Introducing a New Product

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Final Fate of a Massive Star
Pankaj S. Joshi
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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

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One of the Most Important Key Issues in
Relativistic Astrophysics and CosmologyWhat
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?
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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...
Dark Energy and Exploding Stars




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Recall the earlier Chandra comments in 1935!
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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
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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

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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

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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!!

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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

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COSMIC CENSORSHIP HYPOTHESIS
Will a generic star go the Oppenheimer-Snyder-Da
tt 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
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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

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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

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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

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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

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Gravitational Collapse in a Comoving Coordinate
System
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Introducing a scaling function Rrv, and F(r,v)
r3 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.

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The function t(v,r) gives time for a shell at r
to reach a coordinate value v, the Spacetime
singularity being at v0

• OSD Model is then given by,

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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 MM_0 only).
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The Singularity Curve and Apparent Horizon are
given by
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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

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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 backas opposed to getting lost in Black
  hole forever!!

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Angela Shelton Black Hole

• The Social
• Analogies!!
• "Do you believe
• in Black hole?"
• Becoming a
• Rebel Star--
• Escaping a
• Black Hole

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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
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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!!

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• 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!!

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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!