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"Everywhere is far afield."
THE DAILY ASTRONOMER
Wednesday, September 7, 2016
Wednesday, September 7, 2016
Dragonfly 44
Imagine a galaxy as large and massive as the Milky Way, but consisting almost entirely of dark matter. Dark matter is that mysterious material that pervades the Universe and may account for as much as eighty percent of the matter within it. One might dismiss such a notion as being pure science fiction, but, in fact, astronomers have discovered such dark matter rich galaxies. They are known as "ultra diffuse,"or -if you're partial to esoteric terms- "fluffy" galaxies. Astronomers have only recently started finding these galaxies because they are so faint that only the most sensitive telescopes have been able to detect them. It was only in 2015 that researchers discovered a dark matter galaxy as large as our own Milky Way, tucked away within the myriad galaxies of the Coma Cluster. (See "From the Catacombs of Infinite Knowledge" for more about the Coma Cluster.") This enigmatic galaxy is now known simply as "Dragonfly 44."
Yale astrophysicist Pieter van Dokkum led a team of researchers who imaged the Coma Galaxy Cluster with the Dragonfly Telephoto Array in New Mexico. This array consists of eight telephoto lenses specially treated to reduce scattered light so as to allow it to detect objects too faint for most other telescopes to observe. In 2015, these astronomers discovered "faint smudges" within the Coma Cluster of Galaxies. Further investigation revealed that these were highly diffuse galaxies: those that even the Hubble Space Telescope overlooked.
The Dragonfly Telephoto Array. Designed by astronomers Pieter van Dokkum and
Roberto Abraham, the Dragonfly Telephoto Array is specially equipped to detect celestial
objects too faint for most telescopes to observe. They named their device "Dragonfly" because the telephoto lenses resemble the insect's compound eye.
One galaxy in particular commanded their attention. Though it appeared quite large, it was nevertheless faint: merely one percent as luminous as the Milky Way. This galaxy, Dragonfly 44, seemed to be a self-contradiction: it was big, but appeared to contain relatively few stars. If the only matter present within Dragonfly 44 were the visible stars, the gravity wouldn't be strong enough to maintain the galaxy's structure. It would have long since dissipated.
The research team then observed Dragonfly 44 through the Deep Imaging Multi-Object Spectrograph, located on Mauna Kea in Hawaii. Through this spectrograph, the astronomers were able to measure some of the velocities of the stars within Dragonfly 44. Measuring such velocities provides scientists with information pertaining to a galaxy's total mass. The more massive the galaxy, the faster the stellar motions within the galaxy. The Dragonfly 44 stars were found to be moving quite swiftly; so swiftly that the van Dokkum's team surmised that only 0.01 percent of the galaxy actually consists of "ordinary"matter. Dark matter comprises the rest. Even though dark matter remains mysterious, astronomers do know that its gravitational effects are the same as that of other material. It was through observations of visible matter that astronomers discerned the influence of dark matter in the first place
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This image, captured by the Dragonfly Telephoto Array, shows a "close up"of the Dragonfly 44 Galaxy to the left. We see it as a minuscule part of the Coma Cluster to the right. Image: P. van Dokkum, R. Abraham, and J Brodie.
Many astronomers who investigate dark matter are hopeful that these "dark matter galaxies" might provide even more clues as to dark matter's nature. Dark matter is one of astronomy's most exciting and important fields of research. One cannot hope to understand the physical Universe without knowing about the matter that comprises so much of it.
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FROM THE CATACOMBS OF INFINITE KNOWLEDGE:
The Coma Cluster
The Coma Cluster
The Coma Cluster
Image by "KuriousG"
Within the small and rather unremarkable constellation Coma Berenices (Bernice's Hair), one will find the rich galaxy cluster simply named the "Coma Cluster." The central region of this cluster is about 321 million light years from Earth. In the above photo we can observe the rich galaxy field. Although we do see some foreground stars, most of those lights are individual galaxies. Most of these galaxies are elliptical, not spiral like the Milky Way. Elliptical galaxies tend to lack the well defined structure of spirals. American astronomer Edwin Hubble once theorized that elliptical galaxies would ultimately evolve into spirals. This theory was found to be incorrect once astronomers determined that ellipticals tended to be older than spirals.
Although our naked eyes show us a dazzling array of stars, so much exists within the deep infinitude beyond them.
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