The cluster CL0024+17 is a
cluster of galaxies
A galaxy cluster, or a cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity, with typical masses ranging from 1014 to 1015 solar masses. They are the second-lar ...
located in
Pisces
Pisces may refer to:
* Pisces, an obsolete (because of land vertebrates) taxonomic superclass including all fish
* Pisces (astrology), an astrological sign
* Pisces (constellation), a constellation
**Pisces Overdensity, an overdensity of stars in ...
, and about 4 billion light years distant.
Cl 0024+17 is allowing
astronomer
An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...
s to probe the distribution 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 a ...
in
space
Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually cons ...
. The blue streaks near the center of the image are the smeared images of very distant
galaxies that are not part of the cluster. The distant galaxies appear distorted because their
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...
is being bent and magnified by the powerful
gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
of Cl 0024+17, an effect called
gravitational lensing
A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer. This effect is known ...
.
Because dark matter does not shine or reflect light, it cannot be seen. Astronomers can only detect its influence by how its gravity affects light. By mapping the distorted light created by gravitational lensing, astronomers can trace how dark matter is distributed in the cluster. While mapping the dark matter, astronomers found a dark-matter ring near the cluster's center (although this is disputed by other independent studies
). The ring's discovery is among the strongest evidence that dark matter exists.
References
{{reflist
External links
HubbleSite NewsCenter: Hubble pictures of CL0024+17 group
Pisces (constellation)
Galaxy clusters