While astronomers have yet to completely deduce the nature of dark matter after more than seven decades, David Weinberg can break down its history into a 5-minute rap song.
“Dark matter. What is it? Do we need it? Where is it?” Weinberg rapped, in the closing minutes of his lecture on dark matter and dark energy.
In commemoration of Einstein’s contribution to astronomy, the astronomy department’s distinguished lecture series this semester will examine Albert Einstein’s legacy in the field.
Last Friday, Weinberg, an Ohio State University astronomy Prof., spoke on the mysteries of dark matter and dark energy that have dogged astronomers for decades.
Weinberg began his lecture by detailing the origins of dark matter, adding that astronomers began to notice the phenomenon when examining abnormal galaxy clusters.
In 1933 Swiss astrophysicist Fritz Zwicky observed a cluster of galaxies called the Coma Cluster that according to his measurements, did not exhibit enough gravity to hold the cluster together.
Zwicky concluded the cluster must contain something that would produce enough gravity to hold the galaxies together.
“The galaxies were moving so fast that there was not enough gravity to hold them together. So Zwicky decided to call it the missing mass problem.”
This “missing mass problem” would later become known as dark matter,
Not until about the 1970s did the phenomenon re-emerge into the field of astronomy, Weinberg said. By then astronomers had observed that the rotational speed of spiral galaxies did not act according to the rules of gravity.
Weinberg used the example of a solar system, saying that as planets move away from the sun, the gravitational force binding the planet to the star becomes less. As a result, planets further away from the center of the solar system move at a slower rate around the sun.
In spiral galaxies this is usually not the case, Weinberg said. Astronomers expected that the velocity of the outer fringes of a galaxy would be significantly less than near the inner areas of the galaxy.
But measurements of galaxies found that the velocity of a galaxy’s rotation plateaus as one moves out from the center of a galaxy.
“It’s the single most convincing evidence of dark matter,” Weinberg said.
Since those observations, astronomers worldwide have attempted to shed light on the composition of dark matter. To explain the phenomenon, astronomers in the past have suggested black holes, undetectable gas cloud, dim gas giants and neutrinos produced the extra gravity.
But Weinberg said so far no explanations have completely been able to answer the dark matter question.
Neither has anyone been able to shed light on the mystery dark energy. Although the combined mass in the universe should cause the galaxies to gravitate toward one another, observations of supernovae have found that galaxies are in fact moving away from each other. This unknown force is called dark energy and has astronomers even more puzzled.
“There is in fact lots of activity going on to understand – what dark energy is. But my conclusion is what you see is not what you get.”
To wrap up his lecture, Weinberg then turned on a boom box and began to rap a song he made in 1992 called “The Dark Matter Rap: A Cosmological History for the MTV Generation.”
LSA Freshman Varun Vaidya said of the lecture, “Although it was new to me, it was pretty easy to grasp.”
For more information on upcoming lectures please visit the astronomy department’s homepage at www.astro.lsa.umich.edu.