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2010-12-03 05:51:41
By SETH BORENSTEIN, AP Science Writer Seth Borenstein, Ap Science Writer Wed
Dec 1, 9:32 pm ET
WASHINGTON The universe may glitter with far more stars than even Carl Sagan
imagined when he rhapsodized about billions upon billions. A new study suggests
there are a mind-blowing 300 sextillion of them, or three times as many as
scientists previously calculated. That is a 3 followed by 23 zeros. Or 3
trillion times 100 billion.
The estimate, contained in a study published online Wednesday in the journal
Nature, is based on findings that there are many more red dwarf stars — the
most common star in the universe — than once thought.
But the research goes deeper than that. The study by Yale University astronomer
Pieter van Dokkum and Harvard astrophysicist Charlie Conroy questions a key
assumption that astronomers often use: that most galaxies have the same
properties as our Milky Way. And that conclusion is deeply unsettling to
astronomers who want a more orderly cosmos.
When scientists previously estimated the total number of stars, they assumed
that all galaxies had the same ratio of dwarf stars as the Milky Way, which is
spiral-shaped. Much of our understanding of the universe is based on
observations made inside our own galaxy and then extrapolated to other
galaxies.
But about one-third of the galaxies in the universe are elliptical, not spiral,
and van Dokkum found they aren't really made up the same way as ours.
Using the Keck telescope in Hawaii, van Dokkum and a colleague gazed into eight
distant, elliptical galaxies and looked at their hard-to-differentiate light
signatures. The scientists calculated that elliptical galaxies have more red
dwarf stars than predicted. A lot more.
"We're seeing 10 or 20 times more stars than we expected," van Dokkum said.
Generally scientists believe there are 100 billion to a trillion galaxies in
the universe. And each galaxy the Milky Way included was thought to have
100 billion to a trillion stars. Sagan, the Cornell University scientist and
best-selling author who was often impersonated by comedians as saying "billions
and billions," usually said there were 100 billion galaxies, each with 100
billion stars.
Van Dokkum's work takes these numbers and adjusts them. That's because some of
those galaxies — the elliptical ones, which account for about a third of all
galaxies — have as many as 1 trillion to 10 trillion stars, not a measly 100
billion. When van Dokkum and Conroy crunched the incredibly big numbers, they
found that it tripled the estimate of stars in the universe from 100 sextillion
to 300 sextillion.
That's a huge number to grasp, even for astronomers who are used to dealing in
light years and trillions, Conroy said.
"It's fun because it gets you thinking about these large numbers," Conroy said.
Conroy looked up how many cells are in the average human body 50 trillion or
so and multiplied that by the 6 billion people on Earth. And he came up with
about 300 sextillion.
So the number of stars in the universe "is equal to all the cells in the humans
on Earth — a kind of funny coincidence," Conroy said.
For the past month, astronomers have been buzzing about van Dokkum's findings,
and many aren't too happy about them, said astronomer Richard Ellis of the
California Institute of Technology.
Van Dokkum's paper challenges the assumption of "a more orderly universe" and
gives credence to "the idea that the universe is more complicated than we
think," Ellis said. "It's a little alarmist."
Ellis said it is too early to tell if van Dokkum is right or wrong, but his
work is shaking up the field "like a cat among pigeons."
Van Dokkum agreed, saying, "Frankly, it's a big pain."
Ellis said the new study does make sense. Its biggest weakness might be the
assumption that the chemical composition of dwarf stars is the same in
elliptical galaxies as in the Milky Way. That might be wrong, Ellis said. If it
is, it would mean there are only five times more red dwarf stars in elliptical
galaxies than previously thought, instead of 10 or 20, van Dokkum said.
Slightly closer to home, at least in our own galaxy, another study also
published in Nature looks at a single red dwarf star in a way that is a step
forward in astronomers' search for life beyond Earth. A team led by a Harvard
scientist was able to home in on the atmosphere of a planet circling that star,
using the European Southern Observatory's Very Large Telescope in Chile.
The planet lives up to the word alien. The team reports that this giant
planet's atmosphere is either dense with sizzling water vapor like a souped-up
steam bath, or it is full of hazy, choking hydrogen and helium clouds with a
slightly blue tint. The latter is more likely, say the researchers and others
not involved in the study.
While scientists have been able to figure out the atmosphere of gas giants the
size of Jupiter or bigger, this is a first for the type of planet called a
super Earth something with a mass 2 to 10 times Earth's. The planet is more
comparable to Neptune and circles a star about 42 light years from Earth. A
light year is nearly 6 trillion miles.
The planet is nowhere near livable it's about 440 degrees (about 225 degrees
Celsius). "You wouldn't want to be there. It would be unpleasant," said study
co-author Eliza Kempton of the University of California Santa Clara.
But describing its atmosphere is a big step toward understanding potentially
habitable planets outside our solar system, said study chief author Jacob Bean
at the Harvard Smithsonian Center for Astrophysics.
Bean and Kempton looked at the light spectrum signature from the large planet
as it passed in front of the dwarf star, and the result led to two possible
conclusions: steam bath or haze.
The steam bath is the more interesting possibility because water is key to
life, said outside scientist Alan Boss of the Carnegie Institution of
Washington.
But an upcoming and still unpublished study by Kempton and Bryce Croll at the
University of Toronto points more toward a hydrogen-helium atmosphere, several
astronomers said.