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Another candidate for Dark Matter in spiral galaxies, weighs in...
http://groups.google.com/group/sci.s...9b729a0725bb1d
.... if the Milky Way is not too special... David A. Smith |
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Another candidate for Dark Matter in spiral galaxies, weighsin...
On 26/02/2012 10:30 AM, dlzc wrote:
http://groups.google.com/group/sci.s...9b729a0725bb1d ... if the Milky Way is not too special... David A. Smith Well, invisible planets are part of the MACHO form of dark matter, so it's not really a new candidate. But we mustn't talk about MACHO's, they don't fit in with the prevailing sci-fi aspect of modern cosmology. Besides, even if there are billions of planets floating around out there, they are tiny compared to stars. Each star outweighs a Jupiter mass planet by around a 1000 times. You'd need a trillion Jupiter mass planets just to weigh about the same as the population of stars in the Milky Way, and dark matter is supposed to not just weigh as much as normal matter, but to outweigh it by 10 times at least. So you'd need 10 trillion Jupiters floating out there. If there were 10 trillion Jupiters, then no matter how big the Milky Way was, you should be able to see several of them in the immediate neighbourhood. Yousuf Khan |
#3
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Another candidate for Dark Matter in spiral galaxies, weighs in...
Dear Yousuf Khan:
On Thursday, March 1, 2012 10:57:19 PM UTC-7, Yousuf Khan wrote: On 26/02/2012 10:30 AM, dlzc wrote: http://groups.google.com/group/sci.s...9b729a0725bb1d ... if the Milky Way is not too special... Well, invisible planets are part of the MACHO form of dark matter, so it's not really a new candidate. But we mustn't talk about MACHO's, they don't fit in with the prevailing sci-fi aspect of modern cosmology. Well, as long as they continue to try and disprove such such hypotheses, I can't bitch too much. Besides, even if there are billions of planets floating around out there, they are tiny compared to stars. Each star outweighs a Jupiter mass planet by around a 1000 times. You'd need a trillion Jupiter mass planets just to weigh about the same as the population of stars in the Milky Way, and dark matter is supposed to not just weigh as much as normal matter, but to outweigh it by 10 times at least. So you'd need 10 trillion Jupiters floating out there. And if our estimates of interstellar "gas" density is based on it not being a plasma, we'll have most of what is required. If there were 10 trillion Jupiters, then no matter how big the Milky Way was, you should be able to see several of them in the immediate neighbourhood. We've found brown stars, which brings down the count, and there is still the evidence for a 4x Jupiter planet around the Sun (Tyche). We haven't *seen* it yet. Between neglecting the center of spiral galaxies as swept clean, where luminosity vs. total normal mass is calibrated, and the "surprising" collections of normal mass, I think we are getting much closer to killing Dark Matter as some new exotic particle to be looked for in/around spiral galaxies. More to be seen... David A. Smith |
#4
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Another candidate for Dark Matter in spiral galaxies, weighs in...
On 26/02/2012 10:30 AM, dlzc wrote:
http://groups.google.com/group/sci.s...9b729a0725bb1d (is actually a press release about possible life on nomad planets) In article , Yousuf Khan writes: Well, invisible planets are part of the MACHO form of dark matter, so it's not really a new candidate. Right, not a new candidate at all. Existing upper limits say that nomad planets are at most 10% or so of the Milky Way dark matter halo. But we mustn't talk about MACHO's, they don't fit in with the prevailing sci-fi aspect of modern cosmology. There have been several past searches for MACHOs, and at least one is ongoing. That's where the upper limits (and recent detections) come from. Besides, even if there are billions of planets floating around out there, they are tiny compared to stars. Each star outweighs a Jupiter mass planet by around a 1000 times. Yes, that's the point. Some years ago, my favorite candidate for baryonic dark matter was very old (hence very cold) white dwarfs. At something close to a solar mass each, you wouldn't need a gigantic number of them. By now, though, the MACHO searches seem to have ruled these out, at least in sufficient numbers to explain the dark matter halo. -- 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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