A Space & astronomy forum. SpaceBanter.com

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Astronomy Misc
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Prospects for observation beyond the CMBR



 
 
Thread Tools Display Modes
  #1  
Old August 13th 03, 10:47 PM
George Dishman
external usenet poster
 
Posts: n/a
Default 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


Ads
  #2  
Old September 18th 03, 08:44 PM
Joseph Lazio
external usenet poster
 
Posts: n/a
Default 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  
Old September 18th 03, 11:12 PM
George Dishman
external usenet poster
 
Posts: n/a
Default 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

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

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


All times are GMT +1. The time now is 11:39 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright 2004-2019 SpaceBanter.com.
The comments are property of their posters.