[Mod. note: this article arrived in my moderation mailbox with a number
of garbled non-ASCII characters. I have fixed things up as best as I can;
my apologies to the author if I've mis-inferred his intended meaning.
-- jt]]
What do people think of the recent claim in Nature that one of the new
wide field instruments has found a candidate diffuse galaxy NGC1052-DF2
which appears to have little or no dark matter in it?
http://nature.com/articles/doi:10.1038/nature25767
[[Mod. note -- Open-access preprint
https://arxiv.org/abs/1803.10237
-- jt]]
If their result is confirmed then it would presumably put the nail in
the coffin of all modified gravity theories and the search for the
mysterious cold dark matter that only interacts via gravity will hot up.
Finding a diffuse galaxy with a velocity dispersion that shows there is
only baryonic matter in suggests that dark matter really does exist.
Dynamically can anyone see how a bunch of stars could be peeled off by a galaxy galaxy interaction without also taking dark matter with it?
Thanks for any enlightenment.
http://nature.com/articles/doi:10.1038/nature25767
[[Mod. note -- Open-access preprint
https://arxiv.org/abs/1803.10237
-- jt]]
If their result is confirmed then it would presumably put the nail in
the coffin of all modified gravity theories
Finding a diffuse galaxy with a velocity dispersion that shows there is
only baryonic matter in suggests that dark matter really does exist.
Dynamically can anyone see how a bunch of stars could be peeled off by a galaxy galaxy interaction without also taking dark matter with it?
In article <p9kvng$nti$1@gioia.aioe.org>,
Martin Brown <newspam@nezumi.demon.co.uk> writes:
http://nature.com/articles/doi:10.1038/nature25767
[[Mod. note -- Open-access preprint
https://arxiv.org/abs/1803.10237
-- jt]]
That's a remarkable result. The authors have covered all the
possible objections that occur to me, though I'm not 100% convinced
that the galaxy can't be rotationally supported and face-on. The
authors make a good case against, though.
If their result is confirmed then it would presumably put the nail in
the coffin of all modified gravity theories
A few more cases such as this one should do it.
Mod. note -- I suspect that the author has inadvertently omitted
"does NOT" or some similar wording in the previous sentence, and meant
to write something like this:
For those not
following, the argument is that in most galaxies and galaxy clusters,
the mass of detectable stars exerting Newtonian gravity does not
account for the observed motions.
My apologies if I've misunderstood the author's intent here!
-- jt
]]
Therefore, _either_ there is more mass than
that of the visible stars ("dark matter"), _or_ the Newtonian gravity
law is wrong. However, we know Newtonian gravity is right in our
solar system (except for tiny GR corrections) and in objects as large
as globular clusters, so if the gravity law is the problem,
modification ("MOND") is required only in objects as large as
galaxies. Here we have a large galaxy where no modified gravity law
is needed. If MOND is right, how can it fail to apply to this
galaxy?
What do people think of the recent claim in Nature that one of the new
wide field instruments has found a candidate diffuse galaxy NGC1052-DF2
which appears to have little or no dark matter in it?
Open-access preprint https://arxiv.org/abs/1803.10237
If their result is confirmed then it would presumably put the nail in
the coffin of all modified gravity theories and the search for the
mysterious cold dark matter that only interacts via gravity will hot up.
Finding a diffuse galaxy with a velocity dispersion that shows there is
only baryonic matter in suggests that dark matter really does exist.
The main problem around dark matter related to galaxies is in the name,
which is is confusing.
In simple language there are three types of matter: visible baryonic invisible baryonic and non-baryonic.
In the case of the solar system it consists of two:
visible baryonic: the Sun. Invisible: the planets and the kuiper belt.
You can consider the Oort Cloud as the Halo of the solar system
There is (almost) no non-baryonic matter.
[[Mod. note -- In the context of dark matter, "visible" means
"interacts with electromagnetic radiation (which includes light,
radio, X-rays, etc)". So anything baryonic (including stars,
planets, the Kuiper belt, neutron stars, interstellar dust, and
the interstellar and intergalactic (gaseous) mediums) are all
"visible". Electrons and positrons are also "visible".
If we assume that all the stars in the disc of our Galaxy are equal
than it means that there is no non-baryonic directly outside each
star. i.e. all non-baryonic can only be in interstellar space (or
in halo)
The reason why there is no non-baryonic matter in the solar system
is because all the planets (the movements) are accordingly (almost)
to Newton's law.
In the paragraph: https://en.wikipedia.org/wiki/Dark_matter#Galaxy_rotation_curves
Keppler's law is mentioned. IMO in relation to galaxy rotation
curves Keppler's law should not be mentioned. Even if you want to
study the movement of the planets you should use Newton's law. If
curve B is what is observed than the true size of the galaxy is
much larger than what is shown. It is easy possible that the full
curve also starts to level off. (MOND does not support such an
behaviour. It will always be flat)
[[Mod. note -- Kepler's law (strictly speaking, Kepler's 3rd law)
is a mathematical consequence of Newton's law (strictly speaking,
Newton's 2nd law & his law of universal gravitation), and vice versa,
so "using Newton's law" is the same thing as using Kepler's law.
-- jt]]
An important "proof" for dark matter has vanished: Astronomers take back
the observation that a cluster was missing its dark matter, "left
behind". See:
Royal Astronomical Society. "Dark matter might not be interactive after
all." ScienceDaily. ScienceDaily, 5 April 2018. <www.sciencedaily.com/releases/2018/04/180405223407.htm>.
This happened with improved observations after several years.
Will this observation of a galaxy without dark matter hold?
Martin Brown
What do people think of the recent claim in Nature that one of the new
wide field instruments has found a candidate diffuse galaxy NGC1052-DF2
which appears to have little or no dark matter in it?
Dynamically can anyone see how a bunch of stars could be peeled off by a galaxy galaxy interaction without also taking dark matter with it?
Thanks for any enlightenment.
--
Regards,
Martin Brown
To see how the steller masses are calculated see: https://arxiv.org/abs/1607.04678
My impression is that this is not simple (Figure 9)
The main problem around dark matter related to galaxies is in the name,
which is is confusing.
In simple language there are three types of matter: visible baryonic invisible baryonic and non-baryonic.
The reason why there is no non-baryonic matter in the solar system
is because all the planets (the movements) are accordingly (almost)
to Newton's law.
The question is if the same can be said for binary stars in our
galaxy, (or for clusters of three or 4 stars) of which the masses
accurately can be observed. If that is the case than, within such
clusters, there is no extra non-baryonic matter required.
In the original document...
What is missing (?) is the ratio: visible-baryonic/invisible-baryonic
An important "proof" for dark matter has vanished: Astronomers take back
the observation that a cluster was missing its dark matter, "left
behind".
Royal Astronomical Society. "Dark matter might not be interactive after
all." ScienceDaily. ScienceDaily, 5 April 2018. <www.sciencedaily.com/releases/2018/04/180405223407.htm>.
What do people think of the recent claim in Nature that one of the new
wide field instruments has found a candidate diffuse galaxy NGC1052-DF2
which appears to have little or no dark matter in it?
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