Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Peter Dow on 13/04/2021 12:52:33

Title: Are galaxies bigger on the inside and galactic πs LESS than 3.14?
Post by: Peter Dow on 13/04/2021 12:52:33

This tweet appeared on my science feed and it got me thinking.

Quote

For decades physicists have found more and more evidence that dark matter is real but not a single sign of the stuff itself. (https://twitter.com/sciam/status/1381717510425210882)

What if there is NO dark matter and the anomalous galaxy rotation curve (https://en.wikipedia.org/wiki/Galaxy_rotation_curve) is an emergent property of the bending of space time by the massive black hole at the centre of galaxies?
(https://pbs.twimg.com/media/Ey0REOGWQAIugfp?format=jpg&name=900x900)

Are galactic πs less than 3.14 - is the ratio of a galactic circumference to its radius from the galactic centre in general less than 2 x 3.14 as we would expect from Euclidean geometry?

Perhaps galaxies with a big black hole at their centre are rather like the TARDIS, bigger on the inside than they are on the outside?

(https://hackaday.com/wp-content/uploads/2018/09/tardis_feature.png?w=800)

So is the galactic centre actually much further away from the outer circumference than it appears; inner galactic circumferences as big or even bigger than outer galactic circumferences?

Such warping of space might explain why the angular rotation of stars can remain constant or even increase with greater distance from the centre - the velocity is indeed slower with the greater distance from the galactic centre but the circumferential distance is also paradoxically smaller and so the angular rotation much faster with distance from the centre than expected?

In which case those looking for dark matter might be barking up the wrong tree and not find anything?

Title: Re: Are galaxies bigger on the inside and galactic πs LESS than 3.14?
Post by: Halc on 13/04/2021 14:20:06

The graphic is massively exaggerated, illustrating why it's probably not a good idea to get your science from social media. Except within the event horizon, a black hole bends space no more than the same mass that is not in a black hole. In other words, if our sun was compressed to a black hole, no orbit of anything would change and the only way we'd notice is:
"Hey, Who turn out the lights?" - proper Dave.

The black hole in the center of our galaxy is tiny and comprises less than 0.000003 of the mass of the galaxy. The bending shown in the picture is nonsense. Yes, they take bending of spacetime into account when computing orbits and such, but the effect is so negligible that it takes very fine measurements of something very close (S2) to the black hole to detect the difference from Newtonian orbital motion.

It has also been measured in Mercury due to the precession of the orbit, but S2 has I think a 17 year orbit and it takes a seriously long time to get precession numbers from it.