|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Questions about Lyman-alpha forest
In the web site:
https://medium.com/starts-with-a-ban...r-1b2f992ac353 Astronomer Ethan Siegal writes: quote Ask Ethan #66: Did we just find dark matter? Not a chance. What we've found may be a mystery, but it’s definitely not our Universe's missing mass. end quote Then, he comes to the proof. He says: quote By looking at how deep these 'forest lines' are, especially early on, we can constrain how light dark matter is allowed to be. Even under the most liberal of circumstances, we can see that the absorption lines are incredibly strong --- consistent with dark matter being incredibly cold --- which means it has to be at least above a certain mass threshold. Well, what is that threshold? It has to be, at this point in time, heavier than about 10 keV, based on the strength of the observed absorption lines. In other words, about a factor of 3 heavier (or 50% heavier, for a decaying particle) that this supposed 'dark matter signal' is! end quote I would like to have a reference (or book, whatever) where I could understand (1) why "deep" lines imply cold matter (2) why cold matter imposes a mass threshold. Actually, a book would be better than a paper, if possible. Thanks in advance [Mod. note: non-ASCII characters removed. Please, please, please, learn to do this yourself -- mjh] |
#2
|
|||
|
|||
Questions about Lyman-alpha forest
In article , jacob navia
writes: In the web site: https://medium.com/starts-with-a-ban...r-1b2f992ac353 Astronomer Ethan Siegal writes: quote Ask Ethan #66: Did we just find dark matter? Not a chance. What we've found may be a mystery, but it's definitely not our Universe's missing mass. end quote Then, he comes to the proof. He says: quote By looking at how deep these 'forest lines' are, especially early on, we can constrain how light dark matter is allowed to be. Even under the most liberal of circumstances, we can see that the absorption lines are incredibly strong --- consistent with dark matter being incredibly cold --- which means it has to be at least above a certain mass threshold. Well, what is that threshold? It has to be, at this point in time, heavier than about 10 keV, based on the strength of the observed absorption lines. In other words, about a factor of 3 heavier (or 50% heavier, for a decaying particle) that this supposed 'dark matter signal' is! end quote I would like to have a reference (or book, whatever) where I could understand (1) why "deep" lines imply cold matter (2) why cold matter imposes a mass threshold. Apparently he is talking about absorption lines in a spectrum. If the material is hot, Doppler broadening will make the lines less "deep". He seems to be saying as well that the particles have a minimum mass which is heavier than that of putative dark-matter particles. |
#3
|
|||
|
|||
Questions about Lyman-alpha forest
On 12/14/14, 3:35 AM, jacob navia wrote:
[Mod. note: entire quoted article removed -- mjh] "deep lines" may relate to spectral absorbance as related to hydrogen species concentration. Ethan may be using the term 'deep' representing the area under absorbance curve related to a particular species concentration (or density). The deeper the absorbance, the greater the concentration (or density). Then density~1/Temperature is used to conceptually indicate a mass (density?) threshold. This concept is used in chemistry instrumental analysis but there is always a standard, something that is not obvious here. Richard D Saam |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Lyman alpha question | sean | Astronomy Misc | 9 | June 28th 06 11:37 PM |
"our mind is a virgin forest | Twittering One | Misc | 16 | September 24th 05 06:59 PM |
'forest' of solar proms | nytecam | Amateur Astronomy | 8 | September 22nd 05 08:27 AM |
lyman-inf absorption spectra | Oz | Research | 6 | December 3rd 04 03:01 PM |