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Polish astronomers have improved their "space ruler"

16.06.2017 Space, Recommended

Magellan telescopes against the starry sky at the Las Campanas observatory in northern Chile. The two blue spots on the left are the Great Magellanic Cloud and the Small Magellanic Cloud, the galactic neighbours of the Milky Way. Photo by Yuri Beletsky.

Measurements of distances to galaxies may become more accurate. International research group led by Polish scientists has precisely determined the relationships of stars used as a "space ruler" to measure distances in space.

Cepheids - as the stars of this type are called - are among the most important objects in the Universe. These stars periodically change their diameters (they pulsate). The radius of the star and its temperature increase and decrease by a few percent. This results in changes in brightness that can be observed by telescopes in astronomical observatories on Earth. The relationship between the brightness of Cepheids and the period of their pulsation was discovered more than 100 years ago.


Since then, astronomers have been using Cepheids as so-called standard candles for distance measurements in space. This resulted in many revolutionary discoveries and influenced our understanding of the Universe. For example, Cepheids allowed to measure distances to the nearest galaxies. With these measurements, we now know that these are other galaxies of billions and even hundreds of billions of stars. Previously, the prevailing view was that they were fragments of the Milky Way.


Another fundamentally important aspect of Cepheids is their use in the process of determining the Hubble parameter that describes the physical scale of the Universe and its evolution. This is essential in the study of expansion of the Universe. Cepheids are needed to precisely calibrate the maximum brightness of type Ia supernovae, which are then directly used to determine the Hubble parameter, and to determine distances to very distant galaxies. Currently the main problem in this procedure is the precise determination of how the brightness of Cepheids depends on the metal content. It is worth pointing out that astronomers call all elements heavier than hydrogen and helium metals.


"Previous attempts to solve this problem have not produced the expected results" - noted Piotr Wielgórski. "Despite the great efforts of theorists and observers, it has not even been possible to determine whether an increase in metallicity results in an increase in Cepheid brightness, or its decrease" - he explained.


International team of scientists, led by researchers from the Nicolaus Copernicus Astronomical Center in Warsaw, has shown that the effect of metallicity on the brightness of Cepheids is very small and to the accuracy of measuring errors (2%) it is zero. "This is another very important discovery made within our project that paves the way to measuring the Hubble parameter with unprecedented accuracy of 1 percent" - said the project leader Prof. Grzegorz Pietrzyński.


The researchers analyzed high-quality brightness measurements of stars in the Large Magellanic Cloud and Small Magellanic Clouds, in both visible and infrared ranges. Optical data came from the Polish OGLE survey. In turn, the infrared data came from the observations with the IRSF telescope in South Africa.


In recent years, the Araucaria team gained recognition for extremely accurate determination of distances to nearby galaxies, including the Universe distance standard - the Great Magellanic Cloud. For his research, Prof. Grzegorz Pietrzyński was awarded the prestigious Advanced Grant by the European Research Council, established by the European Commission.


The Araucaria team also won the second place in the "Science is Freedom" poll for the most interesting invention, scientific achievement and or of the last 25 years. The poll was conducted by the Ministry of Science and Higher Education.


The publication describing the results of the latest research will appear in the Astrophysical Journal. Among the 10 authors of the paper, five are Polish researcher: Piotr Wielgórski (Nicolaus Copernicus Astronomical Center PAS), Grzegorz Pietrzyński (Nicolaus Copernicus Astronomical Center PAS), Bartłomiej Zgirski (Nicolaus Copernicus Astronomical Center PAS), Dariusz Graczyk (Nicolaus Copernicus Astronomical Center PAS) and Igor Soszyński (Astronomical Observatory of the University of Warsaw).


PAP - Science and Scholarship in Poland


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Tags: astronomy
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