If individual star systems show us a wide variety of formation scenarios – and we just examined recent ESO work on circumstellar disks in different star-forming regions – the variety in galaxy evolution is even more spectacular. I’m reminded here of an unusual find when my uncle Roland died unexpectedly and I became his executor. Clearing out his house preparatory to sale, I discovered a series of astronomy photographs that he had blown up to huge scale. An image of M31, the great spiral of Andromeda, was fully six feet long and gorgeously mounted. I remembered nights as a child when he would visit from Florida and point out celestial objects for me to observe with my 3-inch reflector. M31, he told me then, was considerably wider than the Moon in the sky.
When I checked, I found that Andromeda had an angular size of 3 degrees, as opposed to about half a degree for the Moon. Even so, our spectacular sister galaxy is actually a difficult catch, with only its brighter central region visible to the naked eye, and even there tricky to find depending on local conditions of light pollution. Here I chuckle, remembering that I inherited from my uncle his eight-inch Celestron. The bane of his life was his backyard neighbor, who would power up huge outdoor security lights at the most inappropriate times. No luck seeing M31 under those conditions!
Image: M31 through a small telescope, with the Moon’s size shown for reference. Credit: Caradon Observatory.
Timothy Ferris produced a spectacular book called, simply, Galaxies, published by Random House in 1988. If you’re a deep sky devotee, it’s worth seeking out in a used book store, as it’s a coffee-table volume with spectacular photography. The following passage captures some of the grandeur verbally, though it’s from Ferris’ equally valuable Seeing in the Dark (Simon & Schuster, 2002):
The very concept of space is inadequate for dealing with galaxies; one must invoke time as well. The Andromeda galaxy is steeply inclined to our line of sight, only fifteen degrees from edge-on. Since the visible part of its disk is roughly one hundred thousand light years in diameter, the starlight reaching our eyes from its more distant side is about one hundred thousand years older than the light we simultaneously see coming from the near side. When the starlight from the far side of Andromeda started its journey, Homo habilis, the first true humans, did not yet exist. By the time the near-side light started out, they did. So within that single field of view lies a swath of time that brackets our ancestors’ origins – and that, like the incomplete dates in a biographical sketch of a living person (1944-?), inevitably raises the question of our destiny as a species. When the light leaving Andromeda tonight reaches Earth, 2.25 million years from now, who will be here to observe it? We think of Einstein’s spacetime as an abstraction, but to observe a galaxy is to sense its physical reality.
Image: An ultraviolet look at Andromeda, from NASA’s Galaxy Evolution Explorer. Credit: NASA. I owe the reminder for the Ferris quote to the blog Ten Minute Astronomy.
How much more stunning, then, to think about the galaxy recently observed by the team doing the JWST Advanced Deep Extragalactic Survey (JADES). I will mercifully shorten its designation to JADES-GS-z7-01-QU, as the authors of the paper in Nature do. This is a so-called ‘quiescent’ galaxy, meaning that for a variety of possible reasons, star formation within it has all but ceased. The authors describe it as “a compact, discy galaxy.” And as the work of the large team led by Tobias Looser (University of Cambridge) now shows, it is also the first galaxy beyond redshift z=5 to be confirmed and characterized. Indeed, the redshift calculated for this object is z=7.3. The light from this particular galaxy would have been emitted some 13 billion years ago, a ‘mere’ 700 million years after the Big Bang.
We could also look at this galaxy in terms of its ‘comoving distance.’ The latter term is used to accommodate the fact that the universe is expanding, necessary to consider here because if an object is so far away that the light from it has traveled for most of the age of the visible universe, then during that time cosmic expansion has continued. Doing the math on this is beyond my skill set, but my research indicates that at z=7.3, the comoving distance of JADES-GS-z7-01-QU should be in the range of 30 billion light years. Mathematically inclined readers might want to fine-tune that figure.
That ‘chill up the spine’ feeling of encountering deep time/distance never quite goes away. In terms of its significance, though, we can focus in on quiescence, which is a measure of how star formation ceases in a galaxy. The galaxy in question, as observed now, has stopped forming new stars (which means it did that over 13 billion years ago). The paper indicates that the quenching period occurred 10 to 20 million years ago. Star formation seems to have been fast, ending abruptly, but what we don’t know is whether this condition is permanent. Indeed, as the paper on this work points out, how star formation is regulated in galaxies is one of the key open problems in astrophysics.
The authors run through the possibilities for slowing or stopping star formation, which include gas being expelled from galaxies by supermassive black holes or rapid star formation heating the ‘circumgalactic medium,’ thereby preventing the accretion of fresh gases. Low-mass galaxies (this is one) can be affected by feedback mechanisms that deplete the medium within galactic clusters. These differing processes operate over varying timescales, making the significance of JADES-GS-z7-01-QU clear, as noted by Roberto Maiolino (University of Cambridge), a co-author on the paper:
“We’re not sure if any of those scenarios can explain what we’ve now seen with Webb. Until now, to understand the early universe, we’ve used models based on the modern universe. But now that we can see so much further back in time, and observe that the star formation was quenched so rapidly in this galaxy, models based on the modern universe may need to be revisited.”
Image: False-colour JWST image of a small fraction of the GOODS South field, with JADES-GS-z7-01-QU highlighted. Credit: JADES Collaboration.
Thus we have the first of what should become many opportunities to learn about galaxy growth and transformation in the early universe. About the mass of the Small Magellanic Cloud, which continues to form new stars, this galaxy is dead as of the time of observation, but we can’t know what occurred in the 13 billion years before JWST was turned on it. Is quenching a widespread phenomena in the early universe, but a temporary one, so that later epochs see galactic rejuvenation? The scope of future work with JWST is beginning to take shape as we examine finds like these.
The paper is Looser et al. “A recently quenched galaxy 700 million years after the Big Bang,” Nature (06 March 2024). Abstract.
Is this galaxy typical or unusual for galaxies of this age? I have always had the impression that young galaxies were prolifically producing new, metal-depleted stars. Is this impression wrong, based perhaps on analogies of life?
Also, I had no idea galaxy star formation could go in cycles. This is very interesting, again, not like the analogy of metazoa’s one-way aging to senescence.
A dead galaxy…Perfect home for HPL entities:
https://www.universetoday.com/166009/science-fiction-is-learning-about-exoplanets-from-science/
I had Ferris’ book..my Dad bought it for me at a garage sale.
I propped it up against the wall by my window over the bed with its A/C unit.
One night, after a rain—-a thin rivulet went right for that book an ruined it.
The universe hates me.
Coincidentally, while trying to file away old magazines, last night turned to another source for a discussion of ancient galaxies and their implications for cosmology.
The American Institute of Aeronautics and Astronautics (AIAA) has a monthly member publication ( Aerospace America). Kudos to author Karen Kwon for her article Galaxies Everywhere in the May 2023 edition. So I am relating some background and points which she made related to this topic.
The article described JWST data collection methods and sensitivities as well as focusing on six discernible ancient galaxies near the Big Dipper dating back to around 500 million years post Big Bang blast. Galaxies associated with the Abell 2744 galaxy cluster though far more distant, visible as a result of Abell’s gravitational lensing effefct. Images were obtained with the JWST Near Infrared Camera , red shift and distance determined by the associated Near InfraRed Spectrograph ( NIRCam and NIRSpec respectively).
JADES-GS-z7-01-QU was not called out in the article, though there were a couple of other galaxies with similar JADES license plate names.
Stands for JSWT Advanced Deep Galactic Survey. Old in one sense and young in the sense of when we observe them from 13 billion years later. Presumably, they are now at distances of 30 billion light years.
And one comes away with the impression that such large galaxies were rather commonplace back in those days – for reasons we don’t clearly understand.
Likely there are a number of hypotheses that can be tested as more and more images and data are captured, but it is still mysterious. Last spring, enormous stars thousands of times the size of the sun were invoked ( mass or diameter) which burned for a few million years and then exploded. Yet our current bright stars such of 40 solar mass would not burn that long. So, someone explain.
But they are invoked as sources of dust and other molecules ( beside say H2)
“that formed over the next hundreds of millions of years.”
Another consideration, perhaps: When we speak of the current cosmic background radiation we relate it to microwave radiation or temperature of about 2.7 kelvin. When I hear of cosmic expansion, some of it is related to conventional pressure- volume- temperature thermodynamics – and some to the literal expansion of space. I suspect it is a combination of the two. But it does lead me to suspect that there were CBR values between that where particles precipitated into atoms, and then molecules and the current value. I just wonder if higher CBR temperatures would cause odd behaviors in early galaxy formation.
Researcher and Nobel Laureate for Physics John Mather is quoted: ” It is pretty clear that nothing we’ve seen challenges the Big Bang thory….” but as Kwon either paraphrases or summarizes, there are questions about such as how abundant dust was in the early universe and how soon stars and galaxies started forming.
Concluding: “So the search for early, distant galaxies continue. Plenty of questions remain. How did the first stars explode> Did the next ones grow right away afterward? How did the galaxies grow?” But the galactic images seem to suggest that in the old days, stars and galaxies were grown differently.
Could massive stars burn as suggested if the gravitational constant was lower in the past? I am assuming that this would affect other phenomena, some of which would be incompatible with this hypothesis.
A.T.,
In one way or another, there have been questions about how basic constants hold up over time. These observations, of course, might give hints of some such changes, changes suggesting that a constant is not as fundamental as was thought or assumed in other contexts. Now and then though, when people speak of gravity in cosmology or general relativity, the nature or behavior of “inertia” comes into question. Inertia in classical dynamics gives collections of mass of various dimensions certain properties, and if it is related to the interaction of matter ( and energy) throughout the universe, maybe its intensity has changed since the days these galaxies were kicking up dust.
To verify that there is a change in “inertia” perhaps associated with matter and its dynamics – early galaxies might provide some sort of demonstration. But we would need to distinguish motions within a galaxy, I would suspect, some orbital motions or deflections of path.?.. Clearly we’re not there yet.
The answer is no. I am biased against MOND or MGR. I don’t think these principles will ever change since they are first principles.
I’m also biased against MOND, but last week a curious preprint came out stating that their equation is actually a consequence of how quantum particles work in classical spacetime. If the MOND acceleration can truly be deduced from first principles, that breaks the back of my bias. I’ll admit, I read about this in the Guardian … not exactly a peer reviewed journal! For what it’s worth: https://arxiv.org/pdf/2402.19459.pdf
On a more conventional note. What was the temperature of the CMB 700 million years after the BB? Could that affect stellar evolution via less effective heat rejection?
IF there was no big bang, there would be no dark ages, small, compressed universe, and free electrons which block the light of photons from escaping, etc. and another explanation for the cosmic microwave background.
A rough estimate of the temperature is z times the current temperature or 7.3 × 2.7 = 19.7 K. Not sure if that has any effect on star formation.
I recommend finding the largest version of Galaxies you can. I have the hardback and it’s one of my treasures. I open it up and let my mind wander. It’s like taking a trip through the universe.
This may well be covered in the underlying paper, but — over the intervening 13 billion years — there likely would be a “fairly decent” (a lay math term) chance of such a then-young galaxy ultimately at least interacting with (i.e., having a close encounter) if not fully colliding with another galaxy or galaxies.
Thereby re-initiating at least some stellar formation as theretofore diffuse and cold gas clouds — likely with more metal content than earlier in the galaxy’s evolution — experienced renewed compression.
That prospect of interaction/collision perhaps would be even more likely earlier in the universe when things were closer together, including with 13 billions years less of cosmic expansion over that intervening time.
Once/if they’re able to 3D map out this then-young galaxy’s then neighbors, maybe they can do some modeling of how those neighbors potentially would interact directionally and gravitationally to see how much renewed starburst activity might be initiated in an individual galaxy such as this one and/or collectively amongst multiple galaxies over time.
Or perhaps they’ve already done that and such holistic modeling doesn’t yet bridge the gap between what they see in this then-young galaxy in isolation and what they see in the comparatively modern universe that they can see closer in to us and thus more recently.
As in Stanislaw Lem’s work, “a lot can happen over 13 billion years.”
Some of the used bookstores online:
“Galaxies” by Timothy Ferris
The paper on arXiv:
A recently quenched galaxy 700 million years after the Big Bang
I disagree with the premise that we should alter the knowledge and time scale of the process of star formation to fit our conventionally accepted views of cosmology which may be obsolete. We would have to also alter first principles. The Lamda cold dark matter big bang theory is not five sigma and has flaws which will have to be altered to fit the first principles. I will add that I am biased against the idea of a big bang as the beginning our of universe. In otherwords, the models of star formation of our galaxy and other galaxies is correct considering the age of our universe is much older than 13.6 to 13.8 billion years old.
Isn’t the CMB a data point that fixes the age of the universe? If the universe is much older than the CMB Indicates, how would this CMB-inferred age be compatible with a much older universe?
The idea that light can be red shifted into microwaves is a valid hypothesis. The Cosmic microwave back ground could also be ordinary microwaves coming from other cosmic sources than a big bang. AI chat GPT says:
Galactic Dust: Interstellar dust in our own Milky Way galaxy can emit radiation in the microwave range. This emission is often studied to better understand the distribution and properties of dust in our galaxy.
Star-forming Regions: Regions where stars are actively forming, such as molecular clouds and protostellar systems, can emit radio waves in various frequencies, including the microwave range.
Active Galactic Nuclei (AGN): The central regions of some galaxies host supermassive black holes that accrete mass and emit intense radiation, including in the radio frequencies.
Galactic and Extragalactic Radio Sources: Various astrophysical objects, such as radio galaxies, quasars, and pulsars, emit radio waves across a broad range of frequencies, including those in the microwave region.
Sun: The Sun emits radio waves at different frequencies, including the microwave range. Observations of solar activity, such as solar flares, are often conducted in the microwave spectrum.
Consequently, since there are other explanations for the radio frequency 160.2 GHz, our universe could in theory be much older or even infinite and eternal and unchanging without a beginning or end. I won’t deny that this is also a religious idea and dark energy and dark matter have not been proven in the laboratory and are still completely speculative.
It’s hard to see how these various microwave sources could together present a CMB as uniform as the one we observe.
Radio stars and galaxies are everywhere and every direction especially if one considers the size of our universe whether or not it is infinite. It is good to be open to alternative models of cosmology, but I must admit that I don’t easily accept a view which changes first principles to fit a cosmological view such as Mond or modified general relativity.
This might tickle your fancy: Anomalous contribution to galactic rotation curves due to stochastic spacetime.
It is a different interpretation of gravity at the quantum level that supposedly eliminated the need for dark matter.
Article about this controversial idea in the news:
Controversial new theory of gravity rules out need for dark matter
General relativity explains completely all galactic rotation. No quantum theory of gravity needed. Dark Matter used to explain galactic rotation was based on the application of Newton’s laws to galactic rotation, but not GR. Poth 2015.
From what I read on the internet, the suggestion that GR explains the galactic rotation curves is very controversial. If it was cut-and-dried, then the astronomy community would be expected to accept it (eventually). However, there are other pieces of evidence for DM beyond just the requirement to fix the rotation curves including gravitational lensing. At this point, it seems to be a controversial idea based on a few papers using extensive calculations and assumptions of the matter distributions in galaxies, the calculations and assumptions contested by other astrophysicists.
Each advance in data-gathering technology is a bigger spoon, and/or perhaps with a longer handle, resulting in increasing difficulty to chew and swallow each spoonful.
To be specific, the rotation of Earth solar system was compared to galactic rotation. The problem is that our Sun has ninety nine percent of the mass of the entire solar system, but a black hole at the center of a galaxy only has a small fraction of the mass of the it’s hundreds of billions of stars and therefore it is not a correct comparison. Newton’s laws are still valid but solar systems can’t be compared to galactic rotation. Ibid.,
User
Can the high orbital velocity of starts around the center of a galaxy be explained through theories other than Dark Matter, Modified Newtonian Dynamics (MOND), or Self-interacting Dark Matter (SIMD)?
ChatGPT
Certainly, there are additional theories proposed to explain the high orbital velocities of stars around the center of galaxies that do not rely on dark matter, MOND, or self-interacting dark matter. One such concept is gravitational instability in the galactic disk.
According to this theory, the high orbital velocities of stars around the galactic center can be attributed to the gravitational effects of instabilities within the galactic disk itself. Galactic disks are not perfectly smooth; they contain density fluctuations and perturbations due to various processes such as interactions with neighboring galaxies, star formation, and spiral density waves.
These density fluctuations can lead to regions of enhanced gravitational attraction within the disk. As stars orbit within the galaxy, they interact gravitationally with these density perturbations, which can alter their orbital velocities. In regions where the density is higher, the gravitational pull experienced by stars is stronger, leading to higher orbital velocities.
This theory does not require the presence of additional unseen matter like dark matter or modifications to the laws of gravity as in MOND. Instead, it attributes the observed dynamics solely to the gravitational effects of the visible matter within the galactic disk.
However, it’s important to note that gravitational instability alone may not fully account for all observed phenomena in galaxies and may have difficulty explaining certain observations, such as the flat rotation curves observed in many spiral galaxies. Nonetheless, it represents an alternative framework for understanding galactic dynamics without invoking dark matter or modified gravity.
Thanks for that data point. 20 K is not all that hot, but the further back in time you move, the hotter it is going to get and the slope gets steeper and steeper.
A fully mature galaxy at 700GY post Big Bang might have formed several hundred million years earlier. Even if one successively cuts the time in half and doubles the temperature: 350 GY = 40K, 175 = 80K. … Calculating from Z numbers is a little more complicated. However, at some point, the nebular from which stars coalesce – they would have to be of a different nature than the ones in our neighborhood. Mulling that idea, ( or top of my head) “metallicity” in the mix in astronomical terms might be a virtue in cooking up early stars, not that one would expect scads of heavier isotopes floating around.
Oops. On the comment above, that was meant for VIY on the matter of prevailing cosmic background radiation temperature 700 million years post big bang.
But also meant to remark on the Dark Matter question. While there might be issues about high rotation rates of stars around the center of this or other galaxies, if I recall correctly, the reason for Dark Matter’s entrance onto the galactic astronomical stage was due to the orbital rates of stars and globular clusters far from the nucleus. And consequently Dark Matter’s nature or supporting evidence rests more on this behavior. In many galaxies, orbital angular rates appear to speed up, contrary say to those of Saturn’s rings.
Looking at the studies Vera Rubin did back in the 1980s, the rotation rates stood out, sometimes near constant in particular galaxies, but at some remove from the center. And some galaxies had more of this tendency than others. The phenomenon appears for the most part in spiral galaxies. As for ellipticals… well I am curious what rotational rates they display at all. Looking back at Dark Matter history, explanations have been sought for all sorts of conventional matter distribution, but Dark Matter’s cumulative effect without plausible source ( dust, brown dwarfs, gave it an original designation of “non-baryonic” matter. This delights physicists of a certain dye, but when you look at how much unilluminated “baryonic” matter is needed to account for its behavior, by now one can’t accuse those of a Newtonian persuasion of giving up too easily.
Don’t forget that general relativity is not MOND, but keeps Newton’s law of universal gravitation and inverse square law intact so that only with high concentrations of mass or energy does SP and GR predict more precisely the motion of bodies in space like the precession of the orbit of Mercury or any of the other planets. Therefore, I have to reject MOND since we would have to change first principles.
According to my question to AI, it just repeats the consensus of general accepted views on cosmology by astrophysicists, the Lamda cold dark matter theory which includes dark matter and dark energy.
I asked AI what about the latest study that according to general relativity, the speed of the our arms of galactic rotation of galaxies are normal and explained completely by SP and GR. Also Newtons laws of universal gravitation explain them. I asked AI the possible hypothesis that these principles could be used incorrectly applied due to human error and AI agreed, but AI would not support any hypothesis other than the dark matter or MOND. We could conclude that AI needs to be able to analyze an idea or plug into a system of first principles in physics to be better able to think for itself which is does not do, the scientific intuition.
@Geoffrey
LLMs like ChatGPT cannot offer reasoning capabilities and analysis. Despite the hype, they are “stochastic parrots”. In theory, IBM’s logic models that were used to reason, e.g. extracting medical information on cancer to better diagnose and treat cancers, are a better approach for answering your question. Sadly, IBM did not impress the specialists at Sloan Kettering but was much appreciated by less skilled professionals.
We are still not at the stage where AIs (super-AI or AGI) can outthink humans and derive novel ideas from data, or even propose new experimental approaches to test new theories.
Carriages make ruts in unpaved roads. The ruts may fade if not reinforced often enough. These ruts may facilitate the passage of subsequent carriages with the same wheel spacing.
Do boies that are gravitationally active make ruts in spacetime?
That’s “Do bodies”…
Perhaps ships are passing in the night on this debate? If we speak of visible objects such as stars in the arms of spiral galaxies, we have angular velocity data. The visible objects give us an estimate of mass. In a case like Saturn and its rings, we do not observe an inconsistency in our visual picture and our related mass models for planet and matter distributed in rings.
On the other hand, moving from one spiral galaxy to another we see discrepancies and variations. As a result the discrepancies were originally lumped into a category known as Dark Matter, accumulating to an amount larger than visible mass. If it is larger than visible mass, then in all likelihood, it has cosmological consequence since we observe the red shift attributed to “expansion”; perhaps determining if there is a deceleration which would result in contraction the result of mass that was not accounted for in prior estimates.
Deep space observations of distance measuring candles such as supernovae suggest acceleration rather than deceleration, however. Or in other words, that the Hubble constant is not entirely a constant.
So, we come back around again. If galaxies at high red shift seem more “mature” than expected, then perhaps marker supernovae (Type Ia’s – the ones that hate to wait in line) in deep space have some altered characteristics too, characteristics that throw our red shift estimates off? It might take some time to collect and quantify JWST data about such deep space supernovae, but that might be another way to examine some of the oddities of very early galaxies.
And then speaking of oddities about early galaxies, it seems like one of the things invoked in behalf of their formation are very massive and luminous stars. If for no other reason, we refer to the HR diagram and the main sequence to consider the likelihood of life forming on an exoplanet – and rule out its possibility for very luminous and short-lived O or B stars. So in this case, to gage the big stars invoked in early galaxy formation, our attention shifts to the hot stars in the upper left of the diagram. Are the stars discussed in early galaxy formation O and B stars – or something even further to the diagram’s left? And then with the trend of Main Sequence lifetimes, or as Hobb’s would have said, just how “nasty, brutish and short” could their lives have been?
I think you are missing the point that if the physics used to hypothesize the premise of dark matter is wrong then dark matter theory is invalid, then that fact the general relativity describes correctly the rotation speed of all galaxies correct. It idea is that the Sun’s gravity on the planets is stronger than a black hole on the arms of galaxies so the solar systems rotation can’t be used to measure galactic rotation because the scale, gravity and speed are different between the two, the Sun having ninety nine percent of the mass of the solar system, but the black hole having much less a mass ratio than the orbiting stars in a galaxy. I asked this to AI which says that is a misconception.
Another paper says that general relativistic rotation “always exceeds Newtonian velocity. Srivastava, Immirzi, Panella, & Pacwtti 2023. GR is the geometry of space based on the energy and matter in it. There is the gravitational field of the stars in the arms of the galaxy and the black hole that make the difference, so they add energy to the rotation making it faster. No dark matter needed.
In other words, the gravitational field of large bodies has energy or gravitational waves which is independent from their mass according to GR.
GH,
Of course, we are both looking at data coming in and searching for explanations – and with some different takes, but FWIW, here is the way I see it.
The physics used to hypothesize dark matter was decades of observations led by investigative astronomer Vera Rubin. She decided to study spiral galaxy rotation rates and hit a jackpot. Admittedly, spiral galaxies do not have a spherical distribution of matter, but with what distribution they have, their arm rotational velocities were not diminishing. Their rotation rates were not behaving like Saturn’s rings. Sure, energy and matter in terms of gravitational attraction are interchangeable, but you you would need a lot of distributed energy to take the place of the non-luminous matter – and non-radiant energy ( at least for now) is something of a contradiction in terms – unless it’s a whole lot of black holes.
Vera Rubin wrote several survey articles for the AAAS publication Science in the 80s and 90s, summarizing her work, but the Wikipedia articles on Rubin and
galaxy rotation address this story rather well too. As Rubin points out, near the nucleus, stars were rotating more slowly than in the spiral arms and the arms often had close to fixed angular rate. So fast that they should have broken apart – or else there was some other additional and hidden distribution of matter.
Back in the 80s when word was spreading, I felt a little miffed when so many people were willing to fill the void with exotic particles yet where i had gone to school there was a widespread skepticism of exoplanets. But even if exoplanets had proved to be as widespread as they are known to be now, they would have had a really tough job filling the mass deficit, assuming exoplanets as numerous as stars, since generally the mass ratio star to planet is about 1000 to 1.
However, looking at a curve such as displayed at the Wikipedia galaxy rotation site it should be noted ( again) that the rotation rates in the spiral arms is much higher than at the central regions where objects such as large black holes reside. When Rubin initiated here work, black holes had been identified as stellar objects, but I don’t remember much suggestion that they were tens or hundreds of million solar masses at the centers of galaxies. But had that been known, the anomaly would have looked even worse.
Also, galaxies in close passage interact with each other – which causes the spiral arms to attenuate. Likely it is hard to discern what dark matter’s role might be in a situation like that, but I would strongly suspect that such distortions are gravitational effects.
For some time though, I have had to wonder why elliptical galaxies seem to stand on the sideline of this controversy. And then looking at the Wikipedia rotating galaxy site, there was an illustration with two spiral galaxies, one local, perhaps a million light years away and the other several billion farther out. Portrayed as identical, save for one difference: the present day spiral arms were rotating faster.
It was Fritz Zwicky who first came with the idea of dark matter to explain the rotation of galaxies. Whether we use the solar system as a model or Saturn’s rings these are both an incorrect comparison to the speed of galactic rotation. Consequently, there are no problems with general relativity and Newton’s law of universal gravitation and inverse square law which are first principles.
The mass ratio’s of the Saturn or the Sun compared to the total mass of their systems is exponentially larger than the mass ratio of Sagittarius A as the Baycenter of our galaxy. The same is true about all other galaxies. Globular clusters are another example where we should see a faster rotation of the stars due to the mass ratio of the much smaller black hole which is explained by both GR and Newton’s universal gravitation.
These principles have to be used correctly with the same scale analogies like globular clusters compared to galaxies. There are not any shortcuts. One should not assume that it is all the same with every system. The mass ratios must be considered and I don’t think they were with the idea of dark matter. Maybe it has an emotional appeal or just because a astrophysicist of scientist makes a comparison does not mean it must be right. There is always human error to consider. In Jungian psychology, the archetype of authority includes how we are influenced by the conformity of group norms. Astrophysics like physics is not just consensus of opinion, the credentials, or experience of the person that make a theory correct, but the principles and ideas. Sometimes new ideas are accepted uncritically.
The dark matter idea might be one that not anyone has challenged.
When I mean challenged, I mean carefully checking to see if first principles were correctly applied.