If, on a clear, moonless night, you go further out of town and look at the sky, you can see about three thousand flickering dots. From childhood we are taught that if it does not flicker, then it is a planet. If it is moving, then it is a satellite or a meteorite. Behind this tiny scattering are giant stars many billions of kilometers away from us, some of which are tens and hundreds of times larger than our Sun. Our native G2V-class gas ball also represents the universal community of luminaries. Scientists estimate its age at 4.5 billion years. But the solar system is considered relatively young. Where are the most ancient stars hiding?
First, let's find out how stars are born. It is known that the empty space of space is actually not empty - for every two cubic centimeters, there is on average one molecule. First, they form a cold rarefied cloud of interstellar gas. Gradually, under the influence of gravitational instability, it contracts and takes the shape of a ball. In the process of compression, the energy of the gravitational field turns into heat, and the temperature of the cloud increases. When it reaches the level of 15-20 million degrees, the reaction of thermonuclear fusion starts and the compression stops. This is how a star is born. Thermonuclear reactions in the core of a star have been going on for millions and even billions of years, providing the immediate vicinity with an almost inexhaustible flow of energy.
During this, inside the star, hydrogen nuclei merge to form helium. Then helium is fused to carbon, carbon to oxygen, oxygen to silicon, and silicon to iron. The star becomes more massive and creates heavy elements. This continues until it begins to shrink again. Small luminaries like red dwarfs are not massive enough to synthesize anything other than helium, but they can still burn for trillions of years. The fate of a star is determined by its mass, so by the end of its life it turns into a white dwarf, neutron star (pulsar) or black hole, depending on its "weight category".
The very first stars appeared almost immediately after the Big Bang, from which, according to scientists, everything began. But since the universe is only 13.7 billion years old, and some stars can exist for trillions of years, there should be plenty of them at any stage of adulthood. The trick is not only finding the oldest star, but also confirming that its age is the closest to the age of the universe. Astronomy is a complex science that requires perseverance and patience. There are more than 100 billion stars in the Milky Way galaxy alone, and more than 100 billion galaxies in the Universe. Multiply these two numbers - and even hundreds of years will not be enough for us to go through all these lists. Unsurprisingly, estimates of the age of the most ancient gas balls are constantly changing.
One of the oldest stars, HD 140283, was discovered over a hundred years ago. If desired, it can be seen with binoculars or an amateur telescope. Unofficially, it is called "Methuselah", in honor of the oldest man, who according to the Bible lived 969 years. This luminary, slightly more massive than the Sun, is located in the constellation Libra in 190 light years from us and belongs to the second generation of stars with a low metal content. Methuselah appeared several hundred million years after the Big Bang, when the universe was still very, very raw. At first, they thought that he was 16 billion years old, but this is impossible, because then the egg will be older than the chicken that laid it. The current estimate for 2013 is that this star is 13.3 billion years old.
In the same constellation Libra, but already at a distance of 7,500 light-years from us, there is a red giant HE 1523-0901. Like Methuselah, it is a second generation low metallicity star. Discovered in 2007, it quickly earned the title of the oldest in our galaxy - just half a billion years younger than the universe. The mass of this red centenarian is 0.8 solar.
In 2014, a group of Australian National University astronomers investigating the starry sky in the southern hemisphere said they had found the oldest known star. It is 6,000 light years from us and, according to preliminary estimates, the age of the universe itself is 13.7 billion years. Of course, it will take years to refine the analysis, but the fact itself.
It is possible that one day we will be able to say with certainty that we have found the oldest star, which appeared immediately after the Big Bang, as soon as it became possible, and continues to this day. So far, we just have to sort out these billions of billions of points that are hiding thousands and millions of light years away from us, using our best telescopes. Some of these stars have died long ago, and only their light continues to tell us about their former existence. Others will live long after the Earth ceases to exist. Is this not a reason to think for a moment that we are just one molecule in a drop of water in the waves of the ocean called the Universe?
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ILYA KHEL