Everyone loves lasers. And the only thing better than a row of lasers is a row of lasers on one of the (soon) largest telescopes in the world, the E-ELT. Well, maybe a couple of lasers on a time-traveling T. rex that appears in your observatory asking to know the locations and trajectories of the incoming asteroids. That could be better. For the dinosaurs; not for us.
The first light for the European Extreme Large Telescope (E-ELT) is still years away. If it opens its strong and sensitive eye, it will be the world's largest optical / infrared extremely large telescope. Its main mirror will be a whopping 39.3 meters in diameter. Of course, the mirror is not a single monolithic piece of glass; It is divided into 798 hexagonal elements that all work together.
But all of this observation is practically useless, or at least severely limited, without a bunch of lasers to help it do its thing. And what a bouquet it will be.
The EELT should see the first light in 2024. This illustration shows the scale of the telescope and its segmented primary mirror with a diameter of 39.3 meters. Photo credit: ESO
Modern telescopes like the E-ELT use lasers as guide stars in their adaptive optical systems. Without them they would be severely restricted.
We are used to displaying super sharp and detailed astronomical images on our computer screens. The Hubble Space Telescope is particularly responsible for this, and an entire generation grew up with access to these images. But not every telescope can be in space. The greatest and most powerful are here on earth.
Stars twinkle with the naked eye. That's great. However, this sparkle is caused by disturbances in the atmosphere from wind and temperature, which distort astronomical vision. To cope with this, the E-ELT and other terrestrial telescopes use laser guide stars and adaptive optics (AO) systems.
This picture shows schematically astronomical vision, a process in which the light of a (distant) object is disturbed by the earth's atmosphere. The wave front enters at the top and moves through the inhomogeneous atmosphere. The wavefront is distorted, which leads to a blurred image. The two quantities r_0 and t_0 denote the spatial and temporal coherence length. Photo credit: By 2pem – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=15279464
The light from a distant star is a plane wave. For a space telescope like Hubble, it just needs to focus this plane wave on its detector. However, with a ground-based telescope like the E-ELT, the plane wave is distorted by the atmosphere. The laser guide stars and AO system allow the telescope to sense and respond to these atmospheric distortions to keep the plane wave clear.
The lasers create an artificial star in the sky that the AO system can observe. By observing this man-made star, the AO system can see how the star's plane wave is distorted by atmospheric disturbances and give the telescope with its deformable mirror the information it needs to correct. And it corrects itself in real time.
Space telescopes like the Hubble don't have to deal with the atmosphere. This is one of the reasons the Hubble produces such fantastic images and has been able to bring images of fog and other beautiful, distant objects into mainstream culture.
But the E-ELT does. The AO system and laser guide stars allow it to outperform Hubble's image quality. In fact, the European Southern Observatory (ESO), who built the E-ELT, says its scope will produce images 16 times sharper than the Hubble's. 16 times! To do this, it collects more than 100 million times more light than the human eye and has 256 times as much light-collecting area as the Hubble.
What will it do with all that force? Much.
One of the most exciting things about the E-ELT will be studying exoplanets. It will be able to detect distant Earth-sized planets based on indirect observations like measuring the planet's wobble. But it can also be able to take direct images of larger planets and even characterize their atmosphere. It will also be able to peer into the dusty regions of young solar systems and watch planets form, and even spot water and organic matter in those systems.
Artist's impression of a baby star still surrounded by a protoplanetary disk in which planets are forming. The E-ELT should allow astronomers to look into the disk and watch planets form. It should also recognize water and organic matter in these discs. Photo credit: ESO
This will also expand our knowledge of the earliest stars, galaxies, and black holes. Telescopes like the Hubble have contributed a lot to our knowledge of these subjects, and the E-ELT promises another big leap in understanding. The telescope may even be able to measure the extent of the universe itself, which turns out to be very difficult.
These are just a few highlights of the E-ELT's scientific potential. We know from experience that there are always surprises.
If we believe we have come of age at a time of unprecedented access to distant objects in the universe and a time of groundbreaking discovery, just wait for the E-ELT to get going.
Maybe we can finally gracefully retire the Hubble.