In keeping with a brand new Physical Review Letters research, black holes may assist clear up the darkish matter thriller. The shadowy areas in black gap photographs captured by the Occasion Horizon Telescope can act as ultra-sensitive detectors for the invisible materials that makes up a lot of the universe’s matter.
Darkish matter makes up roughly 85% of the universe’s matter, however scientists nonetheless do not know what it really is. Whereas researchers have proposed numerous methods to detect it, this research introduces black gap imaging as a recent detection technique—one which comes with some distinct advantages.
The Occasion Horizon Telescope’s beautiful photographs of supermassive black holes have revealed extra than simply the geometry of spacetime; they’ve opened an sudden window into the seek for darkish matter.
Phys.org spoke to co-authors Jing Shu from Peking College and Yifan Chen from the Niels Bohr Institute.
“I’ve all the time been fascinated by devices just like the Occasion Horizon Telescope (EHT), which permit us to probe the intense environments round supermassive black holes and problem the boundaries of recognized bodily legal guidelines,” Shu stated.
Chen added, “I have been fascinated by the thought of utilizing black holes as detectors for brand new particles. Their excessive gravity makes them pure concentrators of matter, creating a novel assembly level for particle physics, gravity, and astrophysical remark.”
The analysis workforce targeted on a putting function of black gap photographs: the shadow area that seems darkish in EHT observations of M87* and Sagittarius A*.
A cosmic darkroom
The Occasion Horizon Telescope is a worldwide community of radio observatories working in live performance to realize Earth-sized decision by way of Very Lengthy Baseline Interferometry. Working at a frequency of 230 GHz, the telescope captures synchrotron radiation—mild produced when electrons spiral alongside the extreme magnetic discipline traces close to supermassive black holes.
To grasp what they’re seeing, astrophysicists run advanced pc simulations.
The magnetically arrested disk (MAD) mannequin has constantly delivered one of the best settlement with EHT observations. The MAD mannequin depicts sturdy magnetic fields penetrating the accretion disk, the place they each regulate the stream of infalling matter and energy jets that erupt perpendicular to the disk.
Crucially, the MAD mannequin explains why black gap shadows seem darkish: most electrons reside within the accretion disk, whereas the jet areas above and under are comparatively particle-poor, creating a pointy distinction within the photographs.
“Bizarre astrophysical plasma is commonly expelled by highly effective jets, leaving the shadow area particularly faint,” Chen defined. “Darkish matter, nevertheless, may constantly inject new particles that radiate on this area.”
As a result of darkish matter is predicted to pay attention densely close to the black gap’s middle, even faint annihilation alerts may stand out in opposition to this low astrophysical background, making the shadow a perfect testing floor.
Modeling darkish matter
The gravitational pull of supermassive black holes causes darkish matter to pay attention dramatically of their neighborhood, forming what physicists name a “darkish matter spike.” These areas obtain densities orders of magnitude increased than wherever else within the galaxy.
Since darkish matter annihilation charges rely on density squared, these enhanced densities may produce detectable alerts—if the annihilation happens in any respect.
The analysis workforce developed a classy framework that builds straight on the MAD mannequin by including darkish matter physics to the astrophysical baseline.
The workforce utilized common relativistic magnetohydrodynamic (GRMHD) simulations together with detailed particle propagation modeling. With this framework, they may mannequin how electrons and positrons from hypothetical darkish matter annihilation would behave within the magnetic discipline buildings extracted from the MAD mannequin.
In contrast to earlier research that relied on simplified spherical fashions, this strategy makes use of the lifelike, uneven magnetic discipline configurations extracted from the MAD simulations—the identical fields that form the astrophysical emission we observe.
“What we see in black gap photographs will not be the black gap itself, however mild emitted by bizarre electrons within the surrounding accretion disk, whose conduct we will mannequin utilizing well-known physics,” Shu stated.
“If darkish matter particles had been annihilating close to the black gap, they’d produce additional electrons and positrons whose radiation appears to be like barely totally different from the conventional emission.”
The essential distinction emerges in spatial distribution. Within the MAD mannequin, electrons focus within the accretion disk with sparse populations within the jet areas—creating the darkish shadow.
However electrons and positrons from darkish matter annihilation can be distributed extra uniformly all through each disk and jet areas, as a result of darkish matter annihilation constantly provides particles even the place astrophysical processes produce few electrons.
The workforce examined two annihilation channels—backside quark-antiquark pairs and electron-positron pairs—throughout darkish matter lots starting from sub-GeV to roughly 10 TeV.
For every state of affairs, they calculated the ensuing synchrotron radiation and generated artificial black gap photographs that mixed each astrophysical emission (from MAD) and potential darkish matter alerts.
Morphology as a probe
The researchers’ strategy to exploiting the morphology of the black gap photographs relatively than simply the full brightness makes the work stand out.
They required that darkish matter annihilation alerts stay under astrophysical emission at each level within the picture, notably inside the internal shadow area.
“By evaluating these predictions with actual EHT photographs on the ‘darkroom,’ we will seek for delicate alerts that will reveal darkish matter,” Shu stated.
This morphological strategy proves considerably extra highly effective than earlier constraints primarily based on whole depth alone. The evaluation excludes substantial areas of beforehand unexplored parameter house, setting limits on annihilation cross sections all the way down to roughly 10-27 cm³/s for present EHT observations.
“Our exclusions primarily based on present EHT observations already probe giant areas of beforehand unexplored parameter house, surpassing different searches that assume related density profiles,” Chen stated.
The constraints stay strong in opposition to astrophysical uncertainties, together with variations in black gap spin and plasma temperature parameters—components that usually introduce vital uncertainties in oblique darkish matter searches.
Future prospects
The true energy of this strategy will likely be realized with anticipated EHT upgrades. Future enhancements promise to extend dynamic vary by almost 100 instances and obtain angular decision equal to roughly one gravitational radius, enabling them to probe deeper into the darkest areas of the shadow.
“The important thing improve is enhancing the telescope’s dynamic vary, which is its capability to disclose very faint particulars proper subsequent to extraordinarily brilliant options,” Chen defined.
“A typical instance is the ‘excessive dynamic vary’ (HDR) mode on many smartphones, which makes use of superior processing to convey out particulars in each darkish shadows and brilliant highlights in the identical picture.”
These enhancements may allow detection of darkish matter with annihilation cross sections close to the thermal relic worth, a theoretically well-motivated goal, for lots as much as roughly 10 TeV.
Wanting forward, the researchers envision a number of instructions for increasing this analysis.
“The black gap shadow isn’t just a static picture; it’s a dynamic, multi-layered laboratory,” Shu stated. “Past the depth maps, polarization knowledge from the EHT additionally open new home windows, as a result of polarization encodes how magnetic fields and plasma form the radiation.”
Multi-frequency observations can even show essential, based on Shu. Totally different radiation mechanisms scale in another way with frequency, permitting researchers to find out the supply of radiation—primarily utilizing a number of colours to differentiate darkish matter alerts from astrophysical backgrounds.
Written for you by our creator Tejasri Gururaj, edited by Gaby Clark, and fact-checked and reviewed by Robert Egan—this text is the results of cautious human work. We depend on readers such as you to maintain unbiased science journalism alive.
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Extra data:
Yifan Chen et al, Illuminating Black Gap Shadows with Darkish Matter Annihilation, Bodily Overview Letters (2025). DOI: 10.1103/yxqg-363n.
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