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New A&A Paper On Astrophysical Dark Matter
On Thursday, March 12, 2015 at 4:11:27 PM UTC-4, Phillip Helbig (undress to reply) wrote:
40 years ago, it wasn't the leading candidate. By a process of elimination, it is left standing while essentially all other candidates have been ruled out. -------------------------------- Do you still contend that the MACHO dark matter candidacy has been "ruled out", i.e., falsified and/or no longer a viable hypothesis? |
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New A&A Paper On Astrophysical Dark Matter
In article ,
Gary Harnagel writes: If you look at a chart of star types versus fraction of stars in that category, the less massive the star, the larger the fraction. Down to some mass perhaps 1/3 or 1/4 of the Sun's. Below that, the fraction decreases. See review by Chabrier (2003 PASP, 115, 763: http://www.jstor.org/stable/10.1086/376392 , especially Fig 2) for an example. I suppose there's more recent work. Does this relationship continue for smaller masses (to Jupiter-size and below)? It's hard to know, but there are limits based on gravitational lensing observations. Could it not be that interstellar space is full of this junk? Depends on the quantitative definition of "full of." There are quite likely many objects, but their overall contribution to the mass budget is probably negligible. -- 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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New A&A Paper On Astrophysical Dark Matter
In article , "Robert L.
Oldershaw" writes: On Thursday, March 12, 2015 at 4:11:27 PM UTC-4, Phillip Helbig (undress to reply) wrote: 40 years ago, it wasn't the leading candidate. By a process of elimination, it is left standing while essentially all other candidates have been ruled out. -------------------------------- Do you still contend that the MACHO dark matter candidacy has been "ruled out", i.e., falsified and/or no longer a viable hypothesis? If you mean that most of the cosmological dark matter cannot be in the form of planet-to-star--size compact objects, yes. Is there anyone apart from yourself and Mike Hawkins who thinks otherwise? If so, can you point me to a refereed-journal paper published within the last 5 years? |
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New A&A Paper On Astrophysical Dark Matter
On Saturday, March 14, 2015 at 10:03:08 AM UTC-6, Phillip Helbig (undress to reply) wrote:
In article , "Robert L. Oldershaw" writes: Do you still contend that the MACHO dark matter candidacy has been "ruled out", i.e., falsified and/or no longer a viable hypothesis? If you mean that most of the cosmological dark matter cannot be in the form of planet-to-star--size compact objects, yes. Is there anyone apart from yourself and Mike Hawkins who thinks otherwise? If so, can you point me to a refereed-journal paper published within the last 5 years? Well, Steve W. disabused me of that possibility, and I feel relieved :-) However, I'm skeptical of most candidates being tossed around, except this one: http://en.wikipedia.org/wiki/Mirror_matter "If mirror matter does exist in large abundances in the universe and if it interacts with ordinary matter via photon-mirror photon mixing, then this could be detected in dark matter direct detection experiments such as DAMA/NaI and its successor DAMA/LIBRA. In fact, it is one of the few dark matter candidates which can explain the positive DAMA/NaI dark matter signal whilst still being consistent with the null results of other dark matter experiments." Gary |
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New A&A Paper On Astrophysical Dark Matter
On Saturday, March 14, 2015 at 12:03:08 PM UTC-4, Phillip Helbig (undress to reply) wrote:
Is there anyone apart from yourself and Mike Hawkins who thinks otherwise? If so, can you point me to a refereed-journal paper published within the last 5 years? ---------------------------------- The latest paper by Hawkins cites several published papers by microlensing groups that have estimated that 10-30% of the dark matter could reasonably be explained by MACHOs. As Hawkins points out, the limits to how much MACHOs might contribute to the dark matter total are complicated by modeling assumptions and fraught with uncertainties. My guess is that few would dare to believe that 100% of the dark matter will turn out to be MACHOs, but I also think that those with expertise in microlemsing research would not summarily and absolutely rule out that hypothesis given the well-known uncertainties, the positive evidence for MACHOs, the continuing discoveries of new astrophysical populations, and the very long trend of negative results for any form of particle dark matter. But thank you for your answer. It is the kind of line-in-the-sand I like. [Mod. note: reformatted -- mjh] |
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New A&A Paper On Astrophysical Dark Matter
Le 17/03/2015 05:22, Robert L. Oldershaw a écrit :
the continuing discoveries of new astrophysical populations I was surprised you did not comment when I reported here the discover that the plane of Andromeda extends to more than 1 million light years, MUCH bigger than the visible part. (http://arxiv.org/abs/1301.0446) Other examples: For instance (http://www.sciencedaily.com/releases...11124139.htm): quote The Milky Way galaxy is at least 50 percent larger than is commonly estimated, according to new findings that reveal that the galactic disk is contoured into several concentric ripples. end quote |
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