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Black hloes = missing mass ?

by merlinsbyte
Tags: black, hloes, missing mass
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merlinsbyte
#1
Jan24-05, 07:23 PM
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Could the missing mass/dark matter be (migrating)? Black holes of various sizes? I have serious doubts if the missing mass consists of any known "matter".
Also would anyone care to enlighten me to the newest theory on (the missing mass)?

thanks in advance

MB
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Garth
#2
Jan25-05, 10:25 AM
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Hi merlinsbyte welcome to these Forums.

We do not know what Dark Matter is. Using Newton's law of gravity it seems there is more mass in a galaxy than observed and in the space between galaxies in a cluster than observed.

Therefore DM might not exist at all but the observations be the result of a non-Newtonian law of gravity operating, this is the idea behind the MOND theory.

If Newton is right then it does exist but as we cannot see it we do not know what it is composed of. The standard model of cosmology, based on GR, predicts that there can only be about 4% of the universe's mass-energy in the form of baryons (ordinary matter), and it requires about 23% to be Dark (non-baryonic) Matter, required to attract stars and galaxies, and the remaining 73% to be something even more mysterious - Dark Energy; which is required to have an 'anti-gravity' effect and cause the universe to accelerate in its expansion, i.e. to repel on a large scale.

Lots of ideas have been suggested for exotic new particles to be Dark Matter but so far no luck in detecting one in a laboratory.

If the standard cosmological model is modified then the Dark Matter might be baryonic after all. A Concordant “Freely Coasting” Cosmology does not require much or any unknown Dark Matter at all. The problem now is identifying what kind of objects this stuff might be.

One possibility is your suggestion that it is in the form of black holes, however there cannot be too many otherwise they would have been observed through 'microlensing' events. It could be in the form of very dim stars, red dwarfs, or smaller objects 'free Jupiters, see the discussion on the thread 'Gigantic Galactic Blobs'.

I hope this helps,

Garth
hellfire
#3
Jan25-05, 11:20 AM
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Quote Quote by Garth
One possibility is your suggestion that it is in the form of black holes, however there cannot be too many otherwise they would have been observed through 'microlensing' events. It could be in the form of very dim stars, red dwarfs, or smaller objects 'free Jupiters, see the discussion on the thread 'Gigantic Galactic Blobs'.
I agree with you that one could expect more baryonic dark matter depending on the cosmological model, but as far as I know lots of black holes as well as compact objects should lead to "kinematic heating" of stars in galaxies (they would be perturbed more from their orbital plane), which is not observed. I cannot give a reference now, but I will search. I would expect baryonic dark matter to be in form of gas.

ohwilleke
#4
Jan25-05, 11:28 AM
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Black hloes = missing mass ?

Black holes are a poor candidate for dark matter. The current theories propose dark matter "halos" more or less spherically distributed about galaxies. In other words, they predict a highly diffuse distribution of dark matter.

In contrast, black holes are the epitome of a point source. To get the right effect your proposed black holes=dark matter would have to be distributed in something like a Buckminister Fuller type spherical grid around galaxies, and such a distribution wouldn't be stable in the long run unless it was very finely balanced.

Also, while black holes are themselves dark, they tend to attract luminous material to their vicinity. A significant number of black holes are either at galactic cores or in binary systems. Yet, the halos around galaxies are genuinely dark. So, again, this seems unlikely.
Garth
#5
Jan25-05, 12:04 PM
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Those are all sound points hellfire & ohwilleke, not many black holes in the DM then!

Garth
merlinsbyte
#6
Aug24-08, 07:24 AM
P: 5
Thanks for your replies, I was visiting the event horizon of the nearest BH, then my spacecraft was seized by the tidal effect of its gravity, luckily it was rotating and when I entered into the event horizon my craft matched the velocity of c, and a virtual copy of myself and craft was, sad to say made to look like a familiar form of pasta as the real me skipped out in a timely (to say the least) fashion just a nanosecond ago, but I see a few months has passed here.

In other words I'm back.

; {>


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