exploding stars 2011 nobel prize in physics

Exploding Stars As Beacons At the Edge of

the Universe

The Universe is Speeding Up!

By Professor Thomas Madigan

The 2011 Nobel Prize in Physics was awarded to

Saul Pearlmutter, University of California, Berkeley

Adam Riess, Johns Hopkins University and the

Space Telescope Science Institute

Brian Schmidt, Australian National University and Mt.

Stromlo Observatory

For “the discovery of the accelerating expansion

of the Universe through observations of distant

supernovae"

How do we know how distant an object

is and, hence, it’s fundamental or

“intrinsic” brightness?

One method to determine distances in the universe is

based on intrinsic or absolute brightness

By comparing all objects to each other at a standard

distance, we can make valid comparisons between

them. The brightness of an object at this standard

distance is known as its Absolute Magnitude

If we know how intrinsically bright an object is and,

because light behaves according to an Inverse Square

Law (a light source that is twice as distant will be ¼ as

bright), we can easily determine its distance

Objects that allow us to determine distances

are known as

Standard Candles

Brief History1908: Henrietta Swan Leavitt, after observing

variations in the brightness of certain variable

stars, known as Cepheid Variables, and noting

that the brightness depends on that variation,

codifies the “Period-Luminosity” relation

Brief History

1912: Vesto M. Slipher measures the radial

velocities of the Spiral Nebulae, most notably,

the great Spiral Galaxy in Andromeda, M-31.

Brief History

Radial velocity is the speed at which an object is

moving along our light of sight. If the object is

moving relative to us as observers, its light will

be subject to the Doppler Effect: if it is receding,

the light would be “Red Shifted”; if is

approaching, the light would be “Blue Shifted”

Brief History1919: Edwin Hubble is appointed to the Mt.

Wilson Observatory by Carnegie Astronomer,

founder and visionary, George Ellery Hale

Brief History1922 - 1923: through his observations of the

Spiral Nebulae with the 2.5 meter (100”) Hooker

reflector on Mt. Wilson, Edwin Hubble

concludes that the “Spiral Nebulae” are

separate galaxies outside the Milky Way

Brief History1929: along with Milton Humason, Hubble

formally codifies and publishes his Distance/

Velocity Law. Known as the Hubble Metric, it

relates distance with recessional velocity: the

further away an object is, the faster it is

receding. Not only is this observation

consistent with a uniformly expanding space, it

is consistent with Einstein’s General Theory of

Relativity

Hertzprung-Russell DiagramThis diagram is a plot of luminosity

(absolute magnitude) against

the color of the stars ranging

from the high-temperature

blue-white stars on the left

side of the diagram to the

low temperature red stars on

the right side.This diagram below is a plot of 22000 stars

from the Hipparcos Catalogue

together with 1000 low-luminosity

stars (red and white dwarfs). The

ordinary hydrogen-burning dwarf

stars like the Sun are found in a

band running from top-left to

bottom-right called the Main

Sequence. Giant stars form their

own clump on the upper-right side

of the diagram. Above them lie the

much rarer bright giants and

supergiants. At the lower-left is the

band of white dwarfs - these are the

dead cores of old stars which have

no internal energy source and over

billions of years slowly cool down

towards the bottom-right of the

diagram.

The Standard Solar Model indicates that for

a 1 Solar Mass Star 100% of the star’s

luminosity is achieved at 0.30 R, using

0.70 M

Energy transport is radiative for inner 0.70R

With increasing altitude, the solar interior

cools and energy transport transitions

from radiative to convective

All stable stars on the Main Sequence are said to

be in a state of

Hydrostatic Equilibrium

Where outward gas pressure is balanced by the

inward pull of Gravity.

After all but 12% of the initial hydrogen abundance has been consumed in the star’s core, energy production will transition to a hydrogen burning shell surrounding a non-fusing and degenerate helium core

The sun will shine for a total of 12 billion years

and will use the helium that was produced during

that time to make carbon and oxygen

Stellar Evolution

• Solar Mass Stars

– Lifespan 10s of billions of years

– End of life

• Red Giant

• Helium Burning;– He burning is very temperature sensitive: Triple-alpha fusion

rate ~ T40!

– Consequences:

» Small changes in T lead to Large changes in fusion

energy output

• Carbon-oxygen core;

• Carbon-oxygen White Dwarf

Cessation of core hydrogen fusion reactions results in core contraction and gravitational heating

Due to core contraction and the resulting gravitational heating, hydrogen fusion reactions resume in a shell surrounding the core

Core helium fusion reactions begin via the Triple-Alpha process once temperatures reach 100,000,000 K in the core

Star moves up and to the right, ascending the RGB of the HR Diagram, leaving the Main Sequence

Solar-mass stars

the process stops at helium fusion with a carbon-oxygen white

dwarf that cools over billions of years

Electron degeneracy and Degenerate Matter

• Quantum Theory

– Specific electron energy levels

– Pauli Exclusion principle

• No two electrons can occupy the same state– When the triple-alpha process in a red giant star is complete, those

evolving from stars less than 4 solar masses do not have enough energy to initiate the carbon fusion process. They collapse until their collapse is halted by the pressure arising from electron degeneracy. An interesting example of a white dwarf is Sirius-B.

– For stellar masses less than about 1.44 solar masses, the energy from the gravitational collapse is not sufficient to produce the neutrons of a neutron star, so the collapse is halted by electron degeneracy to form white dwarfs. This maximum mass for a white dwarf is called the Chandrasekhar limit.

White Dwarfs

Discovered by Subrahmanyan Chandrasekhar when he

was a graduate student at Cambridge, while in transit

to England, the Chandrasekhar Limit is 1.44

M(sol). It is the maximum nonrotating mass which can

be supported against gravitational collapse by electron

degeneracy pressure.

Born October 19, 1910, Lahore,

British India, now Pakistan

Died August 21, 1995, Chicago,

Illinois

Nobel Prize in Physics (1983)

The CHANDRA Orbiting X-Ray Observatory: An

Example of an X-Ray Telescope and observing

platform: http://chandra.harvard.edu

http://chandra.harvard.edu/

SiriusIs a binary star system 9 light years away that consists of Sirius-A, a main sequence star

and Sirius-B, a 1 solar mass white dwarf

Sirius-B

White Dwarfs

Represent the end-state for sun-like stars

and stars less than 5 solar masses

Planetary Nebulae

Image credit: Thomas Madigan, 3/14/2010

Image acquired with 0.61m R-C

Image credit: Thomas Madigan, 3/14/2010

Image acquired with 0.61m R-C

Planetary Nebulae

SupernovaeA Star’s Spectacular End

Type Ia

the type used as a Standard Candle to determine

the expansion rate of the universe

Type II

Core Collapse

Type Ia Supernovae

A Consequence of Gravity

Type Ia Supernovae


Stellar Dynamics

The Equivalent of 70% of the Sun’s mass or

1.4 x 10^30 Kg is compressed into a

sphere the size of the earth! This results

in the Intense gravity of a White Dwarf

being equal to 230,000 times the gravity of

the earth!

Type Ia Supernovae


As a member of a parasitic binary

star system, the white dwarf draws

material from a victim star

The accreting material, mostly

hydrogen, builds up on the surface

of the White Dwarf

Type Ia Supernovae


When a critical mass has

accumulated on the surface of the

White Dwarf, known as the

Chandrasekhar Limit, conditions

become similar to those present in

the cores of massive stars, stars

that end as Type II supernovae

Type Ia Supernovae


When this happens, a runaway

thermonuclear fusion reaction

engulfs the White Dwarf,

obliterating the star, resulting in a

Type Ia supernova, one of the

brightest, most powerful events in

the universe

Type Ia Supernovae


Could the sun end up as a Type Ia

Supernova?

Type Ia Supernovae


Could the sun end up as a Type Ia

Supernova?

Yes!

Type Ia Supernovae


Key factors as an accurate Standard Candle

High Intrinsic Luminosity: visible at tremendous distances, across

the universe! For a moment in time, the supernova blazes with

the light of a billion suns!

Type Ia Supernovae


Key factors as an accurate Standard Candle

High Intrinsic Luminosity: visible at tremendous distances, across

the universe! For a moment in time, the supernova blazes with

the light of a billion suns!

Predictable, consistent luminosity, tightly constrained by the

precise nature of the Chandrasekhar Mass limit

The Expanding UniverseAnd Dark Energy!

Because of the reliability of Type Ia supernovae as accurate

standard candles, Pearlmutter, Riess and Schmidt observe a

departure from Hubble’s Law in the expansion rates of galaxies

at extreme distances; the Type Ia supernovae were under-

luminous based on the distances implied by their observed Red

Shifts







Shifts

How can this happen?







Shifts

How can this happen?

They are farther away, a result only possible if they are receding

at a greater velocity

Where do we go from here?

Continued observations of very deep objects,

objects whose visible light has been red shifted

deep into the InfraRed, objects that are beyond

the reach of even the mighty Hubble Space

Telescope

James Webb Space Telescope

A Next Generation Space-borne Telescope