Direct images from Fomalhaut bo Dagon reveal that what we thought was an exoplanet is actually a scattering dust cloud, produced by a catastrophic collision between two large planetesimals in an extrasolar planetary system, according to a team of astronomers from the Steward Observatory. from the University of Arizona (USA) in the journal PNAS .
In case you don’t remember, Fomalhaut b was one of the first planets to be shown orbiting another star, having been photographed directly with the Hubble space telescope. And it is that before the databases were full of exoplanets, their number was quite small. The discovery at the time was so significant that it was one of the few exoplanets to be given an official name, Dagon, after a god from the Middle East.
Its disappearance in 2014, according to Hubble images and the failure to find similar objects around other stars, cast doubt on its existence . It was not that the orbit had changed unexpectedly, it was that … it had completely disappeared! The new study points as an explanation to the consequences of a catastrophic collision between two objects in the gray zone between asteroids and comets.
Thus, that bright spot visible in those early Hubble images were the aftermath of a collision between two asteroid-sized planetesimals that was briefly visible and not the first case of an exoplanet detected directly from light in the visible part of the spectrum, which was what we thought when it was announced in 2008.
“These collisions are extremely rare, so it’s a big problem that we can actually see one,” said astronomer András Gáspár of the University of Arizona. “We think we were in the right place at the right time to have witnessed such an unlikely event with the Hubble Space Telescope.”
The star Fomalhaut is located only 25 light years distant from Earth in the constellation Piscis Austrinus. It is twice the size of the Sun and 20 times brighter and is surrounded by a ring of dust and debris.
“The Fomalhaut system is the definitive test laboratory for all of our ideas about how exoplanets and star systems evolve,” says study co-author George Rieke.
“Our study, which analyzed all available archival data from Hubble on Fomalhaut b, including the most recent images taken by Hubble, revealed several features that together paint a picture that the planet-sized object could never have existed in the first place. instance, “the authors explain.
Thus, the authors believe that two super comets about 200 kilometers in diameter collided shortly before Hubble took its first images, producing a debris cloud illuminated by the bright light of the young star.
The James Webb space telescope, if it is finally launched successfully – its launch has been delayed again to 2021 – has Fomalhaut on its priority watch list. With much greater power than Hubble (which is already unable to pick up particles so small that they must remain), you should be able to verify whether these astronomers’ theory and models are correct.
Referencia: András Gáspár & George H. Rieke. New HST data and modeling reveal a massive planetesimal collision around Fomalhaut. PNAS, published online April 20, 2020; doi: 10.1073/pnas.1912506117
