The universe could be 2 billion years older than thought, according to a new report by an international team of astronomers. The scientists have found that a nearby galaxy is 15% farther away than previous results suggested. That could mean the age of the universe is off by the same amount. But other experts think it's too early to draw such far-reaching conclusions.
Astronomers have been able to determine relative distances of remote galaxies using observations of a particular type of star that periodically changes its brightness. But in order to know how many lightyears away all these galaxies are, they need to directly measure the distance between a few galaxies and our own Milky Way. Such measurements are hard to come by--for many years, the only galaxy for which a reliable distance has been determined is the nearby Large Magellanic Cloud, but some astronomers worry its unusual chemical makeup could skew calculations.
Now, Alceste Bonanos of the Carnegie Institution of Washington in Washington, D.C., and colleagues have observed a so-called eclipsing binary star in the Triangulum galaxy, a large neighbor of our own Milky Way. The two stars in the system pass in front of one another during their orbit, and observations of these mutual eclipses allow astronomers to derive the sizes of the two stars and how much energy they emit. A comparison with the observed brightness reveals the distance from Earth: the dimmer the apparent brightness, the further the star.
The result, published in an upcoming issue of The Astrophysical Journal, puts Triangulum (also known as M33) 3 million lightyears away--15% more distant than the generally accepted value of 2.6 million lightyears, which was established by other, less direct techniques. If confirmed, the new distance would imply that more remote galaxies are also 15% further away, because the relative distances haven't changed. And because the size and age of the universe is based on galaxy distances, the result could also increase the age of the universe from 13.7 to 15.7 billion years.
Bonanos's team has done "a solid piece of work," says Wendy Freedman, a cosmologist at the Carnegie Observatories in Pasadena, California, who in the 1990's led a large Hubble Space Telescope project to determine the cosmic distance scale. But, she warns, "I think that it will take more than one eclipsing binary in one galaxy" to change current thinking on the age of the universe.
Edward Guinan, an astrophysicist at Villanova University in Pennsylvania, who pioneered the eclipsing binary technique in the nearby Large Magellanic Cloud dwarf galaxy, agrees. "The method is good, the group is good, and they did a good job," he says. "But it's just one star." He's also worried by the fact that Bonanos's team used a bright, hot eclipsing binary, for which theoretical models are less solid. "My expectation is that Triangulum won't be that far away," he says. "It will probably move in again."
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