A project
aiming to create an easier way to measure cosmic distances has instead turned
up surprising evidence that our large and ancient universe might be even bigger
and older than previously thought.
If
accurate, the finding would be difficult to mesh with current thinking about
how the universe evolved, one scientist said.
A research
team led by Alceste Bonanos at the Carnegie Institution of Washington has found
that the Triangulum
Galaxy, also known as M33, is about 15 percent farther away from our own
Milky Way than previously calculated.
The
finding, which will be detailed in an upcoming issue of Astrophysical
Journal, suggests that the Hubble constant, a number that measures the expansion
rate and age of the universe, is actually 15 percent smaller than other studies
have found.
Currently, most
astronomers agree that the value of the Hubble constant is about 71 kilometers
per second per megaparsec (a megaparsec is 3.2 million light-years). If this
value were smaller by 15 percent, then the universe would be older and bigger
by this amount as well.
Scientists
now estimate the universe to be about 13.7 billion
years old (a figure that has seemed firm since 2003, based on measurements
of radiation leftover from the Big Bang) and about 156 billion
light-years wide.
The new
finding implies that the universe is instead about 15.8 billion years old and about
180 billion light-years wide.
A new
way to measure distance
The
researchers reached their surprising conclusion after using a new method they
invented to calculate intergalactic distances, one that they say is more
precise and requires fewer steps than standard techniques.
"We
wanted an independent measure of distance--a single step that will one day help
with measuring dark
energy and other things," said study team member Krzysztof Stanek from
Ohio State University.
The new
method took 10 years to develop and relied on optical and infrared measurements
gathered from telescopes all around the world. The researchers looked at a
binary star system in M33 where the stars eclipsed each other every five days.
Unlike single stars, the masses of
paired stars can be precisely
calculated based on their movements. With knowledge of the stars' masses,
the researchers could calculate their true luminosities, or how bright they
would appear if they were nearby.
The
difference between the true luminosity and the observed luminosity gives the
distance between the stars and Earth. The team's results suggested that the stars
were about 3 million light-years from Earth--or about half-a-million light-years
farther than would be expected using the commonly accepted Hubble constant
value.
'Not
impossible'
Lawrence
Krauss, a professor of astronomy and chair of the Department of Physics at Case
Western Reserve who was not involved in the study, said the idea of a
significantly reduced Hubble constant would be hard to accommodate.
"Things
fit right now very well for a Hubble constant of a low 70s," Krauss said
in a telephone interview. "It corresponds very well with the age of
globular clusters as we've determined them and the age of the universe. It
would be hard, although not impossible, to change things by 15 percent."
Stanek said
his team plan to follow up their finding with distance measurements for either
another binary star system in M33 or to look for a binary system in another galaxy, perhaps Andromeda.
"It's
extremely important to have independent measurements of the Hubble
constant," Stanek told SPACE.com. "That's what we're working
towards."
advertisement
