5th Confab With CosmosNow
Dr. Abhas Mitra is Former Head, Theoretical Physics Section, BARC and currently an (Hon) Adjunct Professor at Homi Bhabha National Institute. He pioneered theoretical research on Cosmic Gamma-Ray Bursts in India since 1995. He has authored almost 120 research papers & book chapters.
CosmosNow – Hello Dr. Mitra! We are really honored to have you on the 5th Confab with CosmosNow. We are really excited to get some amazing and inspiring answers from you.
Dr. Abhas Mitra – Thank you CosmosNow for letting me indulge! I’m more than excited to answer your questions.
CosmosNow – Were you curious about Astronomy and space as a kid? When did it all start?
Dr. Abhas Mitra – It may sound surprising that in my younger days I had hardly any curiosity for Astronomy expects for wondering for the stars as any kid would do. Astronomy or astrophysics was never taught in my M.Sc. days, though as a student with a specialization in Nuclear Physics, we were compelled to read a bit about Cosmic Rays. On the other hand, my interest lay in theoretical aspects of basic physics like Classical Mechanics, Quantum Mechanics, and Elementary Particle Physics. In particular, the notion of abstract symmetries in particle physics, like U(1) gauge symmetry in Electromagnetism, where U(1) stands for Unitary Group of Rank 1, fascinated me. In particular, the fact that the Standard Model unifying Strong, Weak and Electromagnetic interactions can be described by U(1) X SU(2) X SU(3) symmetry appeared to be magical; here SU means special unitary group”.
In 1979, I was selected for the 23rd batch of BARC training school. Having passed out of, naturally, I wanted to pursue Particle Physics. But there was absolutely no such scope as in BARC, one has to work on assigned projects or topics. Neither was there any chance to pursue Nuclear Physics. Then in order to pursue at least some basic physics, ventured for Nuclear Research Laboratory, Srinagar, Kashmir where I heard one might get a scope for basic physics research. But again there too, I was not allowed to do so, and instead was asked to join Observational Gamma-Ray Astronomy Group. NRL had a primitive Gamma-Ray Telescope at Gulmarg and I was supposed to take observations or do data analysis with desktop calculators. But I was dying to do theoretical physics research; one option was to leave the job and proceed to some US university. However, my financial constraints did not allow this.
And it is here I managed to begin some research on various aspects of High Energy Astrophysics entirely on my own and facing a multitude of difficulties.
CosmosNow – In your journey of becoming an Astrophysicist what has transformed you and in what way?
Dr. Abhas Mitra – It has broadened my perspective on physics, science and to some extent life. From a successful research career in Astrophysics, I shifted to General Relativity & Gravitation, again entirely on my own. Subsequently, I shifted to research in Cosmology in complete isolation. In the 70 year history of BARC, I happen to be the only researcher in General Relativity & Cosmology. Research in astrophysics and cosmology requires some knowledge in particle physics and nuclear physics. Accordingly, I have developed an overall perspective in various aspects of physics which is very rare at least in India. For instance, had I pursued theoretical particle physics, as I was keen for, I might have ended as a String Theory with a rather arrogant and closed mind, without the real pulse of the physical world, astrophysics, and physics.
CosmosNow – Your opinion about India’s investment in science particularly in space science.
Dr. Abhas Mitra – India is far from a rich country, and in many ways, it remains a poor county as far as primary education and basic healthcare are concerned. Given this fact, I feel all Indian Governments, irrespective of their political affiliations, have done a lot of investment in Science & Technology. One good thing is that the NDA govt almost doubled the fellowships of Ph.D. students. But I hear that there is a budget cut for research, and I hope this will be reversed. As for Space Science, ISRO is fully funded by Govt of India and is ready to foot bill for all projects.
CosmosNow – What made you aspire towards research on Black Holes?
Dr. Abhas Mitra – I happened to the first researcher from India who had been working on Cosmic Gamma-Ray Bursts which could be a thousand times more powerful than Supernovae events. Type II supernovae are associated with the birth of Neutron Stars following gravitational Collapse of stars having an initial mass range of 8-15 solar masses. And in the early 1990s, it was believed that the birth of Black Holes following from the collapse of much more massive stars gives rise to WEAK supernovae as NOTHING CAN ESCAPE A BLACK HOLE, and Black Holes have no hard surface from which eruption can occur. But by 1997, we learned that there are indeed many GRBs which could be 100-1000 times more powerful than SN explosions. Then what could be the origin of long-duration most powerful GRBs? In the absence of any clear answer, astrophysicists were compelled to invoke the birth of black holes in the context of GRBs, But there was an obvious self-contradiction in this grand assumption. Even if one would assume that the newborn black hole has a massive disk that somehow accretes onto be a black hole to somehow trigger GRBs, there would be a lot of unanswered questions. For instance, since astrophysical BHs have no intrinsic magnetic field, and disk magnetic field are expected to be modest, how would one explain the conversion of accretion kinetic energy of almost pure gamma rays in a matter of a minute or so.
It is at that this stage, I had a hunch that maybe the collapse of massive stars does not lead to the formation of exact back holes having Event Horizons, and maybe such collapse results in only Black Hole Mimickers having a physical boundary.
CosmosNow – What is the Magnetospheric Eternally Collapsing Object? How did you come up with this model?
Dr. Abhas Mitra – For a proper appreciation of this query, we need to understand the term “Gravitational Redshift” (z) of a compact object such as a Neutron Star. It means that if a photon leaves a compact object with a locally measured energy E, a distant observer will measure energy which is less by a factor of (1+z). So a blue light leaving a compact object may appear as “red” to a faraway observer. While for a Neutron Star, z~0.15, for a Black Hole event horizon z= Infinity! Also, a perfectly static compact object made of normal matter, there is an upper limit on the value of z=2.0.
Now consider the gravitational collapse of a massive star. In order to become a BH, its z has not only to go past this limit z=2.0 but approach z=Infinity too. It is well known that in strong gravity marked by large z, light and radiation trajectories get bent. As a result, I showed that the heat and light from the heated up collapsing star get trapped within the star once its z is sufficiently large. Further, I showed that for z>> 1, the outward radiation pressure due to the trapped radiation must balance the inward pull of gravity (note the star is proceeding towards z=Infinity). Technically this happens when the star attains its EDDINGTON LUMINOSITY.
Once this happens, the collapse must stop and due to extreme heat and radiation, the star turns into an Ultra Hot Ball of Plasma (ionized matter). However, since there cannot be any perfectly static state beyond z=2.0, this ball of plasma must be unstable. Indeed as the ball of plasma keeps on radiating in the absence of any Event Horizon (z=Infinity), it is expected to contract at an infinitesimally small rate. Hence, for generic reasons, collapsing massive stars should end up as Eternally Collapsing Objects (ECOs) instead of theoretical back holes (in some cases the star may be blown away completely due to release of sudden extreme heat (pair-instability supernova of extremely massive stars).
All stars are magnetized plasma (like Sun) and as a magnetized plasma contract, its magnetic field strength increases inversely with the square of the radius of the star. Further in the extreme general relativistic regime (z>> 1), the local magnetic field gets boosted up additionally by general relativistic effects. Thus ECOs are naturally expected to be ultra-magnetized and possess magnetosphere alike magnetized Neutron Stars. Hence ECOs must be Magnetospheic ECOs or MECOs too.
CosmosNow – When Stephen Hawking commented that there isn’t a black hole “in the absolute sense” after your paper was published. How did that impact you?
Dr. Abhas Mitra – Stephen Hawking had been claiming that there cannot be any EXACT Black Hole since 2004 though he never really showed how this would happen due to unspecified Quantum Gravity effects (he made such claims in 2014 and 2015 too). He, of course, feigned ignorance about my research since 1998 which claimed that formation of exact black holes to be inhibited by classical gravity in conjunction with ordinary astrophysics (Attainment of Eddington Luminosity). Anyway, when he made this conjecture first in 2004, my work got a lot of media attention. In fact, I gave live interviews in NDTV 24×7, Headlines Today (which now is India Today). Aajtak shot in my residence for full one hour and it telecast the snippets repeatedly. Also, in 2006, Harvard University Press Release acknowledged the fact the original idea of ECOs was due to an Indian Astrophysicist. Following this, an anonymous Wiki Editor generated a Wiki Bio for me. But I continued to be targeted often below the belt by the mainstream physicists who believed in the Black Hole Paradigm. I think few wiki editors conspired to delete by bio in 2018.
And I have enjoyed media attention and adulation which probably no other Indian scientist has received in recent times. But I do not want to tell anything more about it as it may seem to be bragging. Yet those who are genuinely interested may visit here.
CosmosNow – If we had some way to communicate with physicists/astrophysicist from past whom would you ask your doubts or questions? What would you ask them to solve or answer?
Dr. Abhas Mitra – First and foremost Albert Einstein who never believed in EXACT black holes. I think I would have been able to convince him why true black holes cannot be formed as was believed by him and many others, for instance, Paul Dirac.
CosmosNow – All the discoveries that have been made with the fact that we’re at the cusp of new technology, what you see for future in terms of discoveries?
Dr. Abhas Mitra – As far as discoveries in theoretical physics are concerned, they have very little to “new technology”. However new technological discoveries are important for human lives. Discoveries in the areas of Nano Technology, High-Temperature Superconductivity, material science will certainly improve upon our lives. They could partly ne nuisance too. For example, we all have got addicted to smartphones and have almost lost the habit of reading books, writing beautiful letters, and even our handwritings, calligraphy may be deteriorating. Constant use of mobile phones has been affecting our minds and bodies, and 5G technology may have a further negative effect on the lives of all living beings on this planet.
CosmosNow – What’s one thing you want to impart on Indian students?
Dr. Abhas Mitra – Be sincere, weigh your strengths and weaknesses. It is not necessary that everybody will succeed informal studies, and yet there can be happy and meaningful lives.
CosmosNow – What advice would you like to give to aspiring physicists?
Dr. Abhas Mitra – Again, weigh your strengths and weaknesses. Endeavor to pursue what you like. At the same time avoid flashy speculative areas of Theoretical Physics like Quantum Gravity, String Theory, Black Hole Entropy, Multiverse, wormhole, Time Machine. On the other hand, Astrophysics, Material Science, Nuclear Physics, Experimental Particle Physics, Optical Sciences, Lasers & Biophysics appear to be meaningful lines of research.
Connect with Dr. Abhas Mitra –
Next Interview: Interview With Kevin J DeBruin – Former NASA Rocket Scientist