# Talk:Galaxy formation and evolution

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## structure and scale

Some questions this article needs to address: a. Why are most galaxies 1,000 to 100,000 parsecs in diameter when the process of formation described here could operate on almost any scale? b. Is the process of galaxy formation equivalent (on a different scale) to that of protoplanetary disc formation and of supercluster formation? c. If so, then why do galaxies have structures such as spirals, not observed in the disc structures at other scales? --Tediouspedant (talk) 20:07, 6 February 2010 (UTC)

## some comments

Almost all galaxies have an extrememly large black hole at their center, or many tightly-packed neutron stars formed from collapsing supernovas over billions of years. All of the stars in the galaxy rotate around this massive center.

It has been suggested that the universe will end with neutrons as well, when all stars have collapsed into neutron stars and planets have been pulled into black holes. However, this may not happen for many billions of years.

Maybe true, but it doesn't belong in Galaxy formation and evolution, and is not very well formulated.

rmulated are terms as top-down and bottom-up process models, Zel'dovich's pancake (originally crepe paper). Do someone have enow (an 'old' enough) time to define them better? After all 'at least' our Galaxy must have 'developed' from somewhere.
XJam [2002.03.26] 2 Tuesday (0)

The article currently claims that M31 has a lower mass than the Milky Way; I was fairly sure that it's the other way round, with M31 being about twice the MW's mass. Does anyone know for sure? Will check up on this when I get a chance. --Bth 01:28 Oct 1, 2002 (UTC)

M31 = Andromeda Galaxy ( >4.1 E11 solar masses), Milky Way (5 E11 solar masses) [1] & [2] --mav

The masses seem to be comparable, I really don't know how much effect a 20% diff or so can have, so I eliminated sentence about M31 being affected the most, for precaution. If somebody is familiar with simulations and is really sure of it, you are welcome to put the sentence back.--AN

## The future of galaxies

For an article claiming to be complete, why does it include nothing on the future of galaxies? For example what happens when the Milky Way collides with Andromeda? What happens when galaxies are depleted of gas. Are there white (or even red dwarf or "degenerate matter" galaxies? This needs to be added to the article IMO. John D. Croft 19:38, 4 February 2007 (UTC)

## Galaxy formation

Is it not accepted now that most galaxies form around a massive black hole as the result of starburst triggered by quasar activity? This is not mentioned in the article.

Alan Stafford

Um, I think it is accepted that galaxies form around gravitationally unstable fluctuations in the initial distribution of mass in the universe. As these structures collapse, they become dense enough for stars to form, and the centre of the more dense of such collapsing structures could well form massive black holes. Quasars are thought to be one of the manifestations of the accretion of mass onto such an object.
In your picture, how do the massive black holes form? What causes the black holes to become quasars? How do the quasars trigger starburts? And how do the starbursts create galaxies? -- ALoan (Talk) 20:53, 23 January 2006 (UTC)

Its not my model. I saw a television program about it. The program was, "Supermassive Black Holes" : 'Horizon' , it is a Horizon documentary on the "UKTV Documentary" channel.

Found the transcript: http://www.bbc.co.uk/science/horizon/2000/massivebholes_transcript.shtml

The bulge relation is in this paper http://uk.arxiv.org/abs/astro-ph/0107134 authors David Merritt and Laura Ferrarese (Rutgers Uni). I think it was Martin Rees who calculated how the quasar would turn off to give the quiet galaxies we see lower than redshift ~6.

The television can be wrong, for example there was one where someone claiming a time machine design based on lasers. But this theory seemed more definite.

PS I found this paper http://arxiv.org/abs/astro-ph/9912346

The theory buzzword is "coevolution" or "co-evolution".

Thanks for your interesting links. Merritt and Ferrarese's paper is about the apparent link between the mass of a central black hole and the mass of the galaxy bulge within which they are located, and the correlation between the mass of the black hole and the velocity dispersion of stars in the bulge. They talk about models of formation without drawing any concrete conclusions. Similarly, Rees' paper suggests that black holes could form directly from coalescing gas without stars forming first, or by runway evolution of dense star clusters.

In the program above they were quite definite that the SMBH were responsible for forming galaxies. The reverse of the standard view.

The papers at the symposium also look very intersting but I am unable to open .ps.gz here. -- ALoan (Talk) 19:19, 26 January 2006 (UTC)

If I remember correctly Joseph Silk and Martin Rees said the starburst is triggered by temperature differences in the gas surrounding the quasar caused by the quasar. I think it was the starburst that also helps the quasar become dormant after time but my memory may be faulty here.

This paper summarizes the scenario. http://arxiv.org/abs/astro-ph/0511034 .

## The Future of Galaxies

This article on the formation and evolution of galaxies contains only a tiny fraction of the story - about 1010 years of the story. What happens to galaxies in 10100 years? Has the evolution of galaxies stopped. This is a fundamentalist belief that has no place in an article on the formation and evolution of galaxies.

Regards

John D. Croft 00:11, 21 February 2006 (UTC)

## Galaxy Formation due to He++ to He+ Phase Transformation

Most scholars agree that the galaxies formed in the epoch of recombination. Calculation shows that the galaxies formed as a consequence of the He++ to He+ phase transformation in the expanding and cooling Big Bang fireball, assuming that the universe had expanded to point where its density was down to the average density of the present Milky Way galaxy, ${\displaystyle 2.67x10^{-21}kg/m^{3}}$. At that time it had cooled to the He++ to He+ phase transition temperature, ${\displaystyle 6.31x10^{5}}$ degrees Kelvin, which is determined by the binding energy of singly-ionized helium at 54.39 eV. The sudden reduction in particle number n per unit volume due to the recombination of electrons with helium nuclei caused a shattering pressure jog in P = nkT, allowing gravitation to gather bound clouds of galactic dimensions with the precise dimensions and masses determined by the cloud geometry, which was a function of internal angular momentum in sectors of the turbulent Big Bang fireball relic. These clouds had to be massive enough to prevent evaporation of material from their surfaces in order to be stably bound objects, which can be used to determine the absolute dimensions from an assumed geometry at the transition temperature and overall mass density of the Milky Way. The predicted dimensions and masses of these model galaxies for assumed geometries match observations well enough for us to recognize that the galaxies formed like this. The key event was the first major phase transformation featuring a pressure jog due to the formation of the first bound atomic systems in the Big Bang, the singly-ionized helium atoms. Heavier species were not then abundant, but created later on in supernova explosions. Thus the galaxies were forged at the same time the first bound atoms were formed in the first major recombination event. For details, see Galaxy Formation by James A. Green from Greenwood Research at http://greenwood.s5.com/galaxy.html, and also see further details at http://greenwood.s5.tripod.com/m51gal.html. According to this phase-transformation galaxy formation theory, the barred spiral galaxies such as NGC 1365 in Fornax are considerably smaller than the 88,060 light-year in diameter flat spirals, the barred spirals measuring just 3/2 Jeans lengths along the bar, or 48,070 light-years. A typical 88,060 light-year in diameter flat spiral averaging about 10,200 light-years thick is thought to have been formed from pressure waves featuring an integer number 7 of Jeans half-lengths across and 11 complete waves azimuthally around at the mass-averaged expection radius, automatically excluding most possible initial forms in the flat spiral class by initially requiring integer numbers of pressure wavelets both radially across and azimuthally around. The numbers 7 & 11 come up, like something from a cosmic game of dice, except that all is determined by a pressure wave-mechanical process triggered by a quantum-mechanically fixed atomic transition between He++ and He+. The pressure waves are due to the pressure jog induced by the associated phase transformation He++ to He+ in the cooling Big Bang fireball, which takes place at a well-defined temperature. On the other hand, a galaxy formation process based on the H+ to H recombination event would produce galaxies with linear dimensions reduced by 1/2 and masses down by (1/2)3 = 1/8, no longer matching observations well. The time of galaxy formation may be determined by universe dynamics and the observed dimensions of galaxies. According to the equations for a universe of constant density, the solution for the radius of the universe should vary like ${\displaystyle r=a*[t]^{2/3}}$. From observations, if the universe were shrunken by a factor of Z = 100, the galaxies would all be touching. Let ${\displaystyle r_{B}}$ be the radius of the universe at that time. Then if r is the current radius of the universe,

${\displaystyle Z=r/r_{B}=(t/t_{B})^{2/3}=100.}$

Then ${\displaystyle t/t_{B}=(100)^{3/2}=1000}$, and

${\displaystyle t_{B}=t/1000=13.5x10^{9}}$ years/1000 = 13.5 million years.

This is on the time-scale associated with the matter-dominated era, but it shows that the galaxies formed quite early.

Many of the results of the sophisticated theory based on pressure waves at the Jeans wavelength associated with the He++ to He+ transition phase transformation can be obtained from flocule theory based on models of gas evaporation from galactic surfaces. In flocule theory one considers the escape of a gas particle working against the gravitational potential for the cloud, and from this derives the dimensions of the cloud if the density is assumed to be the average Milky Way density. This density is assumed to be a relic of the Big Bang fireball at the He++ to He+ transition temperature. Using flocule theory, one can then derive the dimensions of spherical galaxies, ellipitical galaxies, and flattened ellipicals. The results agree well with observations of galaxies in clusters, and with the predictions of the model using Jeans length pressure waves. Using the gravitational potential associated with a flat plate, one may estimate the thickness of flattened spiral galaxies using bound flocule theory, which turns out to be 10,200 light-years, although no limit is specified then for the galactic diameter, which is determined by the more elaborate model involving Jeans length pressure waves due to the jog associated with the He++ to He+ phase transformation. This flat spiral galaxy thickness is determined by the thickness required to create a gravitational field strong enough to prevent the escape of particles from its surface to infinity at the transition temperature of ${\displaystyle 6.31x10^{5}}$ degrees Kelvin from a body of Milky Way density. The Jeans theory based on pressure waves must be used to find the flattened spiral radius, however, which is not determined by the bound-cloud flocule theory. A perfectly uniform spherical galaxy formed under these conditions must have a radius of 8.8 Kilolightyears and a mass of ${\displaystyle 0.328x10^{9}}$ solar masses. A disk with a thickness of 10,200 light-years determined by this bound-cloud theory and having a radius of 51 KLY has a mass of ${\displaystyle 9.47x10^{10}}$ solar masses, about right for a typical flattened spiral galaxy, usually estimated at ${\displaystyle 10^{11}}$ solar masses. An flattened-ellipsoid bound-cloud flocule model along these lines gives a central thickness of 14,400 LY, a little thicker than the Jeans model.

For the mythology of the celestial sphere alluded to above, see http://greenwood.s5.com/orionsky.html . Also see http://greenwood.s5.com/galaxyformationlinks.html .

Updated April 23, 2007. - James A. Green, March 25, 2006, http://greenwood.s5.com/home.html . --JamesAGreen 23:10, 25 March 2006 (UTC)

"Spiral galaxies cannot be built up by mergers of already existing smaller galaxies." This sentence is verging on incorrect. See "A Merger-Driven Scenario for Cosmological Disk Galaxy Formation," http://xxx.lanl.gov/abs/astro-ph/0503369

More importantly, it is written as a statement of fact, not verifiability, hence it is not written in NPOV style. --Iantresman 07:32, 2 May 2006 (UTC)

## Spiral formation

Can someone provide a reference for this statement. It also contradicts the rest of the text which talks about how the Milky Way is absorbing other galaxies.

Spiral galaxies cannot be built up by mergers of already existing smaller galaxies. When galaxies collide, the individual stars barely notice. The stars themselves never collide with each other because of the enormous distances between them, compared to their size. So when galaxies collide, they actually simply pass through each other, but the gravitational effects disrupts their structure as this happens. As they separate, gravity slows them down and, if they are gravitationally bound, will eventually bring them back together for another collision. After several collisions their individual structures are so changed, with many stars mixed up between them, that we identify the result as a single merged object. So after a merger, most of the stars originally belonging to both galaxies remain to form the new merged galaxy (a small fraction will have been thrown out entirely). If either galaxy were a spiral before the merger, the violence of the event would disrupt the delicate structure of the disk. The existing stars cannot afterwards change their orbits to form a new disk. The stellar disk must essentially form in place; a dense rotating disk of gas forms first, then stars are born inside it.

Roadrunner 22:44, 2 June 2006 (UTC)

## Can someone add a citation

This is so vague that it is impossible for me to figure out what it is referring to.

Recent data strongly suggests that the first galaxies formed as early as 600 million years after the Big Bang, much earlier than astronomers had previously believed. That leaves hardly enough time for the tiny primordial instabilities to grow sufficiently forming protogalaxies into galaxies.

Roadrunner 22:44, 2 June 2006 (UTC)

## Hubble Tuning Fork

Article incorrectly states that Hubble believed the Fork to be an evolutionary sequence. This is a myth, see the Wiki article for the Tuning Fork itself. — Preceding unsigned comment added by 130.113.172.251 (talk) 03:04, 25 May 2016 (UTC)

## Galaxy formation conflicts with observation

Key Theory Of Galaxy Formation No Longer Conflicts With Observations

This article states: "Astrophysicists led by the University of Chicago's Andrey Kravtsov have resolved an embarrassing contradiction between a favored theory of how galaxies form and what astronomers see in their telescopes."

I can't seem to find any mention of this in the article, which would appear to be a vital criticism. Oversight? Cover-up? Simplification? Uninformed editors? --Iantresman 22:49, 12 June 2006 (UTC)

Indeed, the dwarf galaxy problem is mentioned elsewhere but deserves mention here. --ScienceApologist 01:34, 13 June 2006 (UTC)

## Galactic vs extragalactic astronomy

"A great deal of the research in this area is focused on components of our own Milky Way, since for us it is the easiest galaxy to observe"

This is wrong: actually our own Galaxy is the most difficult galaxy to observe because we're sat right in the middle of it, looking through a lot of dust and gas. Also since galaxy evolution is a slow process, a single galaxy doesn't tell you a whole lot. In fact most research in this area is focused on very distant galaxies, where you have a range of ages and types of galaxy to compare. Cosmo0 03:23, 16 June 2007 (UTC)

## DIDN'T HELP

This article needs some serious primping and pampering. 71.212.121.155`~

71.212.121.155 23:53, 4 October 2007 (UTC)

## Ellipticals "most evolved"

"Astronomers now see elliptical galaxies as some of the most evolved systems in the universe." Would "entropic" be a better term than "evolved" (this coming from a biological sciences major)? 69.243.168.118 (talk) 01:08, 29 April 2008 (UTC) (logged out User:Formerly the IP-Address 24.22.227.53

## Tone tag

I removed the tone tag that was added in July. Since that time, some of the concerns of the original tagger were met, while others were not. This article may be an exception to the recommended guideline ("editorial feel. Avoid writing with "we must" and "We see that..." etc...) The scale is so vast, the language almost requires it. Viriditas (talk) 13:01, 25 October 2008 (UTC)

## Pea galaxies

I have added a link in the "See also" section to the "Pea galaxy" article as I'm sure that it is relevant to this subject. I also put a citation query next to the amount of star-formation in mergers, as these figures seem optimistic. Great article though Richard Nowell (talk) 11:09, 25 January 2010 (UTC)

## Galaxy evolution

Please note that most of this article discusses how galaxies form, not how they evolve or will be like in the future. I am doing a paper on this topic, and I am a big fan of Wikipedia. As we all know this article is called "Galaxy formation and evolution" and not just "Galaxy formation", please add more information. Thanks for your contributions. ~Wimpy Fanboy my talk sign! 22:59, 30 May 2011 (UTC)

--Oldest galactic clusters found: In case these articles are useful to the authors: 1. General Science news article http://news.nationalgeographic.com/2015/04/150406-baby-galaxy-cluster-planck-herschel-sky-watching-virgo/?utm_source=Facebook&utm_medium=Social&utm_content=link_fb20150406news-babygalaxy&utm_campaign=Content&sf8415306=1

2. The Research paper for item 1 above http://www.aanda.org/articles/aa/pdf/forth/aa24790-14.pdf Jcardazzi (talk) 13:04, 7 April 2015 (UTC)jcardazzi

## Galaxy evolution II

I am aware that balancing the needs of the different viewers' levels of interest and expertise, in order to be concise but not missing important content. That's why we have discussions. With that as preamble, I propose these additions. Such as why spiral arms contribute to star formation, that they are composed of shock waves whose leading edges entrain matter in "front" of them, etc. Likewise, I would wish not to see development between two merging galaxies; which will produce an elliptical galaxy, so simplified as here. Surely, it is worth describing as a multi-phase process. The process of cold dust condensation, star formation, supernova warming, resulting in dust warming and dispersion, etc. all this should be worth presenting. In addition re elliptical galaxies as being the end product of galactical evolution, then there should be a wealth of metallics, and thus a greater richness of planets in star orbits than in other galaxy types? Doesn't that provide a good link to other issues of interest to we humans, ie the existence of life? Perhaps my suggestions are already covered elsewhere in Wikipedia, in which case there might be feeder text with links. Just a few newbie comments. Hope they help. Idealist707 (talk) 21:05, 9 June 2011 (UTC)

## Galaxy mergers and the formation of elliptical galaxies

I shortened the "Galaxy mergers and the formation of elliptical galaxies" section, pasting the content in the galaxy merger article, which has only been linked from the aforementioned sectioned.

This way, we give an overview of what a galaxy merger is, but for additional information the reader is redirected to the main article.

RickV88 (talk) 12:46, 5 January 2012 (UTC)

## Cosmology

I've added 'Cosmology' to the 'See also' section because "Galaxy formation and evolution" is part of 'cosmology'. As a one-word term, I didn't see 'cosmology' mentioned in the article here when I did a 'Find' within the article. — Charles Edwin Shipp (talk) 09:36, 28 February 2014 (UTC)

## Commonly Observed Properties - problems.

As I read down through the common properties, there are a number of obvious and less obvious problems: The first is "notable" is NOT even close to being the same as "common"; they are (in some contexts) opposites. The section title is Common Properties, but the first sentence describes it as a partial list of notable properties. Second; "Spiral galaxies and the galactic disk are quite thin" seems to be a clumsy typo. I don't know if the author meant "Sprial and disk galaxies" or "Spiral galaxies' disks" or "Spiral galaxies and their disks are quite thin and ...". Third; it is, imho, a huge mistake to equate the shape of the VISIBLE galaxy with the shape of the galaxy. With our current understanding we can OBSERVE the emr from the normal matter and describe its shape and we infer the bulk of every galaxy is composed of Dark Matter in the shape of a sphere with density diminishing with radius. That is, the "shape" of most galaxies is spherical while their appearance tends to be lenticular (disk, sprial). A clear distinction should be made about what we are talking about. Fourth, the statement that Dark Matter "might not interact through any means except gravity" is a real problem. It almost certainly (if it exists) interacts with itself. So it does interact. I suppose the author meant to say it might not interact with normal matter and electromagnetic radiation, but this needs a citation, since it is my understanding that its not a question of zero interaction, rather a question of the magnitude of the cross-section (the probability of a collision occurring). That said, its also true that we have no clear idea what kind of 'stuff' it is, so talking about any of its positive properties isn't really possible. We can set limits on how much it interacts with normal matter, how much it interacts with emr, and how much it interacts with itself, but we know very little about it other than that. Fifth; "clouds of neutral hydrogen are "raining" down on the galaxy"... THE galaxy?? what is meant by THE galaxy? clouds are either raining down (this is a really poor choice of words, rain suggests 'precipitation from' rather than 'falling down of' the (entire) cloud) on galaxies (on large galaxies?) or they aren't a common property of galaxies. Two other problems with this section: one is that it has zero numbers. Estimates of the rotation speeds, proportions of dark matter, proportions of spiral, elliptical and globular galaxies, estimates of ratio between the two types of galaxies can and should be included. Second, a distinction between old galaxies (at high red-shift) and young ones (near by) should be made since galaxies change with time. It should be made clear which properties change with age and which don't.Abitslow (talk) 17:43, 16 January 2015 (UTC)

## Formation of spiral galaxies - error

"As a galaxy gained mass (by accreting smaller galaxies) the dark matter stays mostly on the outer parts of the galaxy. This is because the dark matter can only interact gravitationally, and thus will not dissipate." this is just so WRONG! First, if galaxies are combining, then it makes little sense to talk about dark matter staying anywhere (the structures are merging, nothing is "staying"). Second, it is absolutely wrong to speak of dark matter "dissipating". Dark matter, we believe, interacts very little with itself or normal matter hence there is no good mechanism for its condensation (normal matter can condense because it can radiate away some of its kinetic energy as a result of collisions). Since dark matter doesn't radiate and doesn't collide, it tends to maintain its velocity and so has little propensity to fall into smaller orbits. Speaking about this as being "mostly on the outer parts" needs a citation, I'd say it tends to be uniform in distribution, certainly more uniform, but I also haven't seen the dynamics simulations which quantify that.Abitslow (talk) 18:13, 16 January 2015 (UTC)

## Fossil Galaxy

In case this article is useful to the authors http://news.nationalgeographic.com/news/2014/05/140510-fossil-galaxy-astronomy-science-space-stars/ Jcardazzi (talk) 13:00, 7 April 2015 (UTC)jcardazzi