(ORDO NEWS) — By studying cooling stars, astronomers have uncovered evidence of past cosmic catastrophes. The planets once fell on these luminaries, and the remnants of the dead worlds still hover over the very surface of their sun.
The details of the space tragedy are presented in the preprint of the scientific article published on the arXiv.org website.
Stars with a mass of ten or more suns end their lives in an all-consuming supernova explosion. This catastrophe destroys any planets without a trace, if they were at the star. Less massive stars die less dramatically, but they almost always take their children with them.
Let us explain how this happens. In the last stages of life, the star gradually sheds its outer layers, losing up to 80% of its mass. These “fiery spits” are capable of dusting the planets closest to the star.
But even more distant worlds may not be good. After shedding the shell, a very dense incandescent core remains from the star – a white dwarf. Its gravity changes the orbits of the planets and creates the danger of their falling onto their own former sun (Vesti.Ru told why this happens).
Unsurprisingly, astronomers observe debris from worlds in orbits around white dwarfs and are very surprised to find a surviving planet there recently.
Now, for the first time, scientists have discovered the remains of dead worlds not in orbit around a dead star, but practically on its surface (more precisely, in a thin atmosphere).
Let us explain. A white dwarf is the bare core of a star, in which thermonuclear reactions once took place. It also consists of the products of these reactions (usually carbon and oxygen). It also has a dense, but thin atmosphere of hydrogen and helium – the remnants of the former outer layers of the luminary.
The authors of the new study found traces of lithium in the spectrum of four white dwarfs. Previously, potassium, sodium and calcium were found on the same celestial bodies. And the relative content of all these metals is very typical for the crust of rocky planets like Earth or Mars.
Experts believe that these are the remnants of the crust of exoplanets that once fell on the aforementioned stars. Of course, these are not rock fragments, but hot gas. After all, the surface of white dwarfs is too hot: its temperature reaches several thousand degrees. But chemical elements from the destroyed planets continue to exist in the atmosphere of the stars that engulfed them, as evidence of a cosmic crime.
By the way, the four white dwarfs in question are very ancient. Thermonuclear reactions in them stopped 5-10 billion years ago. For comparison, the Sun is about 5 billion years old, and the Universe is about 14 billion years old. During this time, the “stellar corpses” cooled to temperatures below 5000 ° C. This allowed astronomers to detect traces of metals in their spectrum (otherwise they would be indistinguishable).
By the way, this study has one more very important conclusion. If these chemical elements do originate from the crust of rocky planets, this means that potentially habitable rocky worlds arose in the universe long before the birth of the Earth.
Another recent finding of scientists hints at this: they directly discovered an Earth-like planet near a star that is much older than the Sun.
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