UH Hilo astronomy professor leads team that solves gravitational lens phenomenon

UH Hilo physics and astronomy students assisted with data analysis, observations, and obtaining spectroscopic measurements using telescopes from Gemini and W.M. Keck observatories.

Silver dome of Gemini Observatory.
Above, Gemini Observatory North, Maunakea. UH Hilo physics and astronomy students Mitchell Rudisel and Po-Chieh Huang, co-authors of a paper on gravitational lens phenomenon, assisted with data analysis, observations, and obtaining spectroscopic measurements using telescopes from Gemini and W.M. Keck observatories. Photo: Wikimedia Commons.

A University of Hawaiʻi at Hilo physics professor led a team of scientists that recently solved the mystery of the light from a single galaxy being split into multiple distorted images, something that has puzzled astronomers for many years.

Richard Griffiths pictured.
Richard Griffiths. Courtesy photo.

Richard Griffiths, an affiliate professor of physics and astronomy at UH Hilo and professor emeritus at Carnegie Mellon University, and his team discovered that dark matter within the galaxy cluster is smoothly distributed on the scale of a few thousand light-years.

“This discovery, called Hamilton’s Object, is important because astronomers still don’t know what dark matter is, nearly a century after its discovery,” says Griffiths. “The search for the nature of dark matter is one of the biggest problems in all of physics.”

Mitchell Rudisel pictured.
Mitchell Rudisel. Photo credit: John Coney/UH Hilo.

UH Hilo physics and astronomy students Mitchell Rudisel and Po-Chieh Huang, an exchange student from Taiwan, are co-authors of the paper. They assisted with data analysis, observations, and obtaining spectroscopic measurements using telescopes from Gemini and W.M. Keck observatories.

Their work shows the dark matter in the cluster of galaxies, which has the gravitational pull to double and stretch the background galaxy image, was smoothly distributed through the center of the cluster.

The analysis by the UH Hilo team, assisted by Jenny Wagner at the University of Heidelberg in Germany, shows that dark matter may consist of ultra-light particles rather than the heavy particles favored by most physicists.


Image of galaxy with inserts of mirrored images.
This Hubble Space Telescope snapshot shows three magnified images of a distant galaxy embedded in a cluster of galaxies. These images are produced by a trick of nature called gravitational lensing. The galaxy cluster’s immense gravity magnifies and distorts the light from the distant galaxy behind it, creating the multiple images. The galaxy cluster, catalogued as SDSS J223010.47-081017.8, is 7 billion light-years from Earth. Hubble has observed many gravitationally lensed galaxies. However, the images spotted in this Hubble snapshot are unique. Two of the magnified images, shown in the pull-out at bottom right, are exact copies of each other. The two bright ovals are the cores of the galaxy. This rare phenomenon occurs because the background galaxy straddles a ripple in the fabric of space. This “ripple” is an area of greatest magnification, caused by the gravity of dense amounts of dark matter, the unseen glue that makes up most of the universe’s mass. As light from the faraway galaxy passes through the cluster along this ripple, two mirror images are produced, along with a third image that can be seen off to the side. A close-up of the third image is shown in the pull-out at top right. This image most closely resembles the remote galaxy, which is located more than 11 billion light-years away. Based on a reconstruction of this image, the researchers determined that the distant galaxy appears to an edge-on, barred spiral with ongoing, clumpy star formation. The mirror images are named “Hamilton’s Object” for the astronomer who discovered them. Credits: Joseph DePasquale (STScI) via NASA.

“Only the Hubble Space Telescope is capable of finding gravitational lenses like this one,” Griffiths explains. “And at the time of the original discovery, there were no similar objects that had been found, so this was one of the first.”

The team discovered that the immense gravity of a foreground cluster of galaxies was warping space, magnifying, brightening, and stretching the image of a distant galaxy behind it, a phenomenon called gravitational lensing. The gravitational pull of the cluster of galaxies is dominated by the dark matter within it.

“We know it’s some form of matter, but we have no idea what the constituent particle is,” says Griffiths. “The significance of the limits of size on the clumping or smoothness is that it gives us some clues as to what the particle might be.”

See UH Hilo media release.

Learn more: NASA media release.