|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Prospects for observation beyond the CMBR
"Steve Willner" wrote in message ... In article , "George Dishman" writes: We are now getting good data from the CMBR in particular from WMAP but that only goes back to around 300k years at z=1089+/-97. The most obvious previous observable would be relic neutrinos. I have not been able to find an estimate of z for them but it would obviously be much higher than that for the CMBR and since even solar neutrinos are hard to detect, relic neutrinos will be even more difficult. As you say, they decouple earlier than the recombination epoch, and then their temperature drops as R^-4 while the temperature of everything else is dropping as R^-3. Thus they will be much colder than the microwave background. I remember seeing that a few times now you mention it. The rate was higher in the 'radiation dominated' era. Can anyone tell me a rough value for z for neutrinos from when they decoupled and say whether there is a credible prospect for producing a detector capable of imaging them like WMAP? It must be approximately at the epoch when temperature corresponded to a few MeV, i.e., about when deuterium and helium are being created, but I bet there's a more precise number around somewhere. Ouch, that's low. Thanks Steve, that gives me another keyword or two for searches, I appreciate your reply. Detecting such low-energy neutrinos looks hopeless to me, but there are plenty of people cleverer than I am. Given what SuperKamiokande and the new one in the Antarctic are achieving, I wouldn't rule out anything over the coming decades. best regards George |
#2
|
|||
|
|||
Prospects for observation beyond the CMBR
"GD" == George Dishman writes:
GD The most obvious previous observable would be relic neutrinos. I GD have not been able to find an estimate of z for them but it would GD obviously be much higher than that for the CMBR and since even GD solar neutrinos are hard to detect, relic neutrinos will be even GD more difficult. GD Can anyone tell me a rough value for z for neutrinos from when GD they decoupled and say whether there is a credible prospect for GD producing a detector capable of imaging them like WMAP? I'm looking at the discussion in MTW's _Gravitation_. They estimate that neutrinos decoupled from matter at a time about 100 seconds or when the scale factor was about 1E-9 of its current value. That would suggest a redshift z ~ 1E9. There's also some discussion at URL:http://www.astro.soton.ac.uk/%7Etrm/PH421/notes/notes/node152.html describing why the temperature of the cosmic neutrino background should be T ~ 2 K, lower than that of the cosmic microwave background. The neutrino temperature is lower because after they decouple, their temperature simply decreases with the Universal expansion. In contrast, the photons are heated by electron-positron annihilation that occurs later. -- Lt. Lazio, HTML police | e-mail: No means no, stop rape. | http://patriot.net/%7Ejlazio/ sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html |
#3
|
|||
|
|||
Prospects for observation beyond the CMBR
"Joseph Lazio" wrote in message ... "GD" == George Dishman writes: GD The most obvious previous observable would be relic neutrinos. I GD have not been able to find an estimate of z for them but it would GD obviously be much higher than that for the CMBR and since even GD solar neutrinos are hard to detect, relic neutrinos will be even GD more difficult. GD Can anyone tell me a rough value for z for neutrinos from when GD they decoupled and say whether there is a credible prospect for GD producing a detector capable of imaging them like WMAP? I'm looking at the discussion in MTW's _Gravitation_. I'm still struggling with D'Inverno :-( They estimate that neutrinos decoupled from matter at a time about 100 seconds or when the scale factor was about 1E-9 of its current value. That would suggest a redshift z ~ 1E9. There's also some discussion at URL:http://www.astro.soton.ac.uk/%7Etrm/PH421/notes/notes/node152.html describing why the temperature of the cosmic neutrino background should be T ~ 2 K, lower than that of the cosmic microwave background. The neutrino temperature is lower because after they decouple, their temperature simply decreases with the Universal expansion. In contrast, the photons are heated by electron-positron annihilation that occurs later. Thank you Joseph, as always you have given me just the start I needed. I doubt we'll be able to detect them in my lifetime. Thanks. George |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Correlation between CMBR and Redshift Anisotropies. | The Ghost In The Machine | Astronomy Misc | 172 | August 30th 03 10:27 PM |
Very heavy lift vehicle prospects? | MattWriter | Policy | 8 | August 23rd 03 05:53 PM |
CMBR question | [email protected] \(formerly\) | Astronomy Misc | 1 | August 14th 03 12:56 AM |