What if there is no Dark Matter?

[Elizabeth90125]

I need some smart people to explain to me why this idea I have, doesn't work. It's impossible for me to believe others have not thought it, since it's so obvious. What if spacetime is slipping backwards at the black hole at the center of every galaxy? So like a helicopter with no rotar, spacetime slips backwards against the spin of the black hole, which has become unpinned to spacetime by virture of it's infinite gravity at the singularity. With no spacetime solidly anchored to the black hole, it exerts a force on spacetime outside the event horizon. In this way, the stars at the center of galaxies are not going the same speed as those orbiting on the outside edge of the galaxy. Because spacetime is going backwards, they are actually going a much greater distance than we see, meaning they are going faster than they appear. The amount of spacetime slippage breaks away with respect to mass and distance so the stars on the very outside edge of the galaxy are not slipping at all.

What is the reason, this can't be the case?

Elizabeth

 

[phinds]

I mean you no disrespect but it appears to me that you have just strung together some science words in a way that has no meaning. What, for example, do you mean by "spacetime slipping backwards" ? How would your hypothesis account for gravitational lensing?

 

[Drakkith]

What is the reason, this can't be the case?

Because spacetime does not work that way. I would suggest getting familiar with special and general relativity if you want to know why, as those theories explain spacetime.

 

[EdgePenguin]

Elizabeth,

Regardless of what may be happening to spacetime in or near the central black hole of a galaxy, rotation velocities are measured at distances where the gravitational effect of the black hole is well into the Newtonian regime. Even if what you are describing could happen (and frankly I don't really get what you are on about) then it wouldn't have any impact over kiloparsec scales.

You also appear to have some other misconceptions. First, rotation curve decomposition is not the only, nor the first or the arguably the best, evidence for the existence of dark matter. There is galaxy cluster dynamics, gravitational lensing, baryogensis, local group timing (MW+Andromeda must have enough mass to overcome the expansion of the universe moving them apart.) etc.

Second, your post seems to imply that the plane of the black hole spin is the same as the plane of the galactic disk. There is no physical reason why this should be the case. It is possible that the black hole spin isn't even aligned with its own accretion disk (which is an entirely separate entity from the galactic disk)

 

[Lino]

... your post seems to imply that the plane of the black hole spin is the same as the plane of the galactic disk. There is no physical reason why this should be the case. It is possible that the black hole spin isn't even aligned with its own accretion disk (which is an entirely separate entity from the galactic disk)

First off, I agree with the responses thus far in this thread. But EdgePenguin, can I ask if you have any examples / references for you comment (and the references could be related to non-blackholes - i.e. stars / planets / other macro objects).

 

[EdgePenguin]

First off, I agree with the responses thus far in this thread. But EdgePenguin, can I ask if you have any examples / references for you comment (and the references could be related to non-blackholes - i.e. stars / planets / other macro objects).

This only applies to SMBHs in galaxies. Planetary systems are dynamically quite different.

I'm a little confused as to what you want me to demonstrate. Why should there be any alignment between rotation planes in this case?

 

[Lino]

... I'm a little confused as to what you want me to demonstrate. Why should there be any alignment between rotation planes in this case?

Thanks EdgePenguin. I haven't really considered if there is / isn't an alignment in anything I have read, but intuitively an alignment between the accretion disc and the BH / SMBH ... just seems logical to me (if one dust particle is falling on to a BH and starts to complete a decaying orbit, the particle would take momentum from its incoming velocity and the drag of the BH rotation - introduce lots of material and the average momentum from the various elements of the momentum cancels, and one is left with the drag / direction of the BH spin).

I was just wondering if you knew of any papers / books that discuss this?

 

[SpecialPerson]

I think the OP should read http://www.scientificamerican.com/article/dark-matter-modified-gravity/

 

[phinds]

I think the OP should read http://www.scientificamerican.com/article/dark-matter-modified-gravity/

I think the OP is a drive-by who hasn't been here in the 2 weeks since the post (no activity since the day after the post)

 

[SpecialPerson]

I'm sorry, I saw that the last post was today so I presumed the OP was still active.

 

[EdgePenguin]

Thanks EdgePenguin. I haven't really considered if there is / isn't an alignment in anything I have read, but intuitively an alignment between the accretion disc and the BH / SMBH ... just seems logical to me (if one dust particle is falling on to a BH and starts to complete a decaying orbit, the particle would take momentum from its incoming velocity and the drag of the BH rotation - introduce lots of material and the average momentum from the various elements of the momentum cancels, and one is left with the drag / direction of the BH spin).

I was just wondering if you knew of any papers / books that discuss this?

I confess my knowledge of this area comes from working in the same department as people who study it rather than reading or publishing the literature, so its hard to point you at anything specific. Some folks I know who have worked on this are Andrew King, and his former student Chris Nixon. You could look up their papers.

As for your point about the incoming matter imparting angular momentum on the black hole - well yes, but which direction is the matter coming from?

I think both you and the OP are reasoning from a flawed mental picture. The black hole and the accreting region are miniscule compared to the scale of the host galaxy. Rotation curves are calculated in radial bins maybe 100pc wide for nearby well resolved galaxies, and azimuthally integrated over all angle. This broad stroke method - by design - tends to blur out non circular motions and inhomogeneity in the rotating matter (usually atomic hydrogen) and so doesn't tell you what's going on at smaller scales.

The non circular motions that are a nuisance in rotation curve analysis mean that you can't assume matter will be delivered to the central black hole in one plane. In fact, you can't assume that the black hole will even lie in the plane that the disk lies in. Or that the disk lies in a single plane - rotation curves are derived using the titled ring method which allows for different radial bins to have different inclinations. The universe has a shocking lack of respect for our chosen coordinate systems.

 

[Lino]

Thanks EdgePenguin.