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.
Both papers
- take advantage of the large survey power of eROSITA.
- present intruiging results indicating we still have a long way to understand the central engine.
- take advantage of the large survey power of eROSITA.
- present intruiging results indicating we still have a long way to understand the central engine.
December 11, 2025 at 10:53 AM
Both papers
- take advantage of the large survey power of eROSITA.
- present intruiging results indicating we still have a long way to understand the central engine.
- take advantage of the large survey power of eROSITA.
- present intruiging results indicating we still have a long way to understand the central engine.
Antonis Georgakakis finds for the first time a U-shaped behaviour of how variable AGN are across the black hole mass - Eddington ratio plane. Perhaps strong winds at the high Eddington end? arxiv.org/abs/2512.09047
Characterising the X-ray variability of QSOs to the highest Eddington ratios and black hole masses with eROSITA light curves
An important diagnostic of the inner structure of accretion flows onto supermassive black holes are the stochastic flux variations at X-ray wavelengths. Despite its significance, a systematic characte...
arxiv.org
December 11, 2025 at 10:53 AM
Antonis Georgakakis finds for the first time a U-shaped behaviour of how variable AGN are across the black hole mass - Eddington ratio plane. Perhaps strong winds at the high Eddington end? arxiv.org/abs/2512.09047
Maria Chira investigates the eternal question of whether the tight UV to X-ray relation evolves or not. Physically, we expect it shouldn't, because the UV powers the corona the same at all epochs ... but alas, evolution is there!
arxiv.org/abs/2512.09767
arxiv.org/abs/2512.09767
Revisiting the X-ray-to-UV relation of Quasars in the era of all-sky surveys
The X-ray--to--UV relation of active galactic nuclei (AGNs), commonly parametrized via the monochromatic luminosities at $2500\,\mathring{A}$ and $2\,keV$, reflects the energetic interplay between the...
arxiv.org
December 11, 2025 at 10:53 AM
Maria Chira investigates the eternal question of whether the tight UV to X-ray relation evolves or not. Physically, we expect it shouldn't, because the UV powers the corona the same at all epochs ... but alas, evolution is there!
arxiv.org/abs/2512.09767
arxiv.org/abs/2512.09767
Panic on the day before the ArXiV posting:
How do I add a GDPR-compliant way for people to opt out of having their name shown?
The day of the arxiv posting ...
Why did you not include my software!111
;-)
How do I add a GDPR-compliant way for people to opt out of having their name shown?
The day of the arxiv posting ...
Why did you not include my software!111
;-)
November 19, 2025 at 8:02 AM
Panic on the day before the ArXiV posting:
How do I add a GDPR-compliant way for people to opt out of having their name shown?
The day of the arxiv posting ...
Why did you not include my software!111
;-)
How do I add a GDPR-compliant way for people to opt out of having their name shown?
The day of the arxiv posting ...
Why did you not include my software!111
;-)
I had made a mistake in a holiday request and only noticed now. Thanks to our flexible administration experience and energy for fighting SAP systems, I was able to get it back! Phew!
September 30, 2025 at 1:11 PM
I had made a mistake in a holiday request and only noticed now. Thanks to our flexible administration experience and energy for fighting SAP systems, I was able to get it back! Phew!
"Let's fix it and not tell anyone nor apologize." same intern one week later, presumably
September 28, 2025 at 3:56 PM
"Let's fix it and not tell anyone nor apologize." same intern one week later, presumably
Gute Besserung!
September 21, 2025 at 8:00 AM
Gute Besserung!
Well, that's not the can-do energy I was hoping for.
September 17, 2025 at 8:28 PM
Well, that's not the can-do energy I was hoping for.
(end of ChatGPT)
September 17, 2025 at 8:28 PM
(end of ChatGPT)
Bottom line: There is no viable method, now or in any foreseeable future, to create or safely manage a small BH near Earth or Moon that lasts >1h. The required energies & focusing are far beyond our capabilities, and the radiation and control issues would make it extraordinarily dangerous.
September 17, 2025 at 8:28 PM
Bottom line: There is no viable method, now or in any foreseeable future, to create or safely manage a small BH near Earth or Moon that lasts >1h. The required energies & focusing are far beyond our capabilities, and the radiation and control issues would make it extraordinarily dangerous.