Dark matter and stars ‘conspire’ to keep elliptical galaxies’ spin stable

There’s more going on here than meets the eye.

An international team of researchers has found what they’re calling a “conspiracy” inside elliptical galaxies. It appears dark matter and stars are working together to alter the speed at which elliptical, as well as spiral, galaxies in our Universe spin. This is the first study to map the motion of stars in large numbers of elliptical galaxies, and has shown that they move much faster than expected. This is the same thing that astronomers found was happening in spiral galaxies like our Milky Way 40 years ago – a result that first led to the discovery of a mysterious presence known as dark matter. Since then, scientists have found that dark matter makes up about 85 percent of the mass in the known Universe, and influences the way that galaxies form, move and evolve. But we still understand very little about it.

This new study, which involved astronomers from Swinburne University of Technology in Australia, is the first to suggest that dark matter is impacting elliptical galaxies in the same way it influences spiral galaxies. If it wasn’t, the stars on the outside of the galaxy would move much slower than those at the inside, due to the waning effects of gravity. “The surprising finding of our study was that elliptical galaxies maintain a remarkably constant circular speed out to large distances from their centres, in the same way that spiral galaxies are already known to do,” the lead researcher, Michelle Cappellari, from the University of Oxford in the UK, told the press. “This means that in these very different types of galaxies, stars and dark matter conspire to redistribute themselves to produce this effect, with stars dominating in the inner regions of the galaxies, and a gradual shift in the outer regions to dark matter dominance.” Source: Dark matter and stars ‘conspire’ to keep elliptical galaxies’ spin stable

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