Which galaxies are moving and the faster rate

Astronomer Vera Rubin pioneered work on galaxy rotation rates, showing that spiral galaxies rotate faster than if their gravity were solely due to the constituent stars and gas. An additional, invisible substance known as dark matter must influence galaxy rotation. A spiral galaxy of a given mass in stars is expected to rotate at a certain speed.

Super spirals also reside in larger than average dark matter halos. The most massive halo that Ogle measured contains enough dark matter to weigh at least 40 trillion times as much as our Sun. That amount of dark matter would normally contain a group of galaxies rather than a single galaxy.

The fact that super spirals break the usual relationship between galaxy mass in stars and rotation rate is a new piece of evidence against an alternative theory of gravity known as Modified Newtonian Dynamics, or MOND.

MOND proposes that on the largest scales like galaxies and galaxy clusters, gravity is slightly stronger than would be predicted by Newton or Einstein. This would cause the outer regions of a spiral galaxy, for example, to spin faster than otherwise expected based on its mass in stars.

MOND is designed to reproduce the standard relationship in spiral rotation rates, therefore it cannot explain outliers like super spirals.

The super spiral observations suggest no non-Newtonian dynamics is required. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Synthesizing nanomaterials from nature's blueprints 11 hours ago. Relevant PhysicsForums posts Temperature of gas in a cluster 4 hours ago.

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Your message to the editors. Your email only if you want to be contacted back. Send Feedback. Thank you for taking time to provide your feedback to the editors. E-mail the story How are galaxies moving away faster than light? Your friend's email. Your email. I would like to subscribe to Science X Newsletter. Learn more. That's the domain of a more general theory. A theory like… general relativity. It's true that in special relativity, nothing can move faster than light.

But special relativity is a local law of physics. Or in other words, it's a law of local physics. That means that you will never, ever watch a rocket ship blast by your face faster than the speed of light.

Local motion, local laws. But a galaxy on the far side of the universe? That's the domain of general relativity, and general relativity says: who cares! That galaxy can have any speed it wants, as long as it stays way far away, and not up next to your face. It goes deeper than this. Concepts like a well-defined "velocity" make sense only in local regions of space.

You can only measure something's velocity and actually call it a "velocity" when it's nearby and when the rules of special relativity apply. Stuff super-duper far away, like the galaxies we're talking about it?

Special relativity doesn't care about the speed — superluminal or otherwise — of a distant galaxy. And neither should you. Learn more by listening to the episode "How can the universe expand faster than light?

Thanks to Mihail Etropolski, Nicolas Gregori, chris, and archerelliott for the question that inspired this piece.