The Origin of the Elements and the Evolution of the Composition of the Cosmos

Jim Truran

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Astronomy and Astrophysics Enrico Fermi Institute University of Chicago andArgonne National Laboratory

Lectures in Nuclear ChemistryAssociated Colleges of the Chicago Area November 4th , 2008

Cosmic Nucleosynthesis Perspective

The Universe emerged from the Big Bang with a composition consisting of hydrogen, deuterium, helium, 3He, and 7Li.

The first stars and galaxies were born with this “primordial” composition.

The “Big Bang”

Star Formation in Orion

Cosmic Nucleosynthesis Perspective

The heavy elements with which we are familiar - from carbon and oxygen, to iron, .. to uranium - are the products of nuclear processes occurring in stars and supernovae.

Cosmic Nucleosynthesis Perspective

History of the Universe?

Courtesy: Jason Tumlinson

Cosmic Nucleosynthesis Perspective This history of the composition of

our Galaxy (and the Cosmos) is written in the compositions of its stars and gas.

Stars are formed in gas clouds in galaxies.

Star Formation in the Large Magellanic Cloud

The Sombrero Galaxy: M104

Disk

Halo

Picture Credit: Hubble (HST)

Picture Credit: Hubble (HST)

Cosmic Nucleosynthesis Perspective

Stars are formed from gas, powered by nuclear energy, and produce heavy elements.

Mass ejected from stars and supernovae is returned to the gas, from which the next generation(s) of stars will be born. (A cycle of enrichment.)

Successive stellar generations produce stars of higher initial metal contents.

Courtesy:Carla Frohlich

Pleiades (HST) Orion’s Belt (HST)

Cosmic Nucleosynthesis Perspective

The heavy element content of the Universe at any point in its history reflects the integrated nucleosynthesis contributions from earlier stellar generations.

The composition of our Solar System (born 4.6 billion years ago) was determined by the nuclear processes that took place in stars during the prior 9 billion years of Galactic history.

Palomar: Crab Nebula HST: Nova Pyxidis

“We are Star Stuff.” (Cosmos: Carl Sagan)

Elemental Composition of the Human BodyElement Symbol Percentage(by mass) Site of Origin Oxygen O 65.0 Supernovae

Carbon C 18.5 Red Giants

Hydrogen H 9.5 Big Bang

Nitrogen N 3.3 Red Giants

Calcium Ca 1.5 Supernovae

Phosphorus P 1.0 Supernovae

Stellar Stability: the Need for Nuclear Energy Stars are ‘born’ in dense clouds of gas in galaxies.

Contraction of a ‘proto-star’ heats the interior to the point at which the pressure is sufficient to counter gravity.

Figure Credit: Carla Frohlich

Horsehead Nebula in Orion: HST

Since the star continues to radiate energy as it contracts, we must identify a sufficient energy source.

Stellar Stability: the Need for Nuclear Energy

Prior to the discovery of the nature of stellar energy input from nuclear processes, it was not possible to understand an age of the earth of more than a billion years (inferred from diverse geological studies of rock strata and of rates of sedimentation).

In the absence of an energy source other than gravity, a star of the Sun’s luminosity would be able to survive only approximately 20 million years.

The currently accepted age of the Earth (and therefore of the Sun and Solar System) is 4.6 billion years.

How can we understand this apparent discrepancy?

Nuclear Energetics and Element Synthesis in Stars The contraction of a star to high temperatures allows nuclear processes to occur in the interior.

In our Sun, at a temperature of 15 million degrees Kelvin, energy is released in the nuclear “burning” of hydrogen to helium. (Four protons are transformed into one helium {4He} nucleus.)

Figure Credits: Carla Frohlich

Nuclear Energetics and Element Synthesis in Stars

It is critical to note the extremely low rate at which the “proton-proton” reaction p + p 2H + + + proceeds in the Sun’s core. Only about one proton-proton collision in one million-billion-billion-billion yields the formation of deuterium.

The slow rate of the p + p reaction has made possible the evolution of life on Earth. The lifetime of the Sun is ~ 12 billion years. Stars more massive than the Sun have shorter lifetimes: e.g.~ 20 million years for 10 solar mass.

Nuclear Energetics and Element Synthesis in Stars

The binding energy per nucleon (protons+neutrons) provides a measure of nuclear stability.

56Fe is the most stable nucleus having the maximum binding energy per nucleon.

Fusion reactions starting with H and He, occurring in stellar interiors, continue to provide energy to power the star up to 56Fe.

Heavy nuclei like thorium (232Th) and uranium (238U) release energy when they break up (decay) by fission.

fusion fissionMaximum Stability56Fe

Nuclear Energetics and Element Synthesis in Stars The progress of nuclear burning in stars is temperature dependent.

Stars of mass less than 10 solar masses do not become hot enough to burn carbon: they end their lives as planetary nebulae and leave carbon-oxygen white dwarf remnants.

Stars of mass greater than 10 solar masses burn to iron leaving a shell-like structure of elements between carbon and iron, viz:

Figure Credits: Carla Frohlich

Significance of Supernovae

They release ≈ 1051 ergs of light and kinetic energy.

They enrich the Galaxy in “heavy” elements (more massive than helium) to levels of order 2 percent (Solar Abundance).

Supernovae of Type II leave condensed remnants - neutron stars and black holes.

Supernovae SNe Ia are probes of the distance scale and provide constraints on the expansion and the geometry of the Universe and the nature of dark energy.

High-Z Supernova Search Team, HSTSNe 1994D

Supernovae - both Type Ia and Type II - are spectacular events:

SNe 1987A

The expected rate in the Milky Way is about 1 every 50 years,

with SNe II being roughly 3 times more frequent than SNe Ia.

Historical Supernovae in our Galaxy

SNIdentification

SN Type

185 Historical descriptions

Ia ?

1006 Historical descriptions

Ia ?

10541572

Crab NebulaTycho Brahe

II ?Ia

1604~1680

Johannas Kepler Cassiopeia A

IaII

Chaco Canyon Petroglyph

SN 1054 Crab Nebula

Type II Supernovae: Theory

“Standard model” (Hoyle & Fowler 1960): SNe II are the product of the evolution of massive stars 10 < M < 100 M

Evolution to criticality: A succession of nuclear burning stages yield a layered compositional structure and a core dominated by 56Fe. Collapse of the 56Fe core yields a neutron star. The gravitational energy is released in the form of neutrinos, which interact with the overlying matter and drive explosion.

Nucleosynthesis contributions: elements from oxygen to iron and neutron capture products from krypton through uranium and thorium.

Courtesy Mike Guidry: guidry@utk.edu

SNe1054: Crab Nebula

SNe1987A Hubble Image

Cas A Supernova Remnant red: iron rich blue: silicon/sulfur richChandra X-ray Observatory

SN 1987A in the Large Magellanic Cloud

30 Doradus Nebula prior to explosion of SN 1987A

30 Doradus subsequent to explosion of SN 1987A

An Exciting Recent Supernova Event

SN 1987A in the Large Magellanic Cloud

A likely supernova candidate forthe next millenium: Betelgeuse

Courtesy: Ernst Rehm, ANL

Type Ia Supernovae: Theory

“Standard model:” (Hoyle & Fowler 1960):

SNe Ia are thermonuclear explosions of carbon-oxygen white dwarf stars.

Evolution to criticality: Accretion from a binary companion leads to growth of the white dwarf to a critical mass (1.4 solar masses).

Complete incineration and disruption occurs in ~ two seconds. (No compact remnant.)

Discovery of a SNe Ia?

One evening when I wascontemplating as usual thecelestial vault, whose aspectwas so familiar to me, I saw,with inexpressible astonishment, near the zenith, in Cassiopeia, a radiant star of extraordinary magnitude. Struck with surprise, I could Hardly believe my eyes.

Tycho Brahe, November 1572

Tycho, SAO, Chandra

“Stella Nova” (1573), discovery chart

Kepler’s Supernova 1604

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SNe Ia and CosmologyIn 1998, SNe Ia played a major role in the “science breakthrough of the year:”

Using SNe Ia as distance indicators, astronomers found evidence for an accelerating cosmic expansion.

Doggett and Branch (1985)

Significance of Type Ia Supernovae

The Phillips relation identifies a correlation between the peak brightness and the rate of decline (brighter SNe Ia decline more slowly) which yields an effective “standard candle.”

Hubble’s Law: Then and Now

(Hubble 1929)

Progenitor: White dwarf in a binary system

Growth to the Chandrasekhar limit by mass transfer

The Standard Model for SNe Ia

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GCD 3D Simulations

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Jordan et al. (2007)

Heavy Element Synthesis and the Age of the Universe

Uranium Thorium

r-Process Synthesis and Stellar Ages

r-process in supernovae

Observations confirm the rapid neutron capture process dominates at the lowest metallicities (in the oldest stars).

(Truran et al. 2002)

Nuclear Radioactive Dating of Halo Stars A knowledge of the abundances of both uranium and thorium in a star allows an age determination.

For the halo star CS31082-0018 (Cayrel et al. 2001), this gives an age of 12.5 +/- 3 billion years. An early halo star.

Probing Early Nucleosynthesis

The farther we see across the Universe, the farther back in time we can explore. The fact that the speed of light is finite allows astronomers to probe the early star formation and nucleosynthesis history of the Universe and its composition as a function of time, using:

Studies of old stars - analysis of the “fossil” record Studies of gas clouds at - high red shift using both

Quasars and Gamma Ray Sources as probes

Astronomers are uniquely able to travel backward in time.

Cosmic Nucleosynthesis Perspective

History of the Universe?

Courtesy: Jason Tumlinson

Abundances when Fe/H < 1/10,000 its Solar Value Frebel et al. (2005)

The abundances in the two most “iron-deficient” stars known differ distinctly from abundances in the Sun.

Abundances in a Galaxy at Redshift z=2.6

(Prochaska 2005)

QSO (background) near galaxy (foreground)Galaxy,J1042, z=0.03;

QSO z=2.66

(Don York 2008)

A Gamma Ray Burst at Redshift z= 2.615

(Hsian Wen Chen 2008)

Gamma Ray Burst: GRB050820A

Hubble Deep Field

Viewing the Distant Universe

Look-back Times versus Redshift

Red Shift Age of the Universe Look-back Time

0 Gyr 14.5 Gyr 10 (First Stars -

0.5 14.0

6 - SNe II) 1.0 13.5 5 1.2 13.3 4 (AGB Stars) 1.6 12.9 3 2.3 12.2 2 (SNe Ia) 3.5 11.0 1 6.2 8.3 0.5 9.1 5.4 0.4 Birth of Sun

9.9 4.6

0 14.5 0(Ho= 65 km s-1 Mpc-1; baryons= 0.022 h-2; M = 0.3; =0.7; cosmos= 14.5 Gyr )

The Origin of the Elements

Thank you for your attention.