How cosmic winds affect galactic evolution

While astronomers already knew that cosmic winds travelling through galaxies could cause star formation to come to an end by sweeping out interstellar material, new observations of a nearby galaxy have given them a better look at exactly what this process entails.

Their research, led by experts from Yale University and detailed in the Astronomical Journal, looked at Hubble images of a spiral galaxy in the Coma cluster, which is located approximately 300 million light years away and is the closest high-mass cluster to our solar system.

Lead author and Yale astronomer Jeffrey Kenney, who first encountered these images back in 2013, analyzed them to see how the cosmic wind was eroding dust and gas located at the leading edge of the galaxy. The wind, also known as “ram pressure”, is caused by the orbital motion of the galaxy through hot gas in the cluster, the researchers explained in a statement Monday.

Kenney found a series of intricate dust formations on that disk’s edge as cosmic wind started to make its way through the galaxy, and while the gas and dust appeared to be piled up in one long ridge on the leading side, he found head-tail filaments protruding from the dust front that might have been caused by the separation of dense gas clouds from lower density gas.

Loss of gas will mark the end of star formation

Lower-density clouds of interstellar gas and dust can be easily carried by the cosmic winds, the study authors explained, but higher-density clouds cannot. As the winds blow, the denser gases begin to separate from lower density gas, which gets blown down stream. However, both higher and lower density lumps appear to be bound together, likely by magnetic fields.

“The evidence for this,” the Yale astronomer said, “is that dust filaments in the [Hubble Space Telescope] image look like taffy being stretched out. We’re seeing this decoupling, clearly, for the first time.” He noted that the dust filaments in this Hubble image are similar to those found in the iconic “Pillars of Creation” image, except that they are roughly 1,000 times larger.

The images reveal that the bulk of the dust and gas is being pushed away by external forces, and that this results in the destruction of most of the cloud. Only the densest material, the pillars, are left behind, but even they have a limited shelf life. Since gas is required for the formation of new stars, once it is removed, the area is no longer able to act as a stellar nursery.

While in the Eagle Nebula, which is home to the “Pillars of Creation,” the pressure comes from the radiation emitted by nearby massive stars, the pressure in the Coma galaxy is produced by the orbital motion of the galaxy through hot gas in the cluster. While new stars are currently still being born in both types of pillars, they represent the last generation that will form in either.

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