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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-SnyderDatt 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
Many Interesting Comments
and Discussions
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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
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The Social
Analogies!!
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"Do you believe
in Black hole?"
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“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!