With its 34 meters in diameter and 26 meters high, the dome of the Great Canary Islands Telescope (GTC) It is a metallic colossus on the top of the island of La Palma. Its futuristic appearance will be accentuated shortly, when the world’s biggest telescope shoots every night a high intensity laser beam towards the dark of heaven. And it won’t do it to destroy worlds, such as Deathbut to create artificial stars with which to calibrate their teams.
“When the system of Adaptive opticswe will see some objects from the sky with a sharpness greater than the James Webb space telescope, ”announces its director, Romano Corradifrom the GTC control room.
As described, the system is pure fantasy: not only subtly deforms the mirrors of the telescope in real time to correct the disturbances produced by the air, but is calibrated from bright stars and, in its absence, with points of light generated at 90 km of altitude by a powerful laser. A light cannon that projects an artificial star of several meters in diameter in the mesosphere, on the remains left by the fleeting stars.
Like the bottom of a pool
The great Canary Islands telescope is found in one of the places with the darkest and darker skies of the planet, recalls its director, but the turbulence of the atmosphere always introduces small alterations. This prevents taking advantage of the spatial resolution offered by the huge mirror of 10 meters, which potentially allows to differentiate celestial objects that are very close to each other, such as a planet and a star.
The astrophysic Francisco Sánchezhistorical founder of the IAC, compares atmospheric turbulence with the effect that occurs when we look far on a reheated road. The objects are broken “because the light has had to cross dancing hot air bubbles that alters its rectilinear path,” he writes in his autobiography. Although in a place like the Observatory of the Rocque de los Muchachos (ORM) the agitation of the air is very low, the phenomenon is proportional to the diameter of the “objective” of the instrument with which it is observed, so that a record of record size such as the GTC has to try to avoid its effects.
“Atmospheric turbulence distorts light as if we were looking through water at the bottom of a pool,” he explains Marcos ReyesChief of instrumentation of the telescope that leads the installation of these new equipment. Adaptive optics is sophisticated technology that makes the atmosphere disappear and what astronomers know as “Seeing” And it does so by measuring that deformation of light in real time and sending a series of commands to a deformable mirror that compensates for these variations and corrects them.
“The mirror deforms such in a way that compensates for the alteration that the light produced by the atmosphere,” describes Corradi. “Thus, it recovers the flat form of what we call wave front and the image, which would otherwise look blurred, it looks with total sharpness.” “We are measuring the deformation of the light a thousand times per second, analyzing it in real time, sending the commands to the deformable mirror so that the light that comes out reflected and reaches the scientific instrument has that high space resolution,” adds Reyes.
Looking for a star
He adaptive optics system for GTC (GTCAO) is installed since 2023 on the Nasmyth B platform of the telescope and, after a period of testing observations, will be available for the scientific community at the end of the year. In this first phase, the team is calibrated with “natural stars”, very bright stars near the object they want to study. “Atmospheric turbulence is different in each site in the sky,” says Reyes. “That is why you have to measure it near where you want to observe.”
In this way, if you want to observe a very weak galaxy, astronomers calibrate the optics before using a brilliant star that is in the same area. “But the night sky is empty of bright stars, so we can aim at few sites and apply the technique of adaptive optics,” warns the expert. “And what do we do? Then emit a laser from the telescope and create an artificial star that serves us to calibrate it. ”
The night sky is empty of bright stars, and what do we do? Well emit a laser from the telescope and create an artificial star that serves us to calibrate it
Marcos Reyes
– GTC instrumentation manager
A 30 cm light ‘chorrazo’
Under the huge mirror of the GTC, consisting of 36 hexagonal segments of 450 kg and almost 2 meters high each, the GTC dome seems the interior of a giant robot. There he works Jesus patronone of the IAC astrophysics who is making the adaptive optics equipment, located on one of the platforms. “The laser has 20 watts and originates with just three millimeters,” he explains. “But then we go to what we call launch telescopewhich transforms the beam of light and takes it through the front into a stream of about 30 centimeters in diameter; We need a sufficient number of molecules to be excited so that something can be seen. ”
The color of the laser is orange, because it works in the wavelength of the sodium, explains Marcos Reyes. “It is the most efficient color because it spreads up to 90 kilometers high, to a layer in the atmosphere called the mesosphere,” he continues. “In this region there are many particles that come from meteoroids, from small asteroid remains that are integrated into the atmosphere, so there are many sodium atoms.”
When this area reaches in which fleeting stars disintegrate, the laser illuminates sodium atoms in an area that can be one or two meters in diameter. This produces a kind of very dim star, of magnitude 8 or 9, but sufficient so that for the powerful eye of the GTC it will take it as reference and adaptive optics adjust the sharpness of the image.
Own technology
In recent months, Reyes and his team have tried the laser cannon in the Teide and in the Roque de los Muchachos. Both this and the adaptive optics system have been designed entirely by IAC scientists. The laser will be installed soon in the elevation ring of the Great Telescope of the Canary Islands, a structure that moves with the set and will allow the beam to any place in the sky.
“The plan is to install it in 2027 and be doing the tests with science instruments until 2028,” says Reyes to eldiario.es. “From that date it will serve to make routine science, after a very long and complex process.”
“If we have a galaxy of interest that is too weak to use it to calibrate the optics, next to you we will put an artificial star made with the laser,” says GTC director, Romano Corradi. “Next, we sent the information to the deformable mirror and corrected. We have already managed to correct turbulence for certain test stars, but we still have to refine. ”
If we have a galaxy of interest that is too weak to calibrate the optics, next to you we will put an artificial star made with the laser
Romano Corradi
– Director of the GTC
From the IAAC they are convinced that this technological leap will place the Granco, as they also call the GTC, at a level of scientific performance even higher than the one has already had since its launch in 2009. “There is a niche in which, indeed, with adaptive optics and the laser, you can gain in resolution the space telescopes,” acknowledges its deputy director, Eva Villaver. Likewise, already difference from what happens in the astronomical facilities of Chile or Hawaii, where they have to ensure not to interfere with the laser in air traffic, in the palm they will have less complications, as flights are restricted on the observatory by the “Law of Heaven”
“The conditions of the Palma Observatory are comparable to those of the Atacama and Hawaii desert; We are in the top category of world observatories, ”presumes Corradi. “The GTC telescope remains the largest telescope in the world and this will open doors to make science that had not been done so far, both star science and extragalactic,” concludes Marcos Reyes. “With the advantage that doing high resolution science from earth is much cheaper than doing it from space.”
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