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View Full Version : Universe could have a fifth less mass than current estimates



Fortunate
2007-Nov-08, 03:33 PM
...the universe...could have 20% less mass than scientists previously thought. According to physicists in the US and Finland, this is because X-rays coming from the centres of galaxy clusters could be produced in collisions between relatively lightweight electrons and photons, rather than being thermal emissions from much heavier atomic gases as has been assumed.

http://physicsworld.com/cws/article/news/31752;jsessionid=5D8DD143DABAD71E1777DAD497BA4934

loglo
2007-Nov-11, 04:07 PM
A non-subscription article (http://www.sciencedaily.com/releases/2007/11/071102152248.htm) on the topic

loglo
2007-Nov-11, 04:12 PM
Love it when they puts quotes like this at the end of an article:-

Andrew Fabian, an astrophysicist at the University of Cambridge, UK is not convinced by Bonamente and colleague's study, however. He points out that the researchers have used outdated absorption values for our own galaxy's interstellar gas, which affect the level of soft X-rays received from Abell 3112. "Results from a newer survey could make the abundance of soft X-rays disappear in that cluster," he said.

Fortunate
2007-Nov-11, 04:50 PM
Acknowledgement of dissenting opinions is a standard feature of scientific articles - there always are some. In this case, the remark might suggest a good project for someone interested in pursuing the matter, namely, repeating the analysis with "results from a newer survey."

loglo
2007-Nov-11, 05:00 PM
I'm a little confused about the implications of the study. Are they saying the traditional mass/light ratio is incorrect so our mass estimates of clusters are too high? Which raises the dark matter to baryonic matter fraction even more?

Or is it more that the total amount of mass is less therefore the total amount of baryonic matter is less by the same proportion, but still in the same ratio to dark matter?

Fortunate
2007-Nov-11, 10:48 PM
I'm a little confused about the implications of the study. Are they saying the traditional mass/light ratio is incorrect so our mass estimates of clusters are too high? Which raises the dark matter to baryonic matter fraction even more?

Or is it more that the total amount of mass is less therefore the total amount of baryonic matter is less by the same proportion, but still in the same ratio to dark matter?

Well, the UAH group seems to think that a lot of the x-rays we see in
Abell 3112 and, presumably, other galaxy clusters, are from collisions between relativistic electrons and photons from the CMB rather than from hot gas. This might mean that galaxy clusters contain a lot less gas than we thought.

The articles both contain dramatic but potentially misleading headlines, presumably composed by the magazine writers. The headlines are fun - they've got punch and swagger - but they are more poetic than informative. Both articles contain a number of speculations and suggestions, but, in many cases, I can't tell which of these come from the UAH group and which come from the authors of the articles. The results seem tentative but also cast doubt upon our inferences about the amount of gas in galaxy clusters. The UAH group says that they "want to be sure this is a sound analysis by looking at other clusters." So, as of now, their claim seems to me to be limited to the possibilty that we have overestimated the amount of gas in galaxy clusters because many of the observed x-rays have been produced by electrons.

This is my take on the contents of the articles. I don't think the UAH group directly addressed any of your three questions; I think they are just trying to procede with their investigation of the more limited question of what inferences we should draw from the x-rays we detect from galaxy clusters without making any bold statements about what they think the broader implications would be.

Noclevername
2007-Nov-11, 11:22 PM
You just know some whackos will cite this as "proof" that the Universe is "shrinking".