David Kirkpatrick

August 27, 2008

Clash of galactic titans

UC Santa Barbara astronomers used the Hubble and Chandra to discover a collision of galaxy clusters.

From the release:

Collision of galaxy clusters captured by astronomers

(Santa Barbara, Calif.) – Two UC Santa Barbara astronomers are part of a team that has made a stunning discovery using the Hubble Space Telescope and Chandra X-ray Observatory, it was announced today by the National Aeronautics and Space Administration.

The capture of a collision of galaxy clusters was made by a team led by Marusa Bradac, a postdoctoral researcher and Hubble fellow in UCSB’s Department of Physics. The international team also included Tommaso Treu, assistant professor of physics at UCSB.

“It is in our view an important step forward to understanding the properties of the mysterious dark matter,” Bradac said. “Dark matter makes up five times more matter in the universe than ordinary matter. This study confirms that we are dealing with a very different kind of matter, unlike anything that we are made of. And were able to study it in a very powerful collision of two clusters of galaxies.”

Below is the complete text of the press release issued today by NASA.

(Cambridge, Mass.) – A powerful collision of galaxy clusters has been captured with NASA’s Chandra X-ray Observatory and Hubble Space Telescope. Like its famous cousin, the so-called Bullet Cluster, this clash of clusters provides striking evidence for dark matter and insight into its properties.

Like the Bullet Cluster, this newly studied cluster, officially known as MACSJ0025.4-1222, shows a clear separation between dark and ordinary matter. This helps answer a crucial question about whether dark matter interacts with itself in ways other than via gravitational forces.

This finding is important because it independently verifies the results found for the Bullet Cluster in 2006. The new results show the Bullet Cluster is not an exception and that the earlier results were not the product of some unknown error.

Just like the original Bullet Cluster, MACSJ0025 formed after an incredibly energetic collision between two large clusters in almost the plane of the sky. In some ways, MACSJ0025 can be thought of as a prequel to the Bullet Cluster. At its much larger distance of 5.7 billion light years, astronomers are witnessing a collision that occurred long before the Bullet Cluster’s.

Using optical images from Hubble, the team was able to infer the distribution of the total mass – dark and ordinary matter – using a technique known as gravitational lensing (colored in blue). The Chandra data enabled the astronomers to accurately map the position of the ordinary matter, mostly in the form of hot gas, which glows brightly in X-rays (pink).

An important difference between the Bullet Cluster and the new system is that MACSJ0025 does not actually contain a “bullet.” This feature is a dense, X-ray bright core of gas that can be seen moving through the Bullet Cluster. Nonetheless, the amount of energy involved in this mammoth collision is nearly as extreme as that found in the Bullet Cluster.

As the two clusters that formed MACSJ0025 (each almost a whopping million billion times the mass of the Sun) merged at speeds of millions of miles per hour, the hot gas in each cluster collided and slowed down, but the dark matter did not. The separation between the material shown in pink and blue therefore provides direct evidence for dark matter and supports the view that dark matter particles interact with each other only very weakly or not at all, apart from the pull of gravity.

One of the great accomplishments of modern astronomy has been to establish a complete inventory of the matter and energy content of the Universe. The so-called dark matter makes up approximately 23 percent of this content, five times more than the ordinary matter that can be detected by telescopes. The latest results with MACSJ0025 once again confirm these findings.

 

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The international team of astronomers in this study was led by Marusa Bradac of UCSB, and Steve Allen of the Kavli Institute for Particle Astrophysics and Cosmology at Stanford and Stanford Linear Accelerator Center (SLAC). Other collaborators included Tommaso Treu, UCSB; Harald Ebeling, University of Hawaii; Richard Massey, Royal Observatory Edinburgh; R. Glenn Morris, SLAC; and Anja von der Linden, and Douglas Applegate, both of Stanford. Their results will appear in an upcoming issue of The Astrophysical Journal.

Collision of clusters from the Hubble Telescope and Chandra Observatory.

Collision of clusters from the Hubble Telescope and Chandra Observatory.

July 24, 2008

The Hubble finds galaxy cluster lenses

Filed under: Science — Tags: , , , , , , — David Kirkpatrick @ 6:59 pm

This a great press release from NASA and ESA on the latest Hubble Space Telescope news. Hit the link for a weatlth of images, video and additional text formats.

The release:

News Release – heic0814: Lenses galore – Hubble finds large sample of very distant galaxies

 
 24-Jul-2008: New Hubble Space Telescope observations of six spectacular galaxy clusters acting as gravitational lenses have given significant insights into the early stages of the Universe. Scientists have found the largest sample of very distant galaxies seen to date: ten promising candidates thought to lie at a distance of 13 billion light-years (~redshift 7.5). 

By using the gravitational magnification from six massive lensing galaxy clusters, the NASA/ESA Hubble Space Telescope has provided scientists with the largest sample of very distant galaxies seen to date. Some of the newly found magnified objects are dimmer than the faintest ones seen in the legendary Hubble Ultra Deep Field, which is usually considered the deepest image of the Universe.

By combining both visible and near-infrared observations from Hubble’s Advanced Camera for Surveys (ACS) and Near Infrared Camera and Multi-Object Spectrometer (NICMOS), scientists searched for galaxies that are only visible in near-infrared light. They uncovered 10 candidates believed to lie about 13 billion light-years away (a redshift of approximately 7.5), which means that the light gathered was emitted by the stars when the Universe was still very young — a mere 700 million years old.

These candidates could well explain one of the big puzzles plaguing astronomy today. We know that the Universe was reionised within the first 5-600 million years after the Big Bang, but we don’t know if the ionising energy came from a smaller number of big galaxies or a more plentiful population of tiny ones”, said Johan Richard, from the California Institute of Technology. The relatively high number of redshift 7.5 galaxies claimed in this survey suggests that most of the ionising energy was produced by dim and abundant galaxies rather than large, scarce ones.

The challenge for astronomers is that galaxies beyond a distance of 13 billion light-years (past a redshift of 7) are exceedingly faint and are only visible in the near-infrared — just at the limit of what Hubble can observe” explained Jean-Paul Kneib from the Laboratoire d’astrophysique de Marseille. This new result was only made possible with some cosmic assistance in the form of gravitational lensing that magnified the light from the distant galaxies enough for Hubble to detect them. A firm confirmation of their distance was beyond even the capabilities of the 10-meter Keck telescope and must await powerful future ground-based telescopes.

First confirmed in 1979, gravitational lenses were predicted by Albert Einstein’s theory of General Relativity, a theory that allows astronomers to calculate the path of starlight as it moves through curved space-time. According to the theory, the bending of light is brought about by the presence of matter in the Universe, which causes the fabric of space-time to warp and curve.

Gravitational lensing is the result of this warping of spacetime and is mainly detected around very massive galaxy clusters. Due to the gravitational effect of both the cluster’s observable matter and hidden dark matter, the light is bent around the cluster. This bending of light allows the clusters in certain places to act as natural gravitational telescopes that give the light of faint and faraway objects a boost.

Where Earth-bound telescopes fail to detect such faint and distant objects due to the blurring introduced by the Earth’s atmosphere, a combination of Hubble’s location in space and the magnification of the gravitation lenses provides astronomers with a birds-eye view of these elusive objects.

This technique has already been used numerous times by Hubble and has helped astronomers to find and study many of the most distant known galaxies.

 

Notes for editors:

 

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

Image credit: NASA, ESA and Johan Richard (Caltech, USA)
Acknowledgement: Davide de Martin & James Long (ESA/Hubble)

 

Links:

Wikipedia site explaining Gravitational Lensing
More Hubble discoveries relating to gravitational lenses