Transcript Stellar Forensics With White Dwarfs

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”
BIG
Heavy
Small
Light
Blue Red
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.
Art: NSBRI
Photo: Dartmouth Chemistry
Dept.
White dwarfs with other elements
must replenish them constantly
Photo: SOHO
© Anglo-Australian Observatory
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