1. Gemini Observatory reveals galaxy that is 99.99% dark matter
SOURCE:
Scientists Discover Galaxy That Is Percent Dark Matter
Using the world's most powerful telescopes, an international team of astronomers have discovered a massive galaxy that consists almost entirely of Dark Matter. Using the W. M. Keck Observatory and the Gemini North telescope – both on Maunakea, Hawaii – the team found a galaxy whose mass is almost entirely Dark Matter. The findings are being published in The Astrophysical Journal on XXX.  
Even though it is relatively nearby, the galaxy, named Dragonfly 44, had been missed by astronomers for decades because it is very dim. It was discovered just last year when the Dragonfly Telephoto Array observed a region of the sky in the constellation Coma.
The team then used the Gemini Multi-Object Spectrograph (GMOS) on the 8-meter Gemini North telescope on Maunakea in Hawai‘i to capture a deep image of the mysterious galaxy. This revealed what hadn’t been resolved before, a halo of globular (spherical) clusters of stars around the galaxy’s core, similar to the halo that surrounds our Milky Way Galaxy. “The near-perfect conditions, and precise imaging Gemini provided gave us a new perspective on this remarkable galaxy,” said Pieter van Dokkum who lead the team of researchers, “that new perspective provided us with a new mystery.”
Upon further scrutiny, the team realized the galaxy had to have more than meets the eye: it has so few stars that it quickly would be ripped apart unless something was holding it together.
To determine the amount of Dark Matter in Dragonfly 44, astronomers used the DEIMOS instrument installed on Keck II to measure the velocities of stars for 33.5 hours over a period of six nights so they could determine the galaxy’s mass.
“Motions of the stars tells you how much matter there is, van Dokkum said. “They don’t care what form the matter is, they just tell you there is mass. The Dragonfly galaxy stars move very fast. So there was a huge discrepancy: using Keck Observatory, we found 50 times more mass indicated by the motions of the stars, then there is mass in the stars themselves.”
The mass of the galaxy is estimated to be a trillion times the mass of the Sun – very similar to the mass of our own Milky Way galaxy. However, only one hundredth of one percent of that is in the form of stars and "normal" matter; the other percent is in the form of dark matter. The Milky Way has more than a hundred times more stars than Dragonfly 44.
Finding a galaxy with the mass of the Milky Way that is almost entirely dark was unexpected. "We have no idea how galaxies like Dragonfly 44 could have formed." XX said. "The Gemini data show that a relatively large fraction of the stars is in the form of very compact clusters, and that is probably an important clue. But at the moment we're just guessing."
“This has big implications for the study of Dark Matter,” van Dokkum said. “It helps to have objects that are almost entire made of DM so we don’t get confused by stars and all the other things that galaxies have. The only galaxies we had to study before were tiny. This finding opens up a whole new class of objects of these massive objects that we can study.
“Ultimately what we really want to learn is what Dark Matter is,” van Dokkum said. “The race is on to find things that are very close to us that for direct detection of Dark Matter.”
Gemini Observatory reveals galaxy that is 99.99% dark matter

2. SCIENCE PEOPLE TECHNOLOGY
National Science Foundation • Division of Astronomical Sciences
Prepared by the Association of Universities for Research in Astronomy
SCIENCE PEOPLE TECHNOLOGY
Scientists Discover Galaxy that is Percent Dark Matter
An international team of astronomers has discovered a massive galaxy that consists almost entirely of dark matter. Even though it is relatively nearby, the galaxy “Dragonfly 44” had been missed previously because it is very dim. It was discovered just last year when the Dragonfly Telephoto Array observed a region of the sky in the direction of the constellation of Coma Berenices. The team used the Gemini Multi-Object Spectrograph (GMOS) on the 8-meter Gemini North telescope on Maunakea in Hawai‘i to analyze the mysterious galaxy.
In addition to measuring the size accurately, Gemini’s deep image revealed what had not been resolved before, a halo of globular clusters around the galaxy’s core, very similar to the halo that surrounds our own Milky Way Galaxy.
Additional spectroscopic observations from the W. M. Keck Observatory determined the galaxy’s mass, showing that the galaxy had to have more matter than meets the eye. In fact, it has so few stars that it would quickly be ripped apart unless something else holds it together. The researchers conclude that dark matter must account for 99.99% of the galaxy’s total mass!
Dragonfly 44 is thought to be a “failed” Milky Way, with both galaxies having similar total mass and a similar number of globular clusters. However, the Milky Way has produced more than a hundred times more stars than Dragonfly 44.
,SOURCE:
Scientists Discover Galaxy That Is Percent Dark Matter
Using the world's most powerful telescopes, an international team of astronomers have discovered a massive galaxy that consists almost entirely of Dark Matter. Using the W. M. Keck Observatory and the Gemini North telescope – both on Maunakea, Hawaii – the team found a galaxy whose mass is almost entirely Dark Matter. The findings are being published in The Astrophysical Journal on XXX.  
Even though it is relatively nearby, the galaxy, named Dragonfly 44, had been missed by astronomers for decades because it is very dim. It was discovered just last year when the Dragonfly Telephoto Array observed a region of the sky in the constellation Coma.
The team then used the Gemini Multi-Object Spectrograph (GMOS) on the 8-meter Gemini North telescope on Maunakea in Hawai‘i to capture a deep image of the mysterious galaxy. This revealed what hadn’t been resolved before, a halo of globular (spherical) clusters of stars around the galaxy’s core, similar to the halo that surrounds our Milky Way Galaxy. “The near-perfect conditions, and precise imaging Gemini provided gave us a new perspective on this remarkable galaxy,” said Pieter van Dokkum who lead the team of researchers, “that new perspective provided us with a new mystery.”
Upon further scrutiny, the team realized the galaxy had to have more than meets the eye: it has so few stars that it quickly would be ripped apart unless something was holding it together.
To determine the amount of Dark Matter in Dragonfly 44, astronomers used the DEIMOS instrument installed on Keck II to measure the velocities of stars for 33.5 hours over a period of six nights so they could determine the galaxy’s mass.
“Motions of the stars tells you how much matter there is, van Dokkum said. “They don’t care what form the matter is, they just tell you there is mass. The Dragonfly galaxy stars move very fast. So there was a huge discrepancy: using Keck Observatory, we found 50 times more mass indicated by the motions of the stars, then there is mass in the stars themselves.”
The mass of the galaxy is estimated to be a trillion times the mass of the Sun – very similar to the mass of our own Milky Way galaxy. However, only one hundredth of one percent of that is in the form of stars and "normal" matter; the other percent is in the form of dark matter. The Milky Way has more than a hundred times more stars than Dragonfly 44.
Finding a galaxy with the mass of the Milky Way that is almost entirely dark was unexpected. "We have no idea how galaxies like Dragonfly 44 could have formed." XX said. "The Gemini data show that a relatively large fraction of the stars is in the form of very compact clusters, and that is probably an important clue. But at the moment we're just guessing."
“This has big implications for the study of Dark Matter,” van Dokkum said. “It helps to have objects that are almost entire made of DM so we don’t get confused by stars and all the other things that galaxies have. The only galaxies we had to study before were tiny. This finding opens up a whole new class of objects of these massive objects that we can study.
“Ultimately what we really want to learn is what Dark Matter is,” van Dokkum said. “The race is on to find things that are very close to us that for direct detection of Dark Matter.”
Gemini Multi-Object Spectrograph images of the Dragonfly 44 galaxy showing halo of globular clusters swarming around the dark matter-rich galaxy.