With three arms ready for astronomical war, X-shooter is located on Unit Telescope 2 (UT2, Kueyen) of the Very Large Telescope (VLT) at the Paranal Observatory. X-shooter is the result of a collaboration by institutes from Denmark, France, Italy and the Netherlands, working with ESO to create the ultimate weapon in intermediate resolution spectroscopy across a wide wavelength range, from the ultraviolet (UV) to the near-infrared (NIR).

Each arm is an individual echelle spectrograph, dispersing the incoming beam of light into many separate wavelengths (equivalent to colours) in the form of a spectrum. Because this spectrum is very long, it cannot fit on the detector. Instead, it is chopped up into smaller pieces called orders, which are then placed one on top of the other with each order allowing astronomers to see the data in great detail (as can be seen in the figure below). The three arms combine to allow astronomers to observe a range of astronomical targets across the spectrum from the ultraviolet, through the visible to the near-infrared. These objects range from faint nearby objects to very bright objects at the other end of the known Universe. With the ability to acquire data over such an extent of wavelengths, there are very few objects beyond X-shooter’s observational firing range!

Science highlights with X-shooter

  • Science goals: Broad-range high-resolution spectroscopy, to study — among many other topics — the properties of brown dwarfs, the progenitors of Type Ia supernovae, gamma-ray bursts, and the formation of metals in the very early Universe.
  • X-shooter helped identify the recently discovered “green bean” galaxy population, that looks bright green because of the disruption caused by giant black holes at their centre. (eso1249)
  • The most powerful quasar to date was measured with X-shooter; its emitting power is equivalent to two million million times that of the Sun, or 100 times more than the entire Milky Way galaxy. (eso1247)
  • A free-floating exoplanet was found wandering 100 light-years away from Earth with no parent star. With no blinding glare from the star, it has been possible to study the planet’s atmosphere in great detail. (eso1245)
  • Such low-mass, metal-poor stars like SDSS J102915+172927 should not even exist! It may be one of the most primitive stars ever detected, with a possible age of over 13 billion years. (eso1132)
  • Blurring the lines between small cold stars and big hot planets, the brown dwarf CFBDSIR 1458+10B is about the same temperature as a nice cup of tea. (eso1110)
  • List of the scientific papers produced by X-shooter, via the ESO library’s telbib database.

Raw images obtained simultaneously by X-shooter’s three detectors. The light of a celestial object, in this case a quasar, is dispersed according to its wavelength, or colour, to form a very long, very high resolution spectrum covering the full wavelength range from ultraviolet to infrared. The optical elements in the spectrograph arrange this long spectrum in a series of consecutive, shorter spectra, called orders. In this image, the wavelength increases from bottom to top of each spectrum, and from left to right. The spectrum of the quasar records its intensity as a function of wavelength, and is made up by the thin bright lines visible in each of the orders. The short, bright and nearly horizontal lines correspond to colours where the atmosphere shines brightly.


The authoritative technical specifications as offered for astronomical observations are available from the Science Operation page.

Site: Paranal
Telescope: VLT UT3
Focus: Cassegrain
Type: Multi-wavelength, medium resolution spectrograph
Wavelength coverage: 300–2500 nm
Spatial resolution: n/a
Spectral resolution: 4000–17 000
First light date: March 2009 (eso0920)
Images taken with the instrument: Link
Images of the instrument: Link

Videos of the instrument:


Press Releases with the instrument: Link



Denmark: Niels Bohr Institute, University of Copenhagen

Italy: Osservatorio Astronomico di Palermo (INAF)

France: Observetoire de Paris (GEPI)

The Netherlands: University of Amsterdam (API); ASTRON