White dwarf atmospheres might comprise the powdered crusts of their useless planets

Astronomers have developed a new technique to look for exoplanets – by looking for their crushed bones in the atmosphere of white dwarfs. And it works.

Finding planets outside of the solar system known as exoplanets has one major limitation: we can only find exoplanets that currently exist. But our universe has existed for over 13 billion years, and many generations of planetary systems have come and gone in this vast expanse of cosmic time.

Unfortunately, when stars die, they usually take their planets with them. Especially the most massive stars that die as supernovae – these deaths usually completely annihilate every orbiting planet. But even if less massive stars like the sun die, it is generally bad news for their planets.

But as a new research paper has shown, this does not remove all clues about the planetary system from the galactic map. If planets (or residual nuclei of planets) survive, they can occasionally disperse from one another through gravity. This does not normally happen in stable systems, but anything is possible (gravitationally speaking) in a star’s agony.

Some of these scattered objects can go inward to the white dwarf, the remaining core of the parent star. This white dwarf is made up of almost entirely pure carbon and oxygen, surrounded by a dense but thin shell of hydrogen and helium. Of course, any object that gets too close will be torn to pieces by the white dwarf’s extreme gravity, with the debris rising to the surface to mix and match with hydrogen and helium.

There, all of the elements of the destroyed object such as lithium and calcium can release their own light and create a spectral fingerprint that astronomers may be able to recognize. Most white dwarfs are too hot, however, and this light outshines any contamination. But the most recent Gaia mission was able to map dozens of ancient, cool white dwarfs, and astronomers have discovered the unique signature of crushed planets in their atmosphere.

Astronomers found that the abundance of enriched elements coincides with what we know from our own solar system, indicating that planetary systems like ours have been in the universe for a very, very long time.

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