27.08.2018 change 27.08.2018

Polish-Lithuanian hunt for black holes

Photo: Fotolia Photo: Fotolia

The Polish-Lithuanian group of astronomers will work on detection of black holes hiding in our Galaxy; small telescopes throughout Europe will also aid their search. Dr. Łukasz Wyrzykowski (Astronomical Observatory of the University of Warsaw) describes for PAP the project he’s leading.

As part of the research project that is just starting, astronomers from Warsaw and Vilnius will look for black holes that should be in the Milky Way.

"Only a few dozen small, stellar black holes have been found in the entire Universe" - Dr. Łukasz Wyrzykowski from the Astronomical Observatory of the University of Warsaw admits in the interview with PAP. - "Meanwhile, there should be millions of them in our Galaxy alone!"

The small number of discovered stellar black holes is just one example showing that we still know little about these objects. "The first known black holes have been found in x-rays from cosmic observatories: they keep +snacking+ on their star companions, so they emit high-energy radiation. Completely different black holes were detected in 2015 thanks to the detection of gravitational waves: a system of two massive black holes during their merger and creation of an even more massive black hole" - reminds Dr. Wyrzykowski.

A Polish-Lithuanian research group wants to use gravitational microlensing to search for black holes. "This is our Polish specialty: it has been used by the Polish OGLE program for over 25 years, mainly to search for planets. We want to extend it to black holes" - the researcher says.

Microlensing uses the fact that massive objects - such as planets or black holes - bend space-time in such a way that the light of the stars behind them is bent in a specific way. But there is a problem: black holes are much more difficult to detect than planets.

"This is because terrestrial observations are not enough to unambiguously determine the nature of the registered phenomenon: in these data, a massive and fast black hole will look just like an ordinary star moving slowly" - explains Dr. Wyrzykowski. Astronomers must complement their information with data from orbital observations. For this purpose they will use the data from the European Gaia mission, in which a satellite sent by the European Space Agency performs precise measurements of the positions of stars. The combination of these two data sources gives hope for the unambiguous detection of black holes.

To fund their research the group led by Dr Wyrzykowski secured a DAINA grant from the Polish National Science Centre. "Polish and Lithuanian astronomers are among the most experienced observers of stars in Europe. We cooperated with the Lithuanians on many observations, so when the opportunity to formalize this cooperation presented itself - we decided to do it" - the researcher told PAP. The leader of the Lithuanian group is Dr. Marius Maskoliunas from the University of Vilnius.

"When looking for temporary phenomena, such as supernovae, you have to watch the whole sky, because it is impossible to predict where and when they will appear. It`s the same with gravitational microlensing caused by black holes, which is why we need an international group of observers" - emphasizes Dr. Wyrzykowski.

As part of the project, astronomers want to create a network of observatories that will conduct coordinated observations of phenomena recorded by the Gaia satellite. "We will use telescopes located in Chile or the Canary Islands, the best places for astronomical observations" - the researcher says.

But those telescopes will not be the core of the network of observatories observatories – that role will be played by small European telescopes. "There are a lot of small telescopes in Europe with diameters below one meter. Although some of them were built even 100 years ago, they are still excellent instruments. Contemporary telescopes are often much worse when it comes to optics precision" - explains Dr. Wyrzykowski.

In addition, the northern part of the Milky Way can be seen very well from Europe - and is the best place to look for black holes in the disc of our Galaxy, because the microlensing phenomenon occurs there once a month on average. "Despite the fact that weather conditions in Europe are not the best for astronomical observation, the extensive network of observatories will allow to collect data practically every night" - adds the researcher.

PAP - Science in Poland

author: Katarzyna Florencka

kflo/ agt/ kap/

tr. RL

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