The upgrade will make it easier for scientists to use the observatory to search for faint, rocky planets around distant stars, ESO representatives said in a statement.
The instrument is called ESPRESSO (Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations). Each of the VLT units sends its light to the instrument using mirrors, prisms and lenses. ESPRESSO can use the light from either all four telescopes at once or just one individual telescope. That design is intended to provide more flexibility in observing time, ESO representatives said. [Amazing Space Views of ESO's Very Large Telescope (Photos)]
Another instrument, called the VLT Interferometer, commonly combines the light from all four unit telescopes, but ESPRESSO does it differently. Interferometry combines multiple telescopes to make observations. The effective size of the telescope "mirror" is the same as the distance between the individual telescopes. Interferometry also takes the phase of an object's light waves into account to form an image.
ESPRESSO, by contrast, is designed to exploit the light-gathering power of the individual telescopes. It has the light-collecting power of a 16-meter (52 feet) telescope. Light gathering is important for telescopes because, as they receive more photons of light, fainter objects appear brighter. Bigger telescopes typically see distant objects such as galaxies more easily because they have more light-gathering power.
The objects ESPRESSO can resolve are at the power of an 8-meter (26 feet) telescope (the same as each individual telescope). Resolving power refers to the ability of a telescope to separate objects that are close together in the sky. A telescope that professionals use tends to have more resolving power than an amateur one, allowing professionals to see stars more clearly in multiple-star systems, for example.
"This impressive milestone is the culmination of work by a large team of scientists and engineers over many years," project scientist Paolo Molaro said in the statement. "It is wonderful to see ESPRESSO working with all four unit telescopes, and I look forward to the exciting science results to come," added Molaro, who is on the research staff of the Astronomical Observatory of Trieste in Italy.
ESPRESSO has a second major scientific goal besides looking for Earth-like worlds: to seek variability in fundamental physics constants. ESPRESSO will observe faint and faraway quasars to uncover more about basic physics, and the combined light of the four telescopes will greatly benefit it in its observations, ESO representatives said.