240
GALAXIES
CHANGE
OVER TIME
UNDERSTANDING STELLAR EVOLUTION
IN CONTEXT
KEY ASTRONOMER
Beatrice Tinsley (1941–1981)BEFORE
1926 Edwin Hubble produces
a classification for galaxies
based on their shapes.Early 1960s American Allan
Sandage proposes that disk
galaxies form through the
collapse of large gas clouds.
He estimates distances to
remote galaxies based on the
idea that the brightest galaxies
have similar luminosity.AFTER
1977 Canadian Brent Tully and
American Richard Fisher find
a link between the luminosity
and rotation of spiral galaxies.
This is useful in estimating
distances to spiral galaxies.1979 Vera Rubin uncovers a
discrepancy between actual
and predicted rotational
velocities in spiral galaxies,
giving evidence of unseen
“dark matter” in such galaxies.U
ntil a young New Zealand
astronomer named Beatrice
Tinsley published a highly
original thesis in 1966, the methods
used by cosmologists to calculate
the distances to remote galaxies
had been flawed. Accurate data
for these distances was important
because it would help to answer some
of cosmology’s most fundamental
questions, namely the average
density of the universe, its age,
and its rate of expansion.
One method used in the 1960s
was based on the idea that galaxies
of the same type (giant ellipticals, forexample) should all have roughly
the same intrinsic brightness.
On this basis, it was thought that
distances to faraway galaxies
should be obtainable simply by
measuring their light output and
comparing it to those of nearby
galaxies of the same type whose
distance was known.Tinsley’s argument
Tinsley challenged this approach,
saying it was crude and unreliable.
In calculating galaxy distances, she
argued, more consideration had to
be given to the fact that galaxiesBeatrice Tinsley
Beatrice Hill was born in Chester,
UK, in 1941, and moved with her
family to New Zealand when
she was four years old. In 1961,
she received a degree in physics
from Canterbury University,
and in the same year married
classmate Brian Tinsley. In 1963,
they moved to Dallas, Texas,
where her husband had been
offered a university job. Beatrice
wasn’t allowed to work at the
same university, so she took a
teaching job at the University
of Texas at Austin.In 1966, she completed her Ph.D.
with a thesis on the evolution
of galaxies. Tinsley soon became
an influential figure in the field
of cosmology. In 1974, she took
a position as assistant professor
at Yale University, becoming
the university’s first female
professor of astronomy in 1978.
She died of cancer in 1981, at
just 40. Mount Tinsley in New
Zealand is named in her honor.Key work1966 Evolution of Galaxies and
its Significance for Cosmology