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Comment by dwaltrip | Hacker News Reader

The comment that you are responding to says that this weakens the case for MOND.

I saw that, it was more so a response to Fermi lab Physicist are taking MOND more seriously. MOND has its problems also.

Its my opinion that there is something about the black hole at the center of these galaxies that's causing discrepancies that we attribute to "dark matter". The fact that this new galaxy is so sparse and distributed and shows no sign of dark matter seems to re-affirm this. I'd be curious to know if it even has a central black hole.

To clarify, no one's taking MOND nearly as seriously as WIMPs in terms of funding for experiments to test it. That said, the lack of evidence has lead to increased interest in alternative theories that could explain the phenomenon. Some of these are alternative dark matter particle candidates though, just not WIMPs.

It's a pointless conversation the argue over which unproven theory is taken most seriously.

The reality is that we don't know.

Wimps have gotten lots of funding. But we are probably on the last generation of wimp detector

How does your theory fit with flat rotation curves?

My "theory" is just a hunch. Flat rotation curves IS the primary foundation for the existence of dark matter:

https://en.wikipedia.org/wiki/Galaxy_rotation_curve

I'm simply saying its more likely an unknown effect of the black hole at the center. Possibly some sort of gravitational modification effect that only occures in the presents of singularities. The fact that a sparse galaxy with possible no black hole center (I assume) shows no sign of dark matter is compelling. It may not prove the specific equations/explanations set forth in MOND, but it may hint to some other alternative gravitational theory that has yet to be flushed out, rather than relying on some invisible particles which may not exist.

While rotation curves were one of the earlier indications of dark matter, we have perhaps stronger evidence now from CMB measurements, gravitational lensing studies, and structure formation considerations.

Got any links for cosmology laymen? I'd be curious to see if my "theory" is negated.

Not sure if this is the right level or not, but one place with nice animations is http://background.uchicago.edu/~whu/animbut/anim2.html

I'm not a physicist, but that was my thought exactly.

Black holes are weird objects, they are enormous, have huge mass and density, almost no radiation, have great gravitational effect on surroundings and they are hard to detect etc.

They seem like a perfect candidate for 'dark matter'.

Could anyone explain why it is wrong?

They're detectable and already taken into account.

So according to wikipedia [1] they have been looked into, they would fall under the category of MACHOs

1. https://en.wikipedia.org/wiki/Dark_matter#Baryonic_matter

Black Holes of reasonable can be detected by gravitational lensing. If Black Holes / Brown Dwarfs / etc. were primarily responsible for the dark matter locally, lensing searches would have detected more. See e.g. https://arxiv.org/abs/astro-ph/0002058 for an overview.

This graphic can explain very clearly, although it’s a little old. The result is that constraints today are even tighter though, so for these purposes it’s still useful.

https://4.bp.blogspot.com/-UN8jPwzj2qI/V9hRVCG1HBI/AAAAAAAAC...

My "theory" is just a hunch.

It looks like Occam's razor. To explain an unexpected result, you label the problem so it looks like it must be a new entity.

The supermassive black holes at the centers of galaxies really can't have anything to do with dark matter or any possible alternatives. A few light years away from the SMBH the black hole behaves like any other ordinary astrophysical object. Moreover, at least in our galaxy, the stars in the central bulge outweigh the SMBH by a factor of about 10,000.

> The supermassive black holes at the centers of galaxies really can't have anything to do with dark matter or any possible alternatives.

What makes you so sure? I think limiting our thinking too much into the confines of regular gravitation is a mistake. Maybe SMB are the source of these theoretical heavy neutrino's we have yet to detect that are the #1 candidate for dark matter/WIMPS. Or maybe the gravitational disturbance of a singularity is far more complex that we imagine?

Take a look at the video on the Galaxy Rotation Curve video in this wiki:

https://en.wikipedia.org/wiki/Galaxy_rotation_curve#Descript...

I stare at it and cant help but wonder is something about that central singularity is unique. We still have no idea what truly happens at the center.

We have observed visible objects (stars) that are close enough to be orbiting a supermassive black hole and they follow the expected orbits.

If supermassive black holes do something new and strange with gravity--something big enough to affect an entire surrounding galaxy--it seems likely it should somewhat affect the trajectories of the nearest objects too.

That's not to rule out something strange about black hole gravitation, but the observations do constrain some versions of how strange things can be.

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