The ALMA astronomical radio telescope has provided the first detailed images showing water molecules in the accretion disk of the very young star HL Tauri, a cosmic region where planets can be born, according to a study published on Thursday, informs AFP, quoted by Agerpres.
An ocean of water vapor has been observed around a star. PHOTO ESO Astronomy
“I never imagined that we would be able to get an image of a water vapor ocean right in a planet-forming region.“, said Stefano Facchini, astronomer at the University of Milan and the main author of the study published in the journal Nature Astronomy.
Located in the Taurus constellation and very close to Earth, at “just“450 light-years away, the star HL Tauri, twice the size of the Sun, has long been the focus of ground-based and space-based telescopes.
HL Tauri offers, through its proximity and youth (at most one million years), a stunning image of its protoplanetary disk, that mass of gas and dust that surrounds a star and allows the formation of planets.
According to theoretical models, this formation process would be particularly fertile in a very well-defined area of the disk: the ice line. Where water, which exists as vapor in the vicinity of the star, turns into a solid state as it cools. The dust grains would coagulate with each other all the more easily because of the ice that covers them.
“Embryos” of planets
Since 2014, the ALMA telescope has taken unparalleled images of the protoplanetary disk, showing an alternation of bright rings and dark streaks. The latter would betray the presence of some “embryos” of planets that form through the accumulation of dust.
Ice line
Water around the star HL Taur has also been detected by other instruments, remind the authors of the study, but with too poor a resolution to accurately determine the ice line. Due to its high altitude location, over 5,000 meters in the Chilean Atacama desert, this radio telescope of the European Southern Observatory (ESO) is the first to identify this limit.
“So far, ALMA is the only instrument capable of detecting in space the presence of water in a cold planet-forming disk”said Professor Wouter Vlemmings from Chalmers University in Sweden, co-author of the study and quoted alongside Professor Stefano Facchini in a press release published by ESO.
Three times the amount of water contained in all the Earth's oceans
The ALMA radio telescope has detected the equivalent of at least three times the amount of water contained in all of Earth's oceans. All the water molecules are in an area quite close to the star, with a radius equivalent to 17 times the distance that separates the Earth from the Sun.
The ALMA images “reveal a significant amount of water vapor at various distances from the star, including in a space where a planet could be forming right now,” according to Professor Stefano Facchini.
The mass of dust is equal to 13 times the mass of the Earth
In other words, there is no lack of raw material for the formation of such a planet, the calculations of another astronomical observer estimating that the mass of dust available in that area is equivalent to 13 times the mass of the Earth.
According to Stefano Facchini, the study would look like this “how the presence of water can influence the development of a planetary system, as was the case 4.5 billion years ago in our solar system.”
However, scientists' understanding of the mechanism by which planets are formed in a solar system remains incomplete.
