and heavier stars recycle the burning fuel into the interstellar medium to form the next generation of stars, which will contain more heavy elements.
Our sun is a star formed 4.5 billion years ago. It contains about 70% hydrogen, 28% helium and 1- 2% helium. Heavy elements? (of any element heavier than helium). There are few heavy elements in stars, because heavy elements need stars to fuse! So the earlier a star forms, the less heavy elements there are, which means that if we measure the element content of a star, we can get its age information.
The stars in messier 56 are only 1% of the heavy elements in the sun, which is called metal abundance in astronomy. As far as we know, there are two stars in the Milky Way galaxy older than it: one is HE 1523? 090 1, which is only 0. 1% of the solar metal content, while the other star HD 140283, which is considered as the oldest star at present, is only 0.4% of the solar metal content.
Which is the oldest star in the universe?
The problem of determining the age of a star is that there is only one star, and it is impossible for us to know the whole history of that part of the universe when this star was formed. Why? Because the universe is so chaotic when its structure is formed, we can't trace the origin of an ancient star.
Do you remember what the universe was like at first? If you can't remember clearly, you should have seen the following picture, which represents the perfect and smooth temperature fluctuation in the early universe.
The blue area, or cold spot, is only 0.003% lower than the average temperature, which represents the area with higher density in the universe or the area with slightly higher material density than the average level. Red areas, or hot spots, are only 0.003% higher than the average temperature, representing areas with lower density or areas with slightly lower material density in the universe.
As time goes on, high-density areas will attract more and more substances at first. The densest regions will collapse to form stars, then clusters, then small protogalaxies, and finally large galaxies and clusters.
Gravity works at the smallest scale first, because it is limited by the speed of light. However, for a long time, even the smallest ultra-dense areas, even those relatively independent areas, even those areas that formed the structure at the earliest in the whole universe will eventually merge with other ultra-dense areas.
Eventually, we will get huge spiral galaxies and elliptical galaxies, as well as some dwarf galaxies and small galaxies, but the initially formed stars will not exist independently without being affected. In other words, a single star in the universe will be mixed with other structures under the action of gravity.
According to our best estimate, the earliest stars in the universe may have formed between 50 million years and 1 100 million years after the Big Bang, or the universe is only 0.3 to 0.7% of its present age! Even if james with launches the Webb Space Telescope in the future, we can't see places as far away as in the past. So no matter which of the 10 24 stars in the universe is the oldest star, it is almost certain that we can't find and identify the oldest star.
But we can be sure that some stars in the Milky Way may have originated in the oldest age of the universe, and of course they can be traced back to less than 300 million years ago! We observe every star in the galaxy. Newborn stars are completely mixed with ancient stars in the history of the universe, and we can't tell them apart. This is our current understanding and knowledge of the oldest star in the universe.