Observing the most distant, yet powerful, engines of the Universe helps astronomers to understand its early formation

Radio astronomers have used a technique known as Very Long Baseline Interferometry (VLBI1) to produce high resolution images of the most distant known blazar. The findings, reported in Nature Communications, cover the motion and emission of a jet originating from the heart of the blazar, to provide insights on how galaxies evolve.

At the heart of every galaxy resides a supermassive black hole, in some cases weighing a billion times more than the Sun. It is still not known how, during the early development of the Universe, such massive black holes could form and grow rapidly in the centre of young galaxies.

Studies of Active Galactic Nuclei (AGN) help to answer this question. AGN are the central objects of galaxies in which the gravitation of the black hole converts the infalling material (accretion) into light. AGN also have a highly energetic stream of material that is ejected from their centre, known as a jet. Such AGN are classified according to the direction of the jet relative to the observer. If a jet is pointing towards Earth, the AGN is known as a blazar and is distinguished by highly beamed and variable emission.


Blazars provide efficient opportunities to study the AGN, their accretion disc, the supermassive black hole, the jet and the surrounding galactic environment. All these studies are of special value if the object is at a high-redshift2 and therefore corresponding to an early cosmological epoch.


In the current study, the team used the Very Long Baseline Array (VLBA) in the United States to conduct high resolution radio observations of the luminous blazar J0906+6930. At a redshift of 5.47, the blazar visible today emitted its radiation nearly 13 billion years ago. “This object is actually the most distant one known to date in this class of AGN” says Tao An of Shanghai Astronomical Observatory in China, lead author of the study. “Earlier studies by our team revealed the presence of a jet that is apparently bent quite close to its base, the AGN core. However, these studies could not explain the physical conditions in the source.”


The researchers studied the source over a 14 year period to produce a series of multi-epoch images. In doing so they detected a polarized emission for the first time and measured the motion in the innermost jet of the blazar. The overall properties observed indicate that that AGN is young, with a slightly less relativistic jet than is usually observed in blazars. The astronomers suggest that a possible interpretation of the results could be that the bent jet is embedded in and interacting with a dense surrounding medium.


“Studies of AGN located at extremely large cosmological distances with ultimate angular resolution offered by VLBI provide unrivalled insight into the physics of these most powerful engines of the Universe and help to understand the laws of nature at the global cosmological scale” says Leonid Gurvits of JIVE, a member of the study team.


Zsolt Paragi of JIVE underlines that “observations with future arrays, such as the VLBI enabled Square Kilometre Array, should provide further opportunities to study blazars in increasing detail and from fainter sources”. 


Paper link

Tao An, Prashanth Mohan, Yingkang Zhang, Sándor Frey, Jun Yang, Krisztina É. Gabányi, Leonid I. Gurvits, Zsolt Paragi, Krisztina Perger, Zhenya Zheng. 2020. Evolving parsec-scale radio structure in the most distant blazar known. Nature Communications. https://www.nature.com/articles/s41467-019-14093-2 (only available after embargo release)



Prof. Tao An

Shanghai Astronomical Observatory, Chinese Academy of Sciences

Email: antao [at] shao [dot] ac [dot] cn

Phone: +86 21 34775503


Assistant Prof. Prashanth Mohan

Shanghai Astronomical Observatory, Chinese Academy of Sciences

Email: pmohan [at] shao [dot] ac [dot] cn 


PhD Student Yingkang Zhang

Shanghai Astronomical Observatory, Chinese Academy of Sciences

Email: ykzhang [at] shao [dot] ac [dot] cn


Prof. Zhenya Zheng

Shanghai Astronomical Observatory, Chinese Academy of Sciences

Email: zhengzy [at] shao [dot] ac [dot] cn


Additional Information

1.     VLBI is an observational technique in radio astronomy, characteristic of extremely high resolution (up to milli-arcseconds and sharper) imaging and high positioning accuracy. It is a powerful tool to investigate the compact celestial objects.

2.     Cosmological redshift is an indicator of the distance of a celestial object in the expanding Universe.

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