The "VIMOS Public Extragalactic Redshift Survey" (VIPERS) is an ongoing programme which aims to create an unprecedentedly large three-dimensional map of the Universe, showing the distribution of galaxies as it looked like seven billion years ago.

The programme is carried out by an international team of astronomers, which includes Polish scientists from the Jagiellonian University, the National Centre for Nuclear Research in Warsaw, and the Jan Kochanowski University in Kielce as well as some Polish researchers participating in foreign internships. Using one of the VLT ESO telescopes they have measured distances to 55,000 galaxies.

The dark energy

According to the Standard cosmological model, the Universe was born some 13.7 billion years ago and was initially expanding at a systematically slower rate. However, the tendency reversed some 7 billion years ago: the rate started to accelerate. Measurements of distances to distant supernovae (for which a US physicist Saul Perlmutter and two Australian physicists Brian P.Schmidt and Adam G. Riess were awarded the Nobel Prize in 2011) have shown that the rate of the Universe expansion is growing, so that individual galaxies are moving away at increasing velocities. The factor responsible for the acceleration of the Universe expansion is currently dubbed the "dark energy".

The nature of dark energy remains a mystery. According to some hypotheses, the dark energy is a form of energy that fills up the entire space. It is constantly exerting negative pressure that opposes gravitation and causes the Universe to expand. The nature of that energy, its properties, and evolution in time and space are all debatable.

The goal of the VIPERS project is to create the map of the Universe as it was seven billions years ago, and to estimate the rate of its expansion since the time when dark energy started to play a key role. The acquired data may help discover dark energy properties and unveil its nature. The final version of the catalogue with the information on distances to 100,000 galaxies is to be ready in two years. It will help to work out some more precise prognoses about how the Universe is going to expand in the future, and this may prove very helpful in resolving the dark energy mystery.

Galaxy evolution mystery

The results of the VIPERS project will be used not only to compile the first precise 3D map the Universe as it was 7 billion years ago, but also to study the properties of galaxies.

The galaxies observed in the today's Universe form compound large-scale structures: groups, clusters, sheets, filaments, as well as gigantic voids between them. Galaxies may have various shape, size, colour, and magnitude. Their properties depend first of all on their location in Space. Elliptic galaxies dominate in densely populated regions (e.g. in groups). Such galaxies are most often red, large, bright, but do not create any new stars. On the other hand, moderately-sized, weak, spiral galaxies observed in loosely populated regions are still producing new stars. In spite of the multitude of observations, the astronomers are still not exactly sure how various types of galaxies were born and what factors were decisive for their evolution.

The map of the Universe as it was 7 billion years ago compiled by scientists involved in the VIPERS project has already shown that galaxies of various types observed today were also present then. Mighty large-scale structures with clusters of red galaxies are visible on the map. Blue galaxies that are producing new stars dominate in less-populated regions. The conclusion is that the basic galaxy types had to form earlier. The collected data should enable researchers to develop new effective tools to automatically qualify astrophysical objects, which would be very useful in compiling other spectroscopy surveys in the future.

The Polish Participants of the Programme are: Dr hab. Agnieszka Pollo (Astronomical Observatory of the Jagiellonian University, National Centre for Nuclear Research in Warsaw), Dr Janusz Krywult (Jan Kochanowski University in Kielce), Dr Katarzyna Małek (postdoctoral fellowship at Nagoya University, Japan), Ms Aleksandra Solarz (doctoral student of Nagoya University, Japan, JU graduate). The Jagiellonian University students take part in analyzing the data.

European Southern Observatory

VIPERS is one of the "Large Programmes" of the European Southern Observatory, a European organization for construction and maintenance of telescopes on the southern hemisphere. The observation is conducted with one of the Very Large Telescopes (VLT), which are among the most advanced optical instruments in the world.