Comments on: Really Old Stars? http://asymptotia.com/2006/12/26/really-old-stars/ Sat, 30 Aug 2008 03:38:55 +0000 http://wordpress.org/?v=2.5.1 By: Stephen Uitti http://asymptotia.com/2006/12/26/really-old-stars/#comment-23317 Stephen Uitti Tue, 02 Jan 2007 20:39:42 +0000 http://asymptotia.com/2006/12/26/really-old-stars/#comment-23317 With talk of popIII stars, and the previous post about James Brown, i figured Really Old Stars must include Mic Jagger. Isn't the Milky Way one of the old galaxies - forming in the first billion years? Yeah, we don't have baby pictures of it because we're so close by... With talk of popIII stars, and the previous post about James Brown, i figured Really Old Stars must include Mic Jagger.

Isn’t the Milky Way one of the old galaxies - forming in the first billion years? Yeah, we don’t have baby pictures of it because we’re so close by…

]]> By: Plato http://asymptotia.com/2006/12/26/really-old-stars/#comment-22816 Plato Fri, 29 Dec 2006 14:22:02 +0000 http://asymptotia.com/2006/12/26/really-old-stars/#comment-22816 While an example of luminosity is given, I can't help but think that while gravity had dominated, what would such "lensing" allow us to see what was so far back in time? <a href="http://eskesthai.blogspot.com/2006/12/wolf-rayet-star.html" rel="nofollow">Wolf-Rayet stars?</a> While an example of luminosity is given, I can’t help but think that while gravity had dominated, what would such “lensing” allow us to see what was so far back in time?

Wolf-Rayet stars?

]]> By: Clifford http://asymptotia.com/2006/12/26/really-old-stars/#comment-22708 Clifford Thu, 28 Dec 2006 03:45:11 +0000 http://asymptotia.com/2006/12/26/really-old-stars/#comment-22708 Yes, I'm surprised too. But then we've seen a lot more of these NASA PR drives recently, not all of them with genuinely strong science behind them. It is a bit disturbing. Anybody know if there has been a new policy (or policy-maker) behind the PR offensives? -cvj Yes, I’m surprised too. But then we’ve seen a lot more of these NASA PR drives recently, not all of them with genuinely strong science behind them. It is a bit disturbing.

Anybody know if there has been a new policy (or policy-maker) behind the PR offensives?

-cvj

]]> By: Phil Plait, aka The Bad Astronomer http://asymptotia.com/2006/12/26/really-old-stars/#comment-22704 Phil Plait, aka The Bad Astronomer Thu, 28 Dec 2006 02:58:49 +0000 http://asymptotia.com/2006/12/26/really-old-stars/#comment-22704 Ah, it's good to see Ned here. I have a post entry written up expressing my doubts about this press release as well. My bottom line: even if you have eliminated everything you know, that doesn't eliminate what you don't know. I was a little surprised to see this PR at all, given that it doesn't add a whole lot to the one done in November 2005. I called some folks at Spitzer and found out they did this work on more areas of the sky and at different wavelengths, but all with the same instrument. I suspect that with JWST this can be done better, deeper, and with higher resolution. Maybe then we'll find out one way or another for sure. Ah, it’s good to see Ned here. I have a post entry written up expressing my doubts about this press release as well. My bottom line: even if you have eliminated everything you know, that doesn’t eliminate what you don’t know.

I was a little surprised to see this PR at all, given that it doesn’t add a whole lot to the one done in November 2005. I called some folks at Spitzer and found out they did this work on more areas of the sky and at different wavelengths, but all with the same instrument.

I suspect that with JWST this can be done better, deeper, and with higher resolution. Maybe then we’ll find out one way or another for sure.

]]> By: Clifford http://asymptotia.com/2006/12/26/really-old-stars/#comment-22696 Clifford Thu, 28 Dec 2006 01:52:26 +0000 http://asymptotia.com/2006/12/26/really-old-stars/#comment-22696 Thanks Ned! I have updated my post to point directly to your remarks and paper. Best, -cvj Thanks Ned! I have updated my post to point directly to your remarks and paper.

Best,

-cvj

]]> By: Ned Wright http://asymptotia.com/2006/12/26/really-old-stars/#comment-22688 Ned Wright Wed, 27 Dec 2006 23:08:19 +0000 http://asymptotia.com/2006/12/26/really-old-stars/#comment-22688 You might want to look at http://www.astro.ucla.edu/~wright/cosmolog.htm#18Dec06 When galaxies visible in the HST ACS are masked the IR fluctuation signal goes away [<a href="http://arxiv.org/abs/astro-ph/0612609" rel="nofollow" rel="nofollow">Cooray et al.</a>]. So as usual fluctuations are due to things just barely too faint to catalog and mask, and not to [tex]z > 10[/tex] mystery objects. While the IR background is  [tex]\propto \int nL dr[/tex], with [tex]n[/tex] the number density and [tex]L[/tex] the luminosity of the sources, the fluctuations are   [tex]\propto \int nL^2 r^{-2} dr[/tex] which diverges for small distance   [tex]r[/tex]. You might want to look at http://www.astro.ucla.edu/~wright/cosmolog.htm#18Dec06
When galaxies visible in the HST ACS are masked the IR fluctuation signal goes away [Cooray et al.]. So as usual fluctuations are due to things just barely too faint to catalog and mask, and not to z > 10 mystery objects. While the IR background is  \propto \int nL dr, with n the number density and L the luminosity of the sources, the fluctuations are   \propto \int nL^2 r^{-2} dr which diverges for small distance   r.

]]> By: Plato http://asymptotia.com/2006/12/26/really-old-stars/#comment-22682 Plato Wed, 27 Dec 2006 19:53:04 +0000 http://asymptotia.com/2006/12/26/really-old-stars/#comment-22682 Maybe the stars and galaxies need to rely on geometrical explanations? What came before and what came after? <a href="http://eskesthai.blogspot.com/2006/12/geometrics-behind-supernova-and-its.html" rel="nofollow">Starshine</a> I wonder too how they shall tell the difference of the oldest stars even with our current experimental measures of satellites in space? Maybe the stars and galaxies need to rely on geometrical explanations? What came before and what came after?

Starshine

I wonder too how they shall tell the difference of the oldest stars even with our current experimental measures of satellites in space?

]]> By: Clifford http://asymptotia.com/2006/12/26/really-old-stars/#comment-22680 Clifford Wed, 27 Dec 2006 18:57:11 +0000 http://asymptotia.com/2006/12/26/really-old-stars/#comment-22680 Black holes don't need stars to produce fuel for them. I imagine that it would be enough to have lots of unprocessed light elements like hydrogen and helium. I don't see why stars need be neccessary as a significant percentage of the population int their own right. I did not take your remark as an insult. I was just puzzled as to what the perceived "line" was, since I was not aware of one. I'm happy to hear that you like the posts. -cvj Black holes don’t need stars to produce fuel for them. I imagine that it would be enough to have lots of unprocessed light elements like hydrogen and helium. I don’t see why stars need be neccessary as a significant percentage of the population int their own right.

I did not take your remark as an insult. I was just puzzled as to what the perceived “line” was, since I was not aware of one. I’m happy to hear that you like the posts.

-cvj

]]> By: Cynthia http://asymptotia.com/2006/12/26/really-old-stars/#comment-22678 Cynthia Wed, 27 Dec 2006 18:40:46 +0000 http://asymptotia.com/2006/12/26/really-old-stars/#comment-22678 You're right Clifford! However, I'd like to clarify my point with the following thought... If there were only black holes around without the fuel from popIII stars, then I can't see how black hole accretion ever could have taken place, especially on a cosmic scale. After all, blackholes need some sort of fuel to induce the process of accretion. Otherwise, the black holes would remain in a dormant state, hence, in a permanent Dark Age. In other words, it seems more likely that black holes--along with the fuel from popIII stars--triggered reionization. By the way, I was merely pointing out that you tend to post on astronomy topics slightly more often than other high-energy physics bloggers: a tendency which I truly enjoy alot! Please don't take this comment as an insult. In fact, I was trying to give you a sincere compliment! Best, Cynthia You’re right Clifford! However, I’d like to clarify my point with the following thought… If there were only black holes around without the fuel from popIII stars, then I can’t see how black hole accretion ever could have taken place, especially on a cosmic scale. After all, blackholes need some sort of fuel to induce the process of accretion. Otherwise, the black holes would remain in a dormant state, hence, in a permanent Dark Age. In other words, it seems more likely that black holes–along with the fuel from popIII stars–triggered reionization.

By the way, I was merely pointing out that you tend to post on astronomy topics slightly more often than other high-energy physics bloggers: a tendency which I truly enjoy alot! Please don’t take this comment as an insult. In fact, I was trying to give you a sincere compliment!

Best,
Cynthia

]]> By: Clifford http://asymptotia.com/2006/12/26/really-old-stars/#comment-22672 Clifford Wed, 27 Dec 2006 17:17:48 +0000 http://asymptotia.com/2006/12/26/really-old-stars/#comment-22672 <blockquote> In my mind’s eye, a blanket of black holes stretching across the Cosmos could only act to keep the Universe in a state of a permanent Dark Age. </blockquote> I don't see what your minds' eye sees. Why can't this be powered by accretion phenomena surrounding a black hole just as well as fusion processes in a star. At least to a first approximation, I'm not seeing why the former can't work. <blockquote> occasionally stepping out of line and posting on astronomy matters </blockquote> Huh? Which line? I post on any topic I care about whether it be, in science, physics, mathematics, chemistryh, biology, ..... Actually, I think I've posted more on astronomy than any other topic so far. I don't understand what you mean. Cheers, -cvj

In my mind’s eye, a blanket of black holes stretching across the Cosmos could only act to keep the Universe in a state of a permanent Dark Age.

I don’t see what your minds’ eye sees. Why can’t this be powered by accretion phenomena surrounding a black hole just as well as fusion processes in a star. At least to a first approximation, I’m not seeing why the former can’t work.

occasionally stepping out of line and posting on astronomy matters

Huh? Which line? I post on any topic I care about whether it be, in science, physics, mathematics, chemistryh, biology, ….. Actually, I think I’ve posted more on astronomy than any other topic so far. I don’t understand what you mean.

Cheers,

-cvj

]]> By: Cynthia http://asymptotia.com/2006/12/26/really-old-stars/#comment-22669 Cynthia Wed, 27 Dec 2006 16:11:28 +0000 http://asymptotia.com/2006/12/26/really-old-stars/#comment-22669 I'm a little skeptical about this claim that black holes triggered a full-scale reionization of the Universe. In fact, I image the contrary. In my mind's eye, a blanket of black holes stretching across the Cosmos could only act to keep the Universe in a state of a permanent Dark Age. However, it seems more plausible that popIII stars and black holes could operate in tandem to generate the second great phase change called reionization: the phase change which induced the brilliant epoch known as "First Light". By the way, Clifford, thanks for occasionally stepping out of line and posting on astronomy matters from time to time.;) I’m a little skeptical about this claim that black holes triggered a full-scale reionization of the Universe. In fact, I image the contrary. In my mind’s eye, a blanket of black holes stretching across the Cosmos could only act to keep the Universe in a state of a permanent Dark Age. However, it seems more plausible that popIII stars and black holes could operate in tandem to generate the second great phase change called reionization: the phase change which induced the brilliant epoch known as “First Light”.

By the way, Clifford, thanks for occasionally stepping out of line and posting on astronomy matters from time to time.;)

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