Far out cosmology: merging galaxies prove dark matter (Introduction)

by David Turell , Sunday, June 13, 2021, 23:16 (1257 days ago) @ David Turell

Dark matter must exist:

https://www.forbes.com/sites/startswithabang/2020/01/20/this-is-how-galaxy-cluster-coll...

"Dark matter — despite the enormous indirect evidence for it — sounds like a colossal misunderstanding.

"It's clear that data from gravitational lensing, galaxy clustering, and the cosmic microwave background, all require masses that don't interact electromagnetically.

"The way galaxies cluster together is impossible to achieve in a Universe without dark matter. The... [+] clustering patterns seen due to baryon acoustic oscillations, imprinted in the Universe's power spectrum, and on the largest scales of the cosmic web are all consistent with dark matter, but have never been explicable via any attempted modification of gravity.

"However, a longstanding alternative suggests modifying gravity could explain them without dark matter.

"In 2005, a team of astronomers devised a clever test to investigate dark matter's existence.

"When two galaxy clusters collide — a cosmically rare but important event — its internal components behave differently.

"The intergalactic gas must collide, slow, and heat up, creating shocks and emitting X-rays.

"If there were no dark matter, this gas, comprising the majority of normal matter, should be the primary source of gravitational lensing.

"Instead, gravitational lensing maps indicate that most of the mass is displaced from the normal matter.

"This remains true for every set of post-collisional X-ray clusters ever measured.

"Only if gravity is non-local, or gravitating where the matter isn't, could the Universe not contain dark matter.

"But in pre-merger clusters, we clearly see that gravity is local: matter and gravity line up.

"Colliding clusters cannot obey different gravitational rules from non-colliding ones.

"Inescapably, dark matter must therefore exist."

Comment: So matter we cannot see is proven. It is not necessary for all matter to light up, no matter that much does. But is needed to hold galaxies together.