Phys 214. Planets and Life

Dr. Cristina Buzea

Department of Physics

Room 259

E-mail: cristi@physics.queensu.ca

(Please use PHYS214 in e-mail subject)

Quiz +Lecture 7. Big Bang evidence and stellar lives

+ Hubble Movies

(Page 58-63)

January 21

Contents

• QUIZ no. 1 (10 minutes)

Contents

• Textbook pages 58-63

• The Big Bang Evidence

• Looking back in time

•• Stellar lives and galactic recycling + movieStellar lives and galactic recycling + movie

•• We are star stuffWe are star stuff

•• Implications for the life in the UniverseImplications for the life in the Universe

• Movie: Hubble 15 years of discovery

• Acknowledgments: NASA/ESA images

The Expanding Universe

•• The Universe has continued to expand ever since the Big Bang.The Universe has continued to expand ever since the Big Bang.

•• For at least the past few billion years, the rate of expansion of theFor at least the past few billion years, the rate of expansion of the

universe has been speeding up.universe has been speeding up.

The Expanding Universe

The Big Bang evidence 1

According to current astronomical data, the Universe is approximately 14 billion years old.

The expansion implies the universe was smaller, denser and hotter in the past.

When the visible universe was only one hundred millionth its present size, its temperature

was much hotter (273 million K) and denser - the hydrogen was completely ionized into

free protons and electrons.

WMAP Science Team, NASA

The Big Bang evidence 1

The strongest evidence that supports the Big Bang theory is the detection of theThe strongest evidence that supports the Big Bang theory is the detection of theremnant heat (cosmic microwave background radiation) from the Big Bang.remnant heat (cosmic microwave background radiation) from the Big Bang.

The heat is only 2.725° above absolute zero and is detected as microwaves.The Cosmic Microwave Background radiation was emitted only a few hundred

thousand years after the Big Bang, long before stars or galaxies ever existed.It fills the universe and can be detected everywhere we look.

WMAP Science Team, NASA

WMAP

Science

Team,

NASA

Looking back in time

WMAP Science Team, NASA

• When we look far into space and back time we cannot see beyond the time the first

stars were formed.

The Big Bang Evidence 2

A second evidence that supports the Big Bang theory is the overallA second evidence that supports the Big Bang theory is the overall

chemical composition of the Universe.chemical composition of the Universe.

Calculations predict that the composition of the Universe should be

about three fourths hydrogen and one fourth helium by mass, being

a closed match to the overall chemical composition of the universe.

This prediction implies that the universe was born only with light

elements, such as hydrogen and helium, and traces of lithium.

Consequently, the universe was born without the elements necessaryConsequently, the universe was born without the elements necessary

for life, such as C, N, O, with the exception of H.for life, such as C, N, O, with the exception of H.

The Expanding Universe

Despite the fact that the Universe is expanding since the Big Bang, on

smaller scale the force of gravity has drawn matter together.

While the universe as a whole expands, individual galaxies and theircontent do not expand, only the space between them.

Stellar Lives and Galactic Recycling

Gravity drives the collapse of clouds ofgas and dust to form stars.

Stars go through life cycles.

Stellar Lives and Galactic Recycling

V838 Monocerotis star burst.

The star brightened to about a million times solar

luminosity ensuring that at the time of

maximum, the star was one of the most

luminous stars in the Milky Way galaxy. The

brightening was caused by a rapid expansion of

the outer layers of the star.

Stellar Lives and Galactic Recycling

• SN 1006 was a

supernova, widely seen

on Earth beginning in

the year 1006 AD;

Earth was about 7200

light-years away.

• Egyptian astrologer -

left us a historical

description of the

supernova - the object

was 2-1/2 to three

times as large as the

disc of Venus, and

about one-quarter the

brightness of the Moon.

Stellar Lives and Galactic Recycling

A star is born when gravity compressesthe material in the cloud that thecenter becomes dense enough andhot enough to generate energy bynuclear fusion.

Nuclear fusion - two or more nucleiNuclear fusion - two or more nucleifuse or stick together to form afuse or stick together to form aheavier nucleus whose combinedheavier nucleus whose combinedmass is slightly less than themass is slightly less than theoriginal nucleus.original nucleus.

He nucleus has slightly less mass than4 H nuclei.

Star formation. The young star issurrounded by a disc of gas and dust.

The matter a) finds its way onto the starthrough magnetic funnels, b) stays inthe disc to form planets, c) or is thrownout of the system by the magnetic field.(ESA)

2mcE =

Stellar Lives and Galactic Recycling

• Once a star is born, it shines with energy released by the nuclear fusion in its core. A starlives until it exhausts its usable fuel for fusion.

• Massive stars, with denser and hotter cores, burn faster their fuel than smaller stars, livingshorter (only a few million years).

• Smaller stars, like our Sun, live much longer, 10 billions years. Very small star can live upto hundreds of billions of years.

NASA/ESA

Stellar Lives and Galactic Recycling

When the fusion fuel is exhausted,the star blows much of itscontent back out into space.

Massive stars die in hugeexplosions - supernovae.

The matter spreads out in cloudsdust and gas, from which newgenerations of stars are born.

Galaxies are recycling plants,Galaxies are recycling plants,reusing material expelled fromreusing material expelled fromdying stars to make newdying stars to make newgenerations of stars andgenerations of stars andplanets.planets.

Crab Nebula – remnant of asupernova witnessed on Earthin 1054 AD.

Stellar Lives and Galactic Recycling

• Movie7a (4 min)• Hubble news Full heic0312 Video News Release

• http://www.spacetelescope.org/videos/html/mov/180px/heic0312p.html

• Movie 7b. (13min)

• Hubble DVD 15 Years of Discovery, Chapter 4, THE LIVES OF STARS• http://www.spacetelescope.org/videos/html/hst15_chapter04.html

• Movie 7c. (3 min)

• Hubble news Full heic0306 Video News Release

• http://www.spacetelescope.org/videos/html/heic0306a.html

Supernovae

Supernovae role in:- stellar evolution- Mutations (gamma rays)- Extinctions

Gamma rays induce a chemical reaction in theupper atmosphere, converting molecularnitrogen into nitrogen oxides, depletingthe ozone layer enough to expose thesurface to harmful solar and cosmicradiation.

The gamma ray burst from a nearbysupernova explosion - the cause ofthe end Ordovician extinction, whichresulted in the death of nearly 60%of the oceanic life on Earth.

A composite image of the Crab Nebulashowing the X-ray (blue), and optical(red) images superimposed. NASA/ESA.

We are star dust!

The Big Bang theory predicts the Universe

was born containing only the simplest

elements, H and He, and a trace of Li.

Living things and the Earth are made

primarily of C, N, O, Fe.

The main chemical building blocks of life –

C, O, N, and heavier elements were

formed in the nuclear burning cores of

stars and then ejected into space when

they died.

Stars spend most of their lives generating

energy by fusing H into He. Towards

the ends of their lives, stars like our Sun

can fuse He into C.

More massive stars can continue to create

heavier elements, fusing C into O and

Si, O into Ne and S, and Fe.

We are star dust!

Evidence 1: Stars of different ages show the expected pattern in the proportions ofelements heavier than helium.

•• Older stars are mostly made up of H and He.Older stars are mostly made up of H and He.

•• Younger stars, like our Sun, contain higher proportions (up to 2%) of theirYounger stars, like our Sun, contain higher proportions (up to 2%) of theirmass in the form of heavier elements.mass in the form of heavier elements.

This suggests that younger stars were born from gas clouds that contained theelements manufactured and released by earlier generations of stars!

We are star dust!

Evidence 2: Studies of overallabundances of chemical elementsin the universe today.

The theory of nuclear fusionpredicts relative abundances ofelements in good agreementwith the observed abundances.

e.g. Carbon and Oxygen are moreabundant than Nitrogen.

Neon is more abundant than Fluorine.

The observed relative abundance ofelements in the galaxy.

We are star dust!

Evidence 3: Studies of gas

from exploding stars.

Models of massive stars

and their deaths allow

astronomers to

calculate the

composition of the

clouds from recently

dead stars.

The observations are in

good prediction with

the models.

Hubble Space Telescope-Image of Supernova 1994D(SN1994D) in galaxy NGC 4526 (SN 1994D is the bright spoton the lower left)

We are star dust!

The recycling of matter and production of heavier elements has been takingplace in the Milky Way galaxy for billions of years before the SolarSystem was born.

The clouds that gave birth to our Solar System was made of about 98% H &He, and 2% of heavier elements (by mass), enough to make the smallrocky planets, including Earth.

On Earth some of these elements became the raw ingredients for life.The materials we are made were created inside stars that died before the birth

of our Sun.

Carl Sagan (1934-1996)

“We are star stuff.”

Implications for Life in the Universe

The process of stellar and galactic recycling operate everywhere in the Universe.The chemical composition of many stars systems is similar to our own.The chemical composition of many stars systems is similar to our own.Many (perhaps most) other star systems have the necessary raw ingredients toMany (perhaps most) other star systems have the necessary raw ingredients to

build Earth-like planets and LIFE!build Earth-like planets and LIFE!

Next lecture

• The scale of time

• The observable Universe

• The nature of worlds

• Movies