Indian Astronomers have found an active galaxy in a very bright state with 10 times more X-ray emission than normal, equivalent to more than 10 trillion Sun, and located 5 billion light-years away that could help probe how particles behave under intense gravity and acceleration to the speed of light. It could help study the role of strong gravity and acceleration of matter in the formation, interaction, and evolution of galaxies in the early universe.
Every galaxy in the Universe is believed to host a supermassive black hole (SMBH) at its center. In some galaxies, the black hole is actively devouring a large amount of material and shooting a jet of plasma almost at the speed of light towards us. These are called blazars. OJ 287 belongs to a class of blazars known as BL Lacerate objects which show very rapid and large amplitude flux variations but barely discernible emission line features. This class of sources emit in the whole electromagnetic spectrum, a rather uncommon phenomenon which requires extreme physical conditions. Hence a study of such sources tells us about the behavior of matter in an extreme gravitational field where it is difficult for light also to escape from the vicinity of the black hole.
Astronomers at Aryabhatta Research Institute of Observational Sciences, an autonomous institute of the Department of Science & Technology (DST), Govt. of India, have been monitoring one such black hole system named OJ 287 since 2015. This source shows a repeated optical brightness enhancement almost every 12 years.
The repeated optical enhancement makes OJ 287 very intriguing as this class of sources does not show any repeating features in flux variations. The repeated optical enhancement made the researchers believe that the system hosts a binary black hole.
In 2020, the source was very bright at optical and X-ray bands with X-ray flux more than 10 times the normal (non-active phase) flux. This flare was very different as it was not expected in models proposed for this source and thus, indicated a more complex system and physical conditions. Investigating the extreme brightness shown by OJ 287 at optical and X-ray bands, astronomers led by Dr. Pankaj Kushwaha and Dr. Alok C. Gupta reported the source in a completely new spectral state.
The team argued that this change of state holds the clue to the researcher's quest to understand how matter behaves in very strong gravity and how it accelerates the particle to almost the speed of light – a feat that is out of the scope of even the most advanced CERN accelerator.
The research published in ‘The Astrophysical Journal’ tracked the details of changes in optical to the X-ray emission spectrum of the source with time from 2017 to 2020 – after the 2nd brightest X-ray flare of the source. It revealed how the source gradually started to change its spectral behavior from mid-2018 to the new spectral state in 2020. The study included data recorded by the ground-based facility operated by Physical Research Laboratory (PRL), Ahmedabad operated Mount Abu observing facility in near-infra-red bands and the space-based NASA’s satellites – the Niels Gherel Swift satellite at optical, UV, and X-ray with gamma-ray data from the Fermi satellite.
The study which involved the lead researchers Dr. Pankaj Kushwaha along with Prof Alok C. Gupta from ARIES along with Dr. Main Pal from Jamia Milia Islamia University, Neeraj Kumari – a Ph.D. student with Prof Sachindra Naik from PRL, Ahmedabad, Prof. Elisabete M. de Gouveia Dal Pino from University of Sao Paulo Brazil, Nibediate Kalita, a former Ph.D. student of ARIES with Prof Minfeng Gu from the Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, China shows that the new state originated in the jet of plasma.
The team reported spectral changes at infrared and optical energies that could be associated with the accretion disk of the SMBH of mass equal to around 18 billion Suns. A similar change was also reported by the team during its brightest X-ray flux state in 2017.
Such significant changes in the spectral state of blazars are very rare, and so are the binary SMBH systems in the universe. Multi-wavelength studies of such sources can establish the role of strong gravity and acceleration of particles to the speed of light in the formation of the most energetic jets in the universe, and the formation, interaction, and evolution of galaxies in the early universe.