These exoplanet graveyards have become a hot topic of research among astronomers because scientists can use them to infer properties about the bodies that once circled them. Scientists have estimated that about 25% of all white dwarfs contain the remains of dead exoplanets or are so-called polluted white dwarfs. So, when the light the stars give off shows the presence of other heavier elements, researchers assume that those must come from exoplanet accretion. Normally, the atmosphere of a white dwarf contains only hydrogen and helium, because any heavier elements sink into the star's super-dense core. This is known as tidal disruption and once the planet is ripped apart, the white dwarf pulls the planetary remains inward in a process known as accretion. Some exoplanets can withstand this cosmic barrage, but most get knocked out of their orbit and subsequently ripped apart by the white dwarf's strong gravitational field. During this process, these dying stars release a cloud of superheated gas that engulfs the planets that orbit them. White dwarfs form when main sequence stars, like the sun, run out of fuel to burn and begin to swell up into red giants before collapsing under their own weight into super-condensed and cooled stellar cores. The rocks were so different from those known to science that the researchers even had to create brand new names to classify them. Within the rest of the dead stars, the researchers found the remains of exoplanets made of alien rocks never seen on our planet or the rest of the solar system. The researchers found that only one of the white dwarfs contained the remains of exoplanets with a similar geological make-up to Earth.
Researchers worked out the ratio of different elements in the white dwarf atmospheres by analyzing the light given off by the stars then, they calculated the most likely makeup of the minerals that would have formed the obliterated alien worlds. And so, the atmospheres of these white dwarfs contain the guts from the alien worlds they destroyed. As these stars were dying and transitioning into white dwarfs, they ripped apart their orbiting exoplanets. In the new study, researchers looked at 23 white dwarfs - the small, dense remains of dead low- and medium-mass stars - within 650 light-years of the sun.
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