Gravity Grinch
@gravitygrinch.bsky.social
observational cosmologist -- the particle horizon is the limit!
https://thegravitygrinch.blogspot.com
https://thegravitygrinch.blogspot.com
I asked ChatGPT, Claude, Grok, and deepseek to flip a png that contained text and then flip the text to be readable again. Deepseek can't handle images, Claude did sth crazy & useless output, Grok similarly, Chat just flipped the image but not the text.
Can this be done? How?
#Chatgpt
Can this be done? How?
#Chatgpt
June 11, 2025 at 8:51 PM
I asked ChatGPT, Claude, Grok, and deepseek to flip a png that contained text and then flip the text to be readable again. Deepseek can't handle images, Claude did sth crazy & useless output, Grok similarly, Chat just flipped the image but not the text.
Can this be done? How?
#Chatgpt
Can this be done? How?
#Chatgpt
Happy 91th birthday to #RoyKerr -- the man who made a #BlackHole spin and who assured me that his cat is safe from any thought experiments related to his research! 🥂
(Picture by his lovely wife taken from the bird platform...)
#astronomy #astrophysics #cosmology
(Picture by his lovely wife taken from the bird platform...)
#astronomy #astrophysics #cosmology
May 15, 2025 at 10:04 PM
Happy 91th birthday to #RoyKerr -- the man who made a #BlackHole spin and who assured me that his cat is safe from any thought experiments related to his research! 🥂
(Picture by his lovely wife taken from the bird platform...)
#astronomy #astrophysics #cosmology
(Picture by his lovely wife taken from the bird platform...)
#astronomy #astrophysics #cosmology
Happy Earth Day to everyone and have a try writing your name or anything you like in earthly letters!
landsat.gsfc.nasa.gov/apps/YourNam...
landsat.gsfc.nasa.gov/apps/YourNam...
April 22, 2025 at 3:09 PM
Happy Earth Day to everyone and have a try writing your name or anything you like in earthly letters!
landsat.gsfc.nasa.gov/apps/YourNam...
landsat.gsfc.nasa.gov/apps/YourNam...
Wow! Welcome to my new followers! 🤩
Now that we are friends, I will think of a paper worth submitting (never tried).
Now that we are friends, I will think of a paper worth submitting (never tried).
April 11, 2025 at 7:15 PM
Wow! Welcome to my new followers! 🤩
Now that we are friends, I will think of a paper worth submitting (never tried).
Now that we are friends, I will think of a paper worth submitting (never tried).
5) Yet, for each structure, the velocity dispersion of all infalling galaxies of the minor and major models yield lower (blue) and upper bounds (red) on the true vel disp. For small theta, the vel disp from Delta v is even a great estimate for the true one (grey on the black)!
April 10, 2025 at 9:14 PM
5) Yet, for each structure, the velocity dispersion of all infalling galaxies of the minor and major models yield lower (blue) and upper bounds (red) on the true vel disp. For small theta, the vel disp from Delta v is even a great estimate for the true one (grey on the black)!
4) For small theta, both models yield the difference of the line-of-sight vels ("Delta v"). But we can show that none of these models predicts the full radial velocity (black line), as the perpendicular components always have an impact! (x-axis: true v_rad, y-axis: infall models)
April 10, 2025 at 9:14 PM
4) For small theta, both models yield the difference of the line-of-sight vels ("Delta v"). But we can show that none of these models predicts the full radial velocity (black line), as the perpendicular components always have an impact! (x-axis: true v_rad, y-axis: infall models)
3) Major infall: projects the obs. line-of-sight vels onto the infalling galaxy's line of sight to determine the major infall velocity from these projections (see the green, light red and blue arrows). This is asymmetric and again only an approx. to the full rad. velocity.
April 10, 2025 at 9:14 PM
3) Major infall: projects the obs. line-of-sight vels onto the infalling galaxy's line of sight to determine the major infall velocity from these projections (see the green, light red and blue arrows). This is asymmetric and again only an approx. to the full rad. velocity.
2) Minor infall: takes the observed line-of-sight velocities and projects them onto the radial connection.
It thus misses to include velocity components perpendicular to our lines of sight. Yet, one thinks they have a small impact: the smaller theta, the smaller their impact.
It thus misses to include velocity components perpendicular to our lines of sight. Yet, one thinks they have a small impact: the smaller theta, the smaller their impact.
April 10, 2025 at 9:14 PM
2) Minor infall: takes the observed line-of-sight velocities and projects them onto the radial connection.
It thus misses to include velocity components perpendicular to our lines of sight. Yet, one thinks they have a small impact: the smaller theta, the smaller their impact.
It thus misses to include velocity components perpendicular to our lines of sight. Yet, one thinks they have a small impact: the smaller theta, the smaller their impact.
1) Infall models describe the relative radial motion (red) between galaxies or between a galaxy infalling into a larger structure. How to calculate it when all we have is observations along our lines of sight (grey-blue)? That's the reason there are two infall models!
April 10, 2025 at 9:14 PM
1) Infall models describe the relative radial motion (red) between galaxies or between a galaxy infalling into a larger structure. How to calculate it when all we have is observations along our lines of sight (grey-blue)? That's the reason there are two infall models!
5) Last but not least, the biggest problem is not the lack of highly precise probes but the stats! We need to synchronise all probes to attain >1000 member gals and a representative sample of the cluster volume but this still causes a huge spread for H0 and absolute dists...
April 8, 2025 at 5:41 PM
5) Last but not least, the biggest problem is not the lack of highly precise probes but the stats! We need to synchronise all probes to attain >1000 member gals and a representative sample of the cluster volume but this still causes a huge spread for H0 and absolute dists...
4) For the Hubble flow diagram, we can use caustics to determine masses for our selections. If we use our 212 member gals with CF4 distances, we arrive at the same mass estimates and precision as Rines+2016 who used 1000 gals and a lot of add. model assumptions! 🤩
April 8, 2025 at 5:41 PM
4) For the Hubble flow diagram, we can use caustics to determine masses for our selections. If we use our 212 member gals with CF4 distances, we arrive at the same mass estimates and precision as Rines+2016 who used 1000 gals and a lot of add. model assumptions! 🤩
3) Search for all cluster members that also have Cosmicflows-4 distances to set up a Hubble diagram. Yet, the dists usually has large uncertainties. To alleviate that issue, we anchor the dists at the (precise) cluster centre and Taylor expand around that.
April 8, 2025 at 5:41 PM
3) Search for all cluster members that also have Cosmicflows-4 distances to set up a Hubble diagram. Yet, the dists usually has large uncertainties. To alleviate that issue, we anchor the dists at the (precise) cluster centre and Taylor expand around that.
2) Take this data and perform a density-based clustering on the sky to find the virial and the turnaround radius from the stable regions of the clustering parameters (this algorithm is mathem. more robust than the standard approaches and again involves no further models!)
April 8, 2025 at 5:41 PM
2) Take this data and perform a density-based clustering on the sky to find the virial and the turnaround radius from the stable regions of the clustering parameters (this algorithm is mathem. more robust than the standard approaches and again involves no further models!)
1) Take SDSS DR17 galaxies in the Coma region and select the Coma cluster in redshift space based on the local maxima and minima positions. (i.e. no cosmological model involved, no assumption how to split velocities along the line of sight)
April 8, 2025 at 5:41 PM
1) Take SDSS DR17 galaxies in the Coma region and select the Coma cluster in redshift space based on the local maxima and minima positions. (i.e. no cosmological model involved, no assumption how to split velocities along the line of sight)
Paper day for least-model-dependent astrophysics! On today's menu: an old-new mathem. robust galaxy clustering, a clever way to reduce large distance-uncertainties from non-redshift probes & our favourite friendly neighbouring cluster, Coma! 🧶🧶
arxiv.org/abs/2504.04135
#cosmology #astronomy
arxiv.org/abs/2504.04135
#cosmology #astronomy
April 8, 2025 at 5:41 PM
Paper day for least-model-dependent astrophysics! On today's menu: an old-new mathem. robust galaxy clustering, a clever way to reduce large distance-uncertainties from non-redshift probes & our favourite friendly neighbouring cluster, Coma! 🧶🧶
arxiv.org/abs/2504.04135
#cosmology #astronomy
arxiv.org/abs/2504.04135
#cosmology #astronomy
Here comes the #Highlight of the day! Did you know that you can slice a bagel such that you get two intertwined Möbius strips? Happy breakfast tomorrow and be careful putting creme cheese on the strips. 🤣
(all credits to Peyman Milanfar who posted the idea on X)
#mathematics #outreach #science
(all credits to Peyman Milanfar who posted the idea on X)
#mathematics #outreach #science
March 26, 2025 at 8:29 PM
Here comes the #Highlight of the day! Did you know that you can slice a bagel such that you get two intertwined Möbius strips? Happy breakfast tomorrow and be careful putting creme cheese on the strips. 🤣
(all credits to Peyman Milanfar who posted the idea on X)
#mathematics #outreach #science
(all credits to Peyman Milanfar who posted the idea on X)
#mathematics #outreach #science
Happy Birthday to Albert Einstein! (and since it's Pi-Day, too, enjoy the view of my little raspberry-blueberry pies with a smile)
March 14, 2025 at 4:13 PM
Happy Birthday to Albert Einstein! (and since it's Pi-Day, too, enjoy the view of my little raspberry-blueberry pies with a smile)
February 5, 2025 at 11:13 AM
Visited the #Sonneberg Obs for an outreach talk on Monday. Really worth going! They have a 7-billion-year-old meteorite, the first telescope of Cuno Hoffmeister (who discovered variable stars), and the largest collection of photo plates from a single observatory!
#science #Outreach #astronomy
#science #Outreach #astronomy
January 15, 2025 at 9:46 AM
Visited the #Sonneberg Obs for an outreach talk on Monday. Really worth going! They have a 7-billion-year-old meteorite, the first telescope of Cuno Hoffmeister (who discovered variable stars), and the largest collection of photo plates from a single observatory!
#science #Outreach #astronomy
#science #Outreach #astronomy
Thanks a lot for all the #citations in 2024! I am very happy about the increase and how many people value my work in #astronomy, #astrophysics, and #cosmology!
December 30, 2024 at 10:46 AM
Thanks a lot for all the #citations in 2024! I am very happy about the increase and how many people value my work in #astronomy, #astrophysics, and #cosmology!
#HappyWinterSolstice, Yalda Chrisnukkah Night and #Grinchmas! Today is finally the turning point towards summer again. It can't be warm and cosy soon enough for me.
#HappyHolidays to all of you whatever you want to celebrate or if you want to celebrate at all.
#HappyHolidays to all of you whatever you want to celebrate or if you want to celebrate at all.
December 21, 2024 at 4:18 PM
#HappyWinterSolstice, Yalda Chrisnukkah Night and #Grinchmas! Today is finally the turning point towards summer again. It can't be warm and cosy soon enough for me.
#HappyHolidays to all of you whatever you want to celebrate or if you want to celebrate at all.
#HappyHolidays to all of you whatever you want to celebrate or if you want to celebrate at all.
Since my #Waiting4WinterSolstice didn't go well with astro talks, how about some pictures of chocolate Santas and Rudolphs?
December 6, 2024 at 9:50 PM
Since my #Waiting4WinterSolstice didn't go well with astro talks, how about some pictures of chocolate Santas and Rudolphs?
final) Here is a plot visualising the behaviour of beyond-10^(12)-Msol RN-SNS: zero crossings mark tangential CC, extrema mark radial CC.
(y-axis is tan(source pos) of lens equation with z_lens=0.024 z_source=0.05, x-axis is radius of closest approach / Schwarzschild radius)
(y-axis is tan(source pos) of lens equation with z_lens=0.024 z_source=0.05, x-axis is radius of closest approach / Schwarzschild radius)
November 30, 2023 at 9:10 AM
final) Here is a plot visualising the behaviour of beyond-10^(12)-Msol RN-SNS: zero crossings mark tangential CC, extrema mark radial CC.
(y-axis is tan(source pos) of lens equation with z_lens=0.024 z_source=0.05, x-axis is radius of closest approach / Schwarzschild radius)
(y-axis is tan(source pos) of lens equation with z_lens=0.024 z_source=0.05, x-axis is radius of closest approach / Schwarzschild radius)
Happy Halloween with my favourite stereotype! 🎃
November 1, 2023 at 12:10 AM
Happy Halloween with my favourite stereotype! 🎃
Happy to announce that our paper on A3827 has just been published in MNRAS! Special thanks to Helen Klus for being a great editor! doi.org/10.1093/mnra...
...have a look at this highly odd gravitational lens. 🔭🧪
...have a look at this highly odd gravitational lens. 🔭🧪
October 10, 2023 at 7:43 AM
Happy to announce that our paper on A3827 has just been published in MNRAS! Special thanks to Helen Klus for being a great editor! doi.org/10.1093/mnra...
...have a look at this highly odd gravitational lens. 🔭🧪
...have a look at this highly odd gravitational lens. 🔭🧪