Keck Talk – Ghostly Galaxies challenge the theories of dark matter

NGC 1052-DF2, an ultra-diffuse galaxy. CREDIT: ESA / Hubble, Digitized Sky Survey, Nick Risinger (skysurvey.org)

The mysteries surrounding ghostly galaxies manifested themselves in front of a theater filled with inquisitive minds at last month's astronomical chat of the W.M. Keck Observatory, starring guest speaker Dr. Pieter van Dokkum.

Astronomy professor Sol Goldman of the Yale Family of Yale University presented his research on the destruction of galaxy ghosts at the Gates Performing Arts Center of the Hawaii Preparatory Academy in Waimea, where about 200 people came to learn on "ultra-diffuse galaxies".

Like ghosts, this strange new class of galaxies is transparent; they are as big as the Milky Way but with much less power in the stars – between 100 and 1000 times less stars than our own galaxy, which makes them so weak that they are difficult to detect.

"We discovered them by accident. It was a case of science and chance, "van Dokkum said. "My team and I are studying a distant group of galaxies when we saw many traces in the images. We then studied these tracks with the Keck telescope and were surprised to learn that they were part of a distant group, which meant they were very tall even though they did not have a lot of stars . "

In his speech on astronomy, entitled "Dragonflies, Dark Matter, and Ghostly Galaxy Hunt," van Dokkum explained how he detected UDGs using the Dragonfly telephoto lens in New Mexico, which he had built with a colleague. Similar to an eye composed of dragonfly insect, the telescope records a galaxy through multiple lenses simultaneously to reveal extremely weak structures.

Using the powerful twin telescopes of the Keck Observatory, Van Dokkum's team discovered that UDGs are very strange: their dark matter, mysterious ingredient that is usually found in all galaxies, does not respect the known rules of the universe – there is too much dark matter in some, too little in others, and in at least one case, has completely disappeared.

"What's so exciting about ultra-diffuse galaxies, is that they serve as a natural laboratory for understanding dark matter," van Dokkum said. "This elusive material is the bulk of the material in the universe, but we know very little about its origin, composition, and operation."

"The nature and role of dark matter is one of the most important issues in astronomy today. Astronomers using the Keck Observatory and its state-of-the-art instrumentation are working hard to solve this mystery, "said Hilton Lewis, director of the Keck Observatory. "Van Dokkum's work illustrates the kind of world-class science being conducted here in Hawaii, and we could not be happier to share his important research with our local community."

The Keck Observatory Astronomy Conferences, supported by the Rob and Terry Ryan Foundation and the Rising Stars Fund, will continue to bring renowned scientists to Hawaii for free events open to the public. For more information on upcoming conferences and events or on the excellent work done, visit the Keck Observatory website.