I Illuminating Black Hole Shadows with Dark Matter Annihilation

[fresh_42]

TL;DR Summary

An interesting new aspect of EHT astronomy - DM
Pop Science Version: https://phys.org/news/2025-10-event-horizon-telescope-images-reveal.html

Abstract​

The Event Horizon Telescope (EHT) has significantly advanced our ability to study black holes, achieving unprecedented spatial resolution and revealing horizon-scale structures. Notably, these observations feature a distinctive dark shadow—primarily arising from faint jet emissions—surrounded by a bright photon ring. Anticipated upgrades of the EHT promise substantial improvements in dynamic range, enabling deeper exploration of low-background regions, particularly the inner shadow defined by the lensed equatorial horizon. Our analysis shows that observations of these regions transform supermassive black holes into powerful probes for annihilating dark matter, which is expected to accumulate densely in their vicinity. By analyzing the black hole image morphology and performing electron-positron propagation calculations in realistic plasma backgrounds derived from general relativistic magnetohydrodynamic simulations, we set stringent constraints on dark matter annihilation, requiring contributions below the astrophysical emission. These constraints, derived from both current EHT observations and projections for future upgraded arrays, exclude a substantial region of previously unexplored parameter space and remain robust against astrophysical uncertainties, including black hole spin and plasma temperature variations.

https://journals.aps.org/prl/abstract/10.1103/yxqg-363n

 

[sbrothy]

I like that the link verifies that I'm human without any action on my part. I wonder how that works?

 

[Ibix]

I like that the link verifies that I'm human without any action on my part. I wonder how that works?

It's secret, but it's probable that Google has seen your machine before and regards you as low risk (you don't put in hundreds of requests in very short timeframes, etc), so just checks that your reaction time this time is plausible for a human - which is an instant rate limiter even if you are actually a bot.

The paper is interesting. I think it's basically saying that dark matter should be concentrated by the hole's gravity, and would have a different distribution around the hole because of its not-very-self-interacting nature. Thus the distribution of emissions from dark matter decays would be different from normal baryonic matter decays, so failure to detect that different profile puts constraints on mass and interaction cross section of particle type dark matter candidates. It's a pretty weak constraint with the current EHT, but upgrades that improve the angular resolution check more possible values.

 

[sbrothy]

It's secret, but it's probable that Google has seen your machine before and regards you as low risk (you don't put in hundreds of requests in very short timeframes, etc), so just checks that your reaction time this time is plausible for a human - which is an instant rate limiter even if you are actually a bot.

The paper is interesting. I think it's basically saying that dark matter should be concentrated by the hole's gravity, and would have a different distribution around the hole because of its not-very-self-interacting nature. Thus the distribution of emissions from dark matter decays would be different from normal baryonic matter decays, so failure to detect that different profile puts constraints on mass and interaction cross section of particle type dark matter candidates. It's a pretty weak constraint with the current EHT, but upgrades that improve the angular resolution check more possible values.

Pretty obvious when you put it so pedagogically. My only excuse was that it was pretty late!

 

[sbrothy]

And yes, interesting article, at least. The paper may be a little too dense for me, but that wont prevent me from trying….