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. Clusters consist of galax ...

created by the collision of two galaxy clusters, and is part of the

MAssive Cluster Survey The MAssive Cluster Survey (MACS) compiled and characterized a sample of very X-ray luminous (and thus, by inference, massive), distant clusters of galaxies. The sample comprises 124 spectroscopically confirmed clusters at 0.3 < z < 0.7. Candidate ...

(MACS). Like the earlier discovered

Bullet Cluster The Bullet Cluster (1E 0657-56) consists of two colliding clusters of galaxies. Strictly speaking, the name ''Bullet Cluster'' refers to the smaller subcluster, moving away from the larger one. It is at a comoving radial distance of . The obje ...

, 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 subatomic particle that contains an odd number of valence quarks, conventionally three. Protons and neutrons are examples of baryons; because baryons are composed of quarks, they belong to t ...

, 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 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 ...

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 (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

ACS and WFPC2 detectors and the

Chandra Chandra (), also known as Soma (), 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) and Dikpala (guardians of the directions). Etymology and other ...

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 matter, such as a galaxy cluster, cluster of galaxies or a point particle, that bends light from a distant source as it travels toward an observer. The amount of gravitational lensing is described by Albert Einstein's Ge ...

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 university, public Land-grant university, land-grant research university in Santa Barbara County, California, United States. Tracing its roots back to 1891 as an ...

, and Steve Allen of the Kavli Institute for Particle Astrophysics and Cosmology at

Stanford University Leland Stanford Junior University, commonly referred to as Stanford University, is a Private university, private research university in Stanford, California, United States. It was founded in 1885 by railroad magnate Leland Stanford (the eighth ...

and the Stanford Linear Accelerator Center (

SLAC SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center, is a federally funded research and development center in Menlo Park, California, United States. Founded in 1962, the laboratory is now sponsored ...

). The two clusters that formed MACS J0025 are each almost a quadrillion 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

* *{{NED link, id=MACS+J0025.4-1222 Galaxy clusters Cetus