May 3, 2012
Exoplanet-Consuming White Dwarf Stars Discovered
Astrophysicists at a UK university have found a quartet of white dwarf stars which they say are in the process of consuming exoplanets that were once similar in composition to Earth.
They used the Hubble Space Telescope to survey the chemical composition of those stars' atmospheres, and discovered that the dust contained the four elements which comprise 93% of our planet -- oxygen, magnesium, iron, and silicone.
Furthermore, they also found that the material contained extremely low proportions of carbon, similar not only to the Earth but also to the other rocky planets orbiting closest to our Sun. They also report that this is the first time that such small proportions of that element have been measured in the debris-polluted atmospheres of white dwarf stars, essentially providing "clear evidence" that there were once at least one rocky exoplanet orbiting the stars that has seen been destroyed.
"The observations must also pinpoint the last phase of the death of these worlds," the university said in their press release. "The atmosphere of a white dwarf is made up of hydrogen and/or helium, so any heavy elements that come into their atmosphere are dragged downwards to their core and out of sight within a matter of days by the dwarf´s high gravity. Given this, the astronomers must literally be observing the final phase of the death of these worlds as the material rains down on the stars at rates of up to 1 million kilograms every second.
"Not only is this clear evidence that these stars once had rocky exoplanetary bodies which have now been destroyed, the observations of one particular white dwarf, PG0843+516, may also tell the story of the destruction of these worlds," they added. "This star stood out from the rest owing to the relative overabundance of the elements iron, nickel and sulphur in the dust found in its atmosphere. Iron and nickel are found in the cores of terrestrial planets, as they sink to the centre owing to the pull of gravity during planetary formation, and so does sulphur thanks to its chemical affinity to iron“¦ Therefore, researchers believe they are observing White Dwarf PG0843+516 in the very act of swallowing up material from the core of a rocky planet that was large enough to undergo differentiation, similar to the process that separated the core and the mantle of the Earth."
Their findings will be published in the journal Monthly Notices of the Royal Astronomical Society.
“What we are seeing today in these white dwarfs several hundred light years away could well be a snapshot of the very distant future of the Earth. As stars like our Sun reach the end of their life, they expand to become red giants when the nuclear fuel in their cores is depleted," University of Warwick Physics Professor Boris GÃ¤nsicke, who headed up the research, said in a statement.
Their findings could also foretell the end of our own solar system, GÃ¤nsicke suggested.
"When this happens in our own solar system, billions of years from now, the Sun will engulf the inner planets Mercury and Venus. It´s unclear whether the Earth will also be swallowed up by the Sun in its red giant phase - but even if it survives, its surface will be roasted," he said. "During the transformation of the Sun into a white dwarf, it will lose a large amount of mass, and all the planets will move further out. This may destabilize the orbits and lead to collisions between planetary bodies as happened in the unstable early days of our solar systems."
"This may even shatter entire terrestrial planets, forming large amounts of asteroids, some of which will have chemical compositions similar to those of the planetary core. In our solar system, Jupiter will survive the late evolution of the Sun unscathed, and scatter asteroids, new or old, towards the white dwarf," the professor added.