Johannes Buchner
@johannesbuchner.bsky.social
I study the physics of how gas flows from dark matter halos onto the black hole event horizon. I build data science tools to look closer at how black holes become supermassive.
eROSITA arxiv paper splash by colleagues of the National Observatory of Athens!
December 11, 2025 at 10:53 AM
eROSITA arxiv paper splash by colleagues of the National Observatory of Athens!
Translate to astronomy ...
its.promp.td/its-always-t...
its.promp.td/its-always-t...
It’s Always the Process, Stupid!
Why AI Won’t Save Your Broken Workflow
its.promp.td
December 1, 2025 at 12:20 PM
Translate to astronomy ...
its.promp.td/its-always-t...
its.promp.td/its-always-t...
We are snowed in in Ringberg castle (Multiscale Environment of AGN across cosmic time workshop)
November 26, 2025 at 8:28 AM
We are snowed in in Ringberg castle (Multiscale Environment of AGN across cosmic time workshop)
Under the first snowflakes of the season, today was a group bonding moment - the institute had a fire alarm and everyone had to wait outside for ~30 minutes.
November 21, 2025 at 9:11 PM
Under the first snowflakes of the season, today was a group bonding moment - the institute had a fire alarm and everyone had to wait outside for ~30 minutes.
My advent calendar this year will be to close one browser tab every day (and not open many new ones).
November 20, 2025 at 10:21 AM
My advent calendar this year will be to close one browser tab every day (and not open many new ones).
Reposted by Johannes Buchner
Super cool paper from @johannesbuchner.bsky.social this morning! And very excited to see* X-PSI and NEoST in there 🤩
*NEoST is too small for us to have found it yet but according to search it's in Figure 5 somewhere 😅
arxiv.org/abs/2511.12195
*NEoST is too small for us to have found it yet but according to search it's in Figure 5 somewhere 😅
arxiv.org/abs/2511.12195
High-impact Scientific Software in Astronomy and its creators
In the last decades, scientific software has graduated from a hidden side-product to a first-class member of the astrophysics literature. We aim to quantify the activity and impact of software develop...
arxiv.org
November 18, 2025 at 9:36 AM
Super cool paper from @johannesbuchner.bsky.social this morning! And very excited to see* X-PSI and NEoST in there 🤩
*NEoST is too small for us to have found it yet but according to search it's in Figure 5 somewhere 😅
arxiv.org/abs/2511.12195
*NEoST is too small for us to have found it yet but according to search it's in Figure 5 somewhere 😅
arxiv.org/abs/2511.12195
This is fine, just need to add a few more parameters to the model.
November 7, 2025 at 3:39 PM
This is fine, just need to add a few more parameters to the model.
Optical depth experiment in Garching land
November 6, 2025 at 10:51 AM
Optical depth experiment in Garching land
Immersive fly-through the environment of a super-massive black hole. Accretion disc (bottom) ✓ swirling inward ✓; torus (sides) ✓ with covering factor ~75% ✓. Clumpy structure ✓
1547Z pass through Hurricane Melissa on 27 October
YouTube video by Flynonymous WX
www.youtube.com
November 2, 2025 at 4:24 PM
Immersive fly-through the environment of a super-massive black hole. Accretion disc (bottom) ✓ swirling inward ✓; torus (sides) ✓ with covering factor ~75% ✓. Clumpy structure ✓
Grateful for my 10 day visit to the National Observatory of Athens.
They have three riches:
1) A pipeline for handling all of the 25+ years of the XMM-Newton archive
2) deep expertise in AGN demographics and variability
3) a friendly group that likes to hang out, collaborate and share lunch.
They have three riches:
1) A pipeline for handling all of the 25+ years of the XMM-Newton archive
2) deep expertise in AGN demographics and variability
3) a friendly group that likes to hang out, collaborate and share lunch.
October 31, 2025 at 8:31 PM
Grateful for my 10 day visit to the National Observatory of Athens.
They have three riches:
1) A pipeline for handling all of the 25+ years of the XMM-Newton archive
2) deep expertise in AGN demographics and variability
3) a friendly group that likes to hang out, collaborate and share lunch.
They have three riches:
1) A pipeline for handling all of the 25+ years of the XMM-Newton archive
2) deep expertise in AGN demographics and variability
3) a friendly group that likes to hang out, collaborate and share lunch.
Before LLM / After LLM
October 21, 2025 at 3:24 AM
Before LLM / After LLM
If you reimplement ensemble MCMC, and you only use the first ndim instead of all N walkers for creating proposals, convergence is slow. #notetoself
October 17, 2025 at 1:29 PM
If you reimplement ensemble MCMC, and you only use the first ndim instead of all N walkers for creating proposals, convergence is slow. #notetoself
Imagine my surprise when I saw I took 52 holidays last year. So I have -20 holidays left this year!
September 30, 2025 at 1:11 PM
Imagine my surprise when I saw I took 52 holidays last year. So I have -20 holidays left this year!
Why did they call the lamp post x-ray corona and not an "isco ball"?
September 21, 2025 at 9:11 AM
Why did they call the lamp post x-ray corona and not an "isco ball"?
Question: What would be the steps and technical challenges for creating a small black hole in orbit around the Earth or on the Moon? The black hole should be massive enough to evaporate in longer than 1 hour.
ChatGPT5 answers:
ChatGPT5 answers:
September 17, 2025 at 8:28 PM
Question: What would be the steps and technical challenges for creating a small black hole in orbit around the Earth or on the Moon? The black hole should be massive enough to evaporate in longer than 1 hour.
ChatGPT5 answers:
ChatGPT5 answers:
"Let's cancel all MPG company credit cards on a Friday afternoon, then not communicate for a week." -- an AirPlus intern, presumably
September 16, 2025 at 9:00 AM
"Let's cancel all MPG company credit cards on a Friday afternoon, then not communicate for a week." -- an AirPlus intern, presumably
An important dynamic to counteract with your peers and students behavioralscientist.org/why-we-spiral/ #astronomy #welcomingenvironment #belonging #academicchatter
Why We Spiral - by Gregory M. Walton - Behavioral Scientist
Questions of who we are or what we’re worth can send us into a tailspin. But the very same processes that pull us down can propel us up, too.
behavioralscientist.org
September 15, 2025 at 10:08 PM
An important dynamic to counteract with your peers and students behavioralscientist.org/why-we-spiral/ #astronomy #welcomingenvironment #belonging #academicchatter
I found out Italy has very good wines you can sip after asking the conference table how far away direct dark matter detection is. Opinions range from within 10 years to type III Kardashev civilisation. #darkmatter #cosmology #astronomy #italy #conference #cosmology2025
September 10, 2025 at 8:52 PM
I found out Italy has very good wines you can sip after asking the conference table how far away direct dark matter detection is. Opinions range from within 10 years to type III Kardashev civilisation. #darkmatter #cosmology #astronomy #italy #conference #cosmology2025
Cosmology Conference in Elba, imagination vs. how it is going
September 10, 2025 at 11:50 AM
Cosmology Conference in Elba, imagination vs. how it is going
New picture, does it look sufficiently professional? First one to guess the equation wins either a PhD or a like ;-)
September 2, 2025 at 12:48 PM
New picture, does it look sufficiently professional? First one to guess the equation wins either a PhD or a like ;-)
Someone (unsuccessfully) edited my #stackoverflow question to add "Thank you" at the bottom, which is hilarious. Am I now more thankful? (I was internet-socialised to say thank you after rather than #TIA)
August 26, 2025 at 11:58 AM
Someone (unsuccessfully) edited my #stackoverflow question to add "Thank you" at the bottom, which is hilarious. Am I now more thankful? (I was internet-socialised to say thank you after rather than #TIA)
Black body spectra have a FWHM of 0.284 dex.
August 22, 2025 at 7:14 AM
Black body spectra have a FWHM of 0.284 dex.
Compton and inverse Compton. A new logo for my radiative transfer code xars? github.com/JohannesBuch...
August 12, 2025 at 4:39 AM
Compton and inverse Compton. A new logo for my radiative transfer code xars? github.com/JohannesBuch...
A Caltech employee at their lunch break.
August 12, 2025 at 4:33 AM
A Caltech employee at their lunch break.