Scientists have found a new way to detect a bare or naked singularity – the most extreme object in the universe where the usual laws of physics break down. When the fuel of a very massive star is spent, it collapses due to its own gravitational pull and eventually becomes a very small region of arbitrarily high matter density, that is a ‘singularity’.
If this singularity is hidden within an event horizon, which is an invisible closed surface from which nothing – not even light – can escape, the object is called a black hole.In such a case, we cannot see the singularity and we do not need to bother about its effects, researchers from the Tata Institute of Fundamental Research (TIFR) in Mumbai said.
However, Einstein’s theory of general relativity predicts that the event horizon does not form when massive stars collapse at the end of their life-cycles. In this case, we are left with the tantalizing option of observing a ‘naked singularity’. Researchers, including those from the Institute of Mathematics of Polish Academy of Sciences in Poland, investigated how to observationally distinguish a naked singularity from a black hole.Einstein’s theory predicts an interesting effect – the fabric of spacetime in the vicinity of any rotating object gets ‘twisted’ due to this rotation.
This effect causes a gyroscope spin and makes orbits of particles around these astrophysical objects precess (the axis on which the body rotates changes its orientation).
The team argued that the rate at which a gyroscope precesses (the precession frequency), when placed around a rotating black hole or a naked singularity, could be used to identify this rotating object.
“If an astronaut records a gyroscope’s precession frequency at two fixed points close to the rotating object, then two possibilities can be seen,” researchers said.
“The precession frequency of the gyroscope changes by an arbitrarily large amount, that is, there is a wild change in the behaviour of the gyroscope; or the precession frequency changes by a small amount, in a regular well-behaved manner,” they said.
In the first case, the rotating object is a black hole, while the second is a naked singularity.Researchers showed that the precession frequency of a gyroscope orbiting a black hole or a naked singularity is sensitive to the presence of an event horizon. A gyroscope circling and approaching the event horizon of a black hole from any direction behaves increasingly ‘wildly,’ that is, it precesses increasingly faster, without a bound. However, in the case of a naked singularity, the precession frequency becomes arbitrarily large only in the equatorial plane, but being regular in all other planes.