Today's stars in our space are not the only possible type of stars. After many billions and even trillions of years, new strange objects may appear when our current stars age and begin to turn into completely different celestial bodies. The Smithsonian magazine talks about four types of stars that may arise in the future.
At the initial stage of its existence, the universe was filled with strange and mysterious objects. Shortly after the Big Bang, huge clouds of matter could form black holes directly, without coalescing into stars as we see today. Pseudo galaxies illuminated seas of neutral hydrogen, making the universe transparent, releasing photons where there was only darkness before. And short-lived stars from hydrogen and helium alone appeared and disappeared like sparks in the night.
More than 13 billion years later, the matter of the Universe has formed numerous types of stars of different sizes, degrees of brightness and lifespan. But the stars in our cosmos today are not the only type of stars that can exist. In the distant future, after many billions and even trillions of years, strange objects may appear when our current stars age and begin to turn into completely different celestial bodies. Some of these objects may even be the harbingers of the thermal death of the Universe, after which the unknown will come.
We present four types of stars that can exist in the future - of course, if the Universe lives to the day when it can give them life.
Blue dwarf
Red dwarf stars are considered the most common type of star in the universe. They are small in size, sometimes not exceeding the volume of gas giant planets. They also have low mass and low (for a star) temperature. The smallest dwarfs are only 80 times the mass of Jupiter, while the Sun, which is a type G (yellow dwarf), is about a thousand times the mass of Jupiter.
But these rather small and cool stars have something special about them. Astronomers believe that red dwarfs can last for trillions of years by slowly burning hydrogen and turning it into helium. This means that some red dwarfs live almost as long as the universe. The star, which has a mass of 10% of the mass of the Sun, can live for almost six trillion years, and the smallest stars like TRAPPIST-1 can survive twice as long, as reported in a paper published in 2005. The universe is only about 13.8 billion years old, so red dwarfs have lived less than one percent of their lives.
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In contrast, the Sun has only five billion years left, after which it will run out of hydrogen fuel, and it will begin to convert helium into carbon. These changes will cause a new phase in the evolution of the Sun, which will first increase, becoming a red giant, and then cool down and shrink to the size of a white dwarf. This is the electron-rich corpse of a star that we see throughout the galaxy.
Trillions of years from now, red dwarfs will also begin to destroy their last reserves of hydrogen. Cool little stars will be very hot for a while, emitting blue light. Instead of expanding like the Sun, the red dwarf collapses at a later stage in its existence, that is, collapses inward. Gradually, when the blue dwarf phase ends, only the stellar shell will remain in the form of a small white dwarf.
Black dwarf
But even white dwarfs cannot last forever. When a white dwarf runs out of carbon, oxygen and free electrons, it slowly burns out, turning into a black dwarf. These theoretically predicted objects are composed of degenerate matter. They emit little or no light. At this stage, the star dies for real.
Such is the fate of stars like the Sun, although billions of years will pass before the star begins the process of becoming a black dwarf. By the end of the life of the Sun as a main sequence star (its duration is about 10 billion years, and now the Sun is 4.8 billion years old), it will increase, possibly to the orbit of Venus, and become a red giant. It will retain this size for a billion years, after which it will become a white dwarf. NASA estimates the Sun will be in a white dwarf state for approximately 10 billion years. But there are other estimates indicating that stars may be in this phase for a quadrillion years. Anyway, this is more than the current age of the universe, and therefore none of these exotic objects exist yet.
At the end of the black dwarf's life, proton radioactive decay occurs, and gradually it evaporates, turning into an exotic form of hydrogen. Discovered in 2012, the two white dwarfs are over 11 billion years old, which means they are close to becoming black dwarfs. However, this process can be slowed down by a variety of factors, and therefore it is better for us to observe them for several billion years to understand how they evolve.
Frozen star
Someday the universe will start running out of usable matter, because most of the lighter elements will turn into heavier ones. Then frozen stars will appear, which only heat up to the freezing point of water. They will exist at a temperature of 273 degrees Kelvin (about zero degrees Celsius), filled with various heavy elements due to the lack of hydrogen and helium in space.
According to scientists Fred Adams and Gregory Laughlin, predicting the emergence of such objects, frozen stars will not form in many trillions of years. Some of these stars will come from collisions of objects called brown dwarfs, which are larger than planets but too small to ignite and become stars. Frozen stars, despite their low temperatures, theoretically have enough mass for limited nuclear fusion, but not enough mass to emit their own light in large quantities. Their atmosphere will be polluted by icy clouds with a weak core emitting little energy. If scientists' predictions are correct, they will look more like brown dwarfs than real stars.
In this distant future, the largest stars will be only 30 times the mass of the Sun in mass, while the stars known today are more than 300 times the mass of our star. According to this theory, at that time the stars will, on average, be much smaller, about 40 times the mass of Jupiter. Under the surface, they will have great difficulty converting hydrogen into helium. According to Adams and Laughlin, in this cold and distant future, when the universe will completely stop creating stars, only white dwarfs, brown dwarfs, neutron stars and black holes will remain of large objects.
Iron star
If the Universe is constantly expanding, as it is currently happening, and does not collapse inward (scientists are not sure how it will act), then over time it faces a kind of "heat death" when the atoms themselves begin to scatter. By the end of this period, very unusual objects can form. The most unusual object of this kind would be an iron star.
Stars in outer space are constantly combining lighter elements into heavier ones, and over time, an incredible amount of iron isotopes will appear. It is a stable and durable element. Exotic quantum tunneling will burst through iron at a subatomic level. Over time, this process will create iron stars - giant stellar mass objects made up almost entirely of iron. But such an object can arise only if there is no decay of protons, and this is a big question that humanity has no answer to, because it has lived too little.
Nobody knows how long the Universe will last, and the human race is unlikely to live to see the end of the cosmos. But if we could live longer and observe the sky for several trillions of years, we would surely witness amazing changes.
John Wenz
