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Laser Guide Star at VLT to shine brighter light on stars | Laser Guide Star at VLT to shine brighter light on stars |
(about 6 hours later) | |
By Katia Moskvitch Technology reporter, BBC News | By Katia Moskvitch Technology reporter, BBC News |
It does not twinkle, a rare characteristic for a star. | It does not twinkle, a rare characteristic for a star. |
It appears suddenly over the southern hemisphere, a new neighbour in the crowded black sky. | It appears suddenly over the southern hemisphere, a new neighbour in the crowded black sky. |
But this "star" is not a real one. | But this "star" is not a real one. |
Created by a powerful laser beam, it can be made to shine to order by the astronomers at the Paranal Observatory in Chile's Atacama Desert. | Created by a powerful laser beam, it can be made to shine to order by the astronomers at the Paranal Observatory in Chile's Atacama Desert. |
"We call it a Laser Guide Star, or LGS, and it is an artificial star that we create by illuminating the sodium layer of the atmosphere," explains Frederic Gonte, head of instrumentation at Paranal. | "We call it a Laser Guide Star, or LGS, and it is an artificial star that we create by illuminating the sodium layer of the atmosphere," explains Frederic Gonte, head of instrumentation at Paranal. |
Clad in a white coat and overshoes, he stands in a tiny lab located high above the ground, in the heart of Yepun - one of the four units of the biggest optical telescope on Earth, the Very Large Telescope (VLT). | Clad in a white coat and overshoes, he stands in a tiny lab located high above the ground, in the heart of Yepun - one of the four units of the biggest optical telescope on Earth, the Very Large Telescope (VLT). |
In front of Mr Gonte is a projector that is emitting a laser beam across the room. | In front of Mr Gonte is a projector that is emitting a laser beam across the room. |
The laser that we see is green, but as it starts racing upwards, to the sky, through an opening in the roof of Yepun's huge enclosure, it becomes yellow. | The laser that we see is green, but as it starts racing upwards, to the sky, through an opening in the roof of Yepun's huge enclosure, it becomes yellow. |
Outside, the view is breathtaking: a huge beam disappearing somewhere inside the Milky Way. | Outside, the view is breathtaking: a huge beam disappearing somewhere inside the Milky Way. |
For now, there is only one LGS unit at the VLT. Soon, there will be four - and they will be a lot more powerful. | For now, there is only one LGS unit at the VLT. Soon, there will be four - and they will be a lot more powerful. |
Removing turbulence | Removing turbulence |
Astronomers use a Laser Guide Star to obtain the best possible image of a celestial object. | Astronomers use a Laser Guide Star to obtain the best possible image of a celestial object. |
"When a telescope points at a star from Earth, it encounters the turbulence of the atmosphere, and this turbulence makes stars twinkle and the image blurry," says Mr Gonte. | "When a telescope points at a star from Earth, it encounters the turbulence of the atmosphere, and this turbulence makes stars twinkle and the image blurry," says Mr Gonte. |
This means that although large ground-based telescopes with big mirrors can see much fainter objects in the sky than smaller telescopes, without any correction the resolution is generally no better than that of a 0.1m-aperture telescope. | This means that although large ground-based telescopes with big mirrors can see much fainter objects in the sky than smaller telescopes, without any correction the resolution is generally no better than that of a 0.1m-aperture telescope. |
When observed from the Hubble Space Telescope in orbit, for example, stars do not twinkle. | When observed from the Hubble Space Telescope in orbit, for example, stars do not twinkle. |
To correct the distortion and improve the resolution, astronomers use a technique known as adaptive optics. | To correct the distortion and improve the resolution, astronomers use a technique known as adaptive optics. |
They find a bright reference star close to the object being observed and measure the blurring. | They find a bright reference star close to the object being observed and measure the blurring. |
A deformable mirror in the telescope then largely cancels out the atmospheric distortion. | A deformable mirror in the telescope then largely cancels out the atmospheric distortion. |
"Without the adaptive optics, a telescope like one of the VLT units has a no better resolution than a 20cm telescope," explains Mr Gonte. | "Without the adaptive optics, a telescope like one of the VLT units has a no better resolution than a 20cm telescope," explains Mr Gonte. |
"With the adaptive optics, it is better than Hubble." | "With the adaptive optics, it is better than Hubble." |
But sometimes, there is simply no such bright star nearby - astronomers estimate that only about 1% of stars are bright enough for adaptive optics to work. | But sometimes, there is simply no such bright star nearby - astronomers estimate that only about 1% of stars are bright enough for adaptive optics to work. |
That is when scientists need an artificial one. | That is when scientists need an artificial one. |
More powerful telescope | More powerful telescope |
The laser pierces the atmosphere, giving birth to a "star" somewhere 90km (56 miles) above the Earth. | The laser pierces the atmosphere, giving birth to a "star" somewhere 90km (56 miles) above the Earth. |
Even though to the naked eye this artificial star is still fainter than any natural one, it is bright enough to be a reference for astronomers to correct the effect of the turbulence. | Even though to the naked eye this artificial star is still fainter than any natural one, it is bright enough to be a reference for astronomers to correct the effect of the turbulence. |
The VLT is not the only telescope in the world that uses the Laser Guide Star system. | The VLT is not the only telescope in the world that uses the Laser Guide Star system. |
But it will be the first one to receive a major upgrade of this technology. | But it will be the first one to receive a major upgrade of this technology. |
Over the past several months, a team of engineers and scientists at the headquarters of the European Southern Observatory - the organisation that runs Paranal - in Garching, Germany, has been busy developing a new, much smaller, more mobile and significantly more powerful LGS unit. | Over the past several months, a team of engineers and scientists at the headquarters of the European Southern Observatory - the organisation that runs Paranal - in Garching, Germany, has been busy developing a new, much smaller, more mobile and significantly more powerful LGS unit. |
A prototype was tested last summer. | A prototype was tested last summer. |
"The new unit is going to have a lot more power to create a much brighter artificial star - while the current laser generates 5W when in the air, the new one will have 18W," says astrophysicist Domenico Bonaccini Calia, head of the Laser Guide Star group at ESO. | "The new unit is going to have a lot more power to create a much brighter artificial star - while the current laser generates 5W when in the air, the new one will have 18W," says astrophysicist Domenico Bonaccini Calia, head of the Laser Guide Star group at ESO. |
"It is really a breakthrough in laser technology, some of which we have patented here at ESO. | "It is really a breakthrough in laser technology, some of which we have patented here at ESO. |
"The unit is very compact, requires much less maintenance, is much less delicate than the current one, and is remotely controllable without much human intervention." | "The unit is very compact, requires much less maintenance, is much less delicate than the current one, and is remotely controllable without much human intervention." |
Soon, the VLT's Yepun telescope will harbour four of these new devices, together called 4 Laser Guide Stars facility - and is currently being modified to accommodate them. | Soon, the VLT's Yepun telescope will harbour four of these new devices, together called 4 Laser Guide Stars facility - and is currently being modified to accommodate them. |
The new units are expected to be shipped to Paranal in the coming months. | |
The same technology will also be installed on a telescope that ESO aims to build - on a mountain not far from Paranal, called Cerro Armazones. | The same technology will also be installed on a telescope that ESO aims to build - on a mountain not far from Paranal, called Cerro Armazones. |
If all goes according to plans, the new European Extremely Large Telescope (E-ELT) will have a mirror of some 39m in diameter and have six Laser Guide Star units installed. | |
"The E-ELT will use the Laser Guide Star routinely, right from the start," says Mr Bonaccini Calia. | "The E-ELT will use the Laser Guide Star routinely, right from the start," says Mr Bonaccini Calia. |
"With a Laser Guide Star, it's like having a lamp on your hard-hat in a mine - wherever you look, you always have a bright star in front of you. | "With a Laser Guide Star, it's like having a lamp on your hard-hat in a mine - wherever you look, you always have a bright star in front of you. |
"And only 4-5% of the light from the laser gets absorbed - most goes into space and could reach other solar systems." | "And only 4-5% of the light from the laser gets absorbed - most goes into space and could reach other solar systems." |
It will take a long time to do so, and when the light finally reaches an extra-solar planet, it will be very faint, adds the scientist. | It will take a long time to do so, and when the light finally reaches an extra-solar planet, it will be very faint, adds the scientist. |
But who knows? Maybe one day, it will be spotted by life forms elsewhere in the Universe. | But who knows? Maybe one day, it will be spotted by life forms elsewhere in the Universe. |
Katia Moskvitch was on secondment to ESO for two months leading up to her trip to Chile. |