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#31
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Star age Measurements
Dear Steve Willner:
On Wednesday, May 29, 2013 2:00:02 PM UTC-7, Steve Willner wrote: SW One would have to ask, though, if low-metal stars are SW forming now, why don't we see any low-metal gas? In article , dlzc writes: With space filled (in some sense) with ionized hydrogen and oxygen missing 5 electrons, how would we know if some of the hydrogen was new? What gas has oxygen missing five electrons? http://arstechnica.com/science/2012/...urrounding-us/ http://www.princeton.edu/pr/pwb/00/0...ostfound.shtml http://astronomy.nmsu.edu/cwc/Group/QALsims/ More to the point, I thought you were suggesting stars forming out of "new hydrogen" that lacks metals. If that's happening, where is this low-metallicity gas, and why don't we see it? Ionized gas is hard to see in visible range, unless pressure is high enough to allow recombination. SW As has been written in this thread, globular SW clusters are assumed to be old because of SW their HR diagrams. Which was in turn, scaled in light of a Big Bang. Why do you continue to assert that? What logic was used to arrive at "0 age"? I am continually told I am "wrong", without citation. As has been explained _multiple_ times in this thread, the cluster ages are based entirely on atomic physics. In other words, we observe a cluster with a maximum main sequence luminosity of, say, half a solar luminosity. Via stellar evolution theory (detailed computer models), *calibrated how*? stars of that luminosity have about 0.8 solar masses and take about 9 Gyr to evolve off the main sequence. (I'm making up all the numbers, but they are probably in the ballpark.) Thus the cluster is 9 Gyr old. This has nothing whatever to do with the Big Bang. Yes, you keep saying that... The models might, of course, be wrong (though they are well tested on the Sun, for example, and other stars for which one can measure independent masses or structures), but there is nothing circular about the reasoning. And you keep saying that too. Or the bullet cluster, where "all" the dust is removed, and we can see none of the stars. You have some strange misconception, but I'm baffled by what it could be. Are you equating "dust" with "dark matter?" Dust is lit by visible light, and consequently makes the associated stars look somewhat cooler. But also large enough to see at that distance. Dust is dark in visible light, but it isn't what is meant by "dark matter." In particular, most dust glows quite nicely in the infrared, and in any case there are direct methods of detecting dust. In all cases I can think of, it is a tiny fraction of the mass. Yes, just drying to get to the "visibility". We know there are extra-galactic stars by the "scads", but we cannot see them, since they have no dust... Interpretation of the Bullet Cluster has nothing to do with dust. I disagree, but let's move on. Again, I am simply filling in where the OP is lacking in clarity... and I guess I am doing poorly. When yo look at a nebula, say the ring nebula, what is its most prominent feature, the white dwarf, or the nebula? What does this have to do with the light from galaxies? Visibility. You keep asking me where this gas is, and I keep pointing out we "only" know where the dust is that is "backlit", like a shadow play. So we don't even know where the *stars* are. A gaseous nebula is an extended source of light. Sizes run from perhaps a tenth of a parsec to tens of parsecs. A collection of stars, if you have high enough resolution, can be separated into individual objects. Separations are typically a parsec near the Sun and somewhat smaller in globular clusters or galactic cores. (If you have resolution 7 or 8 orders of magnitude better than a parsec, you could resolve the stellar surfaces themselves, but that's quite a leap from resolving the cluster or galaxy.) Sidelight... if we had three satellites in trojan with Earth, could we do VBLA techniques to achieve such resolution? Seriously Steve, if you need to end this, just don't ask me questions. The OP has lamed out, so no need in continuing unless you need to hammer the lid on some "crap" I have spouted... And thank you. David A. Smith |
#32
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Star age Measurements
SW What gas has oxygen missing five electrons?
In article , dlzc writes: http://arstechnica.com/science/2012/...urrounding-us/ http://www.princeton.edu/pr/pwb/00/0...ostfound.shtml http://astronomy.nmsu.edu/cwc/Group/QALsims/ The first two refer to extremely hot and low-density gas that isn't forming stars. I'm not sure of the point of the third one. Yes, the very tenuous intergalactic gas is probably low metallicity, but I doubt it's primordial. Wasn't the recent detection in X-rays based on an iron line? Ionized gas is hard to see in visible range, unless pressure is high enough to allow recombination. You meant "temperature is low enough" in that last (though density comes into it, too). However, most (if not all) regions in the Milky Way where we know stars are forming are associated with ionized gas, and we can measure the gas metallicity. It's roughly solar, depending on the specific cloud. What logic was used to arrive at "0 age"? Any cluster with high luminosity (=high mass) stars must be young. That mostly means open clusters rather than globulars; the Orion Nebula cluster is (without looking up the actual value) probably at most a few Myr old. The Pleiades age estimate changed a few years ago, but I think it's of order 100 Myr now. I am continually told I am "wrong", without citation. It's easy to look in ADS. http://adsabs.harvard.edu/abs/2013A%26A...549A..60C is a recent detailed analysis of many globular clusters in M31 and the Milky Way. The lowest age they find is 150 Myr. http://adsabs.harvard.edu/abs/2010PASP..122..991D is a detailed analysis of one specific cluster. As I say, it's not hard to find more, and there are probably course lecture notes on the web. SW Via stellar evolution theory (detailed computer models), *calibrated how*? I'm not an expert, but models have to fit the Sun, which has exquisite helioseismology results for all but the inner 5% of its radius. Some other stars have stellar seismology, and stars in binary systems have known masses and distances. Models also have to fit laboratory data on opacity and nuclear cross sections. All that doesn't mean the models are perfect, but the models assume nothing whatever about a Big Bang or any other cosmology. Why do you think the reasoning is circular? Do you think astronomers wouldn't be aware of it if it were? Dust is lit by visible light, and consequently makes the associated stars look somewhat cooler. But also large enough to see at that distance. Ah. That's a misconception all right. You can take credit for its originality. The Sun has an absolute visual magnitude of 4.8. If you put it at the distance of the Virgo Cluster, which has a distance modulus of about 31, the Sun would have an apparent magnitude of about 36. That's far too faint to see with existing instruments, but it's not zero flux density. Add, say, 10^11 similar stars, and the apparent magnitude of the collection would be 8.5, easily visible in a small telescope. In fact, M87, the brightest galaxy in the cluster, has a visual magnitude of around 8.6, pretty close to this figure. None of this has anything to do with dust, let alone making a star "large enough to see." There are only rare instances in astronomy where visible light is seen via reflection from dust. (You can look up "reflection nebulae" for the most prominent examples.) Typically dust along the line of sight absorbs light on its way to us and thereby makes stars appear fainter than they would if there were no dust. Dust absorbs blue light more than red light, so it also makes stars appear redder. (Maybe that's what you were thinking of when you wrote "somewhat cooler.") Taking this into account is not always easy, but most globular clusters have essentially no internal dust. Adding dust would make them fainter, not brighter. (All this refers to visible light. Things are different in the infrared, where the dust actually does emit light, but even there, reflection is not relevant in most cases.) We know there are extra-galactic stars by the "scads", but we cannot see them, since they have no dust... That last isn't the reason. Adding dust would make such stars fainter, not brighter. Such stars are invisible because they are just too faint by themselves. However, you might look up "Magellanic Stream" for stars that have been tidally pulled out of the LMC and are visible in the Sloan Digital Sky Survey. When yo look at a nebula, say the ring nebula, what is its most prominent feature, the white dwarf, or the nebula? SW What does this have to do with the light from galaxies? Visibility. You keep asking me where this gas is, and I keep pointing out we "only" know where the dust is that is "backlit", like a shadow play. So we don't even know where the *stars* are. The Ring Nebula doesn't glow (in visible light) because of dust. In general, gaseous nebulae aside, visible light measures where stars are. You can do even better in the near infrared, out to wavelengths of say 2 microns or so, but that's a minor technical point. The basic point is that your misconception about needing dust to make stars visible has given you the wrong idea. Sidelight... if we had three satellites in trojan with Earth, could we do VBLA techniques to achieve such resolution? There has been satellite VLBA done from low Earth orbit. In principle the technique should work at longer baselines, but depending on the frequency, there may be practical limitations from interplanetary scintillation or other effects. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
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Star age Measurements
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#34
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Star age Measurements
In article ,
Odysseus writes: I'm not sure about the Ring, but in many planetary nebulae, and occasionally elsewhere, the glow we see is fluorescence: The visible glow from gaseous nebulae, including ionized hydrogen regions such as the Orion Nebula, is indeed from the gas, not reflected starlight. The visible light is not continuum emission at all wavelengths but rather is concentrated in emission lines at discrete wavelengths. (There is some continuum emission, too, but it's weak.) The basic physical processes were worked out in the 1930s. Fluorescence is part of the story (look up "Bowen fluorescence mechanism"), but a bigger part is collisional excitation of ions by electrons. The hydrogen and helium lines come from recombination. That's in visible light. Emission processes at other wavelengths differ. In particular, the infrared has continuum emission from dust. This is not reflected starlight either. There are "reflection nebulae" and a few other cases where starlight reflected by dust is important (including the Sun's "F corona"), but overall such cases are pretty rare. X-ray and UV emissions from very hot stars excite the surrounding gas (otherwise cool and invisible) to re-emit down-spectrum in the visible range. Basically right, but UV is pretty much the whole story. There aren't enough X-rays to do much excitation. Stellar temperatures in PN central stars range from roughly 30000 K to upwards of 100000 K. In H II regions, stellar temperatures can be somewhat lower, perhaps down to 15000 K. The UV from the hot stars ionizes nearby gas, and the various processes lead to emission from the gas. Modulated starlight, if you will, rather than simply reflected, and a little like our own aurorae. I think the aurorae are also collisional excitation by electrons, but the specific atoms or ions are not all the same as in ionized nebulae. Dust is harder to excite than gas. Yes, in visible light. When dust absorbs visible or UV light, the dust heats up, and warm dust radiates in the infrared. In equilibrium, the energy in has to equal the energy out. The net effect is converting visible or UV light to infrared, so it's the same sort of outcome, but the physical process is different. The interior of the vast SNR-bubble whose outer margins form the Veil Nebula shows noticeably more stars than the surrounding area, apparently because the region has been 'blown clear'. In general, star counts can be used to measure extinction: more stars, less extinction. Of course you have to be sure the true number of background stars is constant, so the method only works over limited areas. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#35
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Star age Measurements
On May 17, 5:44*am, David Levy
wrote: I would like to get your advice with regards to the Star age Measurements. This is critical element for any theory. This is a key element for confirming the Big bang theory. Therefore, I was quite surprise to find that this key measurement is actually based on the Big Bang theory. Based on Wiki it is stated: "The metallicity of an astronomical object may provide an indication of its age. When the universe first formed, according to the Big Bang theory, it consisted almost entirely of hydrogen which, through primordial nucleosynthesis, created a sizeable proportion of helium and only trace amounts of lithium and beryllium and no heavier elements. Therefore, older stars have lower metallicities than younger stars such as our Sun." So the science is measuring the star age based on the fundamental Idea of the Big bang. With the results of the star age they are coming back and reconfirm the Big bang theory. This might be radicals and contradicts a basic common sense. I assume that without the big bang theory, the Science could develop some other method for Star age measurements. Please advice. -- David Levy Mainstream science and even its physics is highly dependent upon the Big Bang, even though there's nothing objectively supporting the BB. In other words, we get to make do with our mainstream of circular logic instead of objective proof of anything that truly matters. Original BB stars of perhaps at least 1000+ solar mass(2+e33 kg) and supposedly comprised of only hydrogen that lasted at best a few years, is where that initial hydrogen fusion process created helium and eventually every other known element of metallicity. So, newer stars are those of considerably lower mass (under 10 SM), as well as having a much higher helium content and/or hosting those heavier elements of metals as well as their having created numerous planets that by now should far outnumber all the stars (including brown dwarfs that are actually large gas giants with perhaps a hundred moons each) combined. Some of us would speculate there's at least a thousandfold as many planets as stars, and the vast majority of them planets got created a billion years before our solar system even formed. The rate of hydrogen fusion consumption can be used to estimate the given age and/or lifespan of stars, although helium fusion driven stars are entirely another issue. |
#36
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Star age Measurements
Dear Brad Guth:
On Tuesday, June 11, 2013 9:06:45 AM UTC-7, Brad Guth wrote: .... Mainstream science and even its physics is highly dependent upon the Big Bang, even though there's nothing objectively supporting the BB. Say what? In other words, we get to make do with our mainstream of circular logic instead of objective proof of anything that truly matters. We can use actual data to get us back to a few hundred million years of the CMBR. And this data without "assuming" a Big Bang, points to a much smaller Universe at that time. Beyond this CMBR curtain, Science does not do "proof", you know this, yet you continue posturing. We have theory where we have data, and cosmology (including the Big Bang) is largely "extrapolation" at best. Does lying include what you think "truly matters"? Please do not continue to present Science arriving at any sort of proof, or failing because it *never* can do this. Only Religion, Philosophy, and Law have proofs. David A. Smith |
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