Dragonfly 44 is an

ultra diffuse galaxy An ultra diffuse galaxy (UDG) is an extremely low luminosity galaxy, the first example of which was discovered in the nearby Virgo Cluster by Allan Sandage and Bruno Binggeli in 1984. These galaxies have been studied for many years prior to their ...

in the

Coma Cluster The Coma Cluster (Abell 1656) is a large galaxy cluster, cluster of galaxies that contains over 1,000 identified galaxies. Along with the Leo Cluster (Abell 1367), it is one of the two major clusters comprising the Coma Supercluster. It is loc ...

. This galaxy is well-known because observations of the

velocity dispersion In astronomy, the velocity dispersion (''σ'') is the statistical dispersion of velocity, velocities about the Arithmetic mean, mean velocity for a group of astronomical objects, such as an open cluster, globular cluster, galaxy, galaxy cluster, or ...

in 2016 suggested a mass of about one trillion

solar mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

es, about the same as the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

. This mass was consistent with a count of about 90 and 70

globular clusters A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member ...

observed around Dragonfly 44 in two different studies. Later, spatially resolved

kinematics Kinematics is a subfield of physics, developed in classical mechanics, that describes the Motion (physics), motion of points, Physical object, bodies (objects), and systems of bodies (groups of objects) without considering the forces that cause ...

measured a mass of about 160 billion

es, six times less than early mass measurements and one order of magnitude less than the Milky Way's mass. The most recent work found 20

globular cluster A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...

s around the galaxy, which is consistent with the current mass measurement. The lack of

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

emission from the galaxy and its surroundings also shows that the number of

s cannot be as many as was claimed before. The galaxy emits only 1% of the light emitted by the Milky Way. The galaxy was discovered with the

Dragonfly Telephoto Array The Dragonfly Telephoto Array is a ground-based optical telescope array developed at the Dunlap Institute for Astronomy & Astrophysics of the University of Toronto in Canada. The array uses a combination of telephoto lenses to observe extragalacti ...

Early study

To determine the amount of

dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...

in this galaxy, in 2016, astronomers used the DEIMOS instrument installed on

Keck II The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when comp ...

to measure the velocities of stars for 33.5 hours for six nights so they could determine the galaxy's mass. The scientists then used the Gemini Multi-Object Spectrograph on the 8-m

Gemini North The Gemini Observatory is an astronomical observatory consisting of two 8.1-metre (26.6 ft) telescopes, Gemini North and Gemini South, which are located at two separate sites in Hawaii and Chile, respectively. The twin Gemini telescopes prov ...

telescope to reveal a halo of spherical clusters of stars around the galaxy's core. Following this observation, in August 2016, astronomers reported that this galaxy might be made almost entirely of dark matter.

References

Galaxies Coma Cluster Coma Berenices {{galaxy-stub

Early study

See also

References