outline introduction the life cycles of stars the creation of elements a history of the milky...

OutlineIntroduction

The Life Cycles of Stars

The Creation of Elements

A History of the Milky Way

Nucleosynthesis since the Beginning of Time

INTRODUCTION

Abundances of the elements Composition of stars How do we learn what stars

are made of?

The Composition of Stars

M90% hydrogen atoms

10% helium atoms

Less than 1% everything else

Finding the Composition of a Star

Rainbows from

starlight

The Solar Spectrum – In Detail!

Stellar Spectra

Abundances of the Elements

HeH

Eu

BaSr, Y, ZrSc

Li, Be, B

CNO

Fe

-1

2

5

8

11

14

10 20 30 40 50 60 70 80

Atomic Number

Lo

g e

(H

=12)

Solar Abundances EXPANDED

Eu

BaSr, Y, ZrSc

Li, Be, B

CNO

Fe

-1

2

5

8

10 20 30 40 50 60 70 80

Atomic Number

Lo

g e

(H

=12

)

The Life Cycles of Stars• Fundamental

Properties of Stars– Mass– Temperature– Luminosity or radius– Age

• Star Birth• Middle Age• Stellar Senior Citizens

Stars come in many sizes and colors

But only certain

sizes and colors are allowed!

The Main Sequence

The sun is an

ordinary, yellow main

sequence star

Giants are cool and very large

Most stars occur in these main groups in the luminosity-temperature diagram

Main Sequence

Giants Supergiants White

Dwarfs

Quiz: Which star is the biggest?

A B C D

Quiz: Which star is the smallest?

A B C D

The Evolution of Stars

The Ages of Stars

How old is the Jewelbox?

The Jewelbox Cluster is about 12 million years old

Star Birth

• New stars are born continuously• Stars form in dense regions of gas and

dust

Stellar Middle Age

Stars produce energy by converting hydrogen into helium through nuclear reactions in their interiors.

The Proton-Proton Cycle

Stars produce energy by fusing hydrogen nuclei into helium, and helium into heavier nuclei

Stellar Senior Citizens

When stars finally deplete their nuclear fuel, they become white dwarfs, neutron stars, or black holes. In the process, much of the stellar material is returned to interstellar space

“Just between you and me, where does it get enriched?”

The Creation of Elements…

Hydrogen and helium were created during the Big Bang while the Universe was cooling from its initial hot, dense state.

About 10% of the lithium in the Universe today was also created in the Big Bang. We’re still not surewhere the rest comes from.

Primordial Nucleosynthesis

Hydrogen Burning

Stars burn hydrogen in their interiors to produce helium.

Hydrogen burning also rearrangescarbon, nitrogen, and oxygen.

HeliumBurning

Three helium atoms combine to form carbon

Alpha-ProcessElements

Carbon and oxygen atoms combineto form elements with even numbers of protons.

These elements come fromsupernovae.

Eu

BaSr, Y, ZrSc

Li, Be, B

CNO

Fe

-1

2

5

8

10 20 30 40 50 60 70 80

Atomic Number

Lo

g e

(H

=12

)

The Iron Peak Metals

In the cores of massive stars duringsupernova explosions, atomic nuclei exchange protons and neutrons to form the iron peak metals.

Eu

BaSr, Y, ZrSc

Li, Be, B

CNO

Fe

-1

2

5

8

10 20 30 40 50 60 70 80

Atomic Number

Lo

g e

(H

=12

)

Heavy MetalsAll heavier elements are formed

when iron peak elements captureneutrons

Heavy Metals from Ancient Superstars

Some heavy metals are made in supernovae when massive stars explode

The explosion produces many free neutrons, which combine with iron to make heavier metals

Making Heavy Metals in Low Mass Stars

• In low mass stars like the sun, neutrons are created when protons mix into the hot, helium-burning region

• With only a few neutrons available, a different set of heavy metals are created

Neutron Capture Elements in the Solar System

Zn

Ga

Ge

AsSe

Br

Kr

Rb

Sr

Y

Zr

NbMo

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Xe

Cs

Ba

La

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

YbLu

Hf

Ta

W

ReOs

Ir

Pt

Au

Hg

TlPb

Bi

Th

U

0

1

Fra

ctio

n o

f r-

pro

cess

Zn As Kr Y Mo Pd In Te Cs Ce Sm Tb Er Lu W Ir Hg Bi

Purple elements were formedin supernovae (the r-process) and

pink elements were formed inred giant stars (the s-process)

By studying the abundance patterns of the heavy metals, we can learnwhether the metals were made insupernovae or in low mass stars.

A History of the Milky Way

What is a galaxy?Structure of the Milky WayHow did our galaxy form?

You are

here.

The Milky Way….

Bulge

Flattened Inner Halo

Thick Disk

Dwarf Spheroidal Companions

Dark Matter Corona

Halo

Disk

Formation of the Milky Way

Galaxy Collisions and Mergers

Chemical Evolution

The creation of elements in stars leads to chemical enrichment of the Galaxy

The composition of the Galaxy depends on How fast stars form What kinds of stars

form How long it’s been

since stars started to form

The Chemistry of Stars

The chemical compositions of stars reflect the star formation histories of stellar populations

The complexity of the Milky Way’s history is reflected in the compositions of its stars

Heavy Metals in the Early Galaxy

In the early galaxy, elements were forming very quickly from new star formation.

The chemical mixture we see is different from the Solar System

We find a much smaller amount of “metals” mixed in with the hydrogen and helium

Heavy metals come only from supernovae – not from low mass stars

Nucleosynthesis Since the Beginning of Time

• By studying stars of different ages, formed at different times in the Galaxy’s history, we can trace the history of the Milky Way

Low Mass Stars Begin to Contribute Heavy Metals

Low mass stars begin to contribute heavy metals when the Galaxy reaches an age of a few hundred million years.

The abundances of the “light” heavy metalsin ancient stars are too high to explain with our current theory of supernova r-process production

The Mystery Metals

Where to the first metals come from?

Ancient Superstars!

Formation of stars as “pre-galactic” objects from small density fluctuations

Masses from a few tens to a few hundred solar masses

Low mass star formation is suppressed because the first, massive stars reheat the gas

These stars form the first metals

Metals in Very Distant Galaxies Studies of the most metal-poor stars in the

Galaxy give us access to the state of the Universe at very early times

The most metal-poor stars in our Galaxy contain only 1/10,000 of the amount of metal that the sun has.

The most distant galaxies we can study contain 1/100 (1%) of the amount of metal that the sun has

The Epochs of Galactic Chemical Evolution

Primordial Epoch -The Big Bang (hydrogen, helium, lithium)

Epoch of Massive Stars – the first few million years Ca, O, and the “mystery metals”

Supernova Epoch - r-process elements from 8-10 MSun SNII The first few 10’s of millions of years

The Red Giant Epoch yields s-process elements The first few hundreds of millions of years

The Iron Epoch – most of the iron comes from low mass stars The first billion years

The Lithium Epoch – Where does lithium come from??

Websites of Interest

Jewels of the night http://www.noao.edu/education/jewels/home.html

National Optical Astronomy Observatory Image Gallery http://www.noao.edu/image_gallery

Space Telescope Science Institute http://www.stsci.edu

Amazing Space http://amazing-space.stsci.edu

NASA’s Astronomy Picture of the Day http://antwrp.gsfc.nasa.gov/apod/astropix.html

Astronomical Society of the Pacific http://www.astrosociety.org

The Stonebelt Stargazers http://www.mainbyte.com/stargazers/

n-capture Synthesis Paths

Ba

La

Cs

Xe

139

132131130129128

130 132

133

134 136

134 135 136 137 138

138

pp s,rs,r s,r

s,r

s,r

s,r

s

rs,r r

p

s

s,r ss

r-process paths-process path