UH Hilo physics and astronomy students assisted with data analysis, observations, and obtaining spectroscopic measurements using telescopes from Gemini and W.M. Keck observatories.
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, 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.”
- The paper: Hamilton’s Object – a clumpy galaxy straddling the gravitational caustic of a galaxy cluster: constraints on dark matter clumping. (Richard E Griffiths, Mitchell Rudisel, Jenny Wagner, Timothy Hamilton, Po-Chieh Huang, Carolin Villforth. The Monthly Notices of the Royal Astronomical Society. Volume 506, Issue 2, September 2021, Pages 1595–1608.)
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.
“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.”
Learn more: NASA media release.