Gemini Observatory | W.M. Keck Observatory | 2016 Aug 25
Using the world's most powerful telescopes, an international team of astronomers has 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 dark galaxy Dragonfly 44. The image on the left is a wide view of the
galaxy taken with the Gemini North telescope using the Gemini Multi-Object
Spectrograph (GMOS). The close-up on the right is from the same very deep
image, revealing the large, elongated galaxy, and halo of spherical clusters
of stars around the galaxy’s core, similar to the halo that surrounds our Milky
Way Galaxy. Dragonfly 44 is very faint for its mass, and consists almost
entirely of Dark Matter. Image Credit: Pieter van Dokkum, Roberto Abraham,
Gemini Observatory, Sloan Digital Sky Survey, AURA.
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. 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. The team then used the Gemini Multi-Object Spectrograph (GMOS) on the 8-meter Gemini North telescope on Maunakea in Hawaii to reveal a halo of spherical clusters of stars around the galaxy’s core, similar to the halo that surrounds our Milky Way Galaxy. ...
Scientists Discover a 'Dark' Milky Way
Yale University | 2016 Aug 25
A High Stellar Velocity Dispersion and ~100 Globular Clusters for the Ultra Diffuse Galaxy Dragonfly 44 - Pieter van Dokkum et al