Stars are born, stars age, and stars die. But they don't all die quietly. Astronomers have recently discovered evidence of four white dwarfs wreaking havoc on their surrounding planets, which could be Earth-like.
Their findings, say the researchers, could give us a glimpse into our solar system's distant future, and a sneak preview of what might one day be Earth's violent undoing.
When a low-mass star like the Sun ages, it passes through what is known as the red giant phase of its life cycle. In doing so, the star swells; its radius expands several hundred times over, and the nearest of its orbiting planets are engulfed.
Astrophysicists are confident that, in our own solar system, Mercury and Venus will likely be swallowed up by the Sun's expansion when it becomes a red giant in 5 billion years, but they're less certain about the fate of Earth. However, new findings suggest that even if Earth does manage to avoid being consumed by an expanding Sun, it could still meet a violent end — first in the form of planetary collision, and later at the hands of a white dwarf.
In a forthcoming issue of Monthly Notices of the Royal Astronomical Society, astrophysicist Boris Gänsicke and his colleagues hypothesize that any planets that managed to escape the reach of an expanding star would have their orbits destabilized, even as their dying parent star took the form of a dense white dwarf. Destabilized orbits, reason the researchers, could lead to violent planetary collisions. In the aftermath of these collisions, the planets' fragmented remains might eventually find themselves orbiting close enough to the center of the solar system to be sucked in by the white dwarf and devoured.
To test their hypothesis, the researchers used the Hubble Space Telescope to search the atmospheres of 80 white dwarf stars for elemental traces of planets — planetary crumbs, if you will, on the faces of these hungry white dwarfs. Since the atmosphere of a white dwarf usually comprises only light elements like hydrogen and helium (heavier elements being drawn inward by the star's incredibly dense core), traces of heavy elements could be indicative of a recent planetary meal. National Geographic's Rachel Kaufman describes the researchers' findings:
The team found four stars whose atmospheres contain oxygen, magnesium, iron, silicon, and a small bit of carbon-just the elements expected if the stars are absorbing dust from former planets.
"The abundances we find are almost exactly the same as those of the entire Earth," Gänsicke said. "If you could shred the Earth into dust and put it into the white dwarf, it would match the chemical composition."