Article Posted on : - Oct 01, 2009

This composite shows the two ram pressure stripping galaxies NGC 4522 and NGC 4402. Image Credit: NASA & ESA

NEW DELHI (BNS): Two galaxies in the Virgo Cluster are showing signs of being affected by a process known as "ram pressure stripping", which can result in peculiar-looking galaxies, according to scientists.

Astronomers study ram pressure stripping for better understanding of the mechanisms that drive the evolution of galaxies and how the rate of star formation is suppressed in very dense regions of the Universe like clusters.

A newly released set of images taken by the NASA/ESA Hubble Space Telescope highlight the ongoing drama in the galaxies, a Science Daily report said Thursday.

An extremely hot X-ray emitting gas known as the intra-cluster medium lurks between galaxies within clusters. As galaxies move through this intra-cluster medium, strong winds rip through galaxies distorting their shape and even halting star formation.

Ram pressure is the drag force that results when something moves through a fluid and occurs in this context as galaxies orbiting about the centre of the cluster move through the intra-cluster medium, which then sweeps out gas from within the galaxies.

The spiral galaxy NGC 4522 located some 60 million light-years away from Earth is a spectacular example of a spiral galaxy currently being stripped of its gas content. The galaxy is part of the Virgo galaxy cluster and its rapid motion within the cluster results in strong winds across the galaxy as the gas within is left behind.

Scientists estimate that the galaxy is moving at more than 10 million kilometres per hour. A number of newly formed star clusters that developed in the stripped gas can be seen in the Hubble image, the report said.

Hubble's view of NGC 4522 practically swirls off the page with apparent movement. It highlights the dramatic state of the galaxy, with an especially vivid view of the ghostly gas being forced out of it. Bright blue pockets of new star formation can be seen to the right and left of centre. The image is sufficiently deep to show distant background galaxies.

The image of NGC 4402 also highlights some telltale signs of ram pressure stripping such as the curved, or convex, appearance of the disc of gas and dust, a result of the forces exerted by the heated gas. Light being emitted by the disc backlights the swirling dust that is being swept out by the gas, concluded the report.