A new instrument on the four-metre VISTA telescope at the European Southern Observatory in Chile has recently captured its first starlight. This marks the beginning of a new era in astronomy, as researchers prepare to map the sky in unprecedented detail.
The instrument does not take ordinary images of the night sky. Instead, 4MOST - the Multi-Object Spectroscopic Telescope - collects spectra, that is, the light from stars and galaxies split into its wavelengths, or colours. By analysing this rainbow-like pattern, researchers can determine what these stars and galaxies are made of and how fast they are moving through space.
Using 2,438 optical fibres, each as thin as a human hair, the instrument can simultaneously observe the light from 2,400 stars in up to 18,000 colour channels. 4MOST is the instrument in the world with the most fibers combined with spectral resolution, that is, how fine details it is possible to observe in a stellar spectrum.
"Every night for five years, 4MOST will gather star and galaxy spectra and will ultimately have observed several tens of millions of stars in our own galaxy, the Milky Way. The result will be the most detailed picture so far of the Milky Way's structure and chemical evolution", says Thomas Bensby, astronomy researcher at Lund University.
During its first observations, 4MOST was pointed towards several spectacular objects. One of them was NGC 253, the so-called Sculptor galaxy - a spiral galaxy more than eleven million light years away that is still forming new stars at a remarkable rate. Another target was NGC 288, a globular star cluster with around 100,000 very old stars located in the outskirts of the Milky Way. The telescope also managed to collect spectra from more than 2,000 other objects - from nearby stars to galaxies ten billion light years away.
"In my early years as an astronomer I observed and analysed stars one by one. This is an astonishing development that requires careful planning and new analysis methods due to the enormous amount of data produced every night", says Thomas Bensby.
4MOST is the work of an international consortium of 30 universities and research institutes in Europe and Australia, led by the Leibniz Institute for Astrophysics Potsdam. Thanks to a project grant from the Knut and Alice Wallenberg Foundation in 2013, Lund University, together with Uppsala University, has been involved from the start in building the instrument's high-resolution spectrograph, which makes it possible to measure the chemical fingerprints of stars with exceptional precision.
"It feels significant that the work is now underway, as astronomers in Lund have leading roles in several of the surveys and working groups that have worked and continue to work with 4MOST", says Thomas Bensby.
Until 2030, 4MOST will map millions of celestial objects across the entire southern sky. By analysing their temperatures, motions and chemical compositions, researchers hope to answer questions such as: How did the first stars form? How did the Milky Way form and evolve? What are dark matter and dark energy made of?
"Understanding the Milky Way and its stellar populations is one of the key pieces in the puzzle of how large spiral galaxies are generally formed and shaped in the Universe", concludes Thomas Bensby.
