Final Fate of a Massive Star Pankaj S. Joshi

The talk is divided in the following main parts: I. INTRODUCTORY II. A STABILITY ANALYSIS: Introducing Small Pressures in Dust Collapse III. CURRENT PERSPECTIVE AND CONCLUSIONS

One of the Most Important Key Issues in Relativistic Astrophysics and Cosmology What Happens when a Massive Star dies? Chandrasekhar's work: Star collapse and Stable Configuration Limit Continual Collapse for Massive Stars What is the Final End state of such a Continual Collapse?

Dark Energy and Exploding Stars The Observations on Accelerating Universe are intimately related to the Measurements on Exploding Stars, far away in Cosmos. This is linked to a great mystery in Cosmology Today, which is the possible Presence of a Dark Energy in the Universe. In Supernovae, the core collapses in less than a Second, causing a Massive Explosion. A shock wave then blows off the outer layers of the star. The Supernova shines brighter than the Entire galaxy for a short time...

Recall the earlier Chandra comments in 1935!

Spacetime Singularities # General Relativity predicts that under reasonable physical conditions the gravitationally collapsing massive star must terminate into a Spacetime Singularity. # The densities, curvatures, and all physical quantities must go to infinity closer to the Singularity # Are such Singularities of Collapse visible to external observers in the Universe? THIS IS ONE OF THE MOST IMPORTANT ISSUES IN BLACK HOLE PHYSICS TODAY

Oppenheimer-Snyder-Datt Gravitational Collapse Scenario Use General Relativity/Homogeneous Density Spherical Dust cloud with No Rotation or Pressures Dynamical Collapse/Formation of Trapped Surfaces and Event Horizon/Collapse to a Spacetime Singularity/Formation of a Black Hole Region in the Spacetime Collapse settles eventually to a Final Schwarzschild Geometry

The Black Hole Conundrum The Past Status of Black Holes My Seminar on Black Holes at TIFR more than 20 years ago-- Astronomers asked: WHY BLACK HOLES, WHY YOU TALK ON SUCH EXOTIC THINGS? NOW BLACK HOLES EVERYWHERE! (Why your Talk has No Black Holes!!) There are very many unresolved issues also, associated with Existence and Physics Of Black Holes

1960s: Resurgence of Interest A & A DEVELOPMENTS Discovery of Quasars, Radio Galaxies, and Of several High Energy Phenomena in the Universe No known physics explains such High Energy Observations!!

Result Very Many Developments in the Physics & Astrophysics of Black Holes J Wheeler/R Penrose/S Hawking/K Thorne... Investigations in Classical & Quantum Aspects Of Black Holes Interesting Thermodynamic Analogies Astrophysical Applications

COSMIC CENSORSHIP HYPOTHESIS # Will a generic star go the Oppenheimer-Snyder- Datt way only, and make a Black Hole only? Because, real stars are Inhomogeneous, have Internal pressure forces... # This is an Unanswered Q. Therefore the Hypothesis by Penrose: Any Star Collapse will make a black hole only, hiding the Singularity, the ultra-dense regions, behind an Event Horizon THIS HAS BEEN ONE OF THE MOST FUNDAMENTAL QUESTION IN GRAVITATION THEORY TODAY

The Information given by Singularity Theorems on the Existence Aspect is rather general What we need to know specifically is: What happens When a Massive Star collapses under its own gravity. In particular, we need to know on the Visibility or otherwise of the Super-Ultra-dense regions, or the Singularity that forms in such a Gravitational Collapse TOWARDS THIS PURPOSE, EXPLICIT MODELS NEED TO BE WORKED OUT, IN THE ABSENCE OF ANY GENERAL PROOF

Way Out: Back to Basics STUDY GRAVITATIONAL COLLAPSE AS OPPENHEIMER AND SNYDER DID! Over past decade and a half, Numerous Collapse studies carried out... CONCLUSION: Black Holes and Naked Singularity Final States develop as The Collapse Outcome

Basically, we need to understand much more Carefully, what all is possible in Gravitational Collapse To Understand the Rich Structure allowed by the Einstein Equations in Dynamical Collapse, We studied recently Explicitly the Role of Pressures in Collapse Evolutions, by Introducing Small Pressures in otherwise Pressure-free OSD Model (PSJ & D Malafarina, Physical Review, in Press) Such Studies are Extremely Essential in view of our Failure so far towards any Proof, or even making any possible Mathematical Formulation of the Cosmic Censorship Hypothesis

Small Pressure Perturbations in the OSD Dynamical Collapse System What happens to the Collapse outcome when arbitrarily small pressure perturbations are introduced within the OSD Collapse Scenario? We obtain here the Explicit Classes of Pressure Perturbations such that introducing a smallest pressure changes the final outcome of collapse from Black Hole Final State to a Naked Singularity What we see is a Very Rich Structure of the Initial Data Space, in terms of the Collapse Outcomes

Gravitational Collapse in a Comoving Coordinate System

Introducing a scaling function R=rv, and F(r,v) = r^3 M(r,v), it is possible to integrate the Einstein equations to get the Equation of Motion of the Collapsing Fluid, the key point is to understand the structure of trapped surfaces. While doing so, one must ensure that the Collapse develops from a Regular initial Data. The Trapped Surfaces and Spacetime Singularity Develop then as the collapse evolves, and the main task then is to examine the Nature of the Singularity, namely whether it is Covered within Horizon, or Visible to External Observers.

The function t(v,r) gives time for a shell at r to reach a coordinate value v, the Spacetime singularity being at v=0 OSD Model is then given by,

For the OSD model, {g_00} is necessarily Unity. We now allow it to be non-zero, this amounts to introducing small non-zero tangential pressures (with M=M_0 only).

The Singularity Curve and Apparent Horizon are given by

Physically Realistic Collapse implies Naked Singularity always? Examples: Dust Collapse, Radiation Collapse... Why Do Naked Singularities Develop in Gravitational Collapse? How Trapped Surfaces are Naturally Delayed due to Inhomogeneities

Many Interesting Comments and Discussions Numerous discussions can be seen on the Internet and various Websites Many comments from Students, Experts, as well as lay persons... an exciting experience The Podcast talk by the SciAm Editor in Chief Several Interesting Analogies--Nirvikalpa Samadhi of Yoga compared to Going to a Singularity and Coming back—as opposed to getting lost in Black hole forever!!

Angela Shelton & Black Hole The Social Analogies!! "Do you believe in Black hole?" “Becoming a Rebel Star-- Escaping a Black Hole”

A `Hypernova', or a Final Complete disintegration of the Massive Star in late collapse? Advantages: (i) You need not then worry to Prove censorship hypothesis (ii) Infinite density singularity avoided (iii) Observational tests possible, look at and Examine carefully the Burstlike Phenomena In the Universe (iv) Black hole paradoxes avoided

Role of Classical & Quantum Physics * General Relativity: Evolve the Collapse to Very Late Stages--keeping the Causal Communication with the Outside Universe open... *Quantum Physics: Study the Quantum Gravity Effects in such Ultra-Strong-Gravity Regions SOME BIG GURUS HAVE ENDORSED AND EVEN ADVOCATED THIS AS A GOOD POSSIBILITY!!

******* GR implies Existence of Strong Gravity Regions, where Both Quantum Gravity and General Relativity come into their Own. ************** As R Wald pointed out: `If censorship fails, then in a literal sense, we would come face-to-face with the laws of Quantum Gravity whenever gravitational collapse to a naked singularity occurs in distant regions of our Universe..' AN EXCITING POSSIBILITY!!

WHAT IS THE FINAL FATE OF A MASSIVE STAR? IT IS TURNING OUT TO BE ONE OF THE MOST INTERESTING AND EXCITING ISSUES IN MODERN COSMOLOGY AND ASTROPHYSICS TRYING TO UNDERSTAND THE SAME IS TEACHING US AND LEADING TO MANY SECRETS OF THE UNIVERSE!