Turtles All The Way Down

From this physics preprint.

Making Sense Of Cosmological Neutrino Mass Bounds

A new paper tries to make sense of the DESI results that suggest a sum of the three neutrino masses that is equal to or smaller than the minimum value suggested by neutrino oscillation experiments (which is roughly 0.06 eV).

An outlier data point in the DESI data and a known methodological issue in the Planck 18 data that a later version of the analysis of the Planck data has corrected largely resolve this issue. A non-constant "cosmological constant" would also help resolve the discrepancy and is increasingly favored by observation.

Even with relaxed bounds, however, the cosmological constraints on the sum of the three neutrino masses are still considerably tighter than those derived from direct measurements of the lightest neutrino mass. And, cosmological bounds, along with other data sources, continue to favor a "normal hierarchy" of neutrino masses over an "inverted hierarchy."

Cosmological neutrino mass bounds are becoming increasingly stringent. The latest limit within ΛCDM from Planck 2018+ACT lensing+DESI is ∑mν < 0.072eV at 95% CL, very close to the minimum possible sum of neutrino masses (∑mν > 0.06eV), hinting at vanishing or even ''negative'' cosmological neutrino masses. 

In this context, it is urgent to carefully evaluate the origin of these cosmological constraints. In this paper, we investigate the robustness of these results in three ways: i) we check the role of potential anomalies in Planck CMB and DESI BAO data; ii) we compare the results for frequentist and Bayesian techniques, as very close to physical boundaries subtleties in the derivation and interpretation of constraints can arise; iii) we investigate how deviations from ΛCDM, potentially alleviating these anomalies, can alter the constraints. 

From a profile likelihood analysis, we derive constraints in agreement at the ∼10% level with Bayesian posteriors. We find that the weak preference for negative neutrino masses is mostly present for Planck 18 data, affected by the well-known "lensing anomaly". It disappears when the new Planck 2020 HiLLiPoP is used, leading to significantly weaker constraints. Additionally, the pull towards negative masses in DESI data stems from the z=0.7 bin, which is in ∼3σ tension with Planck expectations. Without these outliers, and in combination with HiLLiPoP, the bound relaxes to ∑mν<0.11eV at 95% CL. The recent preference for dynamical dark energy alleviates this tension and further weakens the bound. As we are at the dawn of a neutrino mass discovery from cosmology, it will be very exciting to see if this trend is confirmed by future data.

Daniel Naredo-Tuero, et al., "Living at the Edge: A Critical Look at the Cosmological Neutrino Mass Bound" arXiv:2407.13831 (July 18, 2024).

Outstanding Issues In Human Evolution And Prehistory

About half of this blog's posts are devoted to developments in human evolution and our understanding of human pre-history and ancient history. Midway into 2024, what are the hot issues that are outstanding in these fields?

Archaic Hominins

What ecological pressures drove early hominin evolution from a common ancestor of, or sister clade to chimpanzees and bonobos?

When did early hominins become bipedal and why?

Why did modern humans lose most of their body hair?

Precisely which archaic hominin species were ancestral to modern humans and which were "dead ends"? 

Which archaic hominin species could produce hybrid offspring with each other? We know that there was modern human-Neanderthal admixture, modern human-Denisovan admixture, Neanderthal-Denisovan admixture, and Denisovan-super archaic admixture. Did Homo floresiensis have hybrid offspring with modern humans? Was there any archaic admixture with modern humans in Africa, and if so, in whom is a legacy of this (if any) found today?

What species is the source of super-archaic admixture in Denisovans? Did Denisovans admix with Homo erectus or with Homo floresiensis? 

What did Denisovans look like? What were their lives like? How smart were they?

What was the population structure within Denisovans like and what waves of Denisovan populations existed and replaced each other?

What archaic hominin species were present in Africa and when?

What archaic hominin species were present outside of Africa and when and how did they get there?

When and why did various archaic hominin species go extinct (especially outside of Africa)? Why did the Neanderthals go extinct? Are there any relict archaic hominin populations in the world? If not, when did the last relict population of archaic hominins go extinct? Why did the Neanderthals go extinct? Why did the Denisovans go extinct? Why did Homo floresiensis go extinct? Are our legends of human-like fairies, elves, dwarves, Yeti, trolls, etc. oral history recollections of our contacts with archaic hominins?

Precisely when, where, why, and how (within Africa) did modern humans evolve from archaic hominins?

Which archaic hominin species interacted directly with modern humans?

To what species should the Julurens archaic hominin remains in China be assigned?

Do the Homo erectus-homo sapien mosaic feature skulls in China represent hybrid species individuals, or separate species of the genus Homo?

Prehistory and Ancient History

Why is the archaeological evidence for modern humans in the range from Arabia to India so much earlier than the genetic indications of the main Out of Africa expansion?

What connection was there between the expansion of modern humans from India to Southern Asia, the extinction of Homo erectus, and the Toba eruption?

What were the main waves of modern human expansion into Asia? How much did later waves replace earlier waves?

How much substructure was there in the founding population of the Americas settlement of the Americas?

There is evidence of a modern human presence in the Americas many thousands of years before the main founding population wave(s). Why didn't this early modern human presence thrive and leave more of a mark? Was this a single continuous event, or were there multiple false start migrations that successively failed? Where there any modern humans left in the Americas when the first wave of the founding population of the Americas arrived?

What narrative explains the apparent Paleo-Asian ancestry in select indigenous tribes in South America?

What post-founding era, pre-Columbian contracts were there between the Americas and modern humans from the "Old World"?

What was the biggest level of societal structure in the hunter-gatherer era of humanity? What was life like in those tribes?

Was Göbekli Tepe really pre-Neolithic? Was it connected with a Neolithic era false start? What made it possible? Do its inscriptions document a Younger Dryas causing extra-terrestrial impact?

What did the process of assembling a full Neolithic package of domesticates in the Fertile Crescent from multiple places of domestication in that region look like? What were relations like between Caucasian hunter-gatherers and their first farmer descendants, and Levantine hunter-gatherers and their first farmer descendants, as the two populations were very genetically distinct but cooperated to assemble the full Fertile Crescent Neolithic package?

What did the pre-Indo-European linguistic landscape look like? Did the languages of the European hunter-gatherers leave any trace (e.g. in linguistic substrates or loan words)? Were the languages of the pre-Indo-European farmers of Europe, presumably including Basque, all derived from a single language family of the first farmers of Western Anatolia?

Was there a macro-family of ergative languages in Mesopotamia, Anatolia, the Caucuses, and West Asia? Do the languages of the Caucuses have a common origin, and if so, are they related to this possibly macro-family of ergative languages? Was the Harappan language part of one or both of these language families? Did this language family extend to North Africa?

Was there a cultural and linguistic and religious replacement by conquest in Anatolian sometime between the late Neolithic era and the early Bronze Age giving rise to the Hattic people with a demic component?

When did the various pre-Indo-European languages of Europe and West Asia (except Basque) go extinct?  

Where and how did the Indo-European languages originate?

What is the timeline and geography of Indo-European languages? What is the correct phylogeny of the Indo-European languages? What is the correct origin story for each Indo-European language, particularly, ambiguous and possibly complex cases like Armenian?

Did the Corded Ware people, the Yamnaya people, and the Bell Beaker people speak the same Indo-European language? Why did the Corded Ware people and the Yamnaya people have such distinct Y-DNA ancestry despite having similar autosomal ancestry, familial patterns, and a shared presumed language family?

What Indo-European languages were spoken by the Bell Beaker people and their descendants before Celtic and Germanic languages in the narrow sense emerged? How similar were they culturally and linguistically to the historically attested early Celtic and Germanic peoples? What was the nature of the interactions and feelings of the Bell Beaker people and Corded Ware people towards each other?

What is the story behind the dramatic surge in lactose tolerance genes shortly after Indo-Europeans arrived in Western Europe?

When did the Indo-European Anatolian languages arise and why were they so distinct from other Indo-European languages?

Was the Minoan culture an offshoot of the pre-Hittite Anatolian Hattic culture or a larger linguistic and cultural family?

What was the Harappan culture like and what languages, if any, was its language related to?

What was the exact chronology of Indo-European migration to what is now Iran and to South Asia? What were the main outlines of its waves of expansion within India?

How did Hinduism emerge from Harappan and Indo-Iranian religious practices and beliefs? What caused the divergence between it and the ancient Iranian religion? When did particular practices and beliefs, like vegetarianism and the sacred cow emerge?

What was the social structure in India like between the Indo-Aryan arrival and the establishment of strict jati endogamy much later?

Is the Dravidian language related to any other existing or extinct language? When did it arise? When did its branches arise? How did the Brahui come to speak a version of it? Why does the language family seem less diverse and younger than plausible theories about its time of origin? Did it contract in the face of Indo-Aryan expansion and then reclaim much of South Asia? Does the Dravidian language family and the culture of the Dravidian people have any connections to Niger-Congo languages and the cultures of the people in the Sahel of Africa who domesticated many key crops of the South Indian Neolithic Revolution? Does Y-DNA T, which has a peculiar geographic distribution in India have any connection to the origin story of the Dravidian languages?

What is the origin story of the Chadic people? What about the Fulani people and their languages?

How are the Afro-Asiatic languages related to each other and what are there respective origin stories in time and space?

When did the Berber languages emerge? What preceded them?

What is the origin story of the emergence and spread of the Nilo-Saharan languages?

When did the languages spoken by the Pygmies in Africa die? Are there any traces, such as in linguistic substates or loan words of Bantu languages, of those lost languages?

Was there a historical Atlantis, and if so, when and where was it?

Why do the genealogies of Genesis and the Mesopotamian king lists have such seemingly long lived people?

How much of the books of Genesis and Exodus in the Bible derive from Mesopotamian lore? When and by whom were the various parts of these books of the Bible written? How much did Egyptian beliefs influence the early Hebrews?

Exactly what happened to the Jews in the diaspora after 70 CE and how did they come to be the Jewish peoples we know today?

What was the origin story of the gypsies?

Do the polytheistic deities of Greece, Scandinavia, Egypt, the ancient Mediterranean, the Americas, and India have any connections to real historic people? Is so, when and in what context?

What does the prehistoric and legendary history era chronology of human inhabitation of Southeast Asia and East Asia look like?

How far back can oral histories reliably describe the past? What are the most notable examples of this?

What is the origin story of the Japanese people? Where did the Jomon come from? How representative is the Ainu language of the language(s) of the Jomon people?

Are Korean and Japanese related linguistically? How? Is the larger Altaic linguistic family a legitimate linguistically related group of languages?

What undecipherable scripts of lost languages can we decipher?

What explains the relative strength and weaknesses of polygamy in different cultures at different times?

What was the lost agricultural civilization of the Amazon like?

What was the Mississippian culture like?

What were the dynamics of changing political/cultural region/linguistic control in the Americans in the pre-Columbian era that changed over time?

In Africa, was there an expansion within Africa parallel to the Out of Africa expansion? Why were modern humans suddenly so dynamic and behaviorally modern starting in the Upper Paleolithic era? What were the histories of the pre-Bantu language family expansions of languages in Africa? What is the story of the genetically distinct culture of click language speakers in Mozambique that left no pure blooded members of the "race" and no relict speakers of that language?

Is there any merit to the existence of a mostly lost Indo-Pacific language family made up of relict language isolates across Southern Asia?

Deep Genetic Modern Human Ancestry And Structure In Africa

A new paper at bioRxiv finds that:

The deep history of humans in Africa and the complex divergences and migrations among ancient human genetic lineages remain poorly understood and are the subject of ongoing debate. We produced 73 high-quality whole genome sequences from 14 Central and Southern African populations with diverse, well-documented, languages, subsistence strategies, and socio-cultural practices, and jointly analyze this novel data with 104 African and non-African previously-released whole genomes. We find vast genome-wide diversity and individual pairwise differentiation within and among African populations at continental, regional, and even local geographical scales, often uncorrelated with linguistic affiliations and cultural practices. 

We combine populations in 54 different ways and, for each population combination separately, we conduct extensive machine-learning Approximate Bayesian Computation inferences relying on genome-wide simulations of 48 competing evolutionary scenarios. We thus reconstruct jointly the tree-topologies and migration processes among ancient and recent lineages best explaining the diversity of extant genomic patterns. Our results show the necessity to explicitly consider the genomic diversity of African populations at a local scale, without merging population samples indiscriminately into larger a priori categories based on geography, subsistence-strategy, and/or linguistics criteria, in order to reconstruct the diverse evolutionary histories of our species. 

We find that, for all different combinations of Central and Southern African populations, a tree-like evolution with long periods of drift between short periods of unidirectional gene-flow among pairs of ancient or recent lineages best explain observed genomic patterns compared to recurring gene-flow processes among lineages. 

Moreover, we find that, for 25 combinations of populations, the lineage ancestral to extant Southern African Khoe-San populations diverged around 300,000 years ago from a lineage ancestral to Rainforest Hunter-Gatherers and neighboring agriculturalist populations. 

We also find that short periods of ancient or recent asymmetrical gene-flow among lineages often coincided with epochs of major cultural and ecological changes previously identified by paleo-climatologists and archaeologists in Sub-Saharan Africa.

Gwenna Breton, et al., "Ancient tree-topologies and gene-flow processes among human lineages in Africa" bioRxiv (July 16, 2024).

Thus, human evolution and genetic structure in Africa is not well-described by more or less random genetic exchanges between neighboring populations. Instead, massive, short, unidirectional introgression (i.e. one people conquering another) is the norm.

African and Arabian Paleoclimate

This paper leans heavily on Beyer, R.M. et al., "Climatic windows for human migration out of Africa in the past 300,000 years", 12(1) Nature Communications 4889 (2021) (open access), for its inferences based upon paleoclimate. Beyer (2021) concludes that:

there were a number of windows during the past 300k years when either northern or southern expansions out of Africa would have been climatically feasible. Prior to the last interglacial period, the Nile-Sinai-Land Bridge would have been crossable at several time intervals between 246k and 200k years ago. Following a reopening at 130k years ago, exits would have been intermittently possible until 96k years ago, and again later around 78k and 67k years ago. 

After that, this route likely remained closed until the wet Holocene. Provided that maritime travel was in principle possible, climatic conditions would have made southern exits feasible for a substantial proportion of the last 300k years. 

Before the last interglacial, there were three extended intervals of sufficient rainfall paired with relatively low sea level, from 275k to 242k years ago, from 230k to 221k years ago, and from 182k to 145k years ago. During most of the following window from 135k to 115k years ago, sea levels were particularly high, except at its beginning 135k years ago. This date is close to the proposed timing of an early northern exit; thus, if migration did occur, southern migrants might have encountered their northern counterparts on the Arabian Peninsula. Following a long period when the southern route was blocked, there was a sizeable window of sufficiently wet climate between 65k and 30k years ago. 

Further connections existed just after the Last Glacial Maximum, and during the mid-Holocene, consistent with evidence of Eurasian backflow into Africa. 

A threshold analogous to our estimate for precipitation exists for a Köppen aridity level around 1.7 based on the contemporary hunter-gatherer data, and the inferred periods of climatic connectivity between Africa and Eurasia are almost identical to those estimated for precipitation.

Our reconstructions suggest that there were several windows of suitable climate along either of the two possible dispersal routes that could have allowed the expansion of Homo sapiens out of Africa. 

Some of these windows predate the earliest remains outside of Africa, but are entirely compatible with genetic dating of introgression from Homo sapiens into Neanderthal, sometime between 250k and 130k years ago, and recent dating of material from Israel to possibly 194k years ago and from Greece to 210k years ago. 

Migrations into Eurasia were also likely feasible along both routes during the last interglacial period, when archaeological evidence points to a more sizeable exit. Two distinct scenarios for an exit around 65k years ago, the time that has been long suggested as the main moment of expansion out of the African continent based on archaeological and genetic evidence, are compatible with our estimates. This timing marks both the point shortly after which the northern route last was open before a period of 40k years of unsuitable climate, and the point at which the southern route first reopened for an extended period since the last interglacial period. 

The latter scenario has been a subject of debate based on the empirical palaeoenvironmental record, with conclusions ranging from the Arabian Peninsula being continually too arid for human migration, to intermittent wet intervals, and extended pluvial periods during marine isotope stage 3 (57–29k years ago). 

In any case, these inferences are not directly comparable with our results, both because several empirical proxies are not suitable for detecting rainfall of the small magnitude considered here (e.g. speleothems), and because, for each route, the specific path out of Africa that requires the least tolerance to low precipitation out of all possible paths varies over time, as does the geographic location of its driest segment; thus, our estimates would not be expected to necessarily display the same patterns over time as a localised empirical climate reconstruction. . . .

While archaeological and genetic data strongly suggest that Homo sapiens expanded its range towards Eurasia at least once prior to the large-scale colonisation wave beginning around 65k years ago, the reason for its initial failure to permanently settle outside Africa is less clear. 

Migration beyond the Arabian Peninsula would have been predicated on the ability to cross the Taurus-Zagros Mountain range while competing with Neanderthals in the north, which has previously been argued to have limited human expansions during the last interglacial period, and possibly other hominins, such as Denisovans (whose geographic range is unknown but likely covered a large portion of East Asia), in the east. 

In addition, our reconstructions suggest that climatically favourable intervals along both routes were frequently interrupted by periods of rainfall insufficient to support humans, which would have effectively isolated any of the earlier colonists that might have made it out of Africa. With a lack of demographic influx from further migration out of Africa, remnant populations on the Arabian Peninsula would have been susceptible to stochastic local extinctions driven by climatic fluctuations. 

This constraint would have been less important along the southern route during the unprecedentedly long period of largely favourable climate between 65k and 30k years ago, provided that maritime travel across a then 4 km wide strait of the Bab e-Mandeb made migration along this route possible. This long window would have provided ideal preconditions for a successful large-scale dispersal, allowing for a regular demographic influx from Africa that would have stabilised populations on the Arabian Peninsula, thus facilitating further expansion of Homo sapiens into Eurasia. 

These dynamics would have complemented technological, economic, social, and cognitive changes in human societies, which, possibly combined with the decline of Neanderthal, very probably accounted for the success of the late exit in the subsequent colonisation of Eurasia by Homo sapiens.

Khoisan Origins 

The Khoisan hunter gatherers of Africa have had distinct northern and southern subpopulations since roughly the time of genetic Out of Africa (ca. 50,000-80,000 years ago). This is a branch depth as deep as the divisions between Australian Aboriginal people and Swedish people in populations that live on opposite sides of the Kalahari desert in Southern Africa. The authors hypothesize that:

the global climatic shifts inducing massive ecological changes that have occurred in Africa at that time (e.g. (Beyer et al., 2021)), sometimes proposed to have triggered ancient Homo sapiens movements Out-of-Africa, may also have triggered, independently, the genetic isolation among ancestral Khoe-San populations. Nevertheless, where the ancestors of extant Khoe-San populations lived at that time remains unknown and is nevertheless crucial to further elaborate possible scenarios for the causes of the genetic divergence here inferred.

The common Khoisan ancestor population became distinct from other modern humans around 300,000 years ago, around the time that the modern human species emerged.

The Origins Of The Pygmies And Their Neighbors

Among Rainforest Hunter Gathers (RHG) in the Congo jungle, a.k.a. the Pygmies, there are genetically distinct populations in the West and in the East that date roughly to the Last Glacial Maximum (17,000 to 27,000 years ago). The authors explain that:

Rainforest Hunter-Gatherer populations across the Congo Basin diverged roughly between 17,000 and 27,000 years ago, relatively consistently across pairs of sampled populations used for inferences; estimates highly consistent with previous studies, despite major differences in gene-flow specifications across RHG groups between studies. Interestingly, this divergence time is relatively synchronic with absolute estimates for the Last-Glacial Maximum in Sub-Saharan Africa. The fragmentation of the rainforest massif during this period in the Congo Basin may have induced isolation between Eastern and Western RHG extant populations, as plausibly previously proposed. However, similarly as above for the Northern and Southern Khoe-San populations divergence, where the ancestors of extant Eastern and Western Rainforest Hunter-Gatherers lived remains unknown, which prevents us from formally testing this hypothesis.

This is around the time of the division between the founding population of the Americas and the populations of East Asia and Northeast Asia from which they originated. It is also a time frame during which Europe was depopulated except for relict populations in Iberia, the Italian Peninsula, and the Caucuses. 

The population ancestral to Rain Forest Hunter gathers and their agricultural neighbors branched between the neighboring population and the Rain Forest Hunter gatherer population, about 165,000 years ago. 

Key Short Duration Admixture Events In Africa

But, there were admixture events after that date. The authors explain that:

we found strong indications for almost synchronic events of introgressions having occurred during the Last Interglacial Maximum in Africa (Mazet et al., 2016), between ~90,000 and ~135,000 years ago (when considering 20 or 30 years per generation). They involved gene-flow between lineages ancestral to Khoe-San populations and ancestors of Rainforest Hunter-Gatherer neighbors on the one hand and, on the other hand, between lineages ancestral to Khoe-San populations and the lineage ancestral to all Rainforest Hunter-Gatherers. 

An increase in material-based culture diversification and innovation, possibly linked to climatic and environmental changes locally, has previously been observed during this period of the Middle Stone Age in diverse regions of continental Africa; prompting a long-standing debate as to its causes if human populations were subdivided and isolated biologically and culturally at the time[.] . . .

the instantaneous gene-flow event between the ancestral Rainforest Hunter-Gatherers lineage and that of their extant neighbors seemingly occurred synchronically to the genetic Out-of-Africa ((Beyer et al., 2021); see above). This would imply that possible climatic and ecological shifts at that time may not have only induced population divergences and displacement, but may also have triggered population gene-flow.

There was also a gene flow event between populations in Rain Forest Hunter Gather neighbors population, and the northern and southern Khoisan populations:

around 30,000 years ago, we found two loosely synchronic gene-flow events between ancestors to extant Central African Rainforest Hunter-Gatherer neighbors’ lineages and, separately, Northern and Southern Khoe-San lineages. This corresponds to the end of the Interglacial Maximum and a period of major cultural changes and innovations during the complex transition from Middle Stone Age to Late Stone Age in Central and Southern Africa. Nevertheless, connecting the two lines of genetic and archaeological evidence to conclude for increased population movements at the time and their possible causes should be considered with caution. Indeed, in addition to genetic-dating credibility-intervals being inherently much larger than archaeological dating, this period remains highly debated in paleoanthropology mainly due to the scarcity and complexity of the material-based culture records, and that of climatic and ecological changes locally, across vast regions going from the Congo Basin to the Cape of Good Hope.

And, there were also multiple gene flow events in the early Holocene era (roughly corresponding to the Neolithic era in Europe and into the European Copper/early Bronze Age):

we found strong signals for multiple instantaneous gene-flow events having occurred between almost all five recent Central and Southern African lineages between 6000 and 12,000 years ago, during the onset of the Holocene in that region, shortly before or during the beginning of the last Post Glacial Maximum climatic crisis in Western Central Africa, the emergence and spread of agricultural techniques, and the demic expansion of now-Bantu speaking populations from West Central Africa into the rest of Central and Southern Africa. These results are consistent with previous investigations that demonstrated the determining influence of Rainforest Hunter-Gatherer neighboring populations’ migrations through the Congo Basin in shaping complex socio-culturally determined admixture patterns, including admixture-related natural selection processes.

As our estimates for introgression events are in the upper bound of previous estimates for the onset of the so called “Bantu expansion” throughout Central and Southern Africa, we may hypothesize here that major climatic and ecological changes that have occurred at that time may have triggered increased population mobility and gene-flow events between previously isolated populations, rather than consider that the Bantu-expansions themselves were the cause for all the gene-flow events here identified.

Finally, we did not find signals of more recent introgression events from Bantu-speaking agriculturalists populations into Northern or Southern Khoe-San populations, in particular among the !Xun, albeit such events have been identified in several previous studies (see (Schlebusch and Jakobsson, 2018)). This is likely due to the fact that we considered only a limited number of individual samples from each population, and therefore may lack power to detect these very recent events with our data and approach.

Was There Archaic Admixture In Africa?

The new paper finds that it is possible to fit their data to a narrative without admixture with a ghost population of archaic hominins in Africa, as some studies have suggested, although that possibility is not ruled out either, and the authors of this study acknowledge that they are using fewer kinds of data to build their historical narratives than studies that found evidence of admixture with ghost archaic hominin populations in Africa.

Ragsdale and colleagues included in their models possible very ancient genetic structures, long before Homo sapiens emergence, a feature that is unspecified in our scenarios which considered simply a single ancestral population in which all extant lineages ultimately coalesce. Nevertheless, note that substructure and reticulation within the ancestral population is not per se incompatible with our scenarios. In fact, it may be compatible with our posterior estimates of a large effective population ancestral to all extant populations here investigated, the largest among all inferred ancient and recent Central and Southern African effective population sizes. . . . . 

We did not explore possible contributions from unsampled lineages, whether from non-Homo sapiens or from ancient “ghost” human populations, and therefore cannot formally evaluate the likeliness of the occurrence of such events to explain observed data. In all cases, our results demonstrate that explicitly considering ancient admixture from unsampled populations is not a necessity to explain satisfactorily large parts of the observed genomic diversity of extant Central and Southern African populations, consistently with a previous study (Ragsdale et al., 2023), and conversely to others (Lipson et al., 2022; Fan et al., 2023; Pfennig et al., 2023); at least when considering jointly the 337 relatively classical population genetics summary-statistics used here for demographic inferences. As discussed above, our results formally comparing competing-scenarios rather than comparing posterior likelihoods of highly complex yet vastly differing models, provide a clear and reasonable starting point for future complexification of scenarios comprising possible contributions from ancient or ghost unsampled populations, which will unquestionably benefit from the explicit use of additional novel summary statistics ((Ragsdale and Gravel, 2019; Fan et al., 2023; Ragsdale et al., 2023); see also above). 

In any case, the complexification of scenario-specifications to account for possible past “archaic” or “ancient” introgressions will not fundamentally solve the issue of the current lack of reliable ancient genomic data older than a few hundreds or thousands of years from Sub-Saharan Africa. Indeed, analogously to archaic admixture signals that were unambiguously identified outside Africa only when ancient DNA data were made available for Neanderthals and Denisovans (e.g. (Meyer et al., 2012; Prüfer et al., 2014)), we imperatively need to overcome this lack of empirical ancient DNA data in Africa to formally test whether, or not, ancient human or non-human now extinct lineages have contributed to shaping extant African diversity.

Side Observations Re Non-African Admixture

The study also made some side observations. For example, in its ancestry analysis at K=2 it effectively shows that amount of non-sub-Saharan African admixture present in various African populations. 

Unsurprisingly, this admixture is lowest in hunter-gather populations, modestly higher among non-hunter-gatherer Central and Southern Africans, higher still among the most northern East Africans, high among "Coloured" South Africans who have substantial non-African admixture, and predominantly non-African among North Africans.

Within non-Africans, Papuans pop out as a distinct population at K=5, and indigenous peoples of the Americas pop out as distinct at K=6.

Genetic Variation and Diversity

The paper also confirms conventional wisdom that African populations have more genetic diversity than non-Africans, even within sub-populations (and not merely because it is a large continent with many subpopulation that differ from each other). The amount of genetic variation in any subpopulation is strongly correlated with the amount of non-African admixture in a subpopulation (which less genetic variation associated with more non-African ancestry).

Weaknesses In The Paper

The most notable gap in the sample is a lack of DNA from Mozambique, whose people in Southeast Africa are known to be genetically quite distinct from other Africans, which local Bantu languages have click phonemes, presumably from a pre-Bantu substrate language.

The paper would also benefit from straying beyond its focus on the most basal populations of Africa to explore, at an at least superficial level, how this Central and Southern African population history fits into the larger global population of Homo sapiens.

The Black Plague Swept Northern Europe Ca. 3400 BCE

We've been aware of the population collapse that hit Northern Europe around 5400 years ago (around 3400 BCE) for a long time, for example, in the article below from 2013. 

But new evidence points to the black plague as a major contributing cause. Climate and exhaustion of soils with primitive Neolithic agricultural methods have also been suggested as causes. Of course, causes can interact and aren't mutually exclusive. For example, people can be much more vulnerable to pandemics during period of famine caused by poor agricultural practices and climate events.

Following its initial arrival in SE Europe 8,500 years ago agriculture spread throughout the continent, changing food production and consumption patterns and increasing population densities. 

Here we show that, in contrast to the steady population growth usually assumed, the introduction of agriculture into Europe was followed by a boom-and-bust pattern in the density of regional populations. We demonstrate that summed calibrated radiocarbon date distributions and simulation can be used to test the significance of these demographic booms and busts in the context of uncertainty in the radiocarbon date calibration curve and archaeological sampling. 

We report these results for Central and Northwest Europe between 8,000 and 4,000 cal. BP and investigate the relationship between these patterns and climate. However, we find no evidence to support a relationship. Our results thus suggest that the demographic patterns may have arisen from endogenous causes, although this remains speculative.

Stephen Shennan, "Regional population collapse followed initial agriculture booms in mid-Holocene Europe" 4 Nature Communications 2486 (October 1, 2013).

The new paper is:

In the period between 5,300 and 4,900 calibrated years before present (cal. BP), populations across large parts of Europe underwent a period of demographic decline. However, the cause of this so-called Neolithic decline is still debated. Some argue for an agricultural crisis resulting in the decline, others for the spread of an early form of plague. 

Here we use population-scale ancient genomics to infer ancestry, social structure and pathogen infection in 108 Scandinavian Neolithic individuals from eight megalithic graves and a stone cist. 

We find that the Neolithic plague was widespread, detected in at least 17% of the sampled population and across large geographical distances. We demonstrate that the disease spread within the Neolithic community in three distinct infection events within a period of around 120 years. 

Variant graph-based pan-genomics shows that the Neolithic plague genomes retained ancestral genomic variation present in Yersinia pseudotuberculosis, including virulence factors associated with disease outcomes. 

In addition, we reconstruct four multigeneration pedigrees, the largest of which consists of 38 individuals spanning six generations, showing a patrilineal social organization. 

Lastly, we document direct genomic evidence for Neolithic female exogamy in a woman buried in a different megalithic tomb than her brothers. 

Taken together, our findings provide a detailed reconstruction of plague spread within a large patrilineal kinship group and identify multiple plague infections in a population dated to the beginning of the Neolithic decline.

Frederik Valeur Seersholm, "Repeated plague infections across six generations of Neolithic Farmers" Nature (July 10, 2024).

olume

There Is No Muon g-2 Anomaly

The updated BMW calculation of the hadronic vacuum polarization contribution to the muon anomalous magnetic moment a(μ) in the Standard Model is squarely consistent, at 0.9 sigma with the experimental measurement of muon g-2 (even without one or two additional tweaks to parts of the calculation other than the HVP component that improve the fit further) despite the fact that its uncertainty in this new and improved HVP calculation is 40% smaller (producing a 31% reduction in the uncertainty of the overall theoretical calculation) and the fact that the 2023 experimental measurement has 55% less uncertainty, making agreement of the two values a harder to hit target.

The experimental value is based upon the first three phases of a six phase experiment. Phase four, whose results are tentatively expected late in 2024, will significantly reduce the uncertainty in the experimental result. The improvements from phases five and six are expected to be much smaller. The uncertainty in the experimental result is already about 42% smaller than the uncertainty in the calculation of the Standard Model predicted value. The experimentally measured value will probably continue to have less uncertainty than the Standard Model predicted value calculation for several years to come, at least.

The bottom line value for the new 2024 BMW calculation is:

aµ = 116,592,019(38) × 10^−11.

Partial calculations confirm the BMW result vis-a-vis the partially experimentally based analysis in the so called "window" part of the calculation (as does the recent CMD-3 experimental measurement of the same experimental inputs that went into the "Theory Initiative" calculation):

The apparent anomaly, which has been the source out countless papers proposing dubious proposals for new physics, was a a result of a bad calculation of the Standard Model prediction for muon g-2 that was mostly a result of the incorporation of slightly inaccurate experimental data into the calculation.

Muon g-2 is a strong global test of the accuracy of all parts of the Standard Model at once and the experimentally measured result matches the theoretical calculation of muon g-2's value (at a precision of about 4 parts per ten million, or less with another key tweak). This rules out most new physics that a next generation particle collider could detect. But muon g-2 is less sensitive to new physics at energy scales higher than those of any of the proposed next generation particle colliders.

We present a new lattice QCD calculation of the leading order hadronic vacuum polarization contribution to the muon anomalous magnetic moment a(μ). We reduce uncertainties compared to our earlier computation by 40%, arXiv:2002.12347. We perform simulations on finer lattices allowing for an even more accurate continuum extrapolation. We also include a small, long-distance contribution obtained using input from experiments in a low-energy regime where they all agree. Combined with other standard model contributions our result leads to a prediction that differs from the measurement of a(μ) by only 0.9 standard deviations. This provides a remarkable validation of the standard model to 0.37ppm.

A.Boccaletti, et al., "High precision calculation of the hadronic vacuum polarisation contribution to the muon anomaly" arXiv:2407.10913 (July 15, 2024).

The paper also notes that:

In the near future we expect that other lattice collaborations will also provide precise calculations of a(LO-HVP)(µ) that can confirm or refute our results. Also, more data for the e+e− → π+π− cross section is expected soon.

My prior posts on the subject were summarized on August 10, 2023. 

Two additional non-HVP tweaks to the Standard Model prediction for muon g-2 calculation:

Hadronic Light By Light Calculation (2021)

The hadronic QCD component is the sum of two parts, the hadronic vacuum polarization (HVP) and the hadronic light by light (HLbL) components. In the Theory Initiative analysis the QCD amount is 6937(44) which is broken out as HVP = 6845(40), which is a 0.6% relative error and HLbL = 98(18), which is a 20% relative error.

The presentation doesn't note it, but there was also an adjustment bringing the result closer to the experimental result in the hadronic light-by-light calculation (which is the smaller of two QCD contributions to the total value of muon g-2 and wasn't included in the BMW calculation) which was announced on the same day as the previous data announcement. The new calculation of the hadronic light by light contribution to the muon g-2 calculation increases the contribution from that component from 92(18) x 10^-11 to 106.8(14.7) x 10^-11.

As the precision of the measurements and the calculations of the Standard Model Prediction improves, a 14.8 x 10^-11 discrepancy in the hadronic light by light portion of the calculation becomes more material.

This also reduces the combined uncertainty in the final muon g-2 estimate using the new BMW calculation from 38 to 37 times 10^-11. 

QED Calculation (2024)

A possible (basically immaterial) error in the QED calculation was also discussed in a prior post on April 2, 2024. It is a difference produces a roughly 0.06 x 10^-11 smaller QED contribution than the previously calculation (which is a five sigma difference but in a portion of the calculation which an extremely low uncertainty).

Bottom Line:

For those of you who aren't visual learners (with values time 10^11 shown): 

New BMW calculation + new HLbL + new QED calculation (2024+2021+2024): 116,692,033.74(3700) 

 

Considering the HLbL and QED tweaks as well, this is a bit less than a 0.6 sigma difference from the experimental value. This means that the prediction and measured value (as improved in 2023) are basically perfectly consistent with each other despite a 33% reduction in the uncertainty of the overall theoretical prediction and a 55% reduction in the uncertainty of the experimental measurement compared to 2021. The relative difference is 0.216 parts per million.

 

New BMW calculation plus new HLbL (2024+2021): 116,692,033.8(370)  

 

New BMW calculation (2024): 116,592,019(38)  

 

Theory Initiative calculation (2020): 116,591,810(43) 

 

BMW calculation (2020): 116,591,954(55)

The QED + Electroweak (EW) predicted value (omitting the Hadronic Vacuum Polarization (HVP) and Hadronic Light by Light (HLbL) components, and before the latest QED component tweak) is: 116,584,872.53 (101). Thus, it accounts for only about 3% of the total uncertainty in the value of muon g-2. Given the experimental result, the implied combined hadronic (i.e. QCD) contribution to the total is about 7186.47 times 10^-11. This is 0.00616% of the total  value, despite the fact that it is the source of 97% of the uncertainty in the calculation, because QCD calculations are vastly less precise than electromagnetic and weak force calculations.

 

World Experimental Average (2023): 116,592,059(22)
Fermilab Run 1+2+3 data (2023): 116,592,055(24)
Fermilab Run 2+3 data(2023): 116,592,057(25)
Combined measurement (2021): 116,592,061(41)
Fermilab Run 1 data (2021): 116,592,040(54)
Brookhaven's E821 (2006): 116,592,089(63)

A "No Hype" Science Journalism Stand-Out

Science journalism aimed at the educated (or not so educated) layman in the general public is prone to sensationalism and claims of new discoveries that aren't supported by the body text, or at least, aren't supported by the source and the general scientific community. But there are exceptions. 

One stand out is an article from Phys.org which is a source that often offends in this regard but doesn't this time. Its headline accurately states:

Theoretical physicists find Higgs boson does not seem to contain any harbingers of new physics

The headline conclusion, reached after twelve years of study since its discovery was announced on July 4, 2012, is familiar to readers of this blog, but deserves recognition for resisting sensationalism and restating the scientific consensus.  See, e.g., noting decays to a Z boson and a photon and here (summarizing the data to date). 

The article used as its touchstone has the following abstract and citation (and isn't itself, the headline suggests, a broad review article, and is instead one more mundane article confirming that the experimental study of the Higgs boson confirms the theoretical expectations for it):

We evaluate the top-bottom interference contribution to the fully inclusive Higgs production cross section at next-to-next-to-leading order in QCD. Although bottom-quark-mass effects are power suppressed, the accuracy of state-of-the-art theory predictions makes an exact determination of this effect indispensable. The total effect of the interference at 13 TeV is −1.99⁢(1)+0.30−0.15  pb, while the pure 𝒪⁡(𝛼4𝑠) correction is 0.43 pb. With this result, we address one of the leading theory uncertainties of the cross section.

Michał Czakon et al, "Top-Bottom Interference Contribution to Fully Inclusive Higgs Production", Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.132.211902

As additional context, Peter Higgs after whom the Higgs boson  is named, died in April of this year.

There is actually a slight Higgs boson anomaly, that is barely statistically significant locally (2.2 sigma), which would probably lose its statistical significance after considering look elsewhere effects, involving lower than expected Higgs boson decays to fermions (but the expected number of decays to bosons).

There are also a couple of low significance resonance "bumps" that have been touted as possible additional electromagnetically neutral Higgs bosons that have not been confirmed, one a bit below the Higgs boson mass of about 125 GeV, at about 96 GeV, and one or two a bit above it. Even if these "bumps" were confirmed to be real particles, there is no a priori reason to have any  confidence that they have anything to do with the Higgs boson.

Early Neolithic Arabia

 

Archaeologists in Saudi Arabia have excavated eight ancient "standing stone circles" that they say were used as homes. About 345 of these structures were identified through aerial surveys across the Harrat 'Uwayrid, a lava field near the city of AlUla in northwestern Saudi Arabia, the team reported July 2 in the journal Levant. The circles range from 13 to 26 feet (4 to 8 meters) in diameter and have at least one standing stone at the center. The circles date back around 7,000 years and have the remains of stone walls and at least one doorway. They would have had roofs made of either stone or organic materials, the team wrote. . . . 

Around 7,000 years ago, the environment in northern Saudi Arabia was much wetter than it is today, but farming had not yet come into use. "There's no evidence of farming domesticated species of plants like wheat and barley, but gathering wild plants likely took place, and perhaps manipulating the landscape to increase the likelihood and yield of wild species," McMahon said.

When these standing stone circles were in use, another form of stone structure, known today as a mustatil (Arabic for "rectangle"), was being built as well. Excavations at the mustatils suggest they had a ritual purpose that may have included the sacrifice of cattle. The contemporaneous use of the mustatils and standing stone circles indicates that it is "likely that these two megalithic structure types are aspects of a single cultural entity," the team wrote.

Gary Rollefson, a professor emeritus of anthropology at Whitman College and San Diego State University who was not involved in the research but has conducted extensive archaeological work in the region, said he thinks the people who built the standing stone circles and mustatils are descended from people who lived in Jordan and Syria about 500 years earlier.

He told Live Science that the architecture of the standing stone circles is similar to that of structures found in Jordan dating to about 500 years earlier, and the people who built the structures in Jordan also herded sheep, goats and cattle. The migration may have been spurred by an increase in population brought about by new hunting technologies, such as the "kite," a series of stone walls used to force wild animals into a kill zone. These hunting advances dramatically increased the supply of food, which, in turn, led to an increase in the human population in the Jordan/Syria area.

"They were building up a large population in eastern Jordan and [parts of] Syria," Rollefson said, and they needed to find new hunting grounds, which would have led them to gradually go south, into what is now Saudi Arabia.

Via Live Science.

The paper indicates that there were post-Neolithic early herders, rather than primarily being hunter-gatherers.

The paper and its abstract are as follows:

Recent archaeological investigations in AlUla County have provided the first detailed chrono-cultural evidence for long-term Neolithic domestic occupation in this archaeologically unknown region of north-west Arabia. 

This paper presents the preliminary findings drawn from multi-scalar datasets collected through extensive aerial and ground surveys, and the excavations of ‘monumental’ architectural installations, named in this study as ‘Standing Stone Circles’. These structures were individual dwellings, constructed in concentrations of varying numbers with associated domestic installations, such as hearths. The Standing Stone Cicle sites presented in this paper demonstrate a scale of Neolithic occupation not previously recognized in Saudi Arabia. These structures provide evidence of ongoing occupation throughout the 6th and 5th millennia BCE, concurrent with a general florescence of human activity across north-west Arabia. The faunal remains indicate a mixed subsistence economy, dominated by domesticates but supplemented by wild species. 

Broader considerations of the Neolithic economy, and models of pastoralism and mobility, are made possible on the basis of this, and the associated assemblages of stone artefacts and small finds. The data provided in this article offers a general picture of the Neolithic period in AlUla, addressing the significant geographical and temporal gaps within the archaeological knowledge of north-west Arabia. The identification of diagnostic Late Neolithic Levantine projectile point types, in conjunction with architectural parallels with the Levant, provides further insight into the origins of neolithization in north-west Arabia.

Jane McMahon, et al., "New evidence for Neolithic occupation in north-west Arabia: Standing Stone Circles on the Harrat ‘Uwayrid'" Levant (July 2, 2024) (open access).

Archaic Hominin News

The flow of genes in multiple episodes between Neanderthals and modern humans is now better understood, and we have a new Denisovan genome from 200,000 years ago with better quality than any previous Denisovan genome. Via Razib:

Recurrent gene flow between Neanderthals and modern humans over the past 200,000 years:

Our understanding of admixture between humans and Neanderthals has changed dramatically over the past decade and a half. Once thought not to have occurred at all, there is now ample evidence for gene flow from Neanderthals to humans and vice versa. Li et al. used a new framework to model the increasingly complex dynamics of introgression between humans and Neanderthals and the ramifications for both populations. They identified regions of human ancestry in Neanderthals, estimated population sizes for Neanderthals were about 20% lower than previously thought, and proposed the possibility of two pulses of gene flow from humans to Neanderthals. This study comprehensively synthesizes our current knowledge of hominin admixture. —Corinne N. Simonti.

The most ancient human genome yet has been sequenced—and it’s a Denisovan’s. 24x, high quality, 200,000 years ago.

From the Denisovan link:

“I’m pleased to tell you about a new Denisovan genome from a 200,000-year-old male,” said [Stéphane] Peyrégne, a postdoc at the Max Planck Institute for Evolutionary Anthropology.

The genetic sequence he unveiled is the oldest high-quality human genome yet—80,000 years older than the previous record holder: a Neanderthal that lived about 120,000 years ago. The new results come after more than a decade of effort to find fossilized bones and a second genome of a Denisovan, the mysterious archaic human discovered through its DNA 14 years ago. That first Denisovan genome came from a girl’s pinkie finger bone dated between 60,000 to 80,000 years ago. The genomes of both Denisovans and the ancient Neanderthal all came from the same cold, fossil-rich site: Denisova Cave in the Altai Mountains of Siberia.

According to the analysis by Peyrégne and colleagues, the newly sequenced male comes from a distinct population of early Denisovans that interbred multiple times with a group of Neanderthals whose population had not been detected in DNA before. . . . 

Denisovans are primarily known from their DNA. Researchers have the genome of the girl, as well as bits of nuclear and mitochondrial DNA from fragmentary fossils—teeth, a toe bone—of seven additional individuals, all also from Denisova Cave. Scientists have also identified some Denisovan DNA in living humans, including in Papuans and Han Chinese people, acquired from past interbreeding. DNA in sediments showed that Denisovans were first in the cave 300,000 years ago, and later lived in a cave on the Tibetan Plateau. The scanty fossils reveal this archaic human had larger molars than did the Neanderthals and a robust lower face, known from a jawbone in China. . . . archaeologist Maxim Kozlikin of the Russian Academy of Sciences (RAS) found a molar in a deep layer dated to 200,000 years ago, Peyrégne reported in his talk. The RAS team sent the molar to Max Planck, where evolutionary geneticists extracted enough DNA to provide 24-fold coverage of the genome. . . .

the male Denisovan had inherited 5% of his genome from an ancient, previously unknown population of Neanderthals. The male, labeled Denisova 25, came from a separate population of Denisovans from the girl, known as Denisova 3, and from the other Denisovans in the cave. The girl’s DNA is more closely related to the Denisovan sequences in living modern humans, who got them from at least two Denisovan populations.

All this suggests the older male’s population was replaced in the cave by later Denisovans. . . . the male Denisovan’s ancestors interbred multiple times with Neanderthals. Denisovans were apparently replaced in the cave by Neanderthals for a period, based on the Neanderthal fossil dated to about 120,000 years ago. By about 60,000 years ago, though, the Denisovans had moved back in. The two groups may even have met in the cave—DNA from a bone fragment from a female who was more than 50,000 years old shows her mother was a Neanderthal and her father a Denisovan. Later, both DNA and fossils indicate modern humans occupied the cave and Denisovans and Neanderthals disappear. . . .  

Although Denisovans and Neanderthals apparently interbred repeatedly, their lineages are distinct: They diverged from a common ancestor at least 400,000 years ago. The ancestors of Neanderthals settled in Europe and the Middle East, whereas Denisovans headed farther east into Asia where they evolved separately, acquiring roughly 300,000 genetic changes that differentiate them from Neanderthals, according to the new genome. “Neanderthals and Denisovans remain in separate groups,” and mixed at the edges of their geographic ranges. . . . 

an audience member asked whether the male’s genome also had DNA from an even older, unidentified type of human–perhaps Homo erectus—whose DNA has been spotted in the Denisovan girl’s genome. “If there is any Denisova superarchaic ancestry, it’s also present in this genome,” Peyrégne responded. “[That DNA] is shared between Denisova 3 and Denisova 25.”

See also speculations on the Yeti myth is an oral history recollection of Denisovans in Tibet at the Old European Culture Blog, and John Hawks post about large brained archaic hominin Julurens in China, who could be cousins of Neanderthals and Denisovans.

The Lightest Neutron Star

The maximum neutron star mass is an open question in physics that receives more attention than the minimum neutron star mass. But the range of neutron star masses is quite narrow, with roughly a factor of two separating the least massive ones from the most massive ones, and there are theoretical efforts to establish why this is the case.

Supernova theory has struggled to explain the lightest known neutron star candidate with an accurate mass determination, the 1.174M⊙ companion in the eccentric compact binary system J0453+1559. 

To improve the theoretical lower limit for neutron star birth masses, we perform 3D supernova simulations for five stellar models close to the minimum mass for iron core collapse. We obtain a record-low neutron star mass of 1.192M⊙ and a substantial kick of ∼100kms^−1. Given residual uncertainties in stellar evolution, a neutron star origin for the 1.174M⊙ object remains plausible.

Bernhard Müller, Alexander Heger, Jade Powell, "The minimum neutron star mass in neutrino-driven supernova explosions" arXiv:2407.08407 (July 11, 2024).

Neutron Star Properties

Neutron stars are hard to model from first principles because they involve a regime where general relativity and Standard Model physics intersect with vast numbers of particles condensed in highly dense matter rather than in the small number of particles at time seen in particle colliders where high energy physics is usually done, even though they are, in principle, still rather simple systems. 

But astronomy observations can constrain their properties and provide us with insights about the underlying high energy physics in a domain that otherwise would be inaccessible to solar system bound physics experiments. This requires a mix of physics motivated models of neutron stars and carefully processed and analyzed astronomy data.

This data is homing in on a nearly universal neutron star to be pretty universally close to a 12 kilometer radius, and a maximum neutron star mass of modestly more than two solar masses. 

This maximum neutron star mass is low relative to other data that is more direct, but not by a lot. As I noted in a June 26, 2020 blog post (which later notes that two independent papers think that the 2.5-2.64 solar mass object observed with a gravitational wave detector is much more likely to be a black hole than a neutron star).

Gravitational wave detectors have observed what appears to be an intermediate sized black hole (26 times the mass of the Sun) collide with a "compact object" with a mass of 2.6 (2.5 to 2.64 at a 90% confidence interval) times the mass of the Sun.

Beyond a certain cutoff mass at a given radius, compact masses like neutron stars, collapse and form black holes. But, calculating the cutoff isn't a clean and simple calculation, because you have to model how tightly protons and neutrons can be squeezed together by gravity as nuclear forces push back against being squeezed too tightly, and those are complex systems involving vast numbers of protons and neutrons that can't be modeled exactly.

The most dense, large compact objects in the universe that are not black holes are neutron stars. Neutron stars are just massive, extremely dense, ordinary stars on the continuum of ordinary star behavior.

But black holes are qualitatively different. In classical General Relativity they are mathematical singularities. In theories of quantum gravity, black holes are "almost" singularities (from which nothing can escape) but leak slightly in a theoretically described phenomena called "Hawking Radiation" which is too slight to be observed over the noise of cosmic background radiation with current means.

This compact object is potentially more massive than any previously observed neutron star (it has a higher minimum mass within experimental uncertainties than any previously observed neutron star), but it is lighter than the lightest known black hole (see here), subject to outliers near the boundary with large error margins in their mass estimates.

The least massive black hole ever observed has a mass of 2.72-2.82 solar masses (in a 95% confidence range). The most massive previously observed neutron stars have masses of 2.32-3.15, 1.9-3.00, 2.15-2.70 and 2.16-2.64 solar masses (in a 95% confidence range). So, the cutoff has to be somewhere in the range of 2.32 solar masses to 2.82 solar masses. This object is squarely in the middle of that range.

Another recent study which I blogged on April 30, 2024, puts a 95% confidence interval maximum neutron star mass at 2.38 solar masses and a maximum radius of 12.0 km. 

A new study, whose abstract and citation appear below, puts the most massive possible neutron star at 2.43 solar masses at a 95% confidence interval by one method, and 2.64 solar masses at a 95% confidence interval by another, with best fit maximum neutron star masses of 2.15 solar masses by one method and 2.08 solar masses by another. 

A cutoff maximum neutron star mass of 2.32 to 2.38 solar masses would best harmonize the available information from the newest studies and observations.

The narrowing in of the maximum mass of a neutron star and its radius also fixes a quite narrow range for the highest observed mass per volume of any object at any scale observed in Nature. Maybe I'll calculate that as an exercise at some point in light of the updated data.

Pulse profile modeling of X-ray data from NICER is now enabling precision inference of neutron star mass and radius. Combined with nuclear physics constraints from chiral effective field theory (χEFT), and masses and tidal deformabilities inferred from gravitational wave detections of binary neutron star mergers, this has lead to a steady improvement in our understanding of the dense matter equation of state (EOS). 

Here we consider the impact of several new results: the radius measurement for the 1.42M⊙ pulsar PSR J0437−4715 presented by Choudhury et al. (2024), updates to the masses and radii of PSR J0740+6620 and PSR J0030+0451, and new χEFT results for neutron star matter up to 1.5 times nuclear saturation density. Using two different high-density EOS extensions -- a piecewise-polytropic (PP) model and a model based on the speed of sound in a neutron star (CS) -- 

we find the radius of a 1.4M⊙ (2.0M⊙) neutron star to be constrained to the 95% credible ranges 12.28+0.50−0.76 km (12.33+0.70−1.34 km) for the PP model and 12.01+0.56−0.75 km (11.55+0.94−1.09 km) for the CS model. The maximum neutron star mass is predicted to be 2.15+0.14−0.16 M⊙ and 2.08+0.28−0.16 M⊙ for the PP and CS model, respectively. 

We explore the sensitivity of our results to different orders and different densities up to which χEFT is used, and show how the astrophysical observations provide constraints for the pressure at intermediate densities. Moreover, we investigate the difference R2.0−R1.4 of the radius of 2M⊙ and 1.4M⊙ neutron stars within our EOS inference.

Nathan Rutherford, et al., "Constraining the dense matter equation of state with new NICER mass-radius measurements and new chiral effective field theory inputs" arXiv:2407.06790 (July 9, 2024).