Two city-based scientists are involved in the discovery of two closest-ever black holes, in a super-massive binary black hole system, located about 400 million light years away from earth. The black holes have been detected to be physically separated by just one light year and are part of an active galaxy.
Active galaxies glow unusually intense at their centre, unlike other normal galaxies which appear evenly bright. There are only a handful of active galaxies and they are normally known to have only one black hole situated somewhere near their centre.
The new discovery, by Preeti Kharb and Dharam Veer Lal of TIFR-National Centre for Radio Astrophysics, Pune, and David Merritt from Rochester Institute of Technology, USA, has been published online, in Nature Astronomy, on September 18. What makes the discovery unique is the fact that such a binary black hole system is being housed in a spiral galaxy, identified as NGC 7674 (Mrk 533). Scientists say such systems were known to be present only inside elliptical galaxies.
“Elliptical galaxies are formed when two spiral galaxies collide and merge. They possess one super massive black hole located in its centre. But, in this case, it is a binary super massive black hole inside a spiral galaxy, never known so far,” said Lal.With strong radio jets emanating from this newest discovered object, scientists claim that it could be a potential candidate, only fifth or sixth, from which radio jet speed has been ever calculated.
Kharb, who mostly worked on analysing the images since April this year, obtained high resolution images using a technique called very long baseline interferometry. The central region of Mrk 533 was completely imaged at varying frequencies of 2GHz, 5 GHz, 8GHz and 15 GHz. It would not have been possible to detect the closeness of the two black holes without the high resolution offered by 10 dish antennas, all located in the US.“The powerful antennas, across a distance of 8,900 kms in the US, was used to image this object, that clearly confirmed the one light year separation between the two massive black holes,” informed Lal.
The astronomers will now be working on tweaking the existing theoretical models to obtain an explanation for the presence of such an object inside a spiral galaxy.“Now, whenever there is a merger of two spiral galaxies, it will in reality be the merger of three bodies instead, presenting a completely newer kind of a problem to be solved,” said Lal.