An international team of scientists has made a surprising discovery. The blazar BL Lacertae - a galaxy 900 million light years away from Earth - does not fit into any category of this type of object and quickly 'jumps' from one to another, says Alicja Wierzcholska, PhD, from the Polish Academy of Sciences.
The scientist from the Institute of Nuclear Physics of the Polish Academy of Sciences informed reports in an interview with PAP that the blazar BL Lacertae, observed in the years 2020-2023, shows unprecedented classification variability. The work of researchers from the Institute of Nuclear Physics PAS and the University of Heidelberg (Germany) on this subject was published in the journal Astronomy & Astrophysics.
Blazars are active galaxies whose nuclei emit intense electromagnetic radiation. This phenomenon, as the astrophysicist points out, probably results from complex processes occurring during the fall of matter onto the supermassive black hole located at the centre of galaxy.
'A characteristic feature of blazars are jets, i.e. narrow streams of ionised plasma ejected from the vicinity of the black hole's poles at speeds close to the speed of light. In the case of blazars, the jet is directed almost exactly towards the Earth', Wierzcholska explains.
Blazars are classified based on their electromagnetic spectrum. They are divided into radio quasars and lacertids (with weaker emission lines). Within lacertids, there are also subclasses: HBL (High-frequency peaked BL Lac), LBL (Low-frequency peaked BL Lac) and IBL (Intermediate BL Lac), one of whose energy maxima lies in the range of high, low and medium frequencies.
'The blazar spectrum has two +peaks+ and depending on their position on the graph showing the distribution of radiation energy, we can talk about different types', the researcher clarifies.
Scientists targeted the blazar BL Lacertae, discovered in 1929 in the background of the Lacerta constellation, located 900 million light-years from Earth.
Researchers from Poland and Germany analysed data covering X-ray, optical and ultraviolet radiation. 'We used data from instruments in space, primarily from the Swift satellite observatory. We supplemented observations in the range of soft X-ray radiation with data from the NuSTAR (Nuclear Spectroscopic Telescope Array) satellite in the higher energy range', Wierzcholska says.
The scientists discovered that BL Lacertae, previously classified as IBL, showed surprising variability.
'We were surprised to notice that in the X-ray range, in some phases of the observation period it looked like HBL, in others like LBL, and at other times it gave the impression of an IBL-type object. The type changes occurred very quickly. The deeper we look at this object, the more interesting it seems', Wierzcholska says.
Scientists do not agree on what to attribute the two peaks in the spectra of blazars to. They suppose that they correspond to phenomena related to various particles in the jet. The first, low-energy peak probably corresponds to synchrotron radiation emitted by electrons. It is less clear what to attribute the second peak to. According to some researchers, it may indicate the activity of electrons (for example, their collisions with low-energy photons) or hadrons (particles composed of +glued+ quarks, e.g. protons or neutrons).
But what causes such rapid changes in the radiation spectrum in the case of the BL Lacertae? The astrophysicist admits that there is no clear explanation for this phenomenon. 'Blazars are celestial objects that we do not fully understand despite many years of observation. Therefore, further, long-term observations of these objects at different frequencies are necessary so that we can better understand their complex nature', Alicja Wierzcholska concludes.
PAP - Science in Poland, Anna Bugajska (PAP)
abu/ agt/ amac/
