Does Dark Matter Still Exist ?

[John Murrell]

At yesterdays RAS General meeting there was an interesting lecture on Cosmology – by Professor Andrew Liddle (Sussex): Titled The Universe, Darkly one of the interesting points he made is that the information we have on the existence of dark matter is from the galaxy surveys and gravitational lensing that are typically at a redshift of 1 or so and are therefore a reasonable time in the past. You need to go back this far to get a large enough volume of space to see the effects.

 

There is also a constraint on dark matter imposed by the CMB.

 

The interesting thing is that if you join these two constraints using equations used to predict the evolution of dark matter when you run the equations forward it is possible their is no dark matter now or equally rather more than was in the past. The problem is that observations of the local universe ( a few million Parsecs !) do not contain enough volume or distance for the effects of dark matter to be seen. The reason there appears to be less dark matter in the relatively local galaxies we can measure the rotation curves of could be that dark matter is decaying and has at the present epoch almost disappeared.

 

This could explain why the dark matter detectors have not found it and why there is no evidence for dark matter in the Solar System.

 

A similar argument can be used for dark energy but the constraints due to observations of SN are even wider.

 

Comments ?

 

John Murrell

Astronomer Without Portfolio

Website www.JohnMurrell.org.uk

 

 

[John Murrell]

Is my posting below related to this news release ? http://www.ras.org.uk/news-and-press/219-news-2012/2187-cosmic-gdp-crashes-97-as-star-formation-slumps

 

If dark matter is required for galaxy formation what impact does it have on star formation rates ??

 

Am I jumping to unwarranted associations ?

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[Mike Ross]

John,

 

For a redshit (z) of 1, I make that 7.9 billion light years (unless my maths is wrong), when the universe was half its current size. Are you saying there is no evidence of dark matter much closer, in space and time, than that? What about the rotation of our own and neighbouring galaxies as pointed out by Zwicky in (I think) the 1940s?

 

In the early Universe, the density of hydrogen clouds was much greater than now, so you would expect star forming rates to be much greater, especially as the first stars would have been going Supernova far more readily than now, causing the kind of shock waves needed to start the process of further star generation.

 

Finally, if Dark Matter has now disappeared. Why? It is bad enough that we have to accept that Inflation started and stopped for unknown reasons, now we have Dark Enery switching off, presumably in all dirrections in unconnected parts of the universe in the last few billion years.

 

Basicaslly, I don't buy it.

 

Regards,

 

Mike 

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[John Murrell]

Mike,

 

The estimates of dark matter at around Z=1 are from the SDSS and the other similar survey I have forgotten at present.

 

The rotation curves of nearby galaxies show less dark matter than that predicted from the CMB & Big Bang – you need to go for clusters of galaxies at large distances to see the most dark matter.

 

As for our galaxy I don’t think we have a rotation curve – from where we are it is difficult enough to get the arm structure right let alone work out the rotation curve.

 

As for the local dark matter there appears to be little agreement – some papers state there is no evidence but others state there is. The dark matter detectors have so far drawn a blank with the possible exception of one disputed result. However Dark Matter may not be WIMPs which is what I think the detectors are looking for.

 

Perhaps we should invite Andrew Liddle to speak to the CAS ?

[Tony Angel]

Zwicky identified the need for Dark Matter when he was looking at Galaxy Clusters. It was Vera Rubin - still going strong - who looked at M31 and analysed the rotational speed of stars way out from the centre. The outer stars were going too slow. Peebles also did some computer modelling when he pinched time on the Los Alamos computer and found that with out adding mass the galaxy would just wind up.

 

I had hoped to have been there as Barbara Becker was given a talk on Huggins - I have her book. We have been emailing each other for a while. I hope her talk went well. She was speaking at Eastbourne tonight. She will be back in the UK when she launches her follow up book. If there is interest I could ask her if she could give a CAS talk.

 

Tony.  

[brian mills]

Hi Tony,

 

I heard the Barbara Becker talk and thought it was very good.

When it came to question time it was obvious from the way she answered that she had done a great deal of research and knew the subject intimately.

 

Regards

Brian

 

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From: alta...@googlegroups.com [mailto:alta...@googlegroups.com] On Behalf Of Tony Angel

Sent: 11 November 2012 23:49
To: alta...@googlegroups.com

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[Mike Ross]

John
The link below leads to a BBC report concerning the failure to find evidence of WIMPs at LHC http://www.BBC.co.UK/news/science-environment-20300100
Mike

[John Murrell]

Mike,

 

The failure to find WIMPs at the LHC shakes people’s faith in Super Symmetry as was said in the article Super Symmetry is not dead but it is in hospital !

 

I believe the LHC should create the WIMPs so even if they have died out there should still be some in the LHCb data.

 

As Tony said it was Zwicky who identified the need for dark matter to hold the coma cluster together – that gets a mention the review of his biography in the November Astronomy Now. The coma cluster is some 320 M light years away. The value of Omega for the cluster appears to be about 0.1 i.e. 1/10 of the value for the Universe as a whole.

[John Murrell]

Have a look at the article in Astronomy at http://astronomy.com/News-Observing/News/2012/11/Astronomers measure the universes deceleration before dark energy took over.aspx

 

It is a pity that the expansion graph does not have a vertical scale or even a zero point ! Is drawing the curve they have chosen consistent with the data points ?