wimvb Posted July 19, 2022 Share Posted July 19, 2022 54 minutes ago, StuartT said: Usually the problem is how to get rid of them in post-processing! Better to get to the cause of the problem: get a Mak-Newt 😁 (that’s what I did) 1 Link to comment Share on other sites More sharing options...
markse68 Posted July 19, 2022 Share Posted July 19, 2022 13 hours ago, IB20 said: Some nice images of Messier 74 yesterday from JWST. Credits: @gbrammer and Judy Schmidt. Incredible! the central eye looks so peaceful and the structure around it so fluid Link to comment Share on other sites More sharing options...
StuartT Posted July 20, 2022 Share Posted July 20, 2022 14 hours ago, wimvb said: Better to get to the cause of the problem: get a Mak-Newt 😁 (that’s what I did) or a SCT like me 1 Link to comment Share on other sites More sharing options...
IB20 Posted July 20, 2022 Author Share Posted July 20, 2022 Anyone fancy having a go at GLASS-z13? 2 Link to comment Share on other sites More sharing options...
robin_astro Posted July 20, 2022 Share Posted July 20, 2022 (edited) On 19/07/2022 at 08:00, IB20 said: Some nice images of Messier 74 yesterday from JWST They have spotted in that image what is left of SN 2013ej , a supernova which reached a bright mag 12 back in August 2013 https://www.wis-tns.org/astronotes/astronote/2022-147 Robin Edited July 20, 2022 by robin_astro 2 Link to comment Share on other sites More sharing options...
StuartT Posted July 20, 2022 Share Posted July 20, 2022 3 hours ago, robin_astro said: a supernova which reached a bright mag 12 back in August 2013 ...although probably a bit earlier back in time than that, in all fairness.. 😉 1 Link to comment Share on other sites More sharing options...
Paul M Posted July 20, 2022 Share Posted July 20, 2022 The Universe seems to be getting "smaller" with each new JWST revelation. And they're only just getting going! Link to comment Share on other sites More sharing options...
robin_astro Posted July 21, 2022 Share Posted July 21, 2022 3 hours ago, StuartT said: ...although probably a bit earlier back in time than that, in all fairness.. 😉 In who's reference frame ? not the photons 😉 1 Link to comment Share on other sites More sharing options...
robin_astro Posted July 21, 2022 Share Posted July 21, 2022 26 minutes ago, robin_astro said: In who's reference frame ? not the photons 😉 ....and any case, since the (apparent) magnitude is a measurement of the photon flux at the earth, the brightness did peak at ~mag 12 in August 2013 😉 1 Link to comment Share on other sites More sharing options...
andrew s Posted July 21, 2022 Share Posted July 21, 2022 6 hours ago, robin_astro said: In who's reference frame ? not the photons 😉 Photons don't have a reference frame. If they did they would be a rest in it? 😊 Regards Andrew 1 Link to comment Share on other sites More sharing options...
robin_astro Posted July 21, 2022 Share Posted July 21, 2022 3 hours ago, andrew s said: photons don't have a reference frame. If they did they would be a rest in it? 😊 Very true. They have no concept of time, a bit like me these days 😀 1 Link to comment Share on other sites More sharing options...
robin_astro Posted July 21, 2022 Share Posted July 21, 2022 10 minutes ago, robin_astro said: Very true. They have no concept of time, a bit like me these days 😀 In which case substitute neutrino for photon in the above 🙂 1 Link to comment Share on other sites More sharing options...
StuartT Posted July 21, 2022 Share Posted July 21, 2022 19 hours ago, robin_astro said: ....and any case, since the (apparent) magnitude is a measurement of the photon flux at the earth, the brightness did peak at ~mag 12 in August 2013 😉 touché my friend. Link to comment Share on other sites More sharing options...
markse68 Posted July 21, 2022 Share Posted July 21, 2022 On 20/07/2022 at 18:16, IB20 said: Anyone fancy having a go at GLASS-z13? They say this about Glass-Z13: "Both of the galaxies are much smaller than Earth’s Milly Way Galaxy, which is 100,000 light-years across. GLASS-z13 is estimated to be about 1,600 light-years across" which seems pretty tiny, but how on earth do they make an estimate like that? Is it using the visible size and an estimate for how much the universe has expanded since the light left it (magnifying its image)? Or is it based on theory for how big early galaxies should be? Do they take into account gravitational lensing effects? They don't really have much to compare it with. Mark Link to comment Share on other sites More sharing options...
gilesco Posted July 22, 2022 Share Posted July 22, 2022 10 hours ago, markse68 said: They say this about Glass-Z13: "Both of the galaxies are much smaller than Earth’s Milly Way Galaxy, which is 100,000 light-years across. GLASS-z13 is estimated to be about 1,600 light-years across" which seems pretty tiny, but how on earth do they make an estimate like that? Is it using the visible size and an estimate for how much the universe has expanded since the light left it (magnifying its image)? Or is it based on theory for how big early galaxies should be? Do they take into account gravitational lensing effects? They don't really have much to compare it with. Mark 1 4 Link to comment Share on other sites More sharing options...
andrew s Posted July 22, 2022 Share Posted July 22, 2022 14 hours ago, markse68 said: They say this about Glass-Z13: "Both of the galaxies are much smaller than Earth’s Milly Way Galaxy, which is 100,000 light-years across. GLASS-z13 is estimated to be about 1,600 light-years across" which seems pretty tiny, but how on earth do they make an estimate like that? Is it using the visible size and an estimate for how much the universe has expanded since the light left it (magnifying its image)? Or is it based on theory for how big early galaxies should be? Do they take into account gravitational lensing effects? They don't really have much to compare it with. Mark I think you'll find it is calculated based on the measured angular dimensions and red shift using models of the gravitational lensing and the LCMD cosmology . Regards Andrew 1 Link to comment Share on other sites More sharing options...
DaveS Posted July 22, 2022 Share Posted July 22, 2022 (edited) https://m.youtube.com/shorts/RJe0s1iDYLc Edited July 22, 2022 by DaveS 1 Link to comment Share on other sites More sharing options...
globular Posted July 22, 2022 Share Posted July 22, 2022 39 minutes ago, andrew s said: I think you'll find it is calculated based on the measured angular dimensions and red shift using models of the gravitational lensing and the LCMD cosmology . Regards Andrew Each measurement and model will have error bounds. I assume 1,600 will be the 50th percentile result when bringing it all together. I wonder what the 10th and 90th percentile results are? Feels to me that the error bounds must me quite large given all the unknowns. They should be published too really (maybe they are somewhere?) Link to comment Share on other sites More sharing options...
Gfamily Posted July 22, 2022 Share Posted July 22, 2022 Published paper here https://arxiv.org/abs/2207.09434 2 Link to comment Share on other sites More sharing options...
andrew s Posted July 22, 2022 Share Posted July 22, 2022 (edited) 33 minutes ago, globular said: Each measurement and model will have error bounds. I assume 1,600 will be the 50th percentile result when bringing it all together. I wonder what the 10th and 90th percentile results are? Feels to me that the error bounds must me quite large given all the unknowns. They should be published too really (maybe they are somewhere?) You will need to find the relevant peer reviewed paper. It will have the relevant error bars. However, it s very difficult to calculate systematic errors and all "cosmological " distances rely on what cosmological model you accept. One advantage of the LCDM cosmology is the it is easiest to apply. Regards Andrew See @Gfamily's post above. Edited July 22, 2022 by andrew s 1 Link to comment Share on other sites More sharing options...
Zermelo Posted July 22, 2022 Share Posted July 22, 2022 This is quite cool: Zoom Into the Southern Ring Nebula Captured by NASA James Webb Space Telescope 6 1 Link to comment Share on other sites More sharing options...
robin_astro Posted July 23, 2022 Share Posted July 23, 2022 On 22/07/2022 at 09:13, gilesco said: "Cows, small or far away?" Bizarrely in our universe this is only true out to about 1.5 redshift. Beyond that all cows look about the same size or even larger 🙂 https://arxiv.org/abs/astro-ph/9905116v4 Section 6 "Angular Diameter Distance" 1 Link to comment Share on other sites More sharing options...
markse68 Posted July 23, 2022 Share Posted July 23, 2022 if these early galaxies really are measured as predicted to be much smaller than the galaxies we see in our time frame, would there not be many more of them given the universe was much smaller and denser back then? Why do we only see the odd one or two of them? Are the others just way too small and dim to see? Or are the distances between them so stretched in the intervening expansion that they look very far apart? Link to comment Share on other sites More sharing options...
markse68 Posted July 23, 2022 Share Posted July 23, 2022 4 hours ago, robin_astro said: Bizarrely in our universe this is only true out to about 1.5 redshift. Beyond that all cows look about the same size or even larger 🙂 https://arxiv.org/abs/astro-ph/9905116v4 Section 6 "Angular Diameter Distance" which is really convenient when trying to observe very distant and possibly relatively small early galaxies! Link to comment Share on other sites More sharing options...
globular Posted July 23, 2022 Share Posted July 23, 2022 9 minutes ago, markse68 said: if these early galaxies really are measured as predicted to be much smaller than the galaxies we see in our time frame, would there not be many more of them given the universe was much smaller and denser back then? Why do we only see the odd one or two of them? Are the others just way too small and dim to see? Or are the distances between them so stretched in the intervening expansion that they look very far apart? Lots of guesswork and approximations in this early, yet to be peer reviewed, paper. But they seem to take an opposite view to you.... "we wouldn't expect these early galaxies to be as common as they appear to be. We estimate that if galaxies were visible at the rates we'd expect, we'd have had to search through an area 10 times larger to come up with them" Isn't the relatively limited time frame in which the universe was in the state necessary to form these "small" galaxies (a few hundred million years) part of the answer as to why there are a lot less of them compared to the billions of years in which the more familiar ones were forming? Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now