Science with the E-ELT

Extremely Large Telescopes are considered worldwide as one of the highest priorities in ground-based astronomy. They will vastly advance astrophysical knowledge, allowing detailed studies of subjects including planets around other stars, the first objects in the Universe, super-massive black holes, and the nature and distribution of the dark matter and dark energy which dominate the Universe.

Since end 2005 ESO has been working together with its user community of European astronomers and astrophysicists to define the new giant telescope needed by the middle of the next decade. More than 100 astronomers from all European countries have been involved throughout 2006, helping the ESO Project Offices to produce a novel concept, in which performance, cost, schedule and risk were carefully evaluated. Dubbed E-ELT for European Extremely Large Telescope, it features a 42m filled aperture collector with exquisite image quality thanks to an internal adaptive optics corrector, and large platforms for putting on-line a dedicated set of powerful post-focal instruments.

The E-ELT Science Case

The science case for a 50-100m diameter ELT has been initially developed by the ESO community under the FP6 OPTICON programme supported by the European Commission. This effort is now being further pursued and extended to the still highly ambitious 30-50m diameter range by the combined ESO-OPTICON Science Working Group (I. Hook, Oxford University & M. Franx, Leiden University co-chairs). Three broad domains are in particular being investigated in depth:

1. search and characterisation of exoplanets and proto-planetary systems;
2. formation and evolution of the large scale structure of our universe from the 1st lights to present day;
3. testing the frontiers of physics (strong gravity, variations of fundamental constants, structure of space-time, etc.).

The April 2006 report of the E-ELT Science Working Group presents the full Science Cases and Requirements for E-ELT.

In September 2008 a symposium "Science with the E-ELT" will be held in Vienna, Austria at the JENAM 2008 meeting.

Examples of exciting research Topics

Discovery and characterisation of planets and proto-planetary systems around nearby stars will advance hugely with the ELTs, perhaps up to the fiendishly difficult feat of finding and studying Earth-like planets located in their parent star's habitable zone.

Artist impression of the planetary system around the red dwarf star Gliese 581, as revealed from minute variations over time of the radial velocity of the star. With a radius only 50% larger than our Earth, the planet (left) is located in the so-called habitable zone of its parent star, i.e. with liquid water. Note however that it is considerably closer to its star than the Earth, going through a full revolution in only 13 days (instead of 365 days in our case). The E-ELT will be able to detect directly such a planet as a faint point of light and reveal its global properties (e.g. rocks versus oceans) from a low-resolution spectrum.

Distant galaxies will appear as if they were in our backyard. In connection with ALMA, the currently being built Atacama Large Millimeter Array which will peer inside even the most dust-shrouded regions, this will bring an unbiased view of the history of stellar formation over most of the age of the Universe. Distant clusters of galaxies will also provide crucial information to understand the origin and early history of our Universe.

ELTs will allow looking back to the youngest galaxies, born just a mere 500 million years after the origin of time and space. They will also likely detect the even earlier first lights in the universe when ultra-massive stars made from primordial (zero metal content) gas underwent titanic hypernova explosions.

The most distant galaxy known as of September 2006 with a redshift z = 6.964 (courtesy Subaru Telescope). This observation provides a rare view of our Universe when it was only 780 millions years old (compared to its respectable present age of 13.66 billion years). ELTs are expected to probe even further this “dark age” period.

Our Universe is the ultimate laboratory where the frontiers of physics can be tested and extended: black holes, dark matter and dark energy have been identified and explored so far only through astronomical observations. With the ELT's huge photon gathering power, extremely precise (a few cm/s absolute accuracy maintained over 20 years) radial velocities of intergalactic gas clouds illuminated by distant quasars will permit to 'see' directly the cosmic acceleration of the universe. Similar observations will also test eventual variations of fundamental physical constants linked to possible extra dimensions of the universe.

This composite picture illustrates how the light of a very distant quasar (after being analysed by a very high resolution spectrometer) can be used to probe the outskirts of distant galaxies and the intergalactic medium itself along the line of sight towards us. The enormous light collecting power of an ELT will permit extremely precise wavelength measurements.

Further Reading

For more information please read The European Extremely Large Telescope in the ESO Messenger No. 127 (March 2007). To know (almost) everything on this exciting and demanding technical development, browse the detailed E-ELT project pages.