A wave spanning 200,000 light-years (about twice the size of our Milky Way Galaxy) is rolling through the Perseus Cluster, according to observations from NASAs Chandra X-ray Observatory coupled with radio observations and computer simulations.

This X-ray image of the hot gas in the Perseus Cluster was made from 16 days of Chandra observations. An oval highlights the location of an enormous wave found to be rolling through the gas. Image credit: NASAs Goddard Space Flight Center / Stephen Walker et al.

Galaxy clusters are the largest structures bound by gravity in the Universe today.

Approximately 11 million light-years across and located 240 million light-years away, the Perseus Cluster (Abell 426) is named for its host constellation.

Like all galaxy clusters, most of its observable matter takes the form of a pervasive gas averaging tens of millions of degrees, so hot it only glows in X-rays.

Observations from NASAs Chandra X-ray Observatory have revealed a variety of structures in this gas, from vast bubbles blown by the supermassive black hole in the clusters central galaxy, NGC 1275, to an enigmatic concave feature known as the bay.

The bays concave shape couldnt have formed through bubbles launched by the black hole.

Radio observations using the Karl G. Jansky Very Large Array show that the bay structure produces no emission, the opposite of what astronomers would expect for features associated with black hole activity.

In addition, standard models of sloshing gas typically produced structures that arc in the wrong direction.

A team of astronomers led by Dr. Stephen Walker of NASAs Goddard Space Flight Center turned to existing Chandra observations of the Perseus Cluster to further investigate the bay.

The scientists combined a total of 10.4 days of high-resolution data with 5.8 days of wide-field observations at energies between 700 and 7,000 electron volts. For comparison, visible light has energies between about two and three electron volts.

The authors then filtered the Chandra data to highlight the edges of structures and reveal subtle details.

Next, they compared the edge-enhanced Perseus image to computer simulations of merging galaxy clusters.

One simulation seemed to explain the formation of the bay.

In it, gas in a large cluster similar to Perseus has settled into two components, a cold central region with temperatures around 54 million degrees Fahrenheit (30 million degrees Celsius) and a surrounding zone where the gas is three times hotter.

Then a small galaxy cluster containing about a thousand times the mass of the Milky Way skirts the larger cluster, missing its center by around 650,000 light-years.

The flyby creates a gravitational disturbance that churns up the gas like cream stirred into coffee, creating an expanding spiral of cold gas.

After about 2.5 billion years, when the gas has risen nearly 500,000 light-years from the center, vast waves form and roll at its periphery for hundreds of millions of years before dissipating.

These waves are giant versions of Kelvin-Helmholtz waves, which show up wherever theres a velocity difference across the interface of two fluids, such as wind blowing over water. They can be found in the ocean, in cloud formations on Earth and other planets, in plasma near Earth, and even on the Sun.

We think the bay feature we see in Perseus is part of a Kelvin-Helmholtz wave, perhaps the largest one yet identified, that formed in much the same way as the simulation shows, said Dr. Walker, who is the lead author of the paper reporting the results in the Monthly Notices of the Royal Astronomical Society (arXiv.org preprint).

We have also identified similar features in two other galaxy clusters, Centaurus and Abell 1795.

The team also found that the size of the waves corresponds to the strength of the clusters magnetic field.

If its too weak, the waves reach much larger sizes than those observed. If too strong, they dont form at all.

This study allowed astronomers to probe the average magnetic field throughout the entire volume of these clusters, a measurement that is impossible to make by any other means.

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S.A. Walker et al. 2017. Is there a giant Kelvin-Helmholtz instability in the sloshing cold front of the Perseus cluster? MNRAS 468 (2): 2506-2516; doi: 10.1093/mnras/stx640

This article is based on text provided by NASAs Goddard Space Flight Center.

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Astronomers Find Enormous Wave of Hot Gas Rolling through Nearby Galaxy Cluster - Sci-News.com