Final Fate of a Massive Star

Pankaj S. Joshi

Science tries to Understandthe 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 inCosmology 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 collapseand 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 observedAppearance 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 theFaraway 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 StarsSmall stars like Sun live for

Billions of years.But stars which are 10 or 20

times the Sun live for only a fewcrores 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 Existenceof 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 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 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 ASOPPENHEIMER 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 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

SECTRETS OF THE UNIVERSE!