Press Release

NAS RA V. Ambartsumian Byurakan Astrophysical Observatory (BAO)
Press release 09.05.2023

“NEW ERUPTIVE VARIABLE(S) IN THE RAFGL7009S HII REGION” WAS PUBLISHED IN THE BRITISH JOURNAL MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

Researchers of the Byurakan Astrophysical Observatory Nikoghosyan, E. H., Azatyan, N. M., Andreasyan, D. H., Samsonyan, A. L., Yeghikyan, A. G., Baghdasaryan, D. S. together with Kaper, L. and Harutyunyan, N. A. published their new paper, “New eruptive variable(s) in the RAFGL7009S HII region”, in the Monthly Notices of the Royal Astronomical Society.

The Byurakan Astrophysical Observatory has always been at the forefront of this direction of astrophysical research. Over the past decades, several FUors were discovered and studied. This list was completed with another object that was discovered this year. A comparison of the observations made almost over the past 20 years showed that the brightness of the new FUor, J183421.85-055951.0, has increased almost a thousand times (see Figure). The object itself is a young star located in the active region of star formation RAFGL7009S, at a distance of about 2 kpc (6·1016 km). Its spectral characteristics indicate that this young star is surrounded by a massive circumstellar disk, the accretion activity of which could lead to such a significant increase in brightness. In addition, this young star is a source of intense collimated outflow, which is also one of the properties of FUors.

Studying stars, understanding the basic laws of their formation and evolution is one of the fundamental questions of modern astrophysics. Therefore, great attention is paid to this issue. The efforts of astrophysicists of the whole world gave significant results, revealing some secrets of the Universe. However, among the very rich and diverse stellar population, there are objects among young stars that still remain a mystery. These are the so-called FUor - young eruptive stars, the brightness of which can increase more than a thousand times in a few days, and remain at the same level for several decades. These objects, since the middle of the last century, when the first three such objects were discovered, are objects of intensive study by astrophysicists.

It's interesting to know that it was Viktor Ambartsumian (BAO founder) to name these stars FUors (after the FU star of Orion Constellation, FU-Or).

However, despite the increased attention, they remain a mystery. Moreover, only about 30 such stars are known. Until today, several different models have been proposed to explain the FUors phenomenon. They are based on various physical processes that can lead to a sharp increase in the accretion of matter from the circumstellar disk to the surface of the star. However, none of the proposed models can fully explain all the observational properties of these objects. A number of issues remain unresolved What causes large accretion events? What disables them or temporarily stops them? Do all stars experience high-amplitude accretion flares in the process of formation, or do special circumstances require this? And this list can be continued. Therefore, it is not surprising that every newly opened FUors is a significant event and it becomes an object of active study.

Meline Asryan