Galaxy Clusters

Galaxy clusters are the largest objects in the universe, spanning distances up to ten million light years, and containing the equivalent mass of a million, billion suns. Our research examines the physics of these remarkable systems using the best available multi-wavelength data, and uses the observed properties of clusters to probe the nature of dark matter, the weakly interacting yet dominant matter component of the universe, and dark energy, the driving force behind cosmic acceleration.

Most of the normal, baryonic matter in galaxy clusters – as in the rest of the universe – is in gaseous form. In galaxy clusters, enormous gravity (from the dominating dark matter) squeezes this gas, heating it to 100 million degrees and causing it to shine brightly at X-ray wavelengths.

In order to better understand the forces at work in these remarkably massive systems, KIPAC researchers are using X-ray observations from satellite observatories such as Chandra and XMM-Newton to measure the masses of both the baryonic and dark, non-baryonic matter within galaxy clusters. Using data from these instruments, scientists from KIPAC were among the first to show that supermassive black holes likely keep stars from forming in galaxy clusters and pump out huge amounts of energy from the hearts of galaxies in the form of relativistic jets. These jets inflate giant cavities and generate enormous sound waves in the hot, X-ray emitting gas.

KIPAC has also been involved in compiling some of the most powerful galaxy cluster catalogs ever made for measuring Dark Matter, including the ROSAT Brightest Cluster Sample, the Extended Brightest Cluster Sample and the Massive Cluster Survey. Scientists here are also carrying out detailed multi-wavelength follow-up of these sources, including deep gravitational lensing studies, optical imaging and spectroscopy, infrared studies, microwave background measurements and radio observations using instruments such as the Hubble Space Telescope, Subaru Telescope, Herschel Space Observatory, and the Very Large Array. These catalogs allow us to track how clusters have grown over the history of the universe and precisely measure the amount of dark energy and dark matter in the universe. We are now even able to evaluate stranger questions, such as “How much do neutrinos weigh?” and “Is General Relativity still true over the vast distances of the universe?”

Finally, KIPAC is also involved in the development of new X-ray satellite observatories such as  the Japanese-led Astro-H mission, and ground-based optical telescopes such as the Large Synoptic Survey Telescope, all of which aim to advance our understanding of the universe by probing into the deepest recesses of space.