MACS J0025.4-1222 is a
galaxy cluster
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 ...
created by the collision of two galaxy clusters, and is part of the
MAssive Cluster Survey (MACS). Like the earlier discovered
Bullet Cluster, this cluster shows a clear separation between the centroid of the intergalactic gas (of majority of the normal, or
baryonic
In particle physics, a baryon is a type of composite particle, composite subatomic particle which contains an odd number of valence quarks (at least 3). Baryons belong to the hadron list of particles, family of particles; hadrons are composed o ...
, mass) and the colliding clusters.
In
the image, intergalactic gas is shown in pink and the mass centroids of the colliding clusters in blue, showing the separation of the two, similar to the Bullet Cluster. It provides independent, direct evidence for
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 ...
and supports the view that dark matter particles interact with each other only very weakly.
Details
The shown image is a composite of separate exposures made by
Hubble Space Telescope
The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...
ACS and WFPC2 detectors and the
Chandra
Chandra ( sa, चन्द्र, Candra, shining' or 'moon), also known as Soma ( sa, सोम), is the Hindu god of the Moon, and is associated with the night, plants and vegetation. He is one of the Navagraha (nine planets of Hinduism) a ...
ACIS detector. The Hubble images were taken on November 5, 2006, and June 6, 2007. The visible light images from Hubble showed
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 ...
which allowed astronomers to infer the distribution of total mass (both dark matter and normal matter)(colored in blue). The distribution of normal matter is mostly in the form of hot gas glowing brightly in X-rays (shown pink). Its distribution was accurately mapped from Chandra data.
From these it was possible to tell that most of the mass in the two blue regions was dark matter.
The international team of astronomers in this study was led by Marusa Bradac of the
University of California, Santa Barbara
The University of California, Santa Barbara (UC Santa Barbara or UCSB) is a public land-grant research university in Santa Barbara, California with 23,196 undergraduates and 2,983 graduate students enrolled in 2021–2022. It is part of the U ...
, and Steve Allen of the Kavli Institute for Particle Astrophysics and Cosmology at
Stanford University and the Stanford Linear Accelerator Center (
SLAC
SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center,
is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S. Departme ...
).
The two clusters that formed MACS J0025 are each almost a million billion times the mass of the Sun. They merged at speeds of millions of miles per hour, and as they did so the hot gas in each cluster collided with the hot gas in the other and slowed down. The dark matter (which interacts weakly) did not. The separation between the normal matter (pink) and dark matter (blue) therefore provides direct evidence for dark matter and supports the view that dark matter particles interact with each other almost entirely through gravity.
References
External links
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*{{NED link, id=MACS+J0025.4-1222
Galaxy clusters
