ASU Research E-Magazine: Cosmic Conundrum

The conflict between the age of the universe and the age of its oldest stars just got worse. A faint galaxy at the far reaches of the universe has joined the list of objects that appear to be older than the universe itself.

An international team of scientists, including ASU astronomer Rogier Windhorst, has determined that the galaxy is about 11 billion years old. The age of the universe as measured by the Hubble Space Telescope, however, is just under 10 billion years.

The finding reinforces a major problem in cosmology, the study of the universe’s origin. Windhorst and his co-authors, led by the University of Edinburgh’s James Dunlop, reported their finding in the June 13 issue of the journal Nature.

Astronomers already were puzzling over the age of the Globular Clusters, collections of hundreds of thousands of stars in the Milky Way Galaxy. The Globular Clusters appear to be about 14 billion years old, based on a well-developed under-standing of how stars evolve.

“We now know that the Globular Cluster age problem is not just a fluke,” Windhorst says.

As members of the Milky Way Galaxy, Globular Clusters are sitting in Earth’s astronomical backyard. The 11-billion-year-old galaxy described in Nature is much farther away, providing an independent verification of the Globular Clusters problem.

Windhorst discovered the galaxy, designated 53W091, in 1986 with David Koo of California’s Lick Observatory. They originally imaged the galaxy using the 200-inch telescope at Palomar Observatory. But they were unable to measure the galaxy’s distance from Earth.

In 1995, members of Dunlop’s team made additional observations of the galaxy using the larger, specially equipped 10-meter Keck Telescope at Mauna Kea, Hawaii. They found remarkable similarities in the light waves emitted by galaxy 53W091 and galaxy M32, a well-studied galaxy in Earth’s neighborhood.

M32 is a dwarf, elliptical galaxy about 3.5 billion years old. Galaxy 53W091 appears to be about the same age, except that it is more than 7 billion light-years away. Astronomers see the galaxy today as it looked when the universe was only one-fourth as old as it is now. A galaxy that old at that distance would make the universe about 14 billion years old.

To illustrate the problem, Windhorst draws an analogy to the historical calendar. Imagine the universe was born about 2,000 years ago, in the year zero. Astronomers living in 1996 figure out that the Globular Clusters were born 2,500 years ago, roughly the year 500 b.c.

Then astronomers come across a reliable document telling them that galaxy 53W091 was found to be 900 years old in the year A.D. 500. The galaxy’s birthdate would be 400 B.C., nearly as old as the Globular Clusters. Now astronomers must come up with a theory that brings creation back in time by at least 500 or 600 years.

The universe should be expanding, according to Albert Einstein’s 1917 theory of general relativity. Einstein preferred the idea of a steady-state universe and introduced a force in his equations called the cosmological constant. In 1929, astronomer Edwin Hubble discovered that the universe does expand. Einstein recanted his cosmo-logical constant, calling it his greatest mistake.

Still, the cosmological constant would help solve the age problem presented by the Globular Clusters. The universe could have expanded more slowly for a long period early in its history. Following this scenario, the Globular Clusters could indeed be 14 billion years old.

“We’ve made [the problem] worse instead of making it better,” Windhorst says. —Conrad J. Storad