A team of astronomers has discovered a giant object — an enormous, Jupiter-like exoplanet or a low-mass brown dwarf — orbiting an ageing red giant called L2 Puppis, and they have also precisely measured the mass and the age of the star.
Composite view of L2 Puppis in visible light. Image credit: Kervella et al / CNRS / University of Chile / Observatory of Paris / LESIA / ESO / ALMA.
“Five billion years from now, the Sun will have grown into a red giant star, more than a hundred times larger than its current size. It will also experience an intense mass loss through a very strong stellar wind,” said team member Prof. Leen Decin, from the KU Leuven Institute of Astronomy in Belgium.
“The end product of its evolution, 7 billion years from now, will be a tiny white dwarf star. This will be about the size of the Earth, but much heavier: one tea spoon of white dwarf material weighs about 5 tons.”
This metamorphosis will have a dramatic impact on the planets of our Solar System. Mercury and Venus, for instance, will be engulfed in the giant star and destroyed.
“But the fate of the Earth is still uncertain,” she added. “We already know that our Sun will be bigger and brighter, so that it will probably destroy any form of life on our planet.”
“But will the Earth’s rocky core survive the red giant phase and continue orbiting the white dwarf?”
To answer this question, Prof. Decin and her colleagues from Chile, France, Belgium and UK observed the evolved star L2 Puppis using a radio telescope known as the Atacama Large Millimeter/submillimeter Array (ALMA).
Also known as HD 56096, HIP 34922, HR 2748 and 2MASS J07133229-4438233, this star lies in the constellation Puppis at a distance of 209 light-years.
It’s one of the closest red giants to Earth known to be entering its final stages of life.
With a mass of 0.66 solar masses, L2 Puppis shines at a luminosity that is somewhere between 1,500 and 2,400 times that of our Sun.
“We discovered that L2 Puppis is about 10 billion years old,” said team member Dr. Ward Homan, also from the KU Leuven Institute of Astronomy.
“About 5 to 6 billion years ago, the star was an almost perfect twin of our Sun as it is today, with the same mass.”
“One third of this mass was lost during the evolution of the star. The same will happen with our Sun in the very distant future.”
This is a schematic view of the candidate planet’s orbit in L2 Puppis disk. Image credit: Kervella et al / CNRS / University of Chile / Observatory of Paris / LESIA.
About 186 million miles (300 million km, or 2 AU) from L2 Puppis the team detected a massive planet-like object orbiting the star.
This object, named L2 Puppis B, has a mass of 12 Jupiter masses.
The astronomers aren’t sure if L2 Puppis B is a Jupiter-like planet or a brown dwarf, a little understood class of celestial object that is too small to sustain hydrogen fusion reactions, like those that power our Sun.
“L2 Puppis B is most likely a planet or low-mass brown dwarf with an orbital period of about 5 years,” they said.
“Its continuum brightness and molecular emission suggest that it may be surrounded by an extended molecular atmosphere or an accretion disk.”
According to the team, L2 Puppis B offers a unique preview of the Earth approximately 5 billion years from now.
“A deeper understanding of the interactions between L2 Puppis and its planet will yield valuable information on the final evolution of the Sun and its impact on the planets in our Solar System,” the scientists said.
The research is published in the journal Astronomy & Astrophysics (arXiv.org preprint).
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P. Kervella et al. 2016. ALMA observations of the nearby AGB star L2 Puppis. I. Mass of the central star and detection of a candidate planet. A&A 596, A92; doi: 10.1051/0004-6361/201629877
