[whiw]

> Galactic spectra, which JWST started to send back in earnest at the end of last year, are useful for two reasons.

> First, they let astronomers nail down the galaxy’s age. The infrared light JWST collects is reddened, or redshifted, meaning that as it traverses the cosmos, its wavelengths are stretched by the expansion of space. The extent of that redshift lets astronomers determine a galaxy’s distance, and therefore when it originally emitted its light.

Won't a photon climbing out of a huge gravity well have a huge redshift, thus confounding estimates of distance from us and estimated age?

[antognini]

The photons that are getting observed are emitted from the accretion disk, which is not very close to the event horizon.

You can estimate how close to the event horizon the disk is based on how broad the spectral lines are. The part of the disk that is coming towards you will be blueshifted and the part of the disk that is rotating away will be redshifted. From that (which is independent of the overall depth of the potential well) you can figure out how fast the disk is rotating. And from that you can figure out how far away the disk is from the black hole.

[quakeguy]

Well, this is awesome.

[pdonis]

> Won't a photon climbing out of a huge gravity well have a huge redshift

It depends; the key factor is not how "huge" the gravity well is (in terms of how massive the object is), but how close to the black hole horizon the light is emitted. The vast majority of the light JWST is seeing from black holes is not from very close to the horizon. It's from the accretion disk, which is much further from the horizon and so the gravitational redshift is much smaller.

[ben_w]

> Won't a photon climbing out of a huge gravity well have a huge redshift,

Yes

> thus confounding estimates of distance from us and estimated age?

Not if you know, or can get a good estimate of, the potential well it's climbing out of.

That said, Brian Cox does sometimes joke that astronomers round π to 1; while I wouldn't know about the reality, it's probably safe to infer at least some frustration on his part about the precision of things in this field.

[marcosdumay]

The joke was way more true at the 20th century. There were many really important measurements where we got unprecedentedly precision, enough to say it's X, 100X, or something in between.

Nowadays astronomy got a lot more precise. But there are disagreements on how much confidence to put on that extra precision.

[gpgn]

These are somewhated dated but well worth watching; the professor does all kinds of approximations.

Frontiers/Controversies in Astrophysics with Charles Bailyn: https://youtu.be/ZiK4lg3Tzfs?t=1628

[hutzlibu]

I also don't know how accurate that description is, but this comic comes to mind:

https://xkcd.com/2205/

But I mean, space is really, really big and we are observing from one single spot with (on cosmological scale probably) primitive technology. So of course most of it is guessing and when you "guess" a lot of things, it maybe does not matter a lot, if you have 3.41 Pi or 1, when the data you have are rough estimates anyway. But sure, when you do sloppy math, when you could have precision - that would be just wrong and unscientific.

[quickthrower2]

I was confused... the symbol π is actually Pi, but it renders as something that looks like a different alphabet entirely on HN.

[ajross]

> Won't a photon climbing out of a huge gravity well have a huge redshift, thus confounding estimates of distance from us and estimated age?

Of course it will. It will also have a redshift related to the expansion of the space it's been travelling through. Both of those corrections are absolutely part of the model. It's not nearly as simple as "Astronomers forgot about General Relativity!".

But I guess it's true (to be clear: I'm just an amateur in this field) that the ΛCDM model for cosmological evolution that we've all been looking at for the past decade or two isn't holding up well at all. It looked like it was pretty much there and just needed some fine tuning. Then we got a bunch of new data and everything's a mess.

That's kind of exciting all by itself, though it's also leading to a bunch of nattering from the existing iconoclasts (MOND nuts in particular) whose theories are also not working very well to explain JWST observations.

New insight needed, basically. We're all watching for updates.

[xigency]

> Both of those corrections are absolutely part of the model

Is there a way to gain a better understanding of how these parameters are modeled and what the scientific evidence is for the various phenomena in astrophysics? It's somewhat perplexing to me as an outsider of the field to understand how things like mass and distance of stars and planetary bodies are determined when 1) the scales are so outside of conventional experience 2) observation is limited to 2D imaging of the night sky 3) the observations in general are not consistent with our knowledge of gravity and relativity without adding hidden parameters.

[codethief]

> Won't a photon climbing out of a huge gravity well have a huge redshift

Yes. Though see the sibling comments on why the (remaining) gravity well the emitted photon has to climb out of is not particularly huge here.

> thus confounding estimates of distance from us and estimated age?

Generally speaking: No, because people are not stupid. :) See the integrated Sachs-Wolfe effect for a very similar situation (CMB photons traveling through gravitational wells) -> https://en.m.wikipedia.org/wiki/Sachs%E2%80%93Wolfe_effect

[mkoubaa]

My understanding is that a particles, like photons, don't have wave shifts. That's an emergent property of many particles

[alecst]

The conventional Doppler shift and the equivalence principle imply a gravitational redshift for a photon. See page 102:

https://preposterousuniverse.com/wp-content/uploads/grnotes-...

[tsimionescu]

In quantum mechanics, a single particle is also a wave and vice versa. Light is in fact the thing where this observation was first discovered - it had been proven to be a wave for at least a few decades when Einstein discovered the quantum nature of the photovoltaic effect, proving it is also a particle. This discovery was the very start of quantum mechanics, in fact.

[stopping]

No, individual particles can indeed be redshifted. The particle's wavelength is a fundamental property.

[blueprint]

Your comment is a bit strange. Light doesn't travel as photons. Photons exclusively exist at the site and instant of detection of the wave of probability of detection that light really travels as.

When light is redshifted, it loses energy, therefore the wavelength becomes longer.