A team of scientists led by astronomer, Prof. Grzegorz Pietrzyński, has won the most prestigious grant awarded by the European Research Council – ERC Synergy – worth almost EUR 14 mln. It is one of the largest research grants in the world and the first of this kind awarded to Polish researchers. The winner project, entitled “Precise calibration of the cosmic distance scale in the age of large-scale surveys” will be carried out in a consortium led by the Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences. Prof. Bożena Czerny will act as the Principal Investigator for the PAS Center for Theoretical Physics.

 

Project in a nutshell:

• The team of prof. Grzegorz Pietrzyński from the Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences is the first in Poland to receive the prestigious ERC Synergy grant.
• The main objective of the project is to make the measurements of distances in the Universe more accurate by using very different spatial scales, from the vicinity of the Sun to the far corners of the Universe. Scientists will create new methods for increasing accuracy of distance measurement.
• The grant will allow for the construction of a new telescope at the Cerro Armazones Observatory in northern Chile.
• The project will be implemented by the consortium consisting of the Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences, the PAS Center for Theoretical Physics, Universidad de Concepción, Paris Observatory and the Heidelberg Institute for Theoretical Studies.

 

Cosmic distance scale now more accurate

 

The main goal of this project is to enable accurate measurement of distances in space by using very different spatial scales, from the vicinity of the Sun to the far corners of the Universe. These measurements will be used to derive the value of the Hubble constant (H₀), which describes the rate of expansion of the Universe, with an unprecedented 1% accuracy. Determining the value of Hubble constant is necessary to understand the evolution of our Universe and to study the essence of dark energy, which accounts for about 70% of the Universe's total mass and energy.

Knowing the precise value of the speed with which our Universe is expanding is essential to understanding its nature. What is more, any significant improvement in this accuracy has always led to groundbreaking discoveries – such as a discovery that the rate of expansion of the Universe is accelerating – which earned three astrophysicists (Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess) a Nobel Prize in 2011.

 

Currently, astronomers have multiple methods at their disposal to determine the Hubble constant. The H₀ can be measured based on cosmological methods, including analysis of cosmic microwave background and baryon acoustic oscillations. Although these methods may seem highly attractive, they are model-dependent and require scientists to make additional assumptions.

The Hubble constant can also be determined using more traditional calibration methods such as standard candles (stars or other group of objects emitting the same amount of energy). This is the simplest, fully empirical, and probably the most precise method. However, it turns out that determining the H₀ true value with the use of cosmological and classical methods produce significantly different answers. This discrepancy, often called crisis, seems to provide evidence that new physics beyond the standard cosmological model might be required to reconcile the different determinations of H₀.

 

Cosmic distance ladder

In order to significantly improve upon our determination of the Hubble constant it is necessary to measure it by means of classical approach, which involves using several different methods. To put it in a nutshell: scientists use the most precise (geometrical) methods to measure distances to nearby objects. Relying on primary indicators, researchers calibrate secondary distance indicators, which in turn allow the calibration of long-range methods for measuring distances to the very distant objects in the Universe. This is often called a distance ladder. It turns out that the hardest part of this arduous task of marking the H₀ is the precise calibration of the first rung of this ladder – the distance to nearby galaxies.

 

Polish cosmic ruler

Prof. Grzegorz Pietrzyński together with Dr. Dariusz Graczyk and the rest of the team of the Araucaria project callibrated the method based on eclipsing binary systems. This simple geometrical method (called the Polish cosmic ruler) allows to determine distances to single eclipsing systems up to 1 Mpc (megaparsec) with an accuracy of 1%. It should be noted that the geometrical method has been used to measure the distances to nearby objects only. Even when the space observatory Gaia achieves its nominal accuracy, it will provide distances with an accuracy of 1% to objects located only about 1 kpc (kiloparsec) away. The Polish cosmic ruler offers the same accuracy at distances thousands of times longer. In the near future and with the help of large telescopes (e.g. 40-m E-ELT), it will be possible to use this method to determine even larger distances.

Thanks to ERC Synergy grant, this method will be refined and used to measure distances to nearby stars and galaxies. Scientists will also calibrate the Baade-Wesselink method that allows measuring geometric distances even at larger distances – based on photometric and spectroscopic observations of classical Cepheids. These two methods together with the distances to the Milky Way Cepheids provided by the Gaia satellite will form an excellent basis for an improved calibration of supernovae and more precise determination of the Hubble constant. 

 

Independently from measuring distances to supernovae, scientists will conduct an extensive monitoring of quasars. Thanks to the registration of signal delays in different colors, they will  determine distances to over 150 of these objects. This method is relatively new and requires some theoretical refinement, but thanks to it, the Hubble constant will be determined completely independently of the previously discussed cosmic distance ladder. This will be an excellent test of both methods, and in addition, the quasar method will allow us to reach further into the Universe and measure not only the Hubble constant, but also other cosmological parameters.

 

We will build a new telescope at the observatory in Chile

A key element in the implementation of this very ambitious project is the Polish Cerro Armazones Observatory (CAO) in northern Chile. It is located in the Atacama Desert, which is considered to be the world’s best stargazing site.

Until now, Polish observatory project has been supported from the funds of the Ministry of Science and Higher Education. Thanks to the ERC funding, a modern telescope with a mirror diameter of 2.5 m and a camera sensitive to infrared wavelengths will be built.

The project will be carried out by the Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences together with the following partner institutions: the Center for Theoretical Physics of the Polish Academy of Sciences, Universidad de Concepción, Paris Observatory and The Heidelberg Institute for Theoretical Studies.

 

Prof. Grzegorz Pietrzyński and the Araucaria project

Prof. Grzegorz Pietrzyński is the winner of many prestigious research grants, including the ERC Advanced grant, Foundation for Polish Science, National Science Center and the Ministry of Science and Higher Education. He is the co-founder and leader of the international Araucaria project. He has won numerous awards for his outstanding contributions to physics, including the Marian Mięsowicz Award of the Polish Academy of Arts and Sciences (2011), the Nature magazine awards (2014), and the Maria Skłodowska-Curie Award of the Polish Academy of Sciences (2019). Together with the team, Prof. Pietrzycki has won the second place in the "Science is Freedom" poll announced by the Ministry of Science and Higher Education for the greatest Polish invention or scientific achievement of the last 25 years (2014).

The greatest success of the Araucaria project is measuring the distance to the Large Magellanic Cloud (LMC) – our nearest neighboring galaxy – with an unprecedented accuracy that astronomers had long dreamed about – uncertainty of just 1%. This is the most accurately measured distance to another galaxy obtained to date. The project resulted in numerous publications, among others in the prestigious Nature journal.

 

Historical contex

The idea to build an astronomical observatory in Poland was behind establishing Institute (Division) of Astronomy of the Polish Academy of Sciences in 1956, which would later become current CAMK PAN. The working name of the observatory was Central Astronomical Observatory (COA in Polish) and it was to be equipped with a 2-m class telescope. The current project assumes a 2.5 m telescope, located in OCA (Observatory Cerro Armazones) - amusingly similar.