Talk:Dark galaxy

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Contradictory information

it has now been proven that some dark galaxies contain stars. Therefore a dark galaxy is held together by dark matter alone. So far, no dark galaxy with a black hole as a center have been discovered This information is contradictory. Also, it isn't appropriately located. Anyone opposed to deletion? Privong 01:17, 3 March 2007 (UTC)[reply]

part of Lyman-alpha forest ?

DGs are small gas-rich, star-less, space clouds. They may have been observed, in fluorescence, at redshift z=2, from a background Quasar:

http://www.sciencedaily.com/releases/2012/10/121030161234.htm

Those DGs resemble, if in reflection, space clouds in the Lyman-alpha forest, observed in absorption (when they reside closer to the sight-line from a background Quasar to earth). Perhaps DGs are relic remnants of neutral space gas, otherwise only detected, as absorption lines in Quasar spectra? If so, then perhaps this article could be improved, with links to the Lyman-alpha forest article. 66.235.38.214 (talk) 03:45, 12 November 2012 (UTC)[reply]

References

Please, check the references as it contains some links without citation in the article. Madmoron (talk) 05:27, 22 December 2012 (UTC)[reply]

Weasel Words ish?

Nothing substantial but the first paragraph just reads as loads of 'someone claims' type statements.

Later on in 'Alternative theories' there is some dodgy grammar (I will sort that out) and it does not read as ... well something from a encyclopedia. — Preceding unsigned comment added by Mtpaley (talk • contribs) 00:51, 26 February 2013 (UTC)[reply]

I need advice. The 'Alternative theories' section is a mess, it is in poor English and full of unreferenced assertions but it is clearly a honest attempt at creating a good section and there is some information in there. What should be done?Mtpaley (talk) 21:23, 28 February 2013 (UTC)[reply]

Malware Link Removal

--Gary Dee 18:20, 21 July 2013 (UTC)[reply]

Sidis section removal

I removed a section added by User:97.123.26.217 that claimed that "W. J. Sidis predicted in 1925 the existence of dark galaxies". Sidis did no such thing. Instead, he postulated the existence of "dark spaces", colossal regions of space that absorb all light entering them. This was his attempt to resolve Olbers' paradox.

From a modern perspective, the theory is completely untenable.

The universe, in his own words, is made up of "a sort of three-dimensional checkerboard" with alternating "bricks" of "black spaces" and "white spaces". Stars travel in and out of these spaces, emitting energy when in the "white spaces", i.e. our normal space, and recharging in the "black spaces" where light from the "white spaces" is absorbed and somehow delivered to the stars that happen to be there at the time.

A dark galaxy is invisible and essentially transparent to light. It's nothing like the "dark spaces" conceived by Sidis.

No evidence was given to back up the claim, and the text was irrelevant to the topic. That is why I removed the section. Sysdepot (talk) 12:25, 25 February 2014 (UTC)[reply]

The following was added by Dmahony1 (talk) 07:09, 24 March 2014 (UTC): OBJECTION TO REMOVAL OF SIDIS'S THEORY[reply]

Here's the first reason given for the removal:

"A dark galaxy is invisible and essentially transparent to light. It's nothing like the "dark spaces" conceived by Sidis."

Webster's defines transparency: "(1) ... having the property of transmitting light without appreciable scattering so that bodies lying beyond are seen clearly ... "

Dark galaxies are the opposite of transparent.

No, dark galaxies consist of dark matter, which neither emits nor absorbs light -- light passes through it. It only interacts with "normal" matter gravitationally. Dark matter is transparent to light, and so are dark galaxies. I'm surprised that you quoted the definition of transparency -- did you really think I didn't know what it meant? Sysdepot (talk) 10:23, 28 March 2014 (UTC)[reply]

The remover claims secondly: "No evidence was given to back up the claim, and the text was irrelevant to the topic. That is why I removed the section."

Sidis is quite specific that evidence can be found in the region of the Magellanic Clouds. ^[1]

I was referring to the claim that "Sidis predicted the existence of dark galaxies". There is no evidence that he did. His "black spaces" are nothing like dark galaxies. Sysdepot (talk) 10:23, 28 March 2014 (UTC)[reply]

Please reinstate the removed text. How can someone, who is not clear about what transparency is, and therefore what a dark galaxy is, simply remove Sidis's theory from consideration? Does Wiki bless with its imprimatur only the popular miracle-based cosmology with its fanciful explosions of nothing and expansions faster than the speed of light? --Dan Mahony (dan@sidis.net) — Preceding unsigned comment added by Dmahony1 (talk • contribs) 06:58, 24 March 2014 (UTC)[reply]

Let me assure Mr. Mahony (dan@sidis.net) that I'm clear about what transparency is, and understand the concept of a dark galaxy -- it consists of dark matter, which does not emit or absorb light or interact with "normal" matter or light in any way except gravitationally -- as I stated, it is "invisible and essentially transparent". Sidis said the Milky Way (a "white space" region) was surrounded by "black spaces" that absorbed light. Dark matter doesn't absorb light. Therefore, dark galaxies are not the "black spaces" that Sidis postulated. Furthermore, the Milky Way is not surrounded by light-absorbing "black spaces" -- we can see far beyond the Milky Way. In 1922, Ernst Öpik estimated the distance to the Andromeda galaxy to be about 450000 parsecs. On November 23, 1924, the New York Times published Edwin Hubble's findings: "spiral nebulae ... are in reality distant stellar systems. ... The number of spiral nebulae is very great". Sidis, in his 1925 work The Animate and the Inanimate, seems to have been unaware of these developments -- he estimates the length of the "white brick/space" containing the Milky Way to be only 7000 light years. In other words, his theory was not even consistent with observations made before its publication. As far as I can tell, no peer-reviewed physics article has ever supported it. It's utterly inconsistent with what we now know. However, I didn't remove the section because the theory is bad -- I removed it because it doesn't belong in this topic. Also, in my opinion, the theory had such little impact that there's no compelling need for a Wikipedia article about it -- if someone feels differently, they're welcome to compose such an article and submit it to the usual editorial review process. Sysdepot (talk) 10:23, 28 March 2014 (UTC)[reply]

Fortunately Sidis's theory is falsifiable. He says what we now call dark matter consists of dark stars. This is falsifiable by observation. It will become clear that dark galaxies consist of dark stars, and not whatever new Dmahony1 (talk) 23:43, 31 March 2014 (UTC)prop-up the present fanciful cosmology requires.[reply]

Another error by the Removal Oracle: Sidis does not say spaces absorb the light. That would be silly. Sidis says it is dark stars that do so. The Oracle seems to have skimmed a few pages of this major philosophical work and is quite ready to assure us of all the above. The very willingness to remove another's writing simply because he/she disagrees, and in this case ill-informed disagreement, is not acceptable in scholarship. PLEASE REINSTATE THE DELETED TEXT IMMEDIATELY.

The universe is infinite and eternal. — Preceding unsigned comment added by Dmahony1 (talk • contribs) 20:38, 31 March 2014 (UTC)[reply]

References

^ http://www.sidis.net/DSGD0114.htm

Wow. This is all completely wrong.

The lede is insane. Try reading the sources you're using:

http://www.zmescience.com/space/dark-galaxy-evidence-spotted-0707201/

A dark galaxy is NOT a galaxy made of dark matter. A dark galaxy is a large clump of normal matter that never formed stars. Dark matter can't form a star because it doesn't respond to EM pressure. It passes right through itself, so the only object dark matter could form by itself would be a black hole (which would look just like any other black hole). 76.181.231.96 (talk) 14:34, 30 August 2015 (UTC)[reply]

Content Notes

Skimming the Alternative Theories section of the page reveals a sentence (multiple, in fact) that feel very biased/out of character for the article. An example: "Martin Haehnel, from Kavli Institute for Cosmology at the University of Cambridge, claims that the precursor to the Milky Way galaxy was actually a much smaller bright galaxy that had merged with dark galaxies nearby to form the Milky Way we currently see." Skimming the cited source for this section actually reveals that (at least this sentence) is a close plagiarism of the article text. This can be easily fixed.

An issue, however, is that I am a bit confused by this page. The introduction states "A dark galaxy is a hypothesized galaxy with no, or very few, stars" where as the structure section states that "Dark galaxies are composed of dark matter." While the two are not necessarily exclusive (of course), is there a definitive statement on the structure? Otherwise the sentences should be edited to be less confusing and to appear less contradictory. Maybe make the dark matter sentence more hypothetical as a following sentence states that we don't really know what they're made of? RedHummingbird (talk) 02:19, 23 January 2017 (UTC)[reply]

What is this supposed to mean?

Dark galaxies are composed of dark matter. Furthermore, dark galaxies are theoretically composed of hydrogen and dust.

So, is it dark matter only, dark matter and mandatory conventional matter, or dark matter and optional conventional matter, or either dark or conventional matter? Besides, it was my understanding that dark galaxies are not dark because they're composed of dark matter, but because conventional matter doesn't coalesce into stars. Is there any theory what would restrict the star-forming process? Ie, why does one galaxy decvelop to be luminous, and the other is dark? --Syzygy (talk) 13:00, 15 July 2021 (UTC)[reply]

[1] ttp://www.sidis.net/DSGD0114.htm

[1]