On Wednesday, 7 November 2018, nearly 200 guests were present at Hawaii Preparatory Academy's Gates Performing Arts Centre in Waimea to attend the W. M. Keck Observatory Astronomy Talk by Dr Pieter van Dokkum, the Yale University Sol Goldman Family Professor of Astronomy.
In his astronomy talk, ‘Dragonflies, Dark Matter, and the Hunt for Ghostly Galaxies', van Dokkum described the findings of the study that enabled his team to discover a ghost ultra-diffuse galaxy (UDG) "by accident".
"We discovered them by accident. It was a case of science and serendipity," said van Dokkum.
According to van Dokkum, UDGs are a new class of galaxies that are difficult to detect due to their very low star power. Like ghosts, they are see-through. They are big in size, almost as big as the Milky Way, but have 100 to 1000 times fewer stars than the Milky Way, which makes them very faint.
In March, van Dokkum and his team discovered a ghost galaxy NGC 1052-DF2 that was so diffuse that astronomers could clearly see distant galaxies behind it. This galaxy missed most of its dark matter, a finding that confirmed the possibility that dark matter could exist as a separate material elsewhere in the universe.
Dr Dokkum discovered NGC 1052-DF2 using the Dragonfly Telephoto Array in New Mexico. This telescope was built by van Dokkum with his colleague Roberto Abraham of the University of Toronto.
The team also used Keck Observatory's powerful twin telescopes to confirm their results. They also found that UDGs exhibit weird behaviour; some of them have too much dark matter, whereas some are characterised by too little dark matter.
"What is so exciting about ultra-diffuse galaxies is that they serve as a natural laboratory for understanding dark matter," said van Dokkum.
For scientists, discovering a galaxy without dark matter is completely unexpected. This discovery challenges the established principles about the working of galaxies. It also suggested that there may be different ways to form a galaxy.
"Astronomers using Keck Observatory and its state-of-the-art instrumentation are working hard to unravel this mystery," said Hilton Lewis, director of the Keck Observatory.
"Van Dokkum's work exemplifies the kind of world-class science being conducted right here in Hawaii, and we couldn't be more thrilled to be able to share his important research with our local community."
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