Final Fate of a Massive Star Pankaj S. Joshi

Science tries to Understand the Nature & Structure of the Universe What are the Fundamental Laws Governing the Cosmos? The Quest begins with Observations And Experiments

The Universe The visible Universe is made of Stars and Galaxies Each Galaxy contains 400 to 500 Billion Stars Universe has Billions of such Galaxies Universe is Expanding NOW, WE FIND THAT THE UNIVERSE ACCELERATES!

Dark Energy and Exploding Stars The Observations on Accelerating Universe are intimately related to the Measurements on Exploding Stars, far away in Cosmos This indicates to a great mystery in Cosmology Today, which is the possible Presence of a Dark Energy in the Universe

One of the Most Important Key Issues in Modern 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?

Chinese Observations In 185 AD, Chinese astronomers observed Appearance of a bright star in our Milky Way galaxy. It took almost eight months to fade away from the sky. It sparkled like a star in the sky. Today we know it was a `Supernova'.

Supernova The core collapses in less than a second, Causing an explosion called Supernova. In which a shock wave blows off the outer layers of the star. The Supernova shines brighter than the entire galaxy for a short time.

We are made of Stars! After all the Hydrogen in the star was converted to Helium, for about a Million years other elements such as Carbon And others are cooked within the Star. The Supernova then throws them out in the Faraway Sky. Thus all the elements of which our Human Bodies are made were Cooked in faraway stars once upon a time!

Stellar Conception A star’s life begins in darkness, in an optically opaque molecular cloud Shielded by dust and gas from galactic starlight and cosmic rays, the cloud cools In the densest clumps of molecular gas, gravity overcomes internal pressure: clumps contract

A zoom-in to a massive star forming region Eagle Nebula (M16) Picture credit: T.A. Rector & B.A. Wolpa

Star and Planet Formation Summary Molecular Cloud Rotating Clump Forming Star + disk

Big Stars & Small Stars Small stars like Sun live for Billions of years. But stars which are 10 or 20 times the Sun live for only a few crores of years. That is because they burn much faster and finish their internal fuel very quickly.

Recall the earlier Chandra comments in 1935!

Spacetime Singularities # General Relativity predicts that the gravitationally collapsing 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

This Information on Existence of Singularities is rather general What we need is a more specific information on What happens When a Massive Star collapses. In particular, we need to know on the Visibility or otherwise of the Super-Ultra-dense regions, or the Singularities forming in Gravitational Collapse

Oppenheimer-Snyder Gravitational Collapse Scenario Use GR/Homogeneous Dust cloud/Dynamical Collapse/Formation of Event Horizon/Spacetime Singularity and a Black Hole Region in the Spacetime/Collapse settles to a Final Schwarzschild Geometry

The Black Hole Conundrum The Past Status of Black Holes My Seminar at TIFR more than 20 years ago-- People asked: WHY BLACK HOLES? 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 Black Hole only? Because, real stars are Inhomogeneous, have Internal pressure forces... # This is an Unanswered Question. Therefore the above Hypothesis, that Any Star Collapse will make a black hole only, hiding the Singularity And the ultra-dense regions behind an Event Horizon

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

Small & Big Stars Some times the core survives the explosion. If the surviving core is between 1.5 to 3 Solar masses, it contracts to become a tiny Very dense neutron star. If the core is greater than 3 solar masses, The core contracts to become a Black Hole or a Fire Ball

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 SECTRETS OF THE UNIVERSE!