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?

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.

--
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Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

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?

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

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]

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