Yale Astronomer Sees New Gravitational Lens

Using a snapshot technique, a Yale astronomer has discovered a bright new gravitational lens.

The gravitational lens was observed on April 25 by Nicholas Morgan, a post-doctoral fellow at the Yale Center for Astronomy and Astrophysics, using the 3.5-meter WIYN Telescope at the Kitt Peak National Observatory near Tucson, Arizona. The lens is located near the constellation Hercules and is officially known as SDSS 1650+4251.

Gravitational lenses are images of bright but extremely distant galaxies known as quasars. The light from these distant quasars is deflected by the gravitational fields of fainter foreground galaxies, distorting the background quasar into multiple copies of itself. Sometimes as many as four copies of the single quasar are possible. About 70 of these systems have been discovered since the first sighting in 1979. How distorted the images become and how many copies are made depends on the alignment between the foreground galaxy and the more distant quasar.

“You need exquisite alignment,” said Morgan.

The value of finding a gravitational lens, he said, is that it can help in deducing the age of the universe by watching how the light from the quasar changes with time. Finding several lenses can also help in calculating the expansion rate of the universe, whether it is decelerating or accelerating, and if the universe will eventually collapse or expand forever.

The snapshot technique used by Morgan involves taking pictures of multiple targets. He looked at over 200 targets during the two nights of observations, taking a picture every few minutes. Astronomers generally look at only a handful of targets in the same period.

“You look at as many distant quasars as possible,” he said. “For each, you have about a one percent chance of finding a gravitational lens. Sometimes you get lucky.”

Ideal conditions are also dependent on the weather and the performance of the telescope.

Morgan said SDSS 1650+4251 appears as a relatively small system with a separation between its two images of about one arcsecond. One arcsecond is about the size a dime would appear if held two miles away. The largest gravitationally lensed quasars currently known are slightly larger than six arseconds.

The WIYN Observatory is owned and operated by the WIYN Consortium, which consists of the University of Wisconsin, Indiana University, Yale University, and the National Optical Astronomy Observatories.