Local astronomer discusses clusters of galaxies

A Mount Hopkins astronomer talked Wednesday about the immense size and distances of the universe, and talked about how dark matter apparently holds it together.

Jeremy Perkins of the nearby Smithsonian’s Whipple Observatory talked on “Clusters of galaxies: a very big laboratory.”

The universe is a very, very huge place where distance is measured in light years, the amount of time it would take light to travel to the farthest corners of the universe—10 billion light years away.

A light year is the distance that light, traveling at about 4 million miles a second, would travel in a year’s time.

Perkins said, for example, light from the sun takes about eight minutes to reach the Earth.

Before the telescope was invented in late 16th century, sky watchers could discern only stars, specks of light in the night-time darkness.

But after Galileo started using one in about 1609, astronomers could see that what they had thought of as stars were actually clusters of them, made up of hundreds or thousands or millions of stars.

There are other nearby galaxies. For example, the Andromeda Galaxy is about 2.5 million light years from our galaxy.

It is the closest one to our solar system.

Andromeda is the nearest spiral galaxy to our own, the Milky Way.

But as telescopes and the understanding of physics improved, there was a concern that all the stars—inferred from stellar observations—didn’t have enough mass and gravity to hold everything together.

In the early 1930s, astronomer Fritz Zwicky, working in California, said that the motions of the stars and galaxies indicated there should be 160 times more observable matter acting as a kind of galactic glue.

What was holding it together, he called unseen matter, which later became known as dark matter.

Since his work and that of others, it was discovered that there were sound waves in galaxies, gravity is so strong it can bend light waves, there is tremendous heat in the galaxies, and all other objects in the universe are pulling away from each other, speeding outward.

Near the end of Perkins’ lecture, he listed what’s been learned by studying clusters within the universe and “what we don’t know.”

And one of those unanswered questions was “What is dark matter?”

The Smithsonian’s next star lecture will be 9 a.m. Tuesday, Feb. 19, on massive stars and Gamma-ray bursts.

The lectures are held at West Center and are free.

jlamb@gvnews.com | 547-9749