The University of Utah’s Adam S. Bolton is using an effect predicted by Albert Einstein to assess galaxies billions of light-years away.
[Adam S. Bolton speaks at the October monthly meeting of the Salt Lake Astronomical Society, Oct. 18, 2011. Photo by Cory Bauman]
An assistant professor in the Department of Physics & Astronomy, Bolton spoke Tuesday at the monthly meeting of the Salt Lake Astronomical Society, held in the U.’s Behavioral Science Auditorium. About 65 members of the group and guests attended the talk.
Bolton is a leader of the Sloan Lens ACS Survey, which searches for and analyzes this effect, dubbed Einstein rings. Sloan refers to the Sloan Digital Sky Survey, using a telescope in New Mexico, while ACS stands for the Hubble Space Telescope’s Advanced Camera for Surveys.
In 1936, responding to a letter from a colleague asking what would happen if one star lined up exactly behind another as seen from Earth, Einstein calculated that gravitational lensing would occur, Bolton said. This is the appearance of a ring around the foreground object, caused by gravity of a massive closer object bending the light from a more distant object.
An “Einstein ring” is “a luminous circle of a particular radius around the center of the other (foreground) star,” Bolton said. “As a focusing device it’s a very poor optical instrument,” with the distant figure highly distorted.
Starting in 1979, more than 40 years after Einstein’s prediction was published, astronomers began finding Einstein rings in space. The first showed two views of a quasar — an ancient, extremely powerful light source — around a massive closer galaxy. “So there were two images of the same quasar,” he said.
Since then, the Sloan Lens ACS Survey has discovered hundreds of such rings. Many are formed by pairs of galaxies.
[Einstein Rings discovered by the Sloan Lens ACS Survey, shown in a 2005 release. Credit: NASA, the European Space Agency, Bolton (who was with the Harvard-Smithsonian Center for Astronomy at the time) and Sloan Lens ACS Survey Team]
Through mathematical transforms, scientists are able to dig out information about both foreground and the more distant objects, describing mass and even shapes.
When he showed a view of an Einstein ring, Nightly News asked how far the galaxies are from Earth. “It’s probably a few billion light-years [for the closer one] and a few more billion light-years [for the farther one],” he said.
Because of their immense distance, these faint objects are so small that — if you pretend they are actually physical rings — it would take some 500 to stretch across the face of the full moon.
“It’s certainly a beautiful phenomenon,” Bolton said. But the scientists must analyze this material in numbers and graphs. He and his team consider how far the light is shifted in the spectrum because of distance, the angular sizes of the foreground galaxy and the ring, how much space has expanded since light left the galaxies and how faint the objects are.
“Galaxies today don’t look like galaxies in the distant past of the universe,” he added. Spiral galaxies like our own tend to merge with other galaxies, eventually becoming absorbed into giant elliptical galaxies. The ellipticals are largely formless other than their general elliptical shape, which is brightest at the center.
The many mergers forming elliptical have “sort of destroyed the detailed structure you see in a spiral galaxy structure,” he said.
Discovering new facts about early galaxies could help in understanding galaxy evolution.
A telltale mark of an Einstein ring is a spectrum where two different red shifts — indicating distance — show up in what seems one object. When one of these is detected by the Sloan Digital Sky Survey telescope in New Mexico, the Hubble Space Telescope can snap a more detailed view from orbit, confirming the presence of a ring.
In turn, that photo is used to calculate a range of information about the galaxies.
An intriguing aspect is the presence of so-called “dark matter,” which has never been seen, but whose gravitational effects can be detected. Dark matter contributes to the lensing effect in Einstein rings.
Even stranger is dark energy, which is speeding up the expansion of the universe. Bolton said ordinary matter making up stars, people and planets amounts to about 4 percent of the stuff of the universe. Dark matter makes up about a quarter and dark energy the rest.
One of the founders of the Sloan Lens ACS Survey, Bolton is working to expand the project to use smaller foreground galaxies instead of only the giant ellipticals measured before.
His Web site notes, “With this new program, we will determine whether the structural regularity that we see in massive galaxies extends to lower masses, or whether there is a characteristic mass at which new trends arise (as has been suggested by other lines of evidence).”