12-Jun-2022: Binary super massive black hole discovered in a system which could be site of future gravitational waves detection

An international collaboration of astronomers has discovered a binary super massive black hole in a system which will be a strong candidate for future detection of gravitational waves (GWs).

Blazars which are super massive black holes (SMBH) feeding on gas in the heart of a very distant galaxy, are among the most luminous and energetic objects in the Universe. When the jet, composed of ionized matter traveling at nearly the speed of light, is pointed towards an observer, it is called a blazar. The blazar AO 0235+164 is unique as it is gravitationally lensed by intervening galaxies (phenomenon by which light shining from far away to be bent and pulled by the gravity of an object between its source and the observer).

A group of astronomers from Argentina, Spain, Italy, USA and India has discovered a binary super massive black hole system in the gravitationally lensed blazar AO 0235+164 using extensive optical photometric observations carried out around the globe during last 4 decades (1982 - 2019). They discovered periodic double-peaked flaring events at an interval of around 8 years, and the separations between two peaks of these flares are around 2 years. Five such periodic patterns were detected, and it was predicted that the next such flaring event will occur between November 2022 and May 2025. To confirm the next periodic pattern, a global optical photometric monitoring campaign has been initiated under WEBT (Whole Earth Blazar Telescope) consortium. The observational campaign will be led by Dr. Alok C. Gupta.

Dr. Alok C. Gupta, Senior Scientist from Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, an autonomous institution of the Department of Science and Technology (DST), Government of India, has participated in this study which has been recently published in the journal Monthly Notices of the Royal Astronomical Society (MNRAS). The study was led by Mr. Abhradeep Roy, a Ph.D. student of the Department of High Energy Physics (DHEP), Tata Institute of Fundamental Research (TIFR), Mumbai. The other members of the Indian team include Prof. V. R. Chitnis, Dr. Anshu Chatterjee and Dr. Arkadipta Sarkar from TIFR, Mumbai.

The team detected five sets of double-peaked flaring activities during time ranges ---  January 1982 - October 1984, March 1989 - July 1993, April 1996 - March 2001, June 2006 - June 2009 and May 2014 - May 2017.

They expect the next such 2 years long flaring episode to happen between November 2022 and May 2025. An intensive multi-wavelength WEBT campaign will be conducted during this period to test the persistence of this apparent nearly-periodic oscillation (QPO) in AO 0235+164.

The blazar AO 0235+164 is the first binary SMBH gravitationally lensed system, which will be a strong candidate of its kind for future detection of gravitational waves (GWs) using the pulsar timing array and future space-based GW detectors.

17-Mar-2021: Possible origin of winds from black hole accretion discs probed

As gas and dust fall toward a black hole, they form a disk around it. As material piles up in the disk, it heats up to temperatures in excess of millions of degrees. A fraction of this infalling matter is ejected in the form of winds.

Scientists have tracked the generation of this wind and how it is driven by the disc of diffused swirling materials around the black hole called an accretion disc.  Matter flowing out due to the wind should contaminate the environment play a major role in the evolution of the region harbouring these black holes. Therefore how such a process can be triggered need to be ascertained. Though these processes are still at the level of theoretical prediction, consensus has not been reached.

By blowing dense gas from the galactic nucleus and by halting inward flows from the galactic halo, the winds play a vital role in shaping the evolution of the black hole host galaxy. Hence the mechanism of generation of these winds and what drives them has intrigued scientists for a long as it helps them explore host galaxies.

Scientists from Aryabhatta Research Institute of observational sciences (ARIES), an autonomous institute under the Department of Science and Technology (DST), Govt. of India, in collaboration with scientists from other institutions Scientists, undertook a time-dependent study of the generation of wind and its subsequent driving by the radiation from the diffuse material in spiral motion around a massive central body called the black hole accretion disc using numerical simulation techniques developed indigenously.

The scientists tried to figure out whether driving of the wind by radiation flux can dominate the radiation drag effect--- a motion resisting effect which is similar to the resistance offered by air to a moving stone or to a descending parachute. This effect is produced when radiation penetrates a moving medium and is proportional to radiation energy density, various components of radiation pressure, and the velocity components of the wind.

The authors showed that luminous discs can produce winds up to speeds which is about ten percent of the speed of light, and also that these winds originated from regions close to the central black hole. Radiation drag plays a key role in reducing the speed of light. For less bright discs, radiation drag quenches the wind completely.

The research was led by Sananda Raychaudhuri of Bose Institute, Kolkata, in collaboration with Mukesh K. Vyas of Bar Ilan University, Israel, and Indranil Chattopadhyay of ARIES and has recently been accepted for publication in the scientific journal Monthly Notices of Royal Astronomical Society (MNRAS). The authors used a numerical simulation code developed earlier by Dr. Chattopadhyay to study the galaxy environment by modifying it suitably to perform the simulations of wind flow from black hole accretion disc.