The position of quasars varies over time


An article published in the journal “Monthly Notices of the Royal Astronomical Society” reports evidence that the position of quasars is not fixed. A team of astrophysicists from the Moscow Institute of Physics and Technology combined global observations of 40 quasars between 1994 and 2016 for this study. Based on the fact that the apparent positions of quasars change according to the frequency of the radiation used to observe them, the researchers wanted to verify if that effect could vary over time. Quasars are used as cosmic reference points, knowing their exact location can increase their reliability.

Quasars are extremely bright galactic nuclei due to supermassive black holes surrounded by rings of materials that fall towards them generating very high amounts of electromagnetic radiation. For this reason they’re part of what are called Active Galactic Nuclei (AGNs).

About 40 years ago researchers relied on synchrotron radiation theory to predict that the apparent positions of quasars change depending on the frequency of the radiation used to observe them and verified that effect. The new research aimed to verify if this effect could vary over time and in that case the timeline and the extent of the apparent position changes.

To obtain the accuracy of the observations needed for the test, the researchers used a version of the interferometry technique called very long baseline interferometry (VLBI) because it’s based on the combination of observations of radio telescopes in different places of the world, as illustrated in NASA’s image. That’s the same technique used by the EHT (Event Horizon Telescope), very sophisticated but exactly for that reason very complex to manage. For this reason, specific procedures are developed to process the data coming from the various instruments and the Russian team did that too.

The result of the work done is that the apparent coordinate of the quasar’s jet apex isn’t static but oscillates back and forth along the axis of the jet. Astrophysicists consider those oscillations a sort of illusion they explain in terms of the complex nature of the radiation emitted. This implies that quasar cores don’t actually move in space. The researchers tested that idea by putting together all the data and the result was that they detected a variability in the position and interpreted it in terms of the jet’s internal physics. To better understand the problem they checked the apparent positions of the quasars looking for potential correlations with variables such as their brightness or magnetic fields.

It turned out that the apparent coordinates of a quasar are directly associated with the density of particles in the jet: the higher the brightness, the greater the displacement of the perceived position. This could be a complement to the theoretical models about quasars given that indicate the role of flares in their nuclei that inject high density plasma into the outflow.

There are applications of astrometric techniques that also rely on the position of quasars, so this research hasn’t a purpose limited to the field of astronomy but can have practical consequences. There are systems such as navigation systems that are becoming increasingly sophisticated but exactly for this reason the positions of the reference points they use must be known with extreme precision.

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