astroH

a lot better...we can excite these atoms in a lab and simply measure what comes out. often times don't even need a model because spectroscopy can be fully empirical for many transitions

And so you have proved my point. The observations presented in this article can be made consistent with both...as such one should think about stronger tests of both LCDM and MOND.

Again, LCDM and galaxy formation are two different things. "...and we didn't see what we were expecting at all..." It depends on who you ask. There were many pre-JWST models that did well in this regard. A particularly interesting one is this from 2018 (https://ui.adsabs.harvard.edu/abs/2018MNRAS.474.2352C/abstra...). That group even had to write another paper reminding everyone of what they predicted (https://ui.adsabs.harvard.edu/abs/2024arXiv240602672L/abstra...). Another example is here (https://ui.adsabs.harvard.edu/abs/2023OJAp....6E..47M/abstra...) which shows results from a simulation from ~2014. I can provide numerous other examples of this. My point isn't which theory is or isn't wrong, my point is that what is presented in this particular article is not a constraint on any realistic theory of gravity as the sensitivity of these particular observations to galaxy formation modeling is so strong.

This is a misrepresentation of what I am saying. By no means am I casting an aspersion on JWST. I am casting an aspersion on this particular observation as a test of MOND and LCDM. Also I highly disagree about your comments on my line of reasoning. The fact that you can obtain a huge range of possible galaxy properties in the context of LCDM indicates that in general, tests of LCDM and MOND that rely on galaxy formation model are in usually not strong tests. This is the key issue with using the abundance of high-z galaxies (or even their masses -- despite the fact that these aren't measured) as a test. In the context of LCDM, you need haloes to form galaxies but it has been shown many times that there are enough haloes to solve the problem (see the paper linked) by a huge amount.

In my opinion, this article is misleading at best. "...scans of ancient galaxies gathered by the JWST seem to contradict the commonly accepted predictions of the most widely accepted Cold Dark Matter theory, Lambda-CDM." --> LCDM doesn't predict what galaxies should look like, it simply predicts how much mass is in collapsed structures and that dark matter haloes grow hierarchically. In contrast, with JWST we see light and need to infer what the underlying properties of the system are. It was shown very early on that the theoretical upper limit (i.e. taking all of the gas that is available in collapsed structures and turning it into stars) predicts a luminosity function (i.e. number of galaxies per unit luminosity) that is orders of above what JWST has observed (e.g. https://ui.adsabs.harvard.edu/abs/2023MNRAS.521..497M/abstra...). This means that there is plenty of space within the context of LCDM to have bright and seemingly large and massive galaxies early on. Based on current JWST data at these early epochs, there are really no convincing arguments for or against LCDM because it's highly sensitive to the galaxy formation model that's adopted.

So I think it is fair to say they did exist. If we believe in Big Bang Nucleosynthesis then heavy elements had to come from somewhere making the first generation of stars (whatever their properties may be) be Population III. I agree that without a catalyst it's hard to initiate the CNO cycle but indeed models predict that it is possible even under these circumstances.

Multiple generations is perhaps an overstatement. The first oxygen in the Universe came from what we call Population III stars which is the first generation of stars to form after the Big Bang and what separates these from other stellar populations is that they do not have elements heavier than hydrogen or helium (except for minuscule traces left over from the Big Bang but these are insignificant). Now we don't know much about Population III stars but many models predict they are massive and when they die, can release 60 times the mass of our sun in the form of oxygen. That's really a lot of oxygen so you don't need too many of these to go off to pollute the early Universe and probably one of the reasons why we haven't yet found Population III stars.

I wouldn't say it's too damaging yet. There is a general trend where these early galaxies are brighter than we had thought by simply extrapolating models that were built prior to JWST, but these make numerous assumptions on how efficiently stars can form and the properties of these stars. Mildly relaxing any of these assumptions can easily solve the problem within our current framework and not significantly change what happens later in the evolution of the Universe.

It's a lot less sophisticated than that. They take images in multiple filters. In the context of JWST of order 10 filters (sometimes more sometimes less). Source extraction is then performed on the images by essentially identifying bright spots and dropping an aperture (separating ones that are nearby and blended if possible). The standard tool for this is called source extractor. They then have catalogs of tens of thousands of sources per image and the next step is to figure out redshift. There is a lot of code to do this but the simplest methods require fitting templates of what we think galaxies look like to these catalogs. High redshift sources tend to "drop" out of filters at shorter wavelengths. This is because neutral hydrogen in the early universe essentially absorbs almost all of the light at shorter wavelengths than 1216 angstroms. So if a galaxy is at redshift 10, the flux should essentially be zero at all filters that cover wavelengths shorter than 1.33 microns. JWST has filters both bluer and redder than this wavelength so we see the source appear in the redder filters and not the bluer ones. This technique was pioneered in the mid 1990s. This gives an approximate redshift called a "photometric redshift". There are other features in a galaxy spectrum that can mimic this "dropout" so not all photometric redshifts are robust. Therefore one has to take a spectrum of the galaxy which was what was done in this paper to confirm that the dropout is in fact the absorption feature we think it is. In this particular case, the authors were skeptical early on because there is a source right next to the object that is at a redshift where one of these other spectral features can mimic absorption by neutral hydrogen (this feature is the Balmer break). In any case, it's really an impressive demonstration of the power of JWST.

While in general, 'metal' means all elements except for hydrogen and helium, in this specific case, 'metal' really means oxygen. They are using the measurement of the [O III] 4363 line to estimate a gas temperature which allows for a determination of oxygen abundance but this gives no information on the other elements. One thing to keep in mind is that the method they use, while considered the gold-standard, is known to be biased such that metallicity is guaranteed to always be underestimated. Regardless, these galaxies are still metal-poor but it's not clear how well they mimic those in the early Universe which is one of the primary motivations for studying such objects.

Indeed, but we define their "metallicity" (mass fraction of elements heaver than helium) typically by the gas that they formed from. And the key point is that since they form from metal-free gas, you don't expect to see emission lines from metals which come from the star illuminating the surrounding gas with radiation.

These systems are very far away because you are looking more than 13 billion years back in time. The argument is JWST has a small field of view and these Pop III stars are like flashes in comparison to the age of the galaxy. So the probability of catching one that is bright enough to be detected is just super low. Which is why there is a strong prior that the HeII could be from other physics that is relatively well understood. But really the OIII emission is the biggest sign that this isn't a "primordial galaxy"

I think this is perfect! If only we can convince the author of the article...

Unfortunately not. These stars have no elements heavier than hydrogen and helium so you wouldn't be able to create a rocky planet that's habitable. Furthermore their lifetimes are only 3 Myr which is much to short to form a rocky planet and also the explosion from SN if it happens or direct collapse of the star to a black hole would immediately destroy any life.

As an expert in this space, I can confidently tell you that nothing about this observation is conclusive about the presence of the "First Stars" or what we call "Pop. III" Stars. By definition, the first stars are nearly completely devoid of elements heavier than hydrogen and helium. The spectra shows absolutely booming emission from Oxygen III ions at 5007A so there are heavy elements in the system and at best there is a mix of Pop III stars and more normal stars. The lifetimes of the stars are very short, ~3 Myr, so the chances of seeing them are very low which is likely the limiting factor (along with their brightness) and thus there is a strong Bayesian prior against seeing them with a narrow field of view. The mass of the system at 10^7.35 solar masses is much greater than what we expect from theoretical models that form Pop. III stars and you must ask how it's possible to not have any metals pollute the gas. The main piece of evidence for Pop III stars is HeII emission at 1640A which is a prediction of Pop. III stars, but you can also get this in many other ways, for example X-ray binaries. We see this plenty in the local Universe and we fully expect this to happen elsewhere. So to me this is headline chasing with little conclusive evidence.

So MOND does predict more galaxies at high redshift however it also predicts earlier reionization than LCDM which it turns out not to be true and the mass function of clusters is not what we see purely based on X-ray temperatures. So getting one thing right at the expense of many others doesn't make this particularly viable.

I have to say, this article is exceptionally disappointing. As someone who works in this space, there are numerous misleading depictions about the state of the field. Almost any respectable simulation shows that disk galaxies are widely present at very early times. This is simply an argument of angular momentum conservation and these rotational states are simply more transient at early times compared to the local Universe.

"Yan found 87 distant galaxies behind the galaxy cluster SMACS 0723" --> this is not true. They found 87 galaxy candidates. To be fair to the article, they do note that these await spectroscopic confirmation but experts only believe those with spectroscopic confirmation. Everything else is tentative and we don't yet have good numbers on confirmation rates. Finally, the Yan et al candidates are wildly inconsistent with almost every other estimate of high-redshift galaxy samples. You can see a comparison in Table 4 here: https://arxiv.org/pdf/2212.06683.pdf. They claim more than double the number of high-redshift sources compared to everyone else. JWST data is still very new and hard to both reduce and analyze. One particular problem is correlated hot pixels which can appear as very high-redshift sources. I don't know if this impacts the Yan et al paper but just an example of something that is not 100% straightforward to deal with. I highly recommend people take this with a healthy amount of skepticism until everything has a spectrum.

I think this is perhaps the wrong way to think about it. 50 million years represents ~14% of the age of the Universe (at 350 Myr) so it's really quite a big jump. Considering stars aren't thought to form until 200-250 Myr after the Big Bang, we're talking 33%-50% closer to this period. That's quite remarkable considering the was well out of reach just a year ago.

A lot of the work on distant galaxies is not being done with gravitational lensing. The idea is that you use massive objects in the foreground, like galaxy clusters, to focus light from the background. Depending on orientation, we can get magnifications of more than 10,000. There was a recent press release of such an example. So in principle, our telescopes combined with gravitational lenses can resolve almost all of the relevant detail we would want of a galaxy if the orientation is correct. It rarely is of course but there are a few examples so such strong lenses.

Echoing previous responses, it depends on what you want to learn. Gravity on large scales is fairly well understood (or at least many astrophysicists believe this to be the case). If there are large scale structure observables that are only dependent on cosmology (i.e. the cosmological parameters) simulations like this will be ideal. However, the major issue here is that a huge amount of the results of these simulations depend on physics that happen below the "grid scale" off the simulation. Thus I would agree that training the ML models on these simulations is the epitome of bias because it is learning a "sub grid" model rather than fundamental physics. Reading through the papers on this work, the vast majority of models that have been trained are not able to generalize between the different classes of sub grid models used which very much limits predicability. This is an inherent limitation of most cosmological simulations, not just these ones.

Couldn't agree more. Moreover, given that a huge part of the value of the degree is related to the prestige of the University, bad-mouthing your own institution only serves to reduce the value of your own degree. Who cares if I write an honest and bad review about a restaurant that I have no stake in. I just can't envision a scenario where people try to devalue their own diploma.

Could you elaborate a bit more on this? I have thought about employing NNs in this way for quite a while but the thing I never wrapped my head around was ensuring how it generalizes to different problems.

Modified gravity is still being actively explored and I would argue taken very seriously but not in the context of dark matter, rather in the context of dark energy. So in a sense, yes, modified and dark matter combined are both possible in the same theory. However, at the moment, there is no real reason to suggest both dark matter and modified gravity are responsible for things like galaxy rotation curves because one of these works just as well without the other. In fact, many modified gravity theories apply "screening mechanisms" so they don't impact galaxy scales

The best evidence for dark matter is arguably the CMB. The strengths of the individual peaks are highly suggestive of dark matter, in particular the third peak. Furthermore, most MOND simulations on cosmological scales still require dark matter (if they evolve the Universe following the Friedmann equation), for example an 11eV sterile neutrino, because there has yet to be an underlying theory that accurately describes the evolution that can reproduce the mass function and galaxy clustering with MOND. This isn't to say that dark matter doesn't have its problem, one of which is the fact that we don't know what it is; however, there still remain numerous candidates that have yet to be sufficiently explored experimentally.

Nebula isn't a physician-ordered test, nor does it come with the bioinformatics pipeline needed for rare conditions or genetic counseling. It's quite simply a different product for a different purpose.

Yes, we could test two potential parents to see if they are carriers. Depending on what you're looking for though, if it's a specific mutation, there might be a slightly cheaper option on the market as our test is very broad spectrum.

Very much appreciate the comment. The sequencing is done at a lab in Maryland.

Our test won't detect Huntington's unfortunately.

Both good suggestions. The hard-drive idea is totally doable and something we have considered. In terms of the analysis, it's not quite a program that you can run on your own computer. You can rank variants this way but you need a trained bioinformatician to interpret them which is why it has to be done on our side.

Thanks for the comment and we totally agree. The only way to prove we care about privacy is to live it and be as transparent as possible.