If a title is posed as a question, the answer is usually
No.
There has been a little bit of noise that dark matter might have been detected near the center of the Milky Way. The chatter seems to have died down quickly, for, as usual, this claim is greatly exaggerated. Indeed, the claim isn’t even made in the actual paper so much as in the scuttlebutt# related to it. The scientific claim that is made is that
The halo excess spectrum can be fitted by annihilation with a particle mass 0.5–0.8 TeV and cross section (5–8) for the channel.
What the heck does that mean?
First, the “excess spectrum” refers to a portion of the gamma ray emission detected by the Fermi telescope that exceeds that from known astrophysical sources. This signal might be from a WIMP with a mass in the range of 500 – 800 GeV. That’s a bit heavier than originally anticipated (~100 GeV), but not ridiculous. The cross-section is the probability for an interaction with bottom quarks and anti-quarks. (The Higgs boson can decay into b quarks.)
Astrophysical sources at the Galactic center
There is a long-running issue with the interpretation of excess signals as dark matter. Most of the detected emission is from known astrophysical sources, hence the term “excess.” There being an excess implies that we understand all the sources. There are a lot of astrophysical sources at the Galactic center:
As you can see, the center of the Galaxy is a busy place. It is literally the busiest place in the Galaxy. Attributing any “excess” to non-baryonic dark matter is contingent on understanding all of the astrophysical sources so that they can be correctly subtracted off. Looking at the complexity of the image above, that’s a big if, which we’ll come back to later. But first, how does dark matter even come unto a discussion of emission from the Galactic center?
Indirect WIMP detection
Dark matter does not emit light – not directly, anyway. But WIMP dark matter is hypothesized to interact with Standard Model particles through the weak nuclear force, which is what provides a window to detect it in the laboratory. So how does that work? Here is the notional Feynman diagram:
The devious brilliance of this Feynman diagram is that we don’t need to know how the interaction works. There are many possibilities, but that’s a detail – that central circle is where the magic happens; what exactly that magic is can remain TBD. All that matters is that it can happen (with some probability quantified by the interaction cross-section), so all the pathways illustrated above should be possible.
Direct detection experiments look for scattering of WIMPs off of nuclei in underground detectors. They have not seen anything. In principle, WIMPs could be created in sufficiently high-energy collisions of Standard Model particles. The LHC has more than adequate energy to produce dark matter particles in this way, but no such signal has been seen$. The potential signal we’re discussing here is an example of indirect detection. There are a number of possibilities for this, but the most obvious^ one follows from WIMPs being their own anti-particles, so they occasionally meet in space and annihilate into Standard Model particles.
The most obvious product of WIMP annihilations is a pair of gamma rays, hence the potential for the Fermi gamma ray telescope to detect their decay products. Here is a simulated image of the gamma ray sky resulting from dark matter annihilations:
The dark regions are the brightest, where the dark matter density is highest. That includes the center of the Milky Way (white circle) and also sub-halos that might contain dwarf satellite galaxies.
Since we don’t really know how the magic interaction happens, but have plenty of theoretical variations, many other things are also possible, some of which might be cosmic rays:
The upshot of all this is that the detection of an “excess” of unexpected but normal particles might be a sign of dark matter.
Sociology: different perspectives from different communities
A lot hinges on the confidence with which we can disentangle expected from unexpected. Once we’ve accounted for the sources we already knew about, there are always new sources to be discovered. That’s astronomy. So initially, the communal attitude was that we shouldn’t claim a signal was due to dark matter until all astrophysical signals had been thoroughly excluded. That never happened: we just kept discovering new astrophysical sources. But at some point, the communal attitude transformed into one of eager credulity. It was no longer embarrassing to make a wrong claim; instead, marginal and dubious claims were made eagerly in the hopes of claiming a Nobel prize. If it didn’t work out, oh well, just try again. And again and again and again. There is apparently no shame in claiming to see the invisible when you’re completely convinced it is there to be seen.
This switch in sociology happened in the mid to late ’00s as people calling themselves astroparticle& physicists became numerous. These people were remarkably uninterested in astrophysics or astrophysical sources in their own right but very interested in dark matter. They were quick to claim that any and every quirk in data was a sign of dark matter. I can’t help but wonder if this behavior is inherited from the long drought in interesting particle collider results, which gradually evolved into a propensity for high energy particle phenomenologists to leap on every two-sigma blip as a sign of new physics, dumping hundreds of preprints on arXiv after each signal of marginal significance was announced. It is always a sprint to exercise the mental model-building muscles and make up some shit in the brief weeks before the signal inevitably goes away again.
Let’s review a few examples of previous indirect dark matter detection claims.
Cosmic rays from Kaluza-Klein dark matter – or not
This topic has a long and sordid history. In the late ’00s, there were numerous claims of an excess in cosmic rays – ATIC saw too many electrons for the astrophysical background, and and PAMELA saw an apparent rise in the positron fraction, perhaps indicating a source with a peak energy around 620 GeV. (If the signal is from dark matter, the rest mass of the WIMP is imprinted in the energy spectrum of its decay products.) The combination of excess electrons and extra positrons seemed fishy enough* to some to point to new physics: dark matter. There were of course more sober analyses, for example:
A few things to note about this plot: first, the data are noisy – science is hard. The ATIC and H.E.S.S. data are not really consistent – one shows an excess, the other does not. The excess is over a background model that is overly simplistic – the high energy astrophysicists I knew were shouting that the apparent signal could easily be caused by a nearby pulsar##. The advocates for a detection in the astroparticle community simply ignored this point, or if pressed, asserted that it seemed unlikely.
One problem that arose with the dark matter interpretation was that there wasn’t enough of it. Space is big and the dark matter density is low, so it is hard to get WIMPs together to annihilate. Indeed, the expected signal scales as the square of the WIMP density, so is very sensitive to just how much dark matter is lurking about. The average density in the solar neighborhood needed to explain astronomical data is around 0.3 to 0.4 GeV cm-3; this falls short of producing the observed signal (if real) by a factor of ~500.
An ordinary scientist might have taken this setback as a sign that he$$ was barking up the wrong tree. Not to be discouraged, the extraordinary astroparticle physicists started talking about the “boost factor.” If there is a region of enhanced dark matter density, then the gamma ray/cosmic ray signal would be boosted, potentially by a lot given the density-squared dependence. This is not quite as crazy as it sounds, as cold dark matter halos are predicted to be lumpy: there should be lots of sub-halos within each halo (and many sub-sub halos within those, right the way down). So, what are the odds that we happen to live near enough to a subhalo that could result in the required boost factor?
The odds are small but nonzero. I saw someone at a conference in 2009 make a completely theoretical attempt to derive those odds. He took a merger tree from some simulation and calculated the chance that we’d be near one of these lumps. Then he expanded that to include a spectrum of plausible merger trees for Milky Way-mass dark matter halos. The noisier merger histories gave higher probabilities, as halos with more recent mergers tend to be lumpier, having had a fresh injection of subhalos that haven’t had time to erode away through dynamical friction into the larger central halo.
This was all very sensible sounding, in theory – and only in theory. We don’t live in any random galaxy. We live in the Milky Way and we know quite a bit about it. One of those things is that it has had a rather quiet merger history by the standards of simulated merger trees. To be sure, there have been some mergers, like the Gaia-Enceladus Sausage. But these are few and far between compared to the expectations of the simulations our theorist was considering. Moreover, we’d know if it weren’t, because mergers tend to heat the stellar disk and puff up its thickness. The spiral disk of the Milky Way is pretty cold dynamically, which places limits on how much mass has merged and when. Indeed, there is a whole subfield dedicated to the study of the thick disk, which seems to have been puffed up in an ancient event ~8 Gyr ago. Since then it has been pretty quiet, though more subtle things can and do happen.
The speaker did not mention any of that. He had a completely theoretical depiction of the probabilities unsullied by observational evidence, and was succeeding in persuading those who wanted to believe that the small probability he came up with was nevertheless reasonable. It was a mixed audience: along with the astroparticle physicists were astronomers like myself, including one of the world’s experts on the thick disk, Rosy Wyse. However, she was too polite to call this out, so after watching the discussion devolve towards accepting the unlikely as probable, I raise my hand to comment: “We know the Milky Way’s merger history isn’t as busy as the models that give a high probability.” This was met with utter incredulity. How could astronomy teach us anything about dark matter? It’s not like the evidence is 100% astronomical in nature, or… wait, it is. But no, no waiting or self-reflection was involved. It rapidly became clear that the majority of people calling themselves astroparticle physicists were ignorant of some relevant astrophysics that any astronomy grad student would be expected to know. It just wasn’t in their training or knowledge base. Consequently, it was strange and shocking&& for them to learn about it this way. So the discussion trended towards denial, at which point Rosy spoke up to say yes, we know this. Duh. (I paraphrase.)
The interpretation of the excess cosmic ray signal as dark matter persisted a few years, but gradually cooler heads prevailed and the pulsar interpretation became widely accepted to be more plausible – as it always had been. Indeed, claiming cosmic rays were from dark matter became almost disreputable, as it richly deserved to be. So much so that when the AMS cosmic ray experiment joined the party late, it had essentially zero impact. I didn’t hear anyone advocating for it, even in whispers at workshops. It seemed more like its Nobel laureate PI just wanted a second Nobel prize, please and thank you, and even the astroparticle community felt embarrassed for him.
This didn’t preclude the same story from playing out repeatedly.
Gamma rays from WIMPs – or not
In the lead-up to a conference on dark matter hosted at Harvard in 2014, there were claims that the Fermi telescope – the same one that is again in the news – had seen a gamma ray line around 126 GeV that was attributed to dark matter. This claim had many red flags. The mass was close to the Higgs particle mass, which was kinda weird. The signal was primarily seen on the limb of the Earth, which is exactly where you’d expect garbage noise to creep in. Most telling, the Fermi team itself was not making this claim. It came from others who were analyzing their data. I am no fan of science by big teams – they tend to become bureaucratic behemoths that create red tape for their participants and often suppress internal dissent** – but one thing they do not do is leave Nobel prizes unanalyzed in their data. The Fermi team’s silence in this matter was deafening.
In short, this first claim of gamma rays from dark matter looked to be very much on the same trajectory as that from cosmic rays. So I was somewhat surprised when I saw the draft program for the Harvard conference, as it had an entire afternoon session devoted to this topic. I wrote the organizers to politely ask if they really thought this would still be a thing by the time the conference happened. One of them was an enthusiastic proponent, so yes.
Narrator: it was not.
By the time the conference happened, the related claims had all collapsed, and all the scientists invited to speak about it talked instead about something completely different, as if it had never been a thing at all.
X-rays from sterile neutrinos – or not
Later, there was the 3.5 keV line. If one squinted really hard at X-ray data, it looked like there might sorta kinda be an unidentified line. This didn’t look particularly convincing, and there are instances when new lines have been discovered in astronomical data rather than laboratory data (e.g., helium was first recognized in the spectrum of the sun, hence the name; also nebulium, which was later recognized to be ionized oxygen), so again, one needed to consider the astrophysical possibilities.
Of course, it was much more exciting to claim it was dark matter. Never mind that it was a silly energy scale, being far too low mass to be cold dark matter (people seem to have forgotten*# the Lee-Weinberg limit, which requires mX > 2 GeV); a few keV is rather less than a few GeV. No matter, we can always come up with an appropriate particle – in this case, sterile neutrinos*$.
If you’ve read this far, you can see how this was going to pan out.
Gamma rays from WIMPs again, maybe maybe
So now we have a renewed claim that the Fermi excess is dark matter. Given the history related above, the reader may appreciate that my first reaction was Really? Are we doing this again?
― Douglas Adams, The Hitchhiker’s Guide to the Galaxy
This is different from the claim a decade ago. The claimed mass is different, and the signal is real, being part of the mess of emission from the Galactic center. The trick, as so often the case, is disentangling the dark matter signal from the plausible astrophysical sources.
Indeed, the signal is not new, only this particular fit with WIMP dark matter is. There had, of course, been discussion of all this before, but it faded out when it became clear that the Fermi signal was well explained by a population of millisecond pulsars. Astrophysics was again the more obvious interpretation*%. Or perhaps not: I suppose if you’re part of a community convinced that dark matter exists who is spending an enormous amount of time and resources looking for a signal from dark matter and whose basic knowledge of astrophysics extends little beyond “astronomical data show dark matter exists but are messy so there’s always room to play” then maybe invoking an invisible agent from an unknown dark sector seems just as plausible as an obvious astrophysical source. Hmmm… that would have sounded crazy to me even back when, like them, I was sure that dark matter had to exist and be made of WIMPs, but here we are.
Looking around in the literature, I see there is still a somewhat active series of papers on this subject. They split between no way and maybe.
For example, Manconi et al. (2025) show that the excess signal has the same distribution on the sky as the light from old stars in the Galaxy. The distribution of stars is asymmetrical thanks to the Galactic bar, which we see at an angle somewhere around ~30 degrees, so one end is nearer to us than the other, creating a classic “X/peanut” shape seen in other edge-on barred spiral galaxies. So not only is the spectrum of the signal consistent with millisecond pulsars, it has the same distribution on the sky as the stars from which millisecond pulsars are born. So no way is this dark matter: it is clearly an astrophysical signal.
Not to be dissuaded by such a completely devastating combination of observations, Muru et al. (2025) argue that sure, the signal looks like the stars, but the dark matter could have exactly the same distribution as the stars. They cite the Hestia simulations of the Local Group as an example where this happens. Looking at those, they’re not as unrealistic as many simulations, but they appear to suffer the common affliction of too much dark mass near the center. That leaves the dark matter more room to be non-spherical so maybe be lumpy in the same was as the stars, and also provide a higher annihilation signal from the high density of dark matter. So they say maybe, calling the pulsar and dark matter interpretations “equally compelling.”
Returning to Totani’s sort-of claimed detection, he also says
This cross section is larger than the upper limits from dwarf galaxies and the canonical thermal relic value, but considering various uncertainties, especially the density profile of the MW halo, the dark matter interpretation of the 20 GeV “Fermi halo” remains feasible.
OK, so there’s a lot to break down in this one sentence.
The canonical thermal relic value is kinda central to the whole WIMP paradigm, so needing a value higher than that is a red flag reminiscent of the need for a boost factor for the cosmic ray signal. There aren’t really enough WIMPs there to do the job unless we juice their effectiveness at making gamma rays. The juice factor is an order of magnitude here: Steigman et al. (2012) give 2.2 x 10-26 cm3s-1 for what the thermal cross-section should be vs. the (5-8) x 10-25 cm3s-1 suggested by Totani (2025).
It is also worth noting that one point of Steigman’s paper is that as a well-posed hypothesis, the WIMP cross section can be calculated; it isn’t a free parameter to play with, so needing the cross-section to be larger than the upper limits from dwarf galaxies is another red flag. If this is indeed a dark matter signal from the Galactic center, then the subhalos in which dwarf satellites reside should also be visible, as in the simulated image from via Lactea above. They are not, despite having fewer messy astrophysical signals to compete with.
So “remains feasible” is doing a lot of work here. That’s the scientific way of saying “almost certainly wrong, but maybe? Because I’d really like for it to work out that way.”
The dark matter distribution in the Milky Way
One of the critical things here is the density of dark matter near the Galactic center, as the signal scales as the square of the density. Totani (2025) simply adopts the via Lactea simulation to represent the dark matter halo of the Galaxy in his calculations. This is a reasonable choice from a purely theoretical perspective, but it is not a conservative choice for the problem at hand.
What do we know empirically? The via Lactea simulation was dark matter only. There is no stellar disk, just a dark matter halo appropriate to the Milky Way. So let’s add that halo to a baryonic mass model of the Galaxy:
The important part for the Galactic center signal is the region at small radius – the first kpc or two. Like most simulations, via Lactea has a cuspy central region of high dark matter density that is inconsistent with data. This overshoots the equivalent circular velocity curve from observed stellar motions. I could fix the fit above by reducing the stellar mass, but that’s not really an option in the Milky Way – we need a maximal stellar disk to explain the microlensing rate towards the center of the Galaxy. The “various uncertainties, especially the density profile of the MW halo” statement elides this inconvenient fact. Astronomical uncertainties are ever-present, but do not favor a dark matter signal here.
We can subtract the baryonic mass model from the rotation curve data to infer what the dark matter distribution needs to be. This is done in the plot below, where it is compared to the via Lactea halo:
The empirical dark matter density profile of the Milky Way does not continue to rise inwards as steeply as the simulation predicts. It shows the same proclivity for a shallower core as pretty much every other galaxy in the sky. This reduced density of dark matter in the central couple of kpc means the signal from WIMP annihilation should be much lower than calculated from the simulated distribution. Remember – the WIMP annihilation signal scales as the square of the dark matter density, so the turn-down seen at small radii in the log-log plot above is brutal. There isn’t enough dark matter there to do what it is claimed to be doing.
Cry wolf
There have now been so many claims to detect dark matter that have come and gone that it is getting to be like the fable of the boy who cried wolf. A long series of unpersuasive claims does not inspire confidence that the next will be correct. Indeed, it has the opposite effect: it is going to be really hard to take future claims seriously.
It’s almost as if this invisible dark matter stuff doesn’t exist.
Note added: Jeff Grube points out in the comments that Wang & Duan (2025) have a recent paper showing that the dark matter signal discussed here also predicts an antiproton signal that is already excluded by AMS data. While I find this unsurprising, it is an excellent check. Indeed, it would have caused me to think again had the antiproton signal been there: independent corroboration from a separate experiment is how science is supposed to work.
#It has become a pattern for advocates of dark matter to write a speculative paper for the journals that is fairly restrained in its claims, then hype it as an actual detection to the press. It’s like “Even I think this is probably wrong, but let’s make the claim on the off chance it pans out.”
$Ironically, a detection from a particle collider would be a non-detection. The signature of dark matter produced in a collision would be an imbalance between the mass-energy that goes into the collision and that measured in detected particles coming out of it. The mass-energy converted into WIMPs would escape the detector undetected. This is analogous to how neutrinos were first identified, though Fermi was reluctant to make up an invisible, potentially undetectable particle – a conservative value system that modern particle physicists have abandoned. The 13,000 GeV collision energy of the LHC is more than adequate to make ~100 GeV WIMPs, so the failure of this detection mode is telling.
^A less obvious possibility is spontaneous decay. This would happen if WIMPs are unstable and decay with a finite half-life. The shorter the half-life, the more decays, and the stronger the resulting signal. This implies some fine-tuning in the half-life – if it is much longer than a Hubble time, then it happens so seldom it is irrelevant; if it is shorter than a Hubble time, then dark matter halos evaporate and stable galaxies don’t exist.
&Astroparticle physics, also known as particle astrophysics, is a relatively new field. It is also an oxymoron, being a branch of particle physics with only aspirational delusions of relevance to astrophysics. I say that to be rude to people who are rude to astronomers, but it is also true. Astrophysics is the physics of objects in the sky, and as such, requires all of physics. Physics is a broad field, so some aspects are more relevant than others. When I teach a survey course, it touches on gravity, electromagnetism, atomic and molecular quantum mechanics, nuclear physics, and with the discovery of exoplanets, increasingly on geophysics. Particle physics doesn’t come up. It’s just not relevant, except where it overlaps with nuclear physics. (As poorly as particle physicists think of astronomers, they seem to think even less of nuclear physicists, whom they consider to be failed particle physicists (if only they were smart enough!) and nuclear physicists hate them in return.) This new field of astroparticle physics seems to be all about dark matter as driven by early universe cosmology, with contempt for everything that happens in the 13 billion years following the production of the relic radiation seen as the microwave background. Anything later is dismissed as mere “gastrophysics” that is too complicated to understand so cannot possibly inform fundamental physics. I guess that’s true if one chooses to remain ignorant of it.
*Fishy results can also indicate something fishy with the data. I had a conversation with an instrument builder at the time who pointed out that PAMELA had chosen to fly without a particular discriminator in order to save weight; he suggested that its absence could explain the apparent upturn in positrons.
##There is a relatively nearby pulsar that fits the bill. It has a name: Geminga. This illustrates the human tendency to see what we’re looking for. The astroparticle community was looking for dark matter, so that’s what many of them saw in the excess cosmic ray signal. High energy astrophysicists work on neutron stars, so the obvious interpretation to them was a pulsar. One I recall being particularly scornful of the dark matter interpretation when there was an obvious astrophysical source. I also remember the astroparticle people being quick to dismiss the pulsar interpretation because it seemed unlikely to them for one to be so close but really they hadn’t thought about it before: that pulsars could do this was news to them, and many preferred to believe the dark matter interpretation.
$$All the people barking were men.
&&This experience opened my eyes to the existence of an entire community of scientists who were working on dark matter in somewhat gratuitous ignorance of the astronomical evidence for dark matter. To them, the existence of the stuff had already been demonstrated; the interesting thing now was to find the responsible particle. But they were clearly missing many important ingredients – another example is disk stability, a foundational reason to invoke dark matter that seems to routinely come as a surprise to particle physicists. This disconnect is part of what motivated me to develop an entire semester course on dark matter, which I’ve taught every other year since 2013 and will teach again this coming semester. The first time I taught it, I worried that there wasn’t enough material for a whole semester. Now a semester isn’t enough time.
**I had a college friend (sadly now deceased) who was part of the team that discovered the Higgs. That was big business, to the extent that there were two experiments – one to claim the detection, and another on the same beam to do the confirmation. The first experiment exceeded the arbitrary 5σ threshold to claim a 5.2σ detection, but the second only reached 4.9σ. So, in all appropriateness, he asked in a meeting if they could/should really announce a detection. A Nobel prize was on the line, so the answer was straightforward: Do you want a detection or not? (His words.)
*#Rather than forget, some choose to fiddle ways around the Lee-Weinberg limit. This has led to the sub-genre of “light dark matter” which means lightweight, not luminous. I’d say this was the worst name ever, but the same people talk about dark photons with a straight face, so irony continues to bleed out.
*$Ironically, a sterile neutrino has also been invoked to address problems in MOND.
*%I was amused once to see one of the more rabid advocates of dark matter signals of this type give an entire talk hyping the various possibilities only to mention pulsars at the end with a sigh, admitting that the Fermi signal looked exactly like that.
Totally fair. This is exactly why I’m cautious with GC “annihilation fits”: the inferred flux scales like rho^2, and the inner MW halo profile is the dominant systematic—DM-only cusps (via Lactea–style) tend to overshoot what the rotation curve + microlensing allow. If the excess also tracks the bar/old-stellar light, MSPs feel like the null hypothesis, and the fact that dwarfs don’t light up at the required cross section is a big consistency check. Interesting fit, not a detection—profile + morphology + dwarfs have to line up before I’d take it seriously.
Kudos to Triton Station for saying the quiet part out loud.
A messy gamma-ray excess near the Galactic center is not a dark-matter detection, it’s a Rorschach test for people already committed to the hypothesis.
When dark matter is always “consistent with” the signal and never falsified by it, the problem isn’t missing particles, it’s missing skepticism.
I had never seen a radio image of the galactic center; it looks surprisingly organic!
Thanks again for an informative post.
A few posts back, I commented something like “Do flat rotation curves fall simply out of the math with MOND?” and you replied something like “MOND was made to describe those, so it doesn’t really fall out of anything, yet”. I suppose I should better have said that I don’t know what the equation for MOND looks like when acceleration is well below a0, how simple or complex it is, and whether it’s usually expressed as a composition of “Newton plus something else” or as a whole force law in its own right so to speak, and what it looks like in either case. Wikipedia hasn’t helped how I’d like. I can’t say for certain whether MOND has gravity leveling off after a0 or just the resulting orbital speeds (I should probably look up the equation translating strength of gravity into orbital speed). I suppose I don’t know how peculiar it is that rotation curves go basically flat when one might imagine them taking any slope. Despite having read a lot of blog posts on MOND, here and elsewhere. I’ve probably missed a few charts, or a few whole posts.
No expectation that you offer a remedial lesson in mathematics. But if you have the time, energy, and interest to write a stupid-simple post for the lay folk, one describing the basic mathematics of MOND and how they translate into rotational speeds might be fun and worthwhile.
Ah, I see. Yes, the math is simple. In Newton, the acceleration a = GM/R^2 for a point mass M. In the deep MOND regime of accelerations much lower than a0, this becomes a^2 = a0(GM/R^2) where the part in parentheses is the same as in Newton. For a circular orbit, the centripetal acceleration a = V^2/R. Equating the two, (V^2/R)^2 = a0GM/R^2. Note that there is now a 1/R^2 term on both sides, so the dependence on radius drops out. Hence V does not vary with R, it remains constant, i.e., flat. This also gives the scaling with mass that is the BTFR: V^4 = a0GM.
There is a slightly more involved description of the procedure for both dark matter and MOND at https://astroweb.case.edu/ssm/mond/mondprocedure.html and a description of how we account for extended mass distributions at https://tritonstation.com/2024/09/09/progressive-approximations-in-mass-modeling/
Thank you very much!
One way to see MOND is that beyond a0 you take the geometric mean between Newton’s acceleration and a0. The acceleration goes on descending as you move outwards, but less steeply, because after reaching a particular value, all accelerations are ‘averaged’ with that value. The line on a graph (not a rotation speed curve, an acceleration curve) lands roughly halfway between a horizontal line (just a0 all the way out), and the steeper Newtonian line.
I once tried a calculation to check what I knew would probably happen: if you take the arithmetic mean instead of the geometric mean, and see if it lands on the ‘universal curve’ of the RAR, which has been extended further and further out via measurements, it doesn’t, it eventually goes way off.
So why the geometric mean, where you multiply the accelerations then take the sqrt? I found (as mentioned in a recent post) that you can get MOND by just taking the geometric mean of the radius, rather than the acceleration, using r’ = (r[M]r)^1/2. So the effective radius gets shorter and shorter compared to the real radius r, and it’s as if the Newtonian field continues outwards, but gets increasingly ‘compressed’ radially.
Because the geometric mean does seem to come into MOND, perhaps at a fundamental level, it’s worth asking what else it comes into. There’s not much – it hardly comes into anything as far as I know, so it might be a good clue. Stefan once asked that question in a post, I thought it was a great question. I didn’t mention it at the time, but it used to come into calculations I did with rates of change, before I even started looking at MOND. In PSG rates of change make accelerations in a gravity field. I came up with a rough and ready way to get an approximate rate of change with radius at any point in the field, you pick two points near each other and use dx/dr, the value that gives will be for a point in between them that has the relevant rate of change. It turned out that you could get the exact point between them needed for the calculation if you took the geometric mean. This only shows a loose connection, but it’s possible that the geometric mean in MOND is related to derivatives, and in PSG derivatives make accelerations.
“The line on a graph (not a rotation speed curve, an acceleration curve) lands roughly halfway between a horizontal line (just a0 all the way out), and the steeper Newtonian line.”
This is helpful, thank you! Before this discussion, I was toying with the disconcerting idea that my own gravity might be equal to a galaxy’s at the same distance if they were both in the MOND regime and there was no external field effect in play, which seemed unlikely. Don’t have to toy with that anymore.
“So the effective radius gets shorter and shorter compared to the real radius r, and it’s as if the Newtonian field continues outwards, but gets increasingly ‘compressed’ radially.”
Vaguely, I’ve toyed with this thought before. Maybe people who suggest gravity is weak because it leaks into another dimension will say it can’t leak as much below a0 😁.
Yes, to make flat rotation curves, you still need less and less gravity as you move outwards, but the Milgrom pattern is different from the Kepler one.
Btw, the last sentence should have been clearer: ‘it’s possible that the geometric mean in MOND is related to derivatives with respect to radius, and in PSG derivatives wrt radius make accelerations (ie. derivatives wrt time).’
It has never been about particulate dark matter but what is dark matter. If you read this article https://arxiv.org/abs/2511.20188 or for the non technical watch this video https://youtu.be/7p_kZKq1g58?si=WAZ4v-XFYywf8j-1 you get to understand at a fundamental level the origins of MOND from quantum gravity
“… a renewed claim that the Fermi excess is dark matter …” Such claims will continue until we get FUNDAMOND. Does FUNDAMOND-QEH string theory actually work?
Milgrom is the Kepler of contemporary cosmology — on the basis of MOND’s many (approximately) successful predictions.
http://www.scholarpedia.org/article/The_MOND_paradigm_of_modified_dynamics
String theory needs to explain FUNDAMOND, dark energy, & quantum entanglement.
Is Green-Schwarz-Witten-Guendelman-Giveon-Itzhaki-Peleg-Steinhardt string theory a highly plausible explanation for quantum field theory, general relativity, dark matter, & dark energy?
Has Guendelman solved string theory’s swampland problem?
Guendelman, E. I. “Strings with a different tension as dark matter.” The European Physical Journal C 85, no. 6 (2025): 671. https://link.springer.com/article/10.1140/epjc/s10052-025-14408-2
Have Giveon, Itzhaki, Peleg, & Steinhardt found a mathematical basis (instant string folding) for explaining dark energy?
Giveon & Itzhaki, ”Stringy Black Hole Interiors”, 2019, https://arxiv.org/abs/1908.05000
Itzhaki & Peleg, “Instant Cosmology”, 2024, https://arxiv.org/abs/2412.02630
Itzhaki, Peleg, & Steinhardt, “Instant Folded Strings, Dark Energy and a Cycling Bouncing Universe”, 2025, https://arxiv.org/abs/2508.09745
Consider 12 hypotheses:
(1) Gravitational energy is conserved & all gravitons have spin 2.
(2) Each pair of string vibrations might have a tachyonic link propagating in the ultra-vacuum of the multiverse.
(3) There are 3 different forms of inertia (Newton-Einstein, FUNDAMOND, and quantum-event-horizon) based on 3 different types of string tension, namely, Green-Schwarz-Witten string tension, string-entanglement string tension, & dilaton-mediated string tension.
(4) String entanglement causes FUNDAMOND inertia.
(5) String disentanglement causes FUNDAMOND increase of gravitational acceleration.
(6) Dilaton-mediated string folding causes QEH inertia.
(7) Dilaton-mediated string unfolding (overcoming of QEH inertia) causes black holes to emit Hawking radiation & inflaton waves — dark energy is the emission of inflaton waves by black holes.
(8) In the standard form of Einstein’s field equations, the –1/2 needs to be replaced by –1/2 + FUNDAMOND-data-function & the Λ needs to be replaced by Λ + dark-energy-data-function.
(9) There might be 3 fundamental types of physical uncertainty: Heisenberg uncertainty is related to Newton-Einstein inertia; Lestone uncertainty is related to FUNDAMOND inertia; Koide uncertainty is related to QEH inertia.
(10) sqrt(energy) = Koide uncertainty with respect to QEH inertia; sqrt(energy) = Lestone uncertainty with respect to FUNDAMOND inertia.
(11) Gravity Probe B’s 4 ultra-precise gyroscopes DID NOT malfunction — instead they functioned correctly & confirmed the hypothesis dark-matter-compensation-constant =
(3.9±.5) * 10^–5 .
(12) The world’s two greatest living scientists are Mordehai Milgrom & Eduardo Guendelman.
I’m afraid nobody is going to take the effort to get the gist of what you’re intending to propose, David.
The most important prediction from the 12 hypotheses is that, in the Newtonian regime, Newton’s law of gravity is slightly false. The G needs to be replaced by (1+ԑ) * G, where the ԑ is derived from the value of
dark-matter-compensation-constant. The gravitational metrologists have some problems measuring G because they assume that ԑ = 0. I say they are wrong and ԑ > 0.
https://bigthink.com/starts-with-a-bang/better-measure-g-gravitational-constant/
I say the first gravitational metrologists who realize that I am correct can easily win a Nobel Prize (at least for their team leader).
Quantum gravity, if a consistent and effective theory is ever found, will say nothing about the large-scale structure of the universe, exactly as the Standard Model of particle physics says nothing about molecular biology, ecology, or any sufficiently complex assembly of quantum objects. In the classical limit, quantum gravity will be required to reproduce General Relativity, and in doing so it will necessarily inherit GR’s limitations.
Decoupling, as formalized in the decoupling theorem of quantum field theory, does not occur only along an energy scale. It also occurs along a complexity scale. At a minimum, the relevant parameter space is two-dimensional: energy and complexity.
Theories built for simple systems, as all so-called “fundamental” theories are, inevitably break down when applied to complex systems.
There are no fundamental theories, only effective theories. These are theories that are valid within specific contexts and over specific ranges of physical conditions in which they have been calibrated. All theories are approximations. Assigning them a supra-objective, fundamental scope is a subjective move and ultimately an unscientific one.
MOND’s empirical success shows that General Relativity fails in the low-acceleration regime, establishing a clear limit to GR’s effective range. But this immediately opens the door to questioning GR at the opposite extreme as well: very high accelerations, ultra-dense objects, and the conditions that give rise to another sacred cow of cosmology, black holes.
Whenever theories are applied beyond their proper context and physical conditions, tensions and contradictions inevitably appear. Modifying or replacing the theory is what the scientific method demands, and this is always cheaper, intellectually and empirically, than inventing unseen entities such as dark matter, dark energy, sterile neutrinos, and the like.
Dogmatism is extremely expensive, and the decades-long “search” for dark matter is a textbook example of that fact.
I partially disagree and partially agree. The disagreement comes from your rejection of possibilities for philosophical reasons. What we expect starting from philosophy might be falsified by a “miracle” such as the Kaluza-Klein miracle unifying electromagnetism and gravity while actually the idea was just to consider an additional dimension.
Yet I agree that from philosophical standpoint it is better to keep the authority of investigations on their primary subject; if quantum gravity quantizes spacetime, it might perhaps have an effect but that should roll out naturally and preferably unexpected. It is less fruitful to actively search for a connection with MOND.
My bet is now on an explanation of what really causes inertia; why does the mass mediate between energy and acceleration? I believe a tiny bit of energy from applying a force is spent on making Unruh radiation which is necessary to get the object to accelerate.
@tritonstation Now, who said that? (“If a title is posed as a question…”)
I dunno, Mike. It’s been a thing for as long as I remember.
Seeing the title of this post immediately grabbed my attention. I have been working on another wildly speculative, amateur theory for a number of weeks that posits a type of dark matter (DM) with very specific properties that originates from a 2nd Higgs field arising in the early Universe. But I was thinking only of the DM that MOND couldn’t account for in galaxy clusters. I’ve long accepted that the supposed DM at galaxy scales probably has something to do with the expansion rate of the Universe as Milgrom and others have hypothesized. The title of the paper is: “Matter/Dark Matter from Two Higgs Doublet Model”. There is a whole class of models that postulate a 2nd Higgs field, many of which also probably make a connection to DM. This latest post by Dr. Mcgaugh is very helpful to my model building in that it condenses all the trials and tribulations involved in efforts to detect particulate DM.
The question still arises:
If you see an invisible particle who do call?
Ghostbusters!
Don’t call Ghostbusters — instead, call dark-matter-particle-busters.
Please invite Yoshio Koide https://en.wikipedia.org/wiki/Yoshio_Koide
and John Paul Lestone (Los Alamos National Lab) as guest bloggers.
I think the Koide formula and Lestone’s theory of virtual cross sections are essential for understanding the foundations of physics.
As I was working on the above mentioned model it was necessary to thoroughly understand the ‘crown jewel’ of the Standard Model – the electroweak synthesis. I understood it at a ‘pop-science’ level, but digging deeper I quickly realized this wasn’t physics for the faint-hearted. It’s formidably complex. But I think I have a pretty good grasp of it now. The problem with particulate DM is its parameter space has been steadily shrinking with negative results from a great number of very sophisticated and expensive terrestrial experiments over decades. This doesn’t leave much space for a viable DM candidate, not to mention astrophysical constraints. On the other hand, while MOND greatly reduces the need for DM in clusters, it doesn’t eliminate it entirely. Perhaps there’s some non-particle explanation for the remaining gravitational evidence for DM in clusters, but I’m currently leaning towards right-handed neutrinos with exotic properties.
As always, thank you for your efforts to explain these matters on your blog. The details are always far beyond me. But, it is refreshing to read discourse motivated by actual curiosity about how things work rather than how to advance a career with dubious claims. I appreciate whatever I can take away from your posts and comments.
“It’s almost as if this invisible dark matter stuff doesn’t exist.” The problem is not with invisibility — the problem is with Einstein’s field equations and the version of string theory having only one type of string tension. The string theory as formulated by Green, Schwarz, and Witten in their 2-volume work “Superstring Theory” seems to indicate that MOND is wrong. MOND is not wrong — Green, Schwarz, & Witten wrongly assumed that there is only one type of string tension.
According to Eduardo Guendelmap, “The string and brane tensions do not have to be put in by hand, they can be dynamically generated, as in the case when we formulate string and brane theories in the modified measure formalism. Then string and brane tensions appears, but as an additional dynamical degree of freedom. It can be seen however that these string or brane tensions are not universal, but rather each string and each brane generates its own tension, which can have a different value for each string or brane. There should be also a considerable effect for the effective gravity theories derived from these theories.”
“Dynamical String Tension Theories with target space scale invariance SSB and restoration” https://arxiv.org/abs/2104.08875
The effective gravity theory we need is one that contains FUNDAMOND (and, probably, FUNDAMOND inertia).
SSB https://en.wikipedia.org/wiki/Spontaneous_symmetry_breaking
HYPOTHESIS: Guendelman is the greatest theoretical physicist since Einstein.
Newton, Einstein, & Guendelman ???
Think about Ghostbusters: https://en.wikipedia.org/wiki/Ghostbusters
Perhaps pro-MOND experts should think about producing a documentary film entitled “Dark-matter-particle-busters”. We might carve a wooden totem pole with images of Newton, Kepler, Einstein, Milgrom, and Guendelman, and then carry this totem pole through the streets of Cleveland and Tel Aviv.
I’m struggling to find the source of this information, but I read that the solar system barycenter acceleration was found using DR3 quasar motions to be about 2.36 x 10^-10 m/s^2 towards ~galactic center with dark matter, or about 1.2 x 10^-10 m/s^2 without dark matter.
First, would that be an accurate statement?
Second, is this understood to just be a bizarre coincidence in the MOND paradigm to have this coordinate acceleration also be about a0?
What is the explanation, if any?
Gaia has a page on this here: https://www.cosmos.esa.int/web/gaia/edr3-acceleration-solar-system#
The science paper (https://www.aanda.org/articles/aa/full_html/2021/05/aa39734-20/aa39734-20.html) gives 2.32E-10 m/s/s. So that’s the solar system acceleration measured relative to QSOs by Gaia.
The circular speed due to the Galactic potential potential at the current location of the sun is 2.17E-10 m/s/s. So that’s most of it.
Then there is the vector sum of the acceleration due to everything else in the universe; for example the LMC would contribute about 0.22E-10 m/s/s and Andromeda about 0.16E-10 m/s/s, albeit pointing in somewhat different directions.
When testing for MOND in other galaxies (under an assumption that DM does not exist) do we first assume that MOND is operating in our own galaxy, and providing the excess acceleration of the solar system barycenter? By excess I mean the measured acceleration which is beyond that expected from Newton plus baryons, and which coincidentally appears to be very close to a0.
So an acceleration near a0 is getting assigned to an observer whether due to dark matter or MOND. Is that what is generally happening here?
Yes: we measure accelerations; any that exceed the amount that can be attributed to the observed baryons is called dark matter. If it is the right amount, it can be ascribed to MOND. That’s a critical distinction: MOND predicts what the acceleration has to be given the observed distribution of stars and gas, while dark matter may be attributed to any excess regardless of its amplitude.
For our location in the Milky Way, the stars and gas we know about explain most of the observed acceleration: 1.45E-10 m/s/s (1.2a0) while the observed amount is 2.17E-10 m/s/s (1.8a0). This is not entirely coincidental, as spiral galaxies only exist around or below a0. Like other bright spirals, the Milky Way is “maximal” in the sense that most of the dynamics interior to the solar system is dominated by the baryons: it is close to the Newtonian regime. However, there are no spirals well into the Newtonian regime; those with a >> a0 would be unstable.
Unfortunately I’m not able to keep up yet. When you say, “For our location in the Milky Way, the stars and gas we know about explain most of the observed acceleration: 1.45E-10 m/s/s (1.2a0) while the observed amount is 2.17E-10 m/s/s (1.8a0).” are you saying that just Newtonian gravity plus known baryons would give 1.45E-10 m/s/s towards roughly our galactic center? Or is this actually GR plus known baryons?
And what is the observed amount 2.17E-10 m/s/s? Is that different than what we said earlier about the measured SSB acceleration of 2.32E-10 m/s/s from DR3? Thank you for taking the time to explain all this!
Yes. Just the baryons and Newton-Einstein give 1.2a0. The observed amount I quote is the centripetal acceleration of the gravitational potential at the solar location (1.8a0). The sun itself is not a perfect test particle; it has a small peculiar motion, hence the slightly higher acceleration from DR3 which also includes that extra component.
Thank you. That perfectly explains it. So the discrepency in our own acceleration attributed to either DM or MOND is only about 0.6a0, not a0. Now I see why you are saying it’s not really as big of a coincidence as I had first thought.
It seems we live in the transition between the two regimes, which starts at around g = 2e-9. (In clusters the similar but different RAR also starts at 2e-9, but it then has far less of a transition, which may be a good clue). In galaxies MOND kicks in at a0, and can only describe what happens after that. But (tell me if this is incorrect), the transition from 2e-9 to 1.2e-10 is described by your equation
g[obs] = g[bar]/(1-e^[- sqrt(g[bar]/a0)])
which I checked most of ten years ago and it worked. I’m glad to tell you it still works…. I put in g[bar] = 1.45e-10, and got g[obs] = 2.17431e-10, which is spot on.
The transition being normal is important, particularly as the rotation curve in our galaxy has been looking a bit not normal – is this how you see it, it seems to me this makes it more likely that it’s some artifact or separate effect altering the result.
Yes, that interpolation function works in galaxies, both above and below a0. The chief uncertainty in the shape of the transition region is the systematic in the stellar mass-to-light ratio. Raise it and you make the transition sharper (at the risk of exceeding Newton at even higher accelerations); lower it and you make the transition more gradual (at the risk of not reaching Newton at high accelerations). So it is pretty well hemmed in, but also hard to nail down completely.
I don’t have anything new to add to what I had to say about the MW rotation curve in the series of posts a couple years ago. Every time someone has bet against the Milky Way being a normal spiral galaxy they have lost, so I expect the departure from normality – which is modest by historical standards – is a systematic error of some sort.
https://tritonstation.com/2023/09/19/recent-developments-concerning-the-gravitational-potential-of-the-milky-way-i/
https://tritonstation.com/2023/09/20/recent-developments-concerning-the-gravitational-potential-of-the-milky-way-ii-a-closer-look-at-the-data/
https://tritonstation.com/2023/09/21/recent-developments-concerning-the-gravitational-potential-of-the-milky-way-iii-a-closer-look-at-the-rar-model/
I didn’t realise it does the whole curve. By g = 9.8 there’s no measurable difference from standard theory. It doesn’t seem to involve MOND apart from a0 (correct me if that’s wrong), but you call it an interpolation function – you of course don’t need me to tell you any of this, but can I ask if you checked to make absolutely sure it’s not a gravity theory? If it stays with the observed RAR curve further out, then with g for g[obs] and GM/r^2 for g[bar], even if it doesn’t necessarily cover every scale, it seems to me it does better than a lot of theories.
Actually I haven’t understood enough yet 🙁
If the 2.32×10^-10 m/s^2 is the DR3 measured net acceleration of solar system barycenter towards roughly galactic center, then what is the acceleration attributed to Newton-Einstein for all baryon sources (including the sources of the Sun’s peculiar motion)? That is really the difference I am looking for, because it should more fully represent the net difference in our measured acceleration that might need to be attributed to DM/MOND without specifying any solution.
Great to see your post focused on gamma-ray astrophysics, bringing up memories for me from the past fifteen or so years of working in the field.
An update on the Totani paper, which is outside of the Fermi LAT collaboration, is that ironically (considering the history of claims you discuss from the AMS group) the AMS-02 antiproton results apparently rule-out the Totani result, according to the paper https://arxiv.org/pdf/2512.12176
Two small public-facing contributions I’ve made to the “are we here again” debate between the pulsar gamma-ray signal explanation versus dark matter interpretation for the Galactic Center are comments I’ve made in New Scientist magazine articles:
April 2022: https://www.newscientist.com/article/2318060-mysterious-gamma-rays-at-centre-of-milky-way-could-be-from-pulsars/
October 2025: https://www.newscientist.com/article/2500462-the-centre-of-our-galaxy-may-be-teeming-with-dark-matter-particles/
(that more recent article is on the Muru and Joe Silk paper on simulation results)
It’s interesting to see your discussion of the via Lactea simulations, thanks for that.
Cool. Thanks for pointing those out. Those those who have read this far will want to read both articles, if they can access New Scientist. The Wang & Duan paper I’ll try to add somewhere above; thanks for pointing that out as well as I had not yet seen it – I think I was too bust writing this!
I found this article in The Conversation ( https://theconversation.com/the-universe-may-be-lopsided-new-research-265256 ) interesting. “Lopsided” is a non-technical term that the editor rather than the author chose.
The matter and CMB dipoles do not match up – the directions are consistent (top panel) but the amplitudes are not (bottom panel). Secrest et al., Reviews of Modern Physics 97 (2025) 041001
The outcome is that the universe fails the Ellis-Baldwin test. The variation in matter does not match that in the CMB.
…
Their conclusion is: The cosmic dipole anomaly has thus established itself as a major challenge to the standard cosmological model, even if the astronomical community has chosen to largely ignore it.
This may be because there is no easy way to patch up this problem. It requires abandoning not just the Lambda-CDM model but the FLRW description itself, and going back to square one.
My response: We live in interesting times.
That’s indeed very interesting. It is tempting to interpret that as another sign of the excess in the growth rate of large scale structure we predicted with MOND. The direction on the sky is preserved – the CMB fluctuations are the source of future structure in either theory – but the growth is faster in MOND so you get larger scale structure and faster kinematics earlier in the history of the universe.
This has been a prediction of MOND for so long that when I refereed https://arxiv.org/abs/astro-ph/0105184 I pointed out that they were low-balling the EFE at high redshift. Well, initially they didn’t know to take it into account and the Lyman alpha forest was way off. After accounting for it they were pretty close but still a bit off. That’s due to using an LCDM growth rate to estimate the EFE, the discrepancy goes away for a MONDian growth rate.
And that was a reasonable paper.
One possibility that rarely gets discussed is that the “Surface of Last Scattering” itself may be a misinterpretation. If the sky is populated by galaxies and structure in every direction at all accessible depths, including galaxies now being observed at epochs overlapping the so called Cosmic Dark Ages (roughly z=20 to z=100) then the background need not be a primordial flash from a unique beginning. It can instead be the cumulative, thermalized radiation of stars, dust, and plasma in a long-lived or effectively unbounded reality.
In that view, the LSS is not a physical creation boundary but an opacity horizon: the distance at which the intervening medium becomes opaque to microwave radiation.
The CMB dipole then reflects local and line-of-sight structure rather than global motion with respect to a universal rest frame. If so, the Ellis–Baldwin failure is not an anomaly to be patched, but a signal that the FLRW picture itself is being overextended.
Even more, it seems increasingly clear that we will keep finding fully formed galaxies at ever higher redshifts, forcing star-formation efficiencies toward 100%, or even beyond, simply to preserve a timeframe that is itself now under direct assault from these observations. Not even MOND-style accelerated structure formation can rescue this situation.
The entire framework is coming apart, and ΛCDM is being kept on life support through selective funding and the effective censorship or blacklisting of alternative ideas.
https://qspace.fqxi.org/news/165301/out-of-the-swampland-a-new-paper-by-eduardo-guendelman
https://www.eurekalert.org/news-releases/1086616
If people say ‘everything is coming apart’ or ‘everything is fine’ then there may be other elements mixed in with the physics. As always, some of our ideas are correct, some are wrong, and we’re getting there slowly. When we look back at the past, we find a mixture of both, and when our descendants look back, they’ll find the same. At present, SR and QM are absolutely fine, and they’re very important. But some other theories are in trouble – GR is widely seen as a large-scale approximation, inflation is looking like it has a major fine-tuning problem (and is only defended to the extent it is to prop up GR over the flatness of space at a large scale). String theory has been effectively falsified by not finding supersymmetry, though in principal it still might exist. Our new measuring instruments are showing some of the old theories to be wrong, including LCDM, which looked fine for a while with the previous generation of measuring instruments. But just because some ideas are failing, it’s important not to throw out everything, or give up on the challenge of explaining the new data.
I see it differently. Forcing star-formation efficiency toward extreme values is not fundamentally different from inventing fictional dark matter to keep the framework intact. In both cases, parameters are being pushed beyond physical plausibility to preserve assumptions that are themselves under strain.
At this point, even the very idea of a singular creation event, the so-called Big Bang, is in question, as is the notion of cosmic expansion as it is usually framed.
General Relativity already fails at the galactic scale. That alone makes any results obtained by applying it beyond that level highly questionable, and using it at the scale of the entire universe even more so.
GR is a “local” theory, accurate only within a limited range of physical conditions. It demonstrably fails in the MOND regime. This is a basic empirical fact that reductionists still fail to fully internalize.
“Supersymmetry has been effectively falsified by not finding supersymmetry …” The simplest form of SUSY has been ruled out, but there might be an infinity of more complicated theoretical forms of SUSY. The search for SUSY might last for centuries or millennia. Witten & Maldacena have a favorable opinion of SUSY. See “When symmetry breaks down” by Edward Witten, June 2004
https://www.ias.edu/sites/default/files/sns/Symmetry(3).pdf
One of my ideas is that SUSY occurs in the form of SO(64) at the very beginning of the big bang. All of the superpartners decay and SO(32) takes over.
An unlikely possibility is that gravitons & gravitinos have MOND charges.
According to Kroupa, LCDM is now ruled out by empirical evidence. It seems that Guendelman has now solved string theory’s swampland problem. Thus, FUNDAMOND inertia is put into play in string theory. I predict that Migrom & Guendelman will share a Nobel Prize in 2026 or 2027. Milgrom is more than 20 years overdue for a Nobel Prizes.
Hi Stacy.
Thank you for this post on “Has dark matter been detected in the Milky Way?” and for your other posts throughout the year.
You raise two interesting points from the Totani paper on gamma ray emission from the Milky Way.
Firstly: whenever an observation is not fully understood, we should ask whether the observation can be explained in terms of existing astrophysical objects; we should not jump in straightaway with a dark matter proposal. In this case it seems that millisecond pulsars (and other options) can explain the data.
Secondly: whenever a new proposal for dark matter is put forward, we should ask whether this explains all dark matter phenomena, or just the observation in hand.
Is there not a standard check list that all ideas for dark matter can be tested against. Such as:
a) How does it explain galaxy rotation curves?
b) How does it explain the acoustic peaks in the CMB power spectrum?
c) How does it explain structure formation?
…
z) How does it explain the gamma ray excess from the Milky Way?
I would be delighted if there was a “McGaugh Test” with a “McGaugh Scale”, so that different dark matter hypotheses could be given their own “McGaugh Score”.
Yes, that would perhaps be useful. It used to be the responsibility of a competent theorist to know these things. The closest thing available at present is https://tritonstation.com/2016/10/22/the-grand-observational-challenge-for-galaxy-formation-simulations/
really appreciate this, each claimed signal seems to rely on optimistic halo cusps, boosted cross sections and hand wavy treatment of baryons. if the milky way’s inner halo is cored like the data suggest, the annihilation rate is way too small for fermi’s excess.
I might feel compelled to write an actual paper about it.
If the only way this “annihilation signal” survives is by leaning on an optimistic inner cusp (to cash in on the rho^2 magic, of course) and then asking dwarfs to politely stay quiet, that’s…interesting? It starts to look less like a discovery and more like a bookkeeping decision: pick the halo profile that makes the fit work, then call the fit “evidence”. Meanwhile, anything that makes the Milky Way behave more like a normal maximal spiral—baryons doing most of the work, with only a modest residual in the transition regime—quietly shrinks the J-factor and the whole story goes limp. Until the sky pattern stops mimicking the bar/old stars and the same parameters behave elsewhere, “detected” feels like the wrong verb. Merry Christmas, btw.