Talk:Reionization

Reionization and galaxy formation

The article says: reionization is the process that reionized the matter in the universe after the epoch of galaxy formation. But Graphical timeline of the Stelliferous Era shows the reionization phase starting at 100 million years after the Big Bang and completing before the formation of the first galaxies at 600 million years after the Big Bang. Which is correct ? Gandalf61 16:41, 23 January 2007 (UTC)

Never mind - found answer in Timeline of the Big Bang. Gandalf61 15:46, 27 January 2007

If Quasars existed during early Reionization epochs (20 > z > 5), then super-massive black holes (SMBH) existed to generate them. And if SMBH existed, then so did surrounding spheroidal proto-galaxies (proto-Ellipticals, proto-Spiral-Bulges). Also, if mega-mass SMBH existed, in the largest proto-galaxies; then intermediate-mass black holes (IMBH) existed, in "Nuclear [Star] Clusters (NC)", which seem to fill the same role, in smaller galaxies, as SMBH in the largest galaxies. Three-quarters of all galaxies have NCs; one-quarter have SMBH instead; see: http://www.eso.org/sci/meetings/2011/dynamics2011/Contributions/Neumayer.pdf. Thus, for every SMBH, three NC existed. Quasars represent sight-lines straight into the hearts of the earliest epochs of star formation ("Population III"). (Hypothetically, high resolution imaging would directly reveal the central SMBH, the structure of the relativistic jets, and at least the central core regions, of surrounding spheroidal star clusters.) Wikipedia seemingly has no article entry for NCs. Perhaps creating such a page, and linking it to this one, would improve this article, as well as Wikipedia's coverage of cosmology. 66.235.38.214 (talk) 04:19, 12 November 2012 (UTC)

According to Galaxy Formation & Evolution by Mo & van den Bosch (pp.58-60), "Ultra Compact Dwarf (UCD)" galaxies may be the biggest & brightest of Globular Clusters (GC); and, also, UCDs resemble NCs, albeit stripped of the latter's surrounding stellar halo. If so, the GC / UCD & NC are all spheroidal clusters of stars (of varying sizes) dating to the earliest epochs of star formation, i.e. they may be the first star formations, the first stellar structures. If so, then the emergence of Quasars, during the Reionization era (20 > z > 5), implies the co-occurring formation of the first star clusters, the largest of which also formed central SMBH, which generated AGNs, some of whose jets aimed towards earth, at present epoch ("here, now"), so being observed as those Quasars. Perhaps the article could be improved, by emphasizing the close connections, between AGNs and star formation? Inexpertly, i understand that the emergence of Quasars implies the co-emergence of GC-like spheroidal star clusters, some of which now reside in the centers of modern galaxies, at present epoch. Perhaps these connections could help improve the article coverage? In particular, i understand that galaxy formation proceeds from the center outward, e.g. Metallicity decreases from the centers of galaxies out towards their peripheries. So i understand that Quasars imply the assembly of the central cores of galaxies (as well as surrounding halos of approximately co-forming GCs). And i understand that "center outwards" process to be important in galaxy formation; over ensuing aeons, dusty gas condensed into outer-lying stars, surrounding central spheroidal star clusters, so forming dwarfish Ellipsoidal galaxies; and dusty gas also "disked down" around some of those, "growing" as NC-cum-Spiral-Bulges. Perhaps a professional could take the time to augment the article, were such warranted? 66.235.38.214 (talk) 06:45, 12 November 2012 (UTC)

According to the same source, GC / UCD star-clusters are qualitatively distinct from even the smallest ellipsoidal galaxies — in the phase-space of size vs. absolute brightness, the former are separated from the latter by a large gap. Ipso facto, a "first burst" of star-formation may have generated the former, with a "second burst" growing some of the former (thusly dubbed NC) into the latter, ages later. Some of those "second bursts" may have been prolonged, or else followed by further bursts, so as to grow the largest isolated Elliptical galaxies (i.e. not cluster-central cD galaxies, known to assemble from many major mergers). i understand Quasars in Reionization to be profoundly important probes of the "first burst" of star-cluster-forming star formation in this universe, and perhaps even subsequent bursts that "grew" some star-clusters into (the cores of) Ellipsoidal proto-galaxies. Perhaps a professional could appropriately update & improve the article, per these concepts? 66.235.38.214 (talk) 07:06, 12 November 2012 (UTC)

Tangentially, i understand from the above, that structurally simple spheroidal star clusters were the first star groupings to form. If so, then GCs are (nearly) the oldest surviving star groupings, and their Population II stars are the oldest surviving stars. I.e. no prior Population III stars ever existed; instead, Population II stars would have acquired their supra-primordial metallicities, from fellow Pop.II stars ("Pop.II-0"), i.e. their own biggest bluest brightest brethren, which larger & more massive stars always (?) form more quickly, whilst smaller & less massive stellar siblings are still coalescing from their common cloud. Quasars & Reionization could connect to crucial aspects of first star formation, and galaxy "growth" therefrom, which might warrant incorporation into the article. Further links to the Lyman-alpha forest could be considered also, since Lyman-alpha clouds are (thought to be) the dusty gaseous halos, of "growing" proto-galaxies. 66.235.38.214 (talk) 08:28, 12 November 2012 (UTC)

If Quasars spewed forth relativistic jets & radiation from redshift (20>z>5), then their central SMBH were accreting gas, which would have wended its way to the central SMBH, through the surrounding star cluster (NC). Perhaps that infalling gas was the material, which both powered AGNs, whilst simultaneously "growing" the SMBH in the center, and "growing" the surrounding star cluster, from a NC, into an ellipsoidal proto-galaxy (proto-Elliptical, proto-Bulge)? If central SMBH began small (hundreds of thousands of star masses, per the ESO article), and grew enormous (millions to billions of star masses), whilst siphoning off a fairly fixed fraction of infalling gas; then the small initial mass of the (NC + small SMBH) would become "drowned out" by the enormous amounts of infalling material, so that central SMBH masses would trend towards that common fixed fraction of the total surrounding star cluster halo, i.e. ellipsoidal proto-galaxy. If so, then Quasars during Reionization imply "growth", both of the central SMBH generating the AGN, and its surrounding star cluster halo, from large star cluster size (NC + small SMBH), to small-to-large galaxy size (SMBH + surrounding ellipsoid). That implicit "growth" seems a crucial concept; and could perhaps help improve the article ? 66.235.38.214 (talk) 09:35, 12 November 2012 (UTC)

To offer a crude & imperfect timeline, perhaps from (30>z>20) the first spheroidal star clusters formed (GC / UCD), within large pre-galactic clouds. The largest (UCD) would also have formed small SMBH (hundreds of thousands of star masses), and sunk towards the centers of their pre-galactic systems. Then, from (20>z>5), during the epoch of Reionization by Quasars, the larger central star clusters "grew" by accretion of remaining gas, infalling from the surrounding pre-galactic cloud, becoming "embedded" NC. And, those with small SMBH generated AGN, with both components (NC + SMBH) growing in tandem, resulting in large SMBH embedded in ellipsoidal proto-galaxies. The end of the Reionization epoch (z≈5) implies the end of "growth", e.g. our Milky Way would then have consisted of the Bulge (w/ central SMBH), grown to present size, and orbiting halo GCs (which never grew), mired amidst the thinning out (and ionizing) pre-galactic cloud. Cosmic Voids were seemingly ionized by this epoch (see following). Afterwards (5>z>1), most galaxies away from crowded clusters slowly "settled", evolving from dusty gas enshrouded star-bursting Irregulars, towards comparatively quiescent Spirals . Meanwhile, the Lyman-alpha forest — remaining regions of neutral hydrogen, being the nascent galactic halos, deriving from aforesaid pre-galactic clouds — dwindled away, as dense (self-shielded?) pre-galactic clouds were ionized, by local star formation bursts, and perhaps by intergalactic ionizing radiation. The modern era, of aging & reddening galaxies, ensued (1>z).66.235.38.214 (talk) 11:02, 12 November 2012 (UTC)

References

Recombination disambiguation

I added the link back to the disambiguation page for the time being, as it give some explanation. I may write create a recombination stub in the next few days and redirect the link there. James McBride 09:14, 15 August 2007 (UTC)

My bad. I went back and looked at the previous version, and I guess I had looked at the wrong recombination. I thought the link had been removed, instead of redirected to the Big Bang timeline. James McBride 08:36, 16 August 2007 (UTC)

Adding more images

I would like to see a few more images in the article. In particular, the graph of the CMB polarization angular anisotropy map and an example Gunn-Peterson trough. A non-copyrighted version of the first should be possible, as it was generated by WMAP, but I only was able to find the image at other sites. James McBride 09:14, 15 August 2007 (UTC)

Current image deletion

I think editors should give serious consideration to deleting the image given at http://imagine.gsfc.nasa.gov/Images/sats_n_data/exhibit/reion.diagram.jpg 1) The universe does not become opaque at the surface of last scattering. It's called that for a reason, and it's not because the universe suddenly starts scattering - the universe becomes transparent then, not opaque (exception being specific neutral hydrogen absorption features as mentioned in the GP trough sections) 2) The universe does not become neutral either for that matter. It was neutral already, but ionized. It becomes unionized at that point, which is not the same as neutral 3) The universe does not become transparent again at reionization. It'd be opaque again, except that the free electron density is low enough that the Thomson scattering cross section remains low and the universe stays opaque. In other words, that diagram from NASA is pretty badly wrong in a number of fundamental points. I'd get rid of it myself, but I'd probably be accused of vandalism for getting rid of something from a reputable source, even when it's got fundamental errors in it —Preceding unsigned comment added by 91.84.172.216 (talk) 00:29, 21 February 2008 (UTC)

I agree that the language used is rather poor. There is some use of opaque and transparent in the sense used in the diagram in some of the literature, but I was initially rather confused by that. Perhaps the article would be stronger without the diagram. James McBride (talk) 02:42, 22 February 2008 (UTC)

I would agree. Having just approached the subject for the first time, I found the diagram misleading. Unless there are further comments to the contrary, I would suggest removing the image soon. 82.24.250.218 (talk) 21:39, 16 October 2008 (UTC)

I asked the NASA people to replace their erroneous image with a correct one, and after a few weeks they did, courtesy of their WMAP staff. Unfortunately I cannot add images to Wikipedia, according to the rules, because I haven't added 10 edits yet (I'm not "autoconfirmed"). Could somebody who is autoconfirmed please put the current version of http://imagine.gsfc.nasa.gov/Images/sats_n_data/exhibit/reion.diagram.jpg in the Wikemedia Commons and point to it from the Reionization page? Thanks in advance! Mike Pelizzari (talk) 22:22, 29 December 2009 (UTC)

Wow, that is great! I just uploaded the new version, and also made a couple of changes in the text you added to reflect the new image. James McBride (talk) 20:20, 30 December 2009 (UTC)

Name change

I suggest that the name of this entry should be changed to "Reionization event," to more clearly indicate its specific subject matter. --Steve, Sm8900 (talk) 14:53, 26 February 2010 (UTC)

Only if you have a reliable source that uses the term "reionization event". Seems to me that something that is spread over two phases, one of which lasts more than 800 million years, is more like a process than an event. Gandalf61 (talk) 15:21, 26 February 2010 (UTC)

I believe the two events are considered to be separate events. this article covers them as distinct though related events. I will try to find sources. --Steve, Sm8900 (talk) 16:01, 26 February 2010 (UTC)

Seeing your edit, I think I may understand the source of confusion. The universe started ionized. It became neutral during recombination. It was then reionized during a single period of time, lasting some hundreds of millions of years, known as reionization. I have frequently heard reionization called the "epoch of reionization," but almost never called the "reionization event." As such, I would strongly oppose any move to change the name to reionization event. James McBride (talk) 20:07, 26 February 2010 (UTC)

Well, how about a parenthetical note to indicate the topical area? Reionization is a word and scientific term with multiple uses and applications, like any other word in the English language. also, it can refer to a reionization process of any object or in any set of conditions. As an article title, it seems rather imprecise. An article title like "Reionization (cosmology)" or "Reionization (astrophysics)" might perhaps be more clear and accurate. --Steve, Sm8900 (talk) 14:57, 2 March 2010 (UTC)

I feel like the first sentence of the article makes clear the scope of the term as used in the article. As there is no other article on reionization, I am not sure what the purpose of renaming would be. Reionization would still redirect to reionization (cosmology) anyway. And, as a final note, the first non-cosmology hit for a simple search of reionization is on the 9th page. James McBride (talk) 04:07, 3 March 2010 (UTC)

More Citations Please

It seems that several citations are lacking from the first few paragraphs. Really, there aren't any until the end of the second paragraph in the 'Quasars and the Gunn-Peterson trough' section. Can anyone cite a reference to this: "which occurred at a redshift z = 1089 (379,000 years after the Big Bang)"? The article seems to assume that we already know a lot, whereas we probably don't. Richard Nowell (talk) 17:08, 19 June 2014 (UTC)

Background - 2nd Paragraph needs work

As of Jul 10, 2014 the 2nd P of the Background has some strange (inappropriate) wordings and sentences. First:"The second phase change occurred once objects started to condense in the early universe that were energetic enough to ionize neutral hydrogen. As these objects formed and radiated energy, the universe reverted from being neutral, to once again being an ionized plasma." Why are the Population III stars called "objects"?!? AFAIK, there is no controversy that the first objects to radiate significant amounts of emr were mostly Pop. 3 stars (whether black holes also formed then and were significant source of emr (from their accretion disks) is something I don't have a handle on (but doubt)). (Whether Pop. 3 stars formed in galactic structures or whether galactic structures formed around those stars, has not (to my knowledge, but it may be out-dated) been conclusively answered. Regardless, it is irrelevant here.)
Second: Isn't "The second phase change" actually called the "Reionization"? Why is that being avoided??
Third:"the universe reverted from being neutral, to once again being an ionized plasma." Wow! Talk about awkward! The Universe is space and time and everything in it. PART, and ONLY part, of it is baryonic matter. To confuse the plasma in the matter(?) dominated Universe with the Universe itself is so egregiously WRONG as to be, to me, incomprehensible. Have you not heard of Dark Matter??? How about Dark Energy?? Wow! This MUST be changed!! Here is a hint: the plasma is roughly 25% of the matter in the Universe and only 4% of the total energy content. So, whether or not you ignore Dark Energy, equating the Universe to the plasma in it is a blunder of epic proportions.
Fourth:"At that time, however, matter had been diffused by the expansion of the universe, and the scattering interactions of photons and electrons were much less frequent than before electron-proton recombination. Thus a universe full of low density ionized hydrogen will remain transparent, as is the case today." "matter had been diffused" is gobble-de-gook. Why not:"By that time the expansion of the Universe had diluted the concentration of matter so that it was too diffuse to obstruct light transmission. Today's Universe is and will remain transparent." — Preceding unsigned comment added by Abitslow (talk • contribs) 15:57, 10 July 2014 (UTC)

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If Lyman alpha galaxies are found in normal numbers

A recent edit by @Fenship added:

• If Lyman alpha galaxies are found in normal numbers, the surrounding gas must be ionized.

I can't figure out what is meant. Assuming "Lyman alpha galaxies means "galaxies observed in regions with Lyman alpha emission, I guess we are not searching "normal numbers", so my first guess is

• An average density of Lyman alpha emission means the surrounding gas must be ionized.

? Johnjbarton (talk) 18:29, 4 August 2024 (UTC)

I think " An average density of galaxies with Lyman alpha emission means the surrounding gas must be ionized." is what was intended: the point is that if you find galaxies emitting, then there's no neutral gas to absorb. Pinging User:Fenship? - Parejkoj (talk) 00:06, 5 August 2024 (UTC)

Thanks for flagging this. "Lyman alpha galaxies" here means "Galaxies with detectable Lyman alpha emission". It's a common enough shorthand in the astronomical literature but should be reworded here since it was not clear.

Rather than saying "An average density of Lyman alpha emission...", how about

"An average density of galaxies with detectable Lyman alpha emission means the surrounding gas must be ionized..."

(The nuance here: The currently practical observations can identify and count sources of Lyman alpha photons that are individually above a particular threshold brightness. However measuring the total density of Lyman alpha photons produced in some volume is difficult, because a substantial part of the total production may come from objects individually too faint to identify. And I would interpret the "density of Lyman alpha emission" to mean the total produced in some volume by all sources, including those too faint to individually detect.)

I'll edit the page for now, can make further edits if it still seems unclear. Thanks. Fenship (talk) 03:34, 5 August 2024 (UTC)