30.10.2017 change 06.11.2017

Article by Polish astronomers highlighted by AAS Nova

Keyboard with glowing programming codes Keyboard with glowing programming codes

Article by Polish astronomers on the origin of ultraluminous x-ray sources has been highlighted by the American Astronomical Society. The calculations necessary for the research were performed by ... "borrowing" computing power from Internet users.

According to information published on the website of the Nicolaus Copernicus Astronomical Center by one of the authors of the paper, Dr. Grzegorz Wiktorowicz, AAS Nova editors recognised both the scientific value of the article and its science promotion value connected with the engagement of Internet users in scientific calculations. Through the Universe@Home project, they shared the computing power of their computers, increasing the available power and computing speed. [We have already written about the Universe@Home project].

The article "The Origin of the Ultraluminous X-Ray Sources" was highlighted at the end of September by the American Astronomical Society\'s website AAS Nova, which provides brief highlights of articles published in the AAS journals. The authors are Grzegorz Wiktorowicz from the University of Warsaw, Malgorzata Sobolewska from the Harvard-Smithsonian Center for Astrophysics and Jean-Pierre Lasota and Krzysztof Belczyński from the Nicolaus Copernicus Astronomical Center in Warsaw.

As Dr. Wiktorowicz explains, the article highlighted by AAS Nova concerns ultraluminous x-ray sources (ULXs) - objects not located in galactic centres, whose X-ray brightness exceeds 10^39 ergs per second (the Eddington limit for a typical black hole). Such brightness can be achieved during the transfer of mass not only to black holes, but also to neutron stars, according to a population synthesis study.

Recently, three pulsars have been detected as ULX components; this shows that the emissions in these objects are significantly above Eddington. Previous research has shown that these pulsars could be the tip of the iceberg, and ULXs may in fact often contain neutron stars. However, only extensive simulations conducted by Polish astronomers have allowed to examine this issue for the first time, according to the information posted on the Nicolaus Copernicus Astronomical Center website.

Simulations have shown that black holes will dominate the ULX populations in star-forming areas. This is consistent with our current knowledge: ULXs are most often observed in these areas that and they are also brightest there. On the other hand, neutron stars will dominate in areas where star-forming activity has ceased or is continuing, and metallicity is comparable to that of a sun.

The research of Polish astronomers has also shown that the ULX population with neutron stars (NSULX) is heterogeneous due to the accompanying stars. The authors presented the relationship between the age at which the object is visible as a ULX and the evolutionary phase of the star-companion.

As it turns out, the youngest NSULXs - the ones most commonly found in star-forming regions - will consist mainly of main sequence stars. In turn, systems that are in the ULX emission phase several hundred years after the formation of the stars will usually contain stars passing through the Hertzsprung gap. The oldest ULXs, found in 1 billion years old or older populations, will consist mainly of red giants. Typical masses of star-companions are in the range of 0.6-1.5 solar masses - this may explain difficulties in observations of the accompanying stars in most known ULXs.

The article was published in the Astrophysical Journal (doi:10.3847/1538-4357/aa821d).

PAP - Science and Scholarship in Poland

author: Katarzyna Florencka

editor: Anna Ślązak

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