Question Where are all the Dark Matter Galaxies?!

Mar 19, 2020
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Using the Keck II and Gemini telescopes on Maunakea , Pieter van Dokkum and colleagues observed a number of ultra-diffuse galaxies (UDGs) in the Coma Cluster, almost local to us at 300 mly. Their first observations*, made in 2015, on the largest of these UDGs suggest it may be made almost entirely of dark matter. They appear to be convinced of it. To be sure, it is a very unusual object, and their observations, while limited, makes it even more curious for that reason alone : there is not much to "see"!

The UDG that stood out is Dragonfly 44. This "object" appears to have a mass approximating the Milky Way, but contains only about 0.01 percent ordinary, visible matter. Or at least that is how it "appears", based on visible imaging, since you cannot "see" dark matter. The velocities of visible stars indicate its mass is enormous, and that something other than ordinary matter must be making up 99.99% of this object, i.e. mass which is not observed.

In a more recent paper** from 2019, using the Keck Cosmic Web Imager***, van Dokkum et al. obtained no evidence for rotation in this "galaxy", suggesting this is not a typical UDG. This observation distinguishes it from the "high-spin tail of the normal dwarf galaxy distribution" found in many of these diffuse objects.

A significant reference search on this object revels very little else about it (with constraints on my search abilities), and nothing to challenge van Dokkum et al.'s conclusions, or any retraction(s). Dragonfly 44 appears to be a rare object, and possibly made almost entirely of dark matter. But how could this be true if so much of the universe's mass is supposed to be dark matter? If dark matter can form one galaxy, it should be able to form many of them. Yet we can apparently "see" only one, and that one is almost next door!

So, where are all the dark matter galaxies?


* https://www.space.com/33850-weird-galaxy-is-mostly-dark-matter.html

** https://arxiv.org/pdf/1904.04838.pdf (preprint, Astrophysical Journal)

*** http://www.keckobservatory.org/spiraling-gas/
 
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May 8, 2020
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Using the Keck II and Gemini telescopes on Mauna Kea, Pieter van Dokkum and colleagues observed a number of ultra-diffuse galaxies (UDGs) in the Coma Cluster, almost local to us at 300 mly. Their first observations*, made in 2015, on the largest of these UDGs suggest it may be made almost entirely of dark matter. They appear to be convinced of it. To be sure, it is a very unusual object, and their observations, while limited, makes it even more curious for that reason alone : there is not much to "see"!

The UDG that stood out is Dragonfly 44. This "object" appears to have a mass approximating the Milky Way, but contains only about 0.01 percent ordinary, visible matter. Or at least that is how it "appears", based on visible imaging, since you cannot "see" dark matter. The velocities of visible stars indicate its mass is enormous, and that something other than ordinary matter must be making up 99.99% of this object, i.e. mass which is not observed.

In a more recent paper** from 2019, using the Keck Cosmic Web Imager***, van Dokkum et al. obtained no evidence for rotation in this "galaxy", suggesting this is not a typical UDG. This observation distinguishes it from the "high-spin tail of the normal dwarf galaxy distribution" found in many of these diffuse objects.

A significant reference search on this object revels very little else about it (with constraints on my search abilities), and nothing to challenge van Dokkum et al.'s conclusions, or any retraction(s). Dragonfly 44 appears to be a rare object, and possibly made almost entirely of dark matter. But how could this be true if so much of the universe's mass is supposed to be dark matter? If dark matter can form one galaxy, it should be able to form many of them. Yet we can apparently "see" only one, and that one is almost next door!

So, where are all the dark matter galaxies?


* https://www.space.com/33850-weird-galaxy-is-mostly-dark-matter.html

** https://arxiv.org/pdf/1904.04838.pdf (preprint, Astrophysical Journal)

*** http://www.keckobservatory.org/spiraling-gas/
Maybe we don't have the correct equipment. Or maybe we're looking for the wrong things, I don't know. Good question.
 

rod

Oct 22, 2019
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Where are the dark stars created after the BB? New computer code allows the formation of the first stars as dark matter stars made of H and He but with a little dark matter. These dark stars could have accelerated the reionization epoch when the cosmos was in the dark ages. 'Shedding Light on Dark Stars', Sky & Telescope 119(3):26-29, 2010 (March 2010).
 
Apr 5, 2020
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It seems to me that dark matter is not that simple as thought before. It's quite more complicated (it all depends on your perspective, if you think something to be simple, it's simple and vice versa). I read the following article and came to know about dark stars. Maybe, there were thousands of these dark-star galaxies in the distant past. A reason for the shortage of such dark matter galaxies might have two reasons:-

First, humans haven't got that powerful telescopes to see them. James Webb Telescope's coming, let's see what we might get.

Second, due to the expansion of the Universe by Dark Energy, Dark Matter has spread out across the Universe and has decreased in density. That is why there is a shortage of Dark Matter. Maybe, they are there in quite a number about some billion lightyears away. Who knows?

 
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While we are with the reference for easy checking, may I please give 3 brief exerrpts which I find very interesting and which are still highly pertinent to this thread. I will then copy them across to another appropriate and, if you wish (though I doubt it) I will delete the reference here, leaving only a one line pointer.

QUOTE
When these partners — the particle and antiparticle — meet, they collide with a bang, utterly destroying one another in a shower of light, energy, and, in some cases, newly conceived lighter particles.

Annihilating dark matter throws a wrench into this system, with the energy from annihilation adding a powerful outward force. During star formation, the particles’ annihilations would have at some point prevented the star from contracting further. At this time, the star would not have reached the density required to begin nuclear fusion, so the outward force generated by annihilating dark matter would solely balance the inward force of gravity.

Even at such a small amount, the dark matter fuel in a dark star is likely to power that star for millions or even billions of years.
QUOTE

If I have understood this correctly, + / - pairings can take billions of years even inside these proto-stars, let alone in the 'open space' of the Universe. This would give extreme perspective to the matter antimatter destruction kinetics.

These are from Astronomy October 10 2018 "Dark stars come into the light".
I should point out that they do not run consecutively in the article.
 
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Feb 14, 2020
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Using the Keck II and Gemini telescopes on Maunakea , Pieter van Dokkum and colleagues observed a number of ultra-diffuse galaxies (UDGs) in the Coma Cluster, almost local to us at 300 mly. Their first observations*, made in 2015, on the largest of these UDGs suggest it may be made almost entirely of dark matter. They appear to be convinced of it. To be sure, it is a very unusual object, and their observations, while limited, makes it even more curious for that reason alone : there is not much to "see"!

The UDG that stood out is Dragonfly 44. This "object" appears to have a mass approximating the Milky Way, but contains only about 0.01 percent ordinary, visible matter. Or at least that is how it "appears", based on visible imaging, since you cannot "see" dark matter. The velocities of visible stars indicate its mass is enormous, and that something other than ordinary matter must be making up 99.99% of this object, i.e. mass which is not observed.

In a more recent paper** from 2019, using the Keck Cosmic Web Imager***, van Dokkum et al. obtained no evidence for rotation in this "galaxy", suggesting this is not a typical UDG. This observation distinguishes it from the "high-spin tail of the normal dwarf galaxy distribution" found in many of these diffuse objects.

A significant reference search on this object revels very little else about it (with constraints on my search abilities), and nothing to challenge van Dokkum et al.'s conclusions, or any retraction(s). Dragonfly 44 appears to be a rare object, and possibly made almost entirely of dark matter. But how could this be true if so much of the universe's mass is supposed to be dark matter? If dark matter can form one galaxy, it should be able to form many of them. Yet we can apparently "see" only one, and that one is almost next door!

So, where are all the dark matter galaxies?


* https://www.space.com/33850-weird-galaxy-is-mostly-dark-matter.html

** https://arxiv.org/pdf/1904.04838.pdf (preprint, Astrophysical Journal)

*** http://www.keckobservatory.org/spiraling-gas/
Very interesting post and references. I glanced over van Doccum ArXiv paper.
Our difficulty lies in the fact that we are either associating Gravitation or Electromagnetic spectrum as tools to measure DM, which as I mentioned in these posts does not necessarily have coupling with matter-energy except where it is creating matter or reabsorbing it. We have no other tools including QCD (bosons, quarks, gluons) to probe DM. My study indicates that as spiral galaxies were early indicators of existence of DM as well as Hubble images mosaics showing Haloes, we will find other clues and DM is what is left after all known effects are eliminated, that is by absence of Matter-energy. My study still does not have a clarity on Dark Energy.
 
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Aug 14, 2020
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In view of the (lack of) importance of baryonic matter, perhaps we are just the (bad) dreams of the majority inhabitants of dark matter.
If we can't find the dreamers, perhaps we should give them fewer nightmares?
What would you suggest? Utopia or suicide? Come to think of it, that is being redundant.
 
Nov 27, 2020
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Dark matter is between two matters in the space itself. So it won't be plausible to call any galaxy Dark Matter Galaxy
 
Feb 14, 2020
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I somewhat agree with the statement, from Astro Guy
"Dark matter is between two matters in the space itself. So it won't be plausible to call any galaxy Dark Matter Galaxy "

Except that Dark matter is everywhere, when we see matter(energy) it is excited state of Dark Matter otherwise as in QFT DM is in ground state.
Dr Ravi Sharma
 

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