Entry for April 22, 2006

  Dr. Margaret Geller of the Smithsonian Astrophysical Observatory was the featured speaker at the University of California Irvine on Monday, April 19, 2006 as part of the Chancellor’s Distinguished Lecturer Series.

  Dr. Geller is probably most famous for her work in mapping the large-scale structure of the universe, with an incredible three-dimensional map revealed a few years ago. She is a nationally known figure and one of the most popular astronomers of our time. She has published many research papers and also articles and books for the lay public. She has also appeared in many astronomy related films and documentaries.

  Her talk, titled “Einstein Meets Newton: Mapping Dark Matter in the Universe”, was in a capacity-filled lecture hall on the UCI campus. Many OCA members were in attendance, along with students, teachers and other members of the general public. Her program included a projected slide show on a very large screen. The slides included animations of large galaxy structures in motion.

She began her lecture with a series of basic questions such as:

“How far can we see with the naked eye?”

“How old is the Universe?”

“What is our place in the cosmos?”

   One profound point she made is that time, not space, limits our view of the universe. Her work is in the mapping of structures of clusters of galaxies on a scale of millions of light years. The number of galaxies she has mapped is in the thousands, including a sheet of galaxies that was dubbed “The Great Wall” of galaxies over 15 million light years thick.

   As her lecture continued, she recounted the discovery story of the planet Neptune, which she called the first instance of the detection of dark matter. Neptune’s position was determined by the gravitational perturbances in the orbit of Uranus. Today, dark matter is detected in the same way, by observing the gravitational pertubances in the light of background galaxies as their light is distorted into arcs by powerful gravitational lensing.

   Dark matter was first theorized or discovered by Fritz Zwicky, the eccentric professor of physics at Caltech in 1933. Dr. Geller gave a few anecdotes about (ahem) Zwicky’s colorful personality, but then concentrated on his powerful intellect and his work in the field of astrophysics.  Zwicky first detected dark matter by observing and measuring the galaxies in the Coma cluster, and released his paper on the topic in 1937. He suggested that gravitational lensing  could be used as a tool for measuring mass.

   The next person mentioned was Vera Rubin, the astronomer that discovered the odd constant rotational velocities in galaxies. She found that the velocities of stars in galaxies were relatively constant from the center to the edges of the galaxies. This inferred that there were massive dark haloes of matter extending far beyond the visible edge of the galaxies.

   Enter Einstein, with a curious graphic showing him surfing on gravitational waves, as massive objects perturb the space around it. The familiar rubber sheet model of gravity was displayed, showing how not only matter but also light itself being stretched by gravity wells.

    The amazing thing today is that all of the predicted effects of gravity in making ring arcs agree with the previously published theories within a few percent, a triumph of modern astrophysics. She displayed many fascinating Hubble and ground based observatory photographs of actual arcs and entire rings of light distorted by foreground gravitational sources.

   She then presented some slides showing the Smithsonian telescope and instruments used in detecting the red shifts of 11,000 galaxies, in order to map the large-scale distribution of matter over space and time. Using fiber optic probes, the telescope imaged the sky one square degree of arc at a time.

    As her lecture closed, she turned to the philosophical aspects of astrophysics, a topic rarely covered in the general media and the science press. We live in an extraordinary time. As we have the ability to image the universe to its absolute visual limits, it shows the reach of the human mind.  The thing that makes us grand is that we have the ability to not only ask the questions about the universe, we now have the capability to answer them.

   Then she made a humorous point. Photons of radiation travel for billions of years and do not hit anything until they reach the top of our heads, which she said was a waste. What she failed to mention is that many other photons are collected and studied by professional and amateur astronomers, and they are put to quite useful endeavors.

    In closing, she wished the audience great joy in asking the questions and getting the answers, which is a great and important part of the human condition. She then opened up the audience to a question and answer session.

 

 

 

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~ by matthewota on April 22, 2006.

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