They have discovered exoplanets and second Earths, and brought us a steady stream of astoundingly beautiful space images.

The European Southern Observatory is celebrating half a century of delving into the wonders of the cosmos, and to mark the occasion we've pulled together 50 amazing images from the 50 years of ESO research, and spoken to Bruno Leibundgut, director for science at the ESO.

Far from picking out sterling individuals or bragging about star finds, Leibundgut emphasised the collaborative nature of the ESO as one of its greatest successes.

"I believe it has become clear from the above that ESO is a community effort," he tells the Huffington Post via email from Vienna. "The community, which has formed in response to the common challenges is, in my opinion, one of the strongest results. ESO (and other international research organisations) are providing a model for collaboration.

Leibundgut may be humble, but the list of achievements by the ESO is impressive, including the first direct image of a planet around another star and flashes from material falling into the supermassive black hole at the centre of our Milky Way.

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Leibundgut admits that ESO has landed many technological firsts too, saying: "At ESO, we are pushing the known all the time as well. The instruments are used in innovative modes, new capabilities are added."

ESO developed powerful lasers to create artificial guide stars and the New Technology Telescope (NTT), one of the first computer-controlled telescopes with a mounting of altitude and azimuth, rather than an equatorial axis.

ESO also provided the first common user interferometer with VLTI, designed to be used by general users. Previously only experts with access to highly specialised facilities could use this kind of technology.

Leibundgut, who's favourite ESO image shows the star-lit sky reflected in the SEST telescope on La Silla (below), says that the greatest reward for working on such a huge project is the opportunity to do good science.

"By doing a good experiment, trying to determine the mean matter density of the Universe, we stumbled upon a completely unexpected result: the opposite of what we were looking for."

"The imagination of scientists is fascinating. Take the flashes at the centre of the Milky Way. The observation of the stellar orbits around the black hole was the prime objective, but it was known that matter falling into a black hole emits light. With the capabilities available the discovery of the black hole was inevitable. However, it is impressive to see astronomers devise their observing strategies to explore new questions."

The first 50 years found much and the next 50 will be just as groundbreaking. The formation of stars and planets, the structure of the Milky Way and the transient sky will all be major areas of focus.

"The next goal is to find Earth-like planets in the habitable zone around the parent star. A handful of these have been discovered, but their characterisation will need the next generation of telescopes. The E-ELT will be decisive in this respect."

Understanding the Universe will remain a hot topic for many years to come says Leibundgut: "Dark matter and dark energy are components that are not understood and they either point at a breakdown of the theory of gravity as we know it now or new particles and fields, which we have so far not detected nor understood. After all, we currently are ignorant of 95% of the energetic content of the Universe."

Click through 50 great ESO images below and rate your favourite.