ANN ARBOR—If you look high up in the southern sky on May evenings, you are actually looking out from our Milky Way Galaxy into the remove universe, according to University of Michigan astronomer Richard Teske. Far beyond the constellation of Virgo, the Reclining Maiden, lies a great cluster of galaxies that only can be seen with medium- or large-sized amateur telescopes. This cluster of 3,000 galaxies is a focal point of astronomers’ efforts to learn the true size and age of the universe.

Galaxy clusters are made up of large numbers of individual galaxies, which are themselves huge aggregations of tens of billions of stars. Some galaxies take the shape of huge spirals, others are football-shaped, while some are ragged and without any recognizable structure. “Galaxies like to stay near other galaxies, and are seldom found alone,” Teske said. “This tendency to form groups or clusters is an important clue to their history.” Before galaxies formed, the universe was filled with immense clouds of gas. These clouds split or fragmented into smaller galaxy-sized clouds. Stars condensed out of gases within the fragments, generating the galaxies we see today. The process gave rise to groups of galaxies, each cluster a descendant of one of the original, huge clouds. Galaxies in a cluster have remained with their original companions since they formed, their mutual gravitational pull upon one another keeping them from parting company as the universe expands.

“Galaxy clusters are often regarded as the true ‘units’ of the universe’s structure, the real bricks of the building,” Teske explained. “Some clusters have many thousands of member galaxies, others only a few,” Teske added. “Our own Milky Way Galaxy has two dozen companions in a small cluster that spreads across three million light-years of space. The actual distance across our difficulties encountered by astronomers in determining the distances to remote galaxies.” The Hubble Space Telescope is now being used in a project designed to improve methods of distance measurement. The Virgo Cluster supplies a key reference point in the project, according to Teske.

Astronomical methods for determining distances to galaxies all make use of the same basic concept, which turns the measurement of distance into a measurement of brightness. For instance, two identical stars seen at different distances will have different brightnesses. When the brightness and the distance of one star is known, measurement of the other’s brightness allows its distance to be calculated. Methods based on the concept employ measurement of the average brightnesses of certain kinds of variable stars, of the brightnesses of exploding stars called supernovas and of other easily identifiable objects that inhabit distant galaxies.

“The central difficulty is knowing the real distance of one of the objects,” Teske said. “This is the problem the Hubble Space Telescope will address through observations of the Virgo Cluster.” Astronomers are using the Hubble to pin down the distance to the Virgo Cluster with measurements of brightnesses of variable stars and other objects in the galaxies there. When the different methods reliably give the same distance to Virgo, they’ll be used to determine distances to even more remote galaxy clusters.

Scientists expect that by the year 2000 most of the uncertainty about distances in the universe will be eliminated. “A longstanding related problem, the uncertainty of the age of the universe, will be automatically solved when the distance problem is settled. The universe’s age is calculated based on the speed of the universe’s expansion,” Teske said. “Determining how fast it expands depends not only on measuring how fast the galaxy clusters recede from us, which is fairly easy to do, but also upon measuring their distances as exactly as possible, which is still hard to do. Estimates of the age have ranged from 8 billion years to 14 billion years, owing to the uncertainty of distances. The expected improvement of distance estimates by Hubble is going to sharpen up knowledge of the universe’s speed of expansion and hence provide a reliable estimate of its age.”