Saturday, 25 February 2012

Scientists see "sloshing" galaxy cluster

A Naval Research Laboratory scientist is part of a team that has recently discovered that vast clouds of hot gas are "sloshing" in Abell 2052, a galaxy cluster located about 480 million light years from Earth. The scientists are studying the hot (30 million degree) gas using X-ray data from NASA's Chandra X-ray Observatory and optical data from the Very Large Telescope to see the galaxies.

"The X-ray images were amazing. We were able to see gas sloshing like liquid in a glass" explains NRL's Dr. Tracy Clarke. "Of course this would be one enormous glass since we see the gas sloshing over a region of nearly a million light years across!"

The Chandra data reveal the huge spiral structure in the hot gas around the outside of the image. Zooming in on the cluster reveals "cavities" or "bubbles" surrounding the central giant elliptical galaxy. The spiral began when a small cluster of galaxies collided off-center with a larger one positioned around that central galaxy.

The gravitational attraction of the smaller cluster drew the hot gas out of the central cluster toward the smaller cluster. Once the smaller cluster passed by the central cluster core, the gas movement reversed and it was pulled back toward the center of the main cluster. The hot cluster gas overshot the cluster center, creating the "sloshing" effect that is like the sloshing that occurs when a glass holding a liquid is quickly jerked sideways. In the cluster, gravity pulls back on the gas cloud, creating the spiral pattern.

For scientists, the observation of the "sloshing" motion in Abell 2052 is important for two reasons. First, the "sloshing" helps to move some of the cooler, dense gas in the center of the core farther away from the core. This cooler gas is only about 10 million degrees, as compared to the average temperature of 30 million degrees. This movement reduces the amount of cooling in the cluster core and could limit the amount of new stars being formed in the central galaxy. The "sloshing" movement in Abell 2052 also helps redistribute heavy elements like iron and oxygen, which are created out of supernova explosions. These heavy elements are an important part of the make-up of future stars and planets. The fact that Chandra's observation of Abell 2052 lasted more than a week was critical in providing scientists with the details detected in this image.

Besides the large-scale spiral feature, the Chandra observations also allowed scientists to see details in the center of the cluster related to outbursts from the supermassive black hole. The data reveal bubbles resulting from material blasted away from the black hole which are surrounded by dense, bright, cool rims. In the same way that the "sloshing" helps to reduce the cooling of the gas at the core of the cluster, the bubble activity has the same effect, limiting the growth of the galaxy and its supermassive black hole.

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