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How do supermassive blackholes stop star formation?
This article has me wondering a few things.
SPACE.com -- Huge Black Holes Stifle Star Formation "As matter falls towards a black hole, momentum forces it to flatten out into a dense, hot disk. A lot of the matter never makes it into the black hole and is ejected in jets that travel at a significant fraction of light-speed, emanating from the poles of the black hole. Those jets might do such a good job of heating gas near the center of a galaxy that there is little fuel available for the creation of new stars, Yi said. " http://www.space.com/scienceastronom...e_tuesday.html If you need cold gas to start star formation, then how cold is cold? And what temperature do these jets heat the surrounding gas upto that prevents the star formation? Is it preventing star formation throughout the whole galaxy, or just around the vicinity of the blackhole? If it's the whole galaxy, then is the temperature of space within that whole galaxy quite high? Yousuf Khan |
#2
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How do supermassive blackholes stop star formation?
"YK" == Yousuf Khan writes:
YK This article has me wondering a few things. SPACE.com -- Huge Black Holes Stifle Star Formation "As matter falls towards a black hole, momentum forces it to flatten out into a dense, hot disk. A lot of the matter never makes it into the black hole and is ejected in jets that travel at a significant fraction of light-speed, emanating from the poles of the black hole. Those jets might do such a good job of heating gas near the center of a galaxy that there is little fuel available for the creation of new stars, Yi said. " http://www.space.com/scienceastronom...e_tuesday.html Yes, this is a topic of active research. YK If you need cold gas to start star formation, then how cold is YK cold? The gas in molecular clouds from which stars form might have temperatures as low as 10 K. In the center of our own Galaxy, the molecular cloud temperatures appear to be somewhat higher, perhaps 100 K, though stars continue to form. YK And what temperature do these jets heat the surrounding gas upto YK that prevents the star formation? The jets may very well ionize the material around them, which would heat the gas to thousands of degrees. YK Is it preventing star formation throughout the whole galaxy, or YK just around the vicinity of the blackhole? If it's the whole YK galaxy, then is the temperature of space within that whole galaxy YK quite high? Probably just in the immediate vicinity. Part of this issue of course concerns the direction of the jet. Gas at large angles from the jet is probably relatively unaffected. Note that a similar effect is thought to occur in clusters of galaxies. Here the gas surrounding the galaxies should cool and start to produce stars. This isn't observed, and one possible explanation is that a jet from the center of one of the galaxies in the cluster can keep the gas "stirred up" enough that it cannot cool. -- 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
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How do supermassive blackholes stop star formation?
Joseph Lazio wrote:
YK If you need cold gas to start star formation, then how cold is YK cold? The gas in molecular clouds from which stars form might have temperatures as low as 10 K. In the center of our own Galaxy, the molecular cloud temperatures appear to be somewhat higher, perhaps 100 K, though stars continue to form. Okay, so anywhere upto 100 Kelvin seems to be ideal. I assume the gas is denser in the galactic core than in the galactic disk, so that's why 100K is okay in the centre, but 10K is better in the disk? YK And what temperature do these jets heat the surrounding gas upto YK that prevents the star formation? The jets may very well ionize the material around them, which would heat the gas to thousands of degrees. What is the maximum radius of ionization from the centre of the jet? Would it be expressed in the 10's, or 100's, or 1000's of light-years? Or maybe a more fun way to ask would be if a starship were travelling above or below the plane of a galaxy towards its central axis, would it feel "a wind" and get blown off-course at some distance away from the central axis? :-) Note that a similar effect is thought to occur in clusters of galaxies. Here the gas surrounding the galaxies should cool and start to produce stars. This isn't observed, and one possible explanation is that a jet from the center of one of the galaxies in the cluster can keep the gas "stirred up" enough that it cannot cool. Is there a significant amount of gas between the galaxies in a cluster? Enough gas to produce another galaxy perhaps? Yousuf Khan |
#4
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How do supermassive blackholes stop star formation?
In article ,
Yousuf Khan writes: SPACE.com -- Huge Black Holes Stifle Star Formation The preprint is at http://arxiv.org/abs/astro-ph/0608517 . I've had it lying around for a couple of weeks now but haven't had time to read it. "[QSO] jets might do such a good job of heating gas near the center of a galaxy that there is little fuel available for the creation of new stars, Yi said. " Is it preventing star formation throughout the whole galaxy, or just around the vicinity of the blackhole? Bearing in mind that I haven't read the preprint... Jets should easily disrupt star formation in any clouds they hit, but I don't see how jets can affect a very large fraction of the galaxy. Jets occupy too small a solid angle. But presumably the authors know that, so maybe they have a new idea. The idea that star-forming clouds can be disrupted by radiation from an accretion disk -- as opposed to jets -- is not new. There is evidence that such disruption is important in the most luminous objects, but I don't think there is a good understanding of when it's important and when it isn't. Whatever effect there may be, there are distant galaxies that show evidence of rapid star formation despite having a luminous active nucleus. -- Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) |
#5
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How do supermassive blackholes stop star formation?
"SW" == Steve Willner writes:
SW In article , Yousuf Khan SW writes: SPACE.com -- Huge Black Holes Stifle Star Formation SW The preprint is at http://arxiv.org/abs/astro-ph/0608517 . [...] "[QSO] jets might do such a good job of heating gas near the center of a galaxy that there is little fuel available for the creation of new stars, Yi said. " Is it preventing star formation throughout the whole galaxy, or just around the vicinity of the blackhole? The authors imply the entire galaxy. SW Bearing in mind that I haven't read the preprint... SW Jets should easily disrupt star formation in any clouds they hit, SW but I don't see how jets can affect a very large fraction of the SW galaxy. Jets occupy too small a solid angle. But presumably the SW authors know that, so maybe they have a new idea. In my quick skim of the paper, I find no stated mechanism for the quenching effect. Rather, the logic appears to be the following: They conducted ultraviolet observations of a series of early-type galaxies (ellipticals). They found that the amount of UV emission, which traces star formation, is anti-correlated with stellar velocity dispersion (i.e., how fast stars are moving). The stellar velocity dispersion is known to be correlated with central black hole mass. Thus, there appears to be an anti-correlation between black hole mass and star formation, from which the authors infer that central black holes affect their entire galactic environment. I didn't see them state explicitly how this would occur, other than by removing gas from the galaxy which would imply strong winds and/or jets. -- 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 |
#6
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How do supermassive blackholes stop star formation?
"b" == bbbl67 writes:
b Joseph Lazio wrote: YK If you need cold gas to start star formation, then how cold is YK cold? The gas in molecular clouds from which stars form might have temperatures as low as 10 K. In the center of our own Galaxy, the molecular cloud temperatures appear to be somewhat higher, perhaps 100 K, though stars continue to form. b Okay, so anywhere upto 100 Kelvin seems to be ideal. I assume the b gas is denser in the galactic core than in the galactic disk, so b that's why 100K is okay in the centre, but 10K is better in the b disk? It's a value that's accurate to astronomical accuracy. There are large deviations, how the temperature is measured can lead to different results, etc. Nonetheless, if one wants some kind of "typical" value, 10 K certainly works. YK And what temperature do these jets heat the surrounding gas upto YK that prevents the star formation? The jets may very well ionize the material around them, which would heat the gas to thousands of degrees. b What is the maximum radius of ionization from the centre of the b jet? Would it be expressed in the 10's, or 100's, or 1000's of b light-years? I don't know the ionization radius off the top of my head. The jets themselves, at least down at their bases, can be fairly narrow, tens of lightyears. However, I would expect that the area potentially influenced by their radiation could be much larger. Also, I just posted a response to Steve Willner in which I noted that the original paper does not specify in any great detail the mechanism by which they think that the black holes suppress star formation. Note that a similar effect is thought to occur in clusters of galaxies. Here the gas surrounding the galaxies should cool and start to produce stars. This isn't observed, and one possible explanation is that a jet from the center of one of the galaxies in the cluster can keep the gas "stirred up" enough that it cannot cool. b Is there a significant amount of gas between the galaxies in a b cluster? Enough gas to produce another galaxy perhaps? In a typical cluster, there's more gas in the intra-cluster medium than in galaxies. However, much of it is way too hot, 10^7 K or hotter, to cool and condense into stars. While typing this response, it occurred to me that perhaps what the authors of the original paper had in mind was something similar to what is thought to happen in clusters. The observed effect is seen for early-type galaxies, i.e., those with large bulges and little or no disk. Thus, one might suspect that these galaxies formed from large, roughly spherical clouds of gas. If the black hole injected a jet into a large cloud of gas, it could induce significant turbulence, which might have the effect of shutting down star formation. -- 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 |
#7
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How do supermassive blackholes stop star formation?
In article ,
Joseph Lazio writes: In my quick skim of the paper, I find no stated mechanism for the quenching effect. Rather, the logic appears to be the following: They conducted ultraviolet observations of a series of early-type galaxies (ellipticals). They found that the amount of UV emission, which traces star formation, is anti-correlated with stellar velocity dispersion (i.e., how fast stars are moving). .... I didn't see them state explicitly how this would occur, other than by removing gas from the galaxy which would imply strong winds and/or jets. Thanks, Joe. As we all know, correlation does not imply causality. My _guess_ would be that big bulges (indicated by the large velocity dispersions) come from past mergers, which converted gas to stars. Thus current star formation is absent because there is no gas left. That would also explain the absence of dust around luminous active galactic nuclei (AGN), as discovered years ago. The absence might have nothing to do with the AGN itself. As we now know (but didn't back then), luminous AGN are markers for massive bulges. As Joe and probably most readers realize, this is a very active topic of ongoing research, and the very complex relations among galaxy assembly, star formation, and active nuclei are not understood. I've certainly been wrong plenty of times before, and the suggestion above should be treated as speculation and nothing more. -- Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) |
#8
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How do supermassive blackholes stop star formation?
I wrote:
My _guess_ would be that big bulges (indicated by the large velocity dispersions) come from past mergers, which converted gas to stars. Thus current star formation is absent because there is no gas left. Good thing I labelled this as speculation! I've just come from a colloquium given by Christy Tremonti (U. Arizona). She and her colleagues have been studying post-starburst galaxies, and in some of the galaxies they found Mg II absorption lines blue-shifted by about 1000 km/s. That indicates strong gas outflows. Thus simply using up all the gas doesn't seem to be the whole story. It is still an open question whether the outflows were powered by an AGN or something else (presumably some aspect of the star formation process). As I wrote before, this is a very active topic of current research! |
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