doi:10.1038/nindia.2015.156 Published online 24 November 2015
Indian astrophysicist Abhas Mitra who has been contesting2 the very existence of 'true' black holes says this only bolsters the theory that black holes are compact balls of plasma called MECOs and not suck-all objects with massive gravities that don’t let even light escape. Mitra was head of theoretical astrophysics at the Bhabha Atomic Research Centre (BARC) in Mumbai till recently and is currently adjunct professor in Homi Bhabha National Institute.
Nature India: What does the X-ray flare from a black hole observed by NASA astronomers say?
Abhas Mitra: A true black hole is just a vacuum except for the central singularity where the star material is supposed to get crushed into a geometrical point. It cannot possess any corona or any magnetic field by itself. So, NASA's explanation of a compact corona around a black hole ejecting the flare is still not very clear.
As per Einstein's General Theory of Relativity, extremely massive stars collapse into ultra-compact objects called black holes. The powerful gravitational field of the black hole does not allow even light to escape and anything that gets within a certain distance of its centre, called the Event Horizon, will be trapped.
NI: What has been your line of contention on this?
AM: Along with American collaborators Darryl Leiter (University of Virgina, now deceased), Stanley Robertson (South Okalohoma State University), Norman Glendenning (Lawrence Berkeley Laboratory) and Rudy Schild (Harvard University), we have shown that these so-called black holes are not exactly black holes.
As a massive star contracts to the size of a black hole, the radiation trapped within the extremely hot star must exert an outward force to counter the gravitational pull. At this stage collapse would get stalled into a state of eternal contraction with an infinitesimally slow rate.
Thus instead of true black holes predicted by Einstein's theory, we proposed that massive stars end up as balls of fire -- called quasi-black holes or Magnetospheric Eternally Collapsing Objects (MECOs). Relevant proof behind this new paradigm have been published in leading peer reviewed journals since 2000.
NI: How does this explain NASA's recent observation of eruption from black hole?
AM: The best example of a magnetised ball (plasma) of fire is the Sun which is surrounded by a tenuous aura of plasma called corona. Instabilities associated with this magnetised plasma result in intermittent eruptions from the Sun in the form of solar flares and coronal mass ejections.
NASA's observation can be most naturally explained by the MECO paradigm. MECOs possess accretion disks around them, something similar to the rings of Saturn, and also may be immersed in a sea of interstellar gases. Gas streams pulled inward by gravity get extremely hot by friction and may radiate X-rays. While a true black hole cannot possess any intrinsic magnetic field, there can be magnetic field associated with the disk or gas surrounding a MECO. Strong magnetic fields have indeed been detected around several so-called `black holes’ suggesting that they are actually MECOs and not true (Einstein's) black holes.
This super strong flare witnessed by NASA, which appeared to originate right from the central compact MECO, is something akin to the well-known phenomenon of ‘Coronal Mass Ejection’ from the Sun.
NI: What does this entail for the astrophysics community?
AM: This latest astrophysical observation by NASA should prompt astrophysicists to take a closer look at the MECO paradigm. Further, if it is realised that the so-called black holes are not true black holes, the Black Hole Information Paradox -- which says that black holes destroy any information that goes into them – could cease to exist.
One of the fundamental shortcomings of Einstein's theory that it is at odds with Quantum Mechanics could then become irrelevant. And, in the absence of event horizons and singularities, there may not be a compelling requirement for ‘Quantum Gravity’ – a theory which could merge Einstein's theory and Quantum Mechanics in a smooth framework.