Dragonfly 44 is an
ultra diffuse galaxy in the
Coma Cluster
The Coma Cluster (Abell 1656) is a large 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 located in and tak ...
.
This galaxy is well-known because observations of the
velocity dispersion
In astronomy, the velocity dispersion (''σ'') is the statistical dispersion of velocities about the mean velocity for a group of astronomical objects, such as an open cluster, globular cluster, galaxy, galaxy cluster, or supercluster. By measu ...
in 2016 suggested a mass of about one trillion
solar mass
The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...
es, about the same as the
Milky Way
The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
. This mass was consistent with a count of about 90 and 70
globular clusters
A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...
observed around Dragonfly 44 in two different studies.
Later, spatially resolved
kinematics
In physics, kinematics studies the geometrical aspects of motion of physical objects independent of forces that set them in motion. Constrained motion such as linked machine parts are also described as kinematics.
Kinematics is concerned with s ...
measured a mass of about 160 billion
solar mass
The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...
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 that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...
s around the galaxy, which is consistent with the current mass measurement.
The lack of
X-ray
An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
emission from the galaxy and its surroundings also shows that the number of
globular cluster
A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...
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 extragalact ...
.
Early study
To determine the amount of
dark matter
In astronomy, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravity, gravitational effects that cannot be explained by general relat ...
in this galaxy, in 2016, astronomers used the DEIMOS instrument installed on
Keck II 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 comprises two 8.1-metre (26.6 ft) telescopes, Gemini North and Gemini South, situated in Hawaii and Chile, respectively. These twin telescopes offer extensive coverage of the northern and southern skies and rank among ...
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.
See also
* (LSB galaxy)
* – a galaxy thought to contain almost no dark matter.
* or ''c-Diffuse'' galaxy type
* or ''Diffuse''-type galaxy
*
References
External links
*
{{DEFAULTSORT:Dragonfly 44
Coma Cluster
Coma Berenices
Dark galaxies