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Galaxy Diets

Crash diet: Astrophysicist finds that galaxies shed a third of their mass or more after joining groups

HAMILTON, ON, May 30, 2017 -- It may be the biggest diet in the universe. 
When galaxies come together to form groups, and when groups join vast clusters, they lose mass to the larger body in a gravitational process called tidal stripping. 

Gandhali Joshi, a McMaster University PhD candidate in Astronomy and Physics who specializes in the evolution of galaxies, has found that a significant loss of mass, once thought to occur in large clusters, actually begins after single galaxies join small groups that eventually join larger clusters. During that first stage, they can lose as much as 40 per cent of their mass, compared to far less substantial losses for galaxies that join clusters individually.  A copy of her paper, which is to be published in Monthly Notices of the Royal Astronomical Society, is here: https://arxiv.org/pdf/1704.01959.pdf.

"If we can definitively say how much mass loss is happening, that helps us ultimately understand the physical processes that affect galaxies," Joshi says. "It all adds up to a picture of how galaxies evolve, and what happens to them in these dense environments."

A group of galaxies features anywhere from three to 20 or 30 galaxies, while clusters feature hundreds or even thousands of galaxies. 
Galaxies in groups and clusters behave differently than freestanding single galaxies. Those in groups and clusters are typically redder in colour, make fewer new stars and tend to be elliptical in shape, compared to spiral-shaped singletons.

Joshi is to present her work May 30 at the annual general meeting of the Canadian Astronomical Society in Edmonton.
Joshi reached her conclusions using the massive computing power of SciNet, Canada's largest supercomputer centre, where she deployed a highly sophisticated model to measure the dark matter that contains distinct galaxies. 

Dark matter is a mysterious, little understood and invisible component of space whose existence is known by inference, not direct observation. Scientists do know that dark matter, which is measured by gravity, accounts for most of the mass in a galaxy, with only a small fraction represented by tangible elements such as stars, planets, moons, gases and dust. 

Joshi's next project, a follow-up to her new findings, is to study the mass of solids and gases in freestanding galaxies and measure what happens to them when they join groups. 

To arrange an interview with Gandhali Joshi, please contact her by email at joshigd@mcmaster.ca or by cell at 519-721-2530, the CASCA press officer. 
Leslie Sage
CASCA Press Officer
+1 301 675 8957
For more information, please contact: 
Wade Hemsworth
Media Relations Manager
McMaster University
905-525-9140, ext. 27988
Cell: 289-925-8382

Michelle Donovan
Media Relations Manager
McMaster University
905-525-9140, ext. 22869
Cell: 905-512-8548