New Delhi: In 1941, Indian physicist Prahlad Chunnilal Vaidya solved Einstein’s equation for a gravitational field for a radiating star like our Sun. Vaidya’s solution provided a classical model, that is known as Vaidya radiation. New research now shows that the Vaidya radiation when it comes to an accreting black hole, or actively feeding black hole is generated by the tidal deformation of the infalling matter. That is the tortured infalling material heats up close to the event horizon, the boundary beyond which nothing, not even light can escape. This radiation is purely classical, and originates from the heating up of the accreting material.
Rituparno Goswami from the University of KwaZulu-Natal in Durban and Naresh Dadhich from the Inter-University Centre for Astronomy and Astrophysics in Pune have demonstrated that the Vaidya radiation allows heat to be eliminated, which is a necessary and sufficient condition for the event horizon to remain unstretched. Material approaching the event horizon is accelerated close to the speed of light, and essentially becomes light, which is why there is no need for the event horizon to expand. The researchers were also able to show that the Vaidya radiation paves the way for the well-known Hawking radiation to propagate outwards, allowing for the black hole to quantum mechanically evaporate.
Classical and Quantum radiation from Black Holes
Both Prahlad Chunnilal Vaidya and Naresh Dadhich were students of Vishnu Vasudev Narlikar. A paper describing the findings has been published in Physical Review D. Naresh Dadhich says, “For a black hole to remain a black hole, infalling fluid must be in consonance with fluid on black hole horizon. For that it has to undergo tidal deformations giving out heat flux which manifests as classical Vaidya radiation emanating from the boundary of accreting zone. It is amazing that an accreting black hole not only radiates quantum Hawking but also classical Vaidya, and the latter paves the way for the former to reach out to infinity.”
