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Scientists Witness the Death of a Solar System, and the Birth of Necroplanetology



Five years ago, astronomers caught a lone white dwarf star, 570 light-years away from Earth, devouring its young like the Greek titan Cronus. They noticed that WD 1145+017 was dimming at an irregular rate, and after closer inspection, realized that the star was devouring the planets in its solar system through a process called tidal disruption.





The discovery marks the beginning of a brand new field of science: Necroplanetology. Slap the Latinized Greek root nekros, meaning "dead," "corpse" and "dead tissue," in front of planetology, the study of planets.
An international team of researchers from Wesleyan University in Connecticut, the University of Colorado, Boulder, and Warwick University in the U.K. first published the findings on the pre-print website arXiv in 2015. It has now been accepted to the Astrophysical Journal for review. They say the discovery could help us understand how planets in different systems get gobbled up by their parent star.

Right before either going supernova or turning into a black dwarf, dying stars turn into white dwarves. Eventually so will our sun, but not for about six billion years. The atmospheres of these stars usually contain lighter elements such as helium and hydrogen.
Several important details clued the researchers in on the discovery. First, the team realized that the dimming occurred repeatedly, ever 4.5 to five hours. Second, they discovered that the star's atmosphere was littered with elements typically found in the cores of rocky exoplanets—heavy elements like iron, oxygen and magnesium.

To figure out how these planets met their doom, the researchers created a series of computer simulations that mapped how 36 different types of planets would have endured these conditions. For each of the 36 planetary bodies they created, they set the orbital period to about 4.5 hours and let the simulation run 100 times.
The results showed that rocky bodies with a tiny core and low-density mantle were the most likely to produce the observations they saw. These high-density planets, similar to rocky asteroids like Vesta, are tough enough to withstand the bulk of the disruption, but weak enough to disintegrate within a short period of time.
WD 1145+017 isn't the only star with a massive appetite. Astronomers have since observed 21 stars who have been caught dimming in a similar way. Despite its name, the field of necroplanetology is thriving.

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