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Davis, California

Saturday, April 20, 2024

Astronomers detect faint satellite galaxy

Chris Fassnacht, a professor in the UC Davis Physics department, has co-authored a paper appearing in Nature, which provides evidence to corroborate a theory of how galaxies form in a process that involves dark matter by detecting a faint satellite galaxy 10 billion light years away.

Fassnacht is currently visiting his alma mater, the California Institute of Technology (Caltech), while on sabbatical in Pasadena.

It was Caltech astronomer Fritz Zwicky who noticed in 1933 that galaxies were “moving too fast and should have flown apart,” said Fassnacht, leading to the theory of dark matter.

By using a larger, nearby galaxy as a “gravitational lens,” when a galaxy functions similar to an optical lens by bending light, Fassnacht and his co-researchers found a way to use sophisticated new computational techniques to discover the smallest galaxy that was ever discovered at the distances they explored.

“The preponderance of the evidence is consistent with General Relativity plus dark matter,” said Fassnacht, referring to Albert Einstein’s theory that space-time is curved, which altered scientists’ view of the structure of the universe.

Since the 1920s, the larger Pasadena area, including the nearby Mount Wilson Observatory, has served as an important locus of activity in scientific circles.

“Einstein was like a rock star when he was here,” said Loma Karklins, an archivist at Caltech whose son attends UC Davis.

During one visit in the winter of 1931, Einstein met with astronomer Edwin Hubble at Mt. Wilson Observatory to reconsider his theories. Hubble had made discoveries regarding specific patterns in the way that light observed emanating from galaxies is shifted to the red side of the spectrum.

Hubble “put ‘distance’ together with ‘recessional speed,‘” said Dave Jurasevich, the superintendent of Mt. Wilson Observatory, explaining how Hubble showed that the universe has a scale to its expansion.

“From 1917 to 1948 the 100-inch [telescope on Mt. Wilson] was the biggest telescope on earth. Hubble had the big picture because he had the biggest telescope on earth,” Jurasevich said.

“If your telescope is bigger,” Fassnacht said, “then you can get sharper images.”

Fassnacht explained that Mt. Wilson is still an excellent place to do work in the infrared spectrum, but he and his colleagues are doing work in the visible spectrum and chose the Keck Observatory in Hawaii. The telescopes at Keck each have a special, smaller mirror which can be continually adjusted to cancel out much of the “twinkling,” or fluctuation effect, that is caused by the light traveling through the earth’s atmosphere.

Computers at Keck can interpret the signal variations in a beam of laser light that is reflected off the sodium layer 90 kilometers up in the atmosphere to make the compensating adjustments, Fassnacht said.

The inventor of the laser, Charles Townes, coincidentally is the Chair of the Mount Wilson Institute Board of Trustees, which oversees the operation of the Mt. Wilson Observatory.

Just as Fassnacht and his colleagues are able to make inferences about the sizes of distant galaxies by interpreting subtle geometric patterns of images in the visible spectrum, Townes and his colleagues are able to make inferences about the sizes and shapes of stars using a technique called “interferometry” that involves combining and comparing images of stars from two or more telescopes.

Townes gives the following advice to the younger generation of scientists hoping to make discoveries in the future: “Explore. Don’t be afraid to try new things. Don’t let other people stop you. Think about [what you do] carefully, but make your own decisions.”

BRIAN RILEY can be reached at science@theaggie.org.


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