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Astronomers using the Multi Unit Spectroscopic Explorer (MUSE) spectrograph on ESO's very large telescope directly photographed two still-emerging gas giants – one of which was previously unknown to scientists – which gravitationally dig a wide hole in a protoplanetary disk surrounding the young star PDS 70.
The PDS 70 is only the second multi-planet system to be directly imaged. Through a combination of adaptive optics and data processing, Haffert et al were able to cancel the light from the central star (marked with a white star) to reveal two protoplanets in orbit. PDS 70b (lower left) weighs 4 to 17 times more than Jupiter while PDS 70c (top right) weighs 1 to 10 times more than Jupiter. Image credit: ESO / S. Haffert, Leiden Observatory.
The PDS 70 is a K7 type pre-sequence star located at a distance of about 370 light-years.
Also known as V1032 Cen, the star is only 5.4 million years old, slightly smaller and less massive than our Sun.
It hosts two infantile planets, named PDS 70b and c, and a protoplanetary disk in which a large region of 20 to 40 AU (astronomical units) is cleared of dust.
The PDS 70b is located in the disk space at a distance of about 21 AU from its star, similar to the orbit of Uranus in our solar system. The planet has a mass between 4 and 17 times that of Jupiter.
PDS 70c, the newly discovered planet, is located near the outer edge of the star's 34.5 AU disk space, at a distance similar to that of Neptune to our Sun.
It is less massive than the PDS 70b and weighs between 1 and 10 times more than Jupiter.
The two planetary orbits have a resonance close to 2: 1, which means that the inner planet surrounds the star twice in the time it takes for the outer planet to go around once.
The illustration of this artist shows two gas giant exoplanets in orbit around the young star PDS 70. Credit: J. Olmsted, STScI.
"This is the first unambiguous detection of a two-planet system digging a disc slot," said Dr. Julien Girard, astronomer at the Space Telescope Science Institute.
Dr. Girard and his colleagues photographed PDS 70b and c from the ground using the MUSE spectrograph of ESO's very large telescope.
"This new mode of observation has been developed to study galaxies and star clusters at higher spatial resolution," said Dr. Sebastiaan Haffert, astronomer at the Leiden Observatory.
"But this new mode also makes it suitable for exoplanet imaging, which was not the original scientific engine of the MUSE instrument."
"We were very surprised when we found the second planet."
The results were published online this week in the journal Nature Astronomy.
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S.Y. Haffert et al. Two protoplanets accross around the young star PDS 70. Nature Astronomy, published online June 3, 2019; doi: 10.1038 / s41550-019-0780-5
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