final fate of a massive star pankaj s. joshi. the talk is divided in the following main parts: i....
TRANSCRIPT
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
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?
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 ConundrumThe 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 PhysicsOf Black Holes
1960s: Resurgence of Interest
A & A DEVELOPMENTS
Discovery of Quasars, Radio Galaxies, andOf several High Energy Phenomena in the
Universe
No known physics explains such High EnergyObservations!!
Result
Very Many Developments in the Physics &Astrophysics of Black Holes
J Wheeler/R Penrose/S Hawking/K Thorne...
Investigations in Classical & Quantum AspectsOf Black Holes
Interesting Thermodynamic AnalogiesAstrophysical 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
CollapseTOWARDS THIS PURPOSE, EXPLICIT
MODELS NEED TO BE WORKED OUT, IN THE ABSENCE OF ANY GENERAL PROOF
Way Out: Back to Basics
STUDY GRAVITATIONAL COLLAPSE ASOPPENHEIMER 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, andF(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 SingularityDevelop 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 andExamine 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!