THE SOUTHWORTH PLANETARIUM
207-780-4249      www.usm.maine.edu/planet
70 Falmouth Street     Portland, Maine 04103
43.6667° N                   70.2667° W
Founded January 1970
Julian date:  2457639.16
             "Everywhere is far afield."



*THE DAILY ASTRONOMERWednesday, 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


​*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   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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