Stellar Forensic Files:

What Dead Stars Tell Us About Living Ones

Dr. Kurtis A. Williams

Steward Observatory

In a galaxy, the life cycles of stars are the major force of change.

We must understand these life cycles to understand our Galaxy.

During its life, a star’s central nuclear heart is hidden from view.

We need to uncover and study this heart.

Like people, stars have life cycles

Stars are born from large clouds of gas

A star’s middle age is similar to an automobile

When stars get old, they get sick and die

This sequence is seen in the “Hertzsprung-Russell Diagram”

Blue Red

Heavy

Light

BIG

Small

When a star dies, its nuclear ashes are left behind

Gravity squeezes this ash into a very hot, compact object.

Photo: Jones, Stern & Forman/SAO Photo: NASA/Bond et al.

Eventually, gravity is stopped by “degeneracy”

Photo: Psycho Therapy Clothing

White dwarfs tell us how much of a star is used as nuclear fuel.

A lack of white dwarfs tells us which stars explode

Star clusters without white dwarfs are still producing supernovae

Image: S. Kohle & T. Credner

When white dwarfs appear we have reached the critical mass

There is a nice relation between the mass of a star and its white dwarf

Unusual elements in a white dwarf atmosphere may signify planets.

Artwork: NASA/G. Bacon

White dwarfs have atmospheres of nearly pure hydrogen or helium

Photos: Theodore Gray

Photo: CRIACC

Gravity is so strong, other elements sink in a matter of weeks.

Photo: Dartmouth Chemistry Dept.

Art

: NS

BR

I

White dwarfs with other elements must replenish them constantly

© Anglo-Australian Observatory

Photo: SOHO

Image: NASA/DIRBE

White dwarfs tell us how matter is recycled and enriched.

We Recycle!

This atmosphere has elements made during the red giant phase

White dwarfs provide forensic evidence on the inner workings and lives of stars.

Many parts of stellar life are hidden from view until a star dies.

White dwarfs are a window into the hearts and lives of stars.

By studying white dwarfs, we learn about stars long gone