Digging up Astronomical Fossils

Imagine looking up at the night sky. With our own eyes we can see at most a few thousand of the nearest stars to us. Now consider looking through a large telescope with a very large field of view. Through such an instrument millions of objects come into view, with most of these objects being galaxies, not stars.

Interestingly, galaxies are not scattered randomly about the sky, as one might expect. Rather, they trace out a structure that looks a bit like a 3D spider web, called by astronomers the “cosmic web.” Fair enough. The story gets more interesting though when we find out that the mean separation between galaxies, equating roughly to the mean separation between the threads of a spider web, was set early on in the universe’s history.

When the universe was only about 370,000 years old, various sound waves that traversed its extent were frozen into place by changing physical conditions. Astronomers maintain that events that happened at this time established the mean distance between the galaxies long before the first galaxy would ever form. These so-called Baryon Acoustic Oscillations (BAOs), named "acoustic" for their sound wave origin, refer to the physical signature of these ancient sound waves expressed in the universe today.

Put another way, just as archaeologists disinter dinosaur bones to learn about human history, astronomers measure the mean distance between galaxies to learn about the distant and early history of the universe. This work is carried out by the Sloan Digital Sky Survey (SDSS) Extended Baryon Oscillation Spectroscopic Survey (eBOSS), a large program which offers free public access to all of its data sets worldwide. If time allows, try visiting the website at legacysurvey.org, enter in your favorite coordinates in the upper right, and enjoy exploring the distant universe.

Dr. Brenda Frye

About Dr. Brenda Frye

Brenda L. Frye is an observational cosmologist at the Department of Astronomy/Steward Observatory, University of Arizona. She earned her Ph. D. in Astrophysics from the University of California at Berkeley, assisted by a National Science Foundation Graduate Research Fellowship.

Her thesis work involved measuring the concentration of the total mass of visible plus dark matter in the fields of massive galaxy clusters, a program requiring the use of some of the largest telescopes in the world.

Moving a mile from her Ph. D. institution, she assumed a postdoctoral position with the Supernova Cosmology Project at Lawrence Berkeley National Laboratory under the direction of Professor Saul Permutter.

She then treked across the country to take a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship and a Princeton Council on Sciences and Technology Fellowship both at Princeton University.

Moving further east, she became a Lecturer in Physics at Dublin City University in Dublin, Ireland, where a number of European collaborations were formed.

From there she crossed back across the pond to the west coast of the U. S. to become a tenure-track Assistant Professor of Physics at the University of San Francisco.

Her travels have now landed her at her Alma Mater in Tucson, where she teaches and does research. The aims of her research continue to be to use gravitational telescopes in space as 'lenses' to study the properties of dark matter and those of distant galaxies back to when the universe was <900 million years old.

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