Four white dwarf stars caught in the act of consuming 'earth-like' exoplanetsMay 04, 2012
Using the Hubble Space Telescope for the biggest survey to date of the chemical composition of the atmospheres of white dwarf stars, the researchers found that the most frequently occurring elements in the dust around these four white dwarfs were oxygen, magnesium, iron and silicon - the four elements that make up roughly 93 per cent of the Earth.
However an even more significant observation was that this material also contained an extremely low proportion of carbon, which matched very closely that of the Earth and the other rocky planets orbiting closest to our own Sun.
This is the first time that such low proportions of carbon have been measured in the atmospheres of white dwarf stars polluted by debris. Not only is this clear evidence that these stars once had at least one rocky exoplanet which they have now destroyed, the observations must also pinpoint the last phase of the death of these worlds.
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.
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.
The study entitled "The chemical diversity of exo-terrestrial planetary debris around white dwarfs" by B. T. Gänsicke, D. Koester, J. Farihi, J. Girven, S.G.Parsons, and E. Breedt is accepted for publication in the Monthly Notices of the Royal Astronomical Society.
Professor Boris Gänsicke of the Department of Physics at the University of Warwick, who led the study, said the destructive process which caused the discs of dust around these distant white dwarfs is likely to one day play out in our own solar system.
"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.
"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.
"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 destabilise the orbits and lead to collisions between planetary bodies as happened in the unstable early days of our solar system. 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.
"It is entirely feasible that in PG0843+516 we see the accretion of such fragments made from the core material of what was once a terrestrial exoplanet."
The University of Warwick led team surveyed more than 80 white dwarfs within a few hundred light years, using the Cosmic Origin Spectrograph on board the Hubble Space Telescope.
University of Warwick
Related White Dwarf Current Events and White Dwarf News Articles
Time-lapse snapshots of a nova's fading light
Scientists in a collaboration led by Dai Takei of the RIKEN SPring-8 Center in Japan have, for the first time, examined a detailed 'time lapse' X-ray image of the expansion of a classical nova explosion using the GK Persei nova -- a binary star system which underwent a nova explosion in 1901.
Queen's astronomers discover fastest ever unbound star in our galaxy
A fast-moving unbound star discovered by astronomers at Queen's University Belfast has broken the galactic speed record.
First time-lapse images of exploding fireball from a 'nova' star
Astronomers at the University of Sydney are part of a team that has taken images of the thermonuclear fireball from a 'nova star' for the first time tracking the explosion as it expands.
Georgia State astronomers image the exploding fireball stage of a nova
Astronomers at Georgia State University's Center for High Angular Resolution Astronomy (CHARA) have observed the expanding thermonuclear fireball from a nova that erupted last year in the constellation Delphinus with unprecedented clarity.
Astronomers see right into heart of exploding star
An international team of astronomers has been able to see into the heart of an exploding star, by combining data from telescopes that are hundreds or even thousands of kilometres apart.
White dwarfs crashing into neutron stars explain loneliest supernovae
A research team led by astronomers and astrophysicists at the University of Warwick have found that some of the Universe's loneliest supernovae are likely created by the collisions of white dwarf stars into neutron stars.
NASA's Hubble Finds Supernova Star System Linked to Potential "Zombie Star"
Using NASA's Hubble Space Telescope, a team of astronomers has spotted a star system that could have left behind a "zombie star" after an unusually weak supernova explosion.
Fermi satellite detects gamma-rays from exploding novae
The Universe is home to a variety of exotic objects and beautiful phenomena, some of which can generate almost inconceivable amounts of energy. ASU Regents' Professor Sumner Starrfield is part of a team that used the Large Area Telescope (LAT) onboard NASA's Fermi Gamma-ray Space Telescope satellite to discover very high energy gamma rays (the most energetic form of light) being emitted by an exploding star.
NASA's Fermi Space Telescope Reveals New Source of Gamma Rays
Observations by NASA's Fermi Gamma-ray Space Telescope of several stellar eruptions, called novae, firmly establish these relatively common outbursts almost always produce gamma rays, the most energetic form of light.
Research finds numerous unknown jets from young stars and planetary nebulae
For many years astronomers have known that young 'protostars' drive supersonic jets of gas from their north and south poles. However, this is the first time that so many of them have been detected at once.
More White Dwarf Current Events and White Dwarf News Articles