Nearby ageing star provides glimpse into the future of our own solar system
An international team of astronomers have observed the nearby evolved star L2 Puppis using the ALMA radio telescope in Chile. Five billion years ago, L2 Pup was an almost perfect twin of our present-day Sun, so these observations allow us to see the distant future of our own solar system.
Five billion years from now, the Sun will grow into a red giant star, more than a hundred times larger than its current size. It will also experience intense mass loss through a very strong stellar wind. The end product of its evolution, 7 billion years from now, will be a tiny white dwarf star, about the size of the Earth, hot and extremely dense - one tea spoon of white dwarf material weighs around 5 tons!
This metamorphosis will have a dramatic impact on the planets of our solar system, including the Earth. While Mercury and Venus will be engulfed in the giant star and destroyed, the fate of the Earth is still uncertain. As the Sun slowly brightens, it is well established that our planet will become inhabitable in a few billion years. But the Earth's rocky core may survive the giant phase and remain in orbit around the solar white dwarf.
To address these questions about our future solar system, an international team of astronomers, including Dr Anita Richards and Dr Iain McDonald from the Jodrell Bank Centre for Astrophysics, observed the nearby evolved star L2 Puppis using the ALMA radio telescope. L2 Pup is a nearby star (208 light-years away), which is surrounded by a disk made of gas and dust which was created by its mass-loss.
Thanks to precise observations of the orbital motion of the gas in this disk using ALMA, the astronomers have determined that it closely follows Kepler's law of rotation. From this motion, the team can very accurately determine the present mass of the star, finding that it is two-thirds of the mass of our Sun. Knowing the mass of L2 Pup, stellar evolution models indicate that the age of L2 Pup is around 10 billion years. Five billion years ago, L2 Pup was an almost perfect twin of the present Sun, with the same mass. The missing third of a solar mass has been lost by L2 Pup during its evolution. So L2 Pup gives us a prime view point on the very distant future of our Sun.
Near L2 Pup itself, the team discovered an object one hundred times fainter, known as L2 Pup B. At a separation of twice the Earth-Sun distance from its parent star (300 million kilometres), its low estimated mass implies that it is very likely a planet (or a low mass "brown dwarf"). The presence of this planet orbiting in the disk of L2 Pup gives a preview of the fate of our solar system planets, 5 billion years from now. The brightness of L2 Pup B and its coincidence with long plumes of dust indicate that it may be accreting material expelled from the central star.
Anita Richards of JBCA commented: "We're very much looking forward to finding out more about this new object. We will be able to continue watching with ALMA to see how it orbits the star L2 Pup. This will give us a more precise idea of its mass and origin."
A deeper understanding of the interactions between L2 Pup and its planet will yield precious information on the final evolution of the Sun, and how it will impact the solar system planets. Whether the Earth will eventually survive the Sun or be destroyed is still uncertain, and L2 Pup may be the key to answering this question.
Research article : ArXiV preprint : "ALMA observations of the nearby AGB star L2 Puppis - I. Mass of the central star and detection of a candidate planet", P. Kervella, W. Homan, A. M. S. Richards, L. Decin, I. McDonald, M. Montarges, and K. Ohnaka, Astronomy & Astrophysics.
ALMA interferometer: http://www.almaobservatory.org
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