Allan Sandage, Astronomer, Dies at 84; Charted Cosmos's Age and Expansion
Matthew Kruk
November 17, 2010
Allan Sandage, Astronomer, Dies at 84; Charted Cosmos's Age and
Expansion
By DENNIS OVERBYE
Allan R. Sandage, who spent his life measuring the universe, becoming
the most influential astronomer of his generation, died Saturday at his
home in San Gabriel, Calif. He was 84.
The cause was pancreatic cancer, according to an announcement by the
Carnegie Observatories, where he had spent his whole professional
career.
Over more than six decades, Dr. Sandage was like one of those giant
galaxies that sit at the center of a cluster of galaxies, dominating
cosmic weather. He wrote more than 500 papers, ranging across the
cosmos, covering the evolution and behavior of stars, the birth of the
Milky Way galaxy, the age of the universe and the discovery of the first
quasar, not to mention the Hubble constant, a famously contested number
that measures the rate of expansion of the universe. Dr. Sandage pursued
the number with his longtime collaborator, Gustav Tammann of the
University of Basel in Switzerland.
In 1949, Dr. Sandage was a young Caltech graduate student, a
self-described "hick who fell off the turnip truck," when he became the
observing assistant for Edwin Hubble, the Mount Wilson astronomer who
discovered the expansion of the universe.
Hubble had planned an observing campaign using a new 200-inch telescope
on Palomar Mountain in California to explore the haunting questions
raised by that mysterious expansion. If the universe was born in a Big
Bang, for example, could it one day die in a Big Crunch? But Hubble died
of a heart attack in 1953, just as the telescope was going into
operation. So Dr. Sandage, a fresh Ph.D. at 27, inherited the job of
limning the fate of the universe.
"It would be as if you were appointed to be copy editor to Dante," Dr.
Sandage said. "If you were the assistant to Dante, and then Dante died,
and then you had in your possession the whole of 'The Divine Comedy,'
what would you do?"
Dr. Sandage was a man of towering passions and many moods, and for
years, you weren't anybody in astronomy if he had not stopped speaking
to you. In later years, beset by controversy, Dr. Sandage withdrew from
public view. But even after retiring from the Carnegie Observatories and
becoming ill, he never stopped working; he published a paper on variable
stars only last June.
In 1991, Dr. Sandage was awarded the Crafoord Prize in astronomy, the
closest thing to a Nobel for a stargazer, worth $2 million.
Wendy Freedman, his boss as director of Carnegie as well as a rival in
the Hubble constant question, referred to him on Tuesday as the last
giant of 20th-century observational cosmology. "Even when we had our
scientific differences, I got a kick out of him," she said. "His passion
for his subject was immense."
James Gunn, an astronomer at Princeton, said of Dr. Sandage in an e-mail
message, "He was probably (rightly) the greatest and most influential
observational astronomer of the last half-century."
Allan Rex Sandage was born in Iowa City, Iowa, on June 18, 1926, the
only child of an advertising professor, Charles Harold Sandage, and a
homemaker, Dorothy Briggs Sandage. The stars were one of his first
loves; his father bought him a commercial telescope.
After two years at the University of Miami, where his father taught,
Allan was drafted into the Navy; he resumed his education at the
University of Illinois, earning a degree in physics.
In 1948 he entered graduate school at the California Institute of
Technology, where an astronomy program had been started in conjunction
with the nearby Mount Wilson Observatory, home of Hubble, among others.
As a result, Dr. Sandage learned the nuts and bolts of observing with
big telescopes from the founders of modern cosmology, Hubble; Walter
Baade, who became his thesis adviser, and Milton Humason, a former mule
driver who had become Hubble's right-hand man.
In the years before World War II, there had been a revolution in the
understanding of the nature and evolution of stars as thermonuclear
furnaces burning hydrogen into helium and elements beyond. Astronomers
could now read the ages of star clusters from the colors and brightness
of the stars in them.
For his thesis, Dr. Sandage used this trick to date a so-called globular
cluster, known as Messier 3, as being 3.2 billion years old, which meant
that the universe itself could not be younger than that. In fact, Hubble's
own measurements of the cosmic expansion suggested an age of about four
billion years - remarkably, even miraculously, consistent.
At the time, astronomers were also still debating whether the universe
had had a Big Bang and a beginning at all, not to mention whether it
would have an ending as well. An opposing view championed by the British
cosmologist Fred Hoyle held that the universe was eternal and in a
"steady state," with new matter filling in the void as galaxies rushed
away from one another.
Choosing between these models was to be the big task of 20th-century
astronomy, and of Dr. Sandage. In 1961 he published a paper in The
Astrophysical Journal showing how it could be done using the 200-inch
telescope. He described cosmology as the search for two numbers: one was
the cosmic expansion rate, known as the Hubble constant; the other,
called the deceleration parameter, tells how fast the expansion is being
braked by cosmic gravity.
That paper, "The Ability of the 200-inch Telescope to Discriminate
Between Selected World Models," may well have been "the most influential
paper ever written in any field even close to cosmology," Dr. Gunn said.
It was to set the direction of observational cosmology for 40 years,
ruling out the Steady State and the Big Crunch and culminating in the
surprise discovery in 1998 that the expansion is not slowing down at all
but speeding up.
Meanwhile, Dr. Sandage investigated the birth of the galaxy. By
analyzing the motions of old stars in the Milky Way, he, Olin Eggen of
Caltech and Donald Lynden-Bell of Cambridge showed in a 1962 paper that
the Milky Way formed from the collapse of a primordial gas cloud
probably some 10 billion years ago. That paper still forms the basis of
science's understanding of where the galaxy came from, astronomers say.
In 1959, Dr. Sandage married another astronomer, Mary Connelly, who was
teaching at Mount Holyoke and had studied at the University of Indiana
and Radcliffe, but did not pursue further research. He is survived by
her and two sons, David and John.
It was measuring the cosmic expansion that was the most backbreaking
part of fulfilling Hubble's legacy. In an expanding universe, the speed
with which a galaxy flies away from us is proportional to its distance.
The constant of proportionality, the Hubble constant, is given in the
mind-numbing terms of kilometers per second per megaparsec. Hubble's
original estimate of his constant of 530 meant that for every million
parsecs (3.26 million light years) a galaxy was farther away from us, it
was retreating 530 kilometers per second (around 300 miles per second)
faster.
Hubble's original estimate, however, corresponded to an age for the
universe of only 1.8 billion years, at odds with both geological
calculations of the Earth's age and Dr. Sandage's later estimate of the
ages of star clusters.
But Hubble had made mistakes - he saw bright patches of gas as stars,
for example - and as Dr. Sandage and Dr. Tammann delved into the subject
in a series of papers, the problematic constant came down and the
imputed age of the universe rose.
In 1956, Dr. Sandage suggested that the Hubble constant could be as low
as 75 kilometers per second per megaparsec. By 1975 the value, they
said, was all the way down to 50, corresponding to an age of as much as
20 billion years, comfortably larger than the ages of galaxies and
globular clusters.
This allowed them to conclude that the universe was not slowing down
enough for gravity to reverse the expansion into a Big Crunch. That was
in happy agreement with astronomers who had found that there was not
enough matter in the universe to generate the necessary gravity.
As Dr. Sandage wrote in The Astrophysical Journal in March 1975, "(b)
the Universe has happened only once, and (c) the expansion will never
stop."
"So the universe will continue to expand forever," Dr. Sandage said in
an interview, "and the galaxies will get farther and farther apart, and
things will just die. That's the way it is. It doesn't matter whether I
feel lonely about it or not."
Shortly thereafter, however, their results on the Hubble constant came
under attack by rival astronomers, who said that Dr. Sandage and Dr.
Tammann had overestimated the distances to galaxies - a crucial part of
the equation for the constant - making the universe appear bigger and
older than it really was. The universe, they said, was really about 10
billion years old.
Stung by the criticisms, Dr. Sandage retreated from public view, even
while he and Dr. Tammann redoubled their efforts to measure the
troublesome constant, always getting a low value. As the groups shot
back and forth at each other, the universe, as reflected in newspaper
headlines, boomeranged back and forth from 10 billion to 20 billion
years.
In 2001, a team led by Dr. Freedman, using the Hubble Space Telescope,
reported a value of 72 kilometers per second per megaparsec, in good
agreement with measurements of relic radiation from the Big Bang that
give an age of 13.7 billion years for the cosmos full of dark energy and
dark matter, and a Hubble constant of 71, which most astronomers now
accept.
To the frustration of colleagues, Dr. Sandage, also using Hubble, kept
getting a lower value.
We may never know the fate of the universe or the Hubble constant, he
once said, but the quest and discoveries made along the way were more
important and rewarding than the answer anyway.
"It's got to be fun," Dr. Sandage told an interviewer. "I don't think
anybody should tell you that he's slogged his way through 25 years on a
problem and there's only one reward at the end, and that's the value of
the Hubble constant. That's a bunch of hooey. The reward is learning all
the wonderful properties of the things that don't work."