Brighter than a shadow: modeling radiation from an Ellis-Bronnikov wormhole and its resemblance to a black hole ✛ ✦
Context
Direct images of shadows of supermassive compact objects from the Event Horizon Telescope have become a new tool for testing gravity in the strong-field regime. Although the data point toward a Kerr black hole, there is still room for exotic alternatives like wormholes — horizonless objects, first named by John Wheeler, connecting distant regions of curved spacetime. Identifying their observational signatures is essential for interpreting future, more precise observations.
Methods
The authors constructed a stationary spherically symmetric solution for the accretion flow in the Ellis-Bronnikov wormhole and Schwarzschild black hole metrics, using a polytropic equation of state. With the CARTOON code, they solved the general relativistic radiative transfer problem including synchrotron radiation and relativistic redshift and Doppler shift effects. The parameters of the accreting plasma and dust (electron density, temperature) were tuned so that the total flux at 230 GHz was ~0.5 Jy, consistent with Event Horizon Telescope observations of the galaxy M87*.
Results
Images of both objects show a central dark region — the shadow — and a bright photon ring formed by photons that circle the compact object multiple times. For the same mass, the wormhole shadow is brighter: radiation passes through the throat and adds from matter on the far side. The photon ring is also brighter due to a longer optical path and less gravitational redshift in the absence of a horizon. Quantitatively, the central depression (ratio of maximum to minimum intensity) for the wormhole was ~2.8, versus ~1.9 for the black hole, and the ring diameter was 45 microarcseconds compared to 42 microarcseconds.
Implications
The results show that horizonless compact objects can successfully mimic black holes given current observational precision. This highlights the need to develop diagnostics sensitive to the event horizon, for example through flux variability or polarization. Moreover, the similarity to active galactic nuclei and quasars leaves open the question of the true nature of central engines.
Future development
Future space-based very-long-baseline interferometry missions like the Black Hole Explorer (BHEX) will probe the fine structure of photon rings and possibly detect radiation that has passed through the wormhole. Improving angular resolution down to a few microarcseconds will be decisive for distinguishing models with and without a horizon.
Impact
The work is directly relevant to black-hole astrophysics, gravitational lensing, testing modified theories of gravity, and interpreting photometric data from active galactic nuclei.
Next steps
Numerical experiments incorporating accretion disks and magnetohydrodynamic effects are needed to account for image asymmetries. Polarimetric observations, which are more sensitive to the magnetic field geometry near the horizon, also hold promise.
Key open problems
The study touches on a fundamental question: are the supermassive compact objects at the centers of galaxies black holes of general relativity, or exotic structures that require violating energy conditions and thus new physics beyond the Standard Model?
The knowledge machine's view
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
The authors constructed a stationary, spherically symmetric accretion flow in the metric of an Ellis–Bronnikov wormhole and a Schwarzschild black hole, performed general-relativistic radiative transfer calculations with synchrotron emission, and compared the images. They found that the shadow and photon ring of the wormhole are brighter due to the absence of an event horizon, and they quantified the differences in the central depression and ring diameter.
Where its strength is
This work provides a concrete quantitative benchmark for distinguishing horizonless objects from black holes based on the brightness of the shadow and photon ring, which could be used in analyzing Event Horizon Telescope data.
Where it could go next
- It might be interesting to compare the obtained images with predictions for other horizonless compact objects, such as singularity-free black holes, which also mimic classical shadows.based on: Black Holes Without Singularities: Almost Indistinguishable arXiv:2607.10713
- A related line of work concerns the effect of dark matter on black hole images; a similar analysis for a wormhole could show how the environment alters brightness characteristics.based on: Black hole in a dark matter cocoon arXiv:2608.05861v1
- Since polarization may be sensitive to the presence of an event horizon, it would be interesting to examine polarization maps, as is done for white holes.based on: A White Hole in the Lens: What the Telescope Will See arXiv:2607.20945
Worth trying
- Test how the brightness ratio of the shadow to the ring changes for a nonzero spin of the wormhole, if such a solution is available.
- Use observed variability constraints on M87* to further test the wormhole versus black hole distinction.
- Assess how well EHT polarization measurements can differentiate the two models at current sensitivity.
Why this may matter
If wormholes are truly indistinguishable from black holes in the electromagnetic spectrum, this raises a fundamental question about the nature of supermassive objects at the centers of galaxies and calls for new observational strategies.
Nearby works in our archive
- Shadow and Ring: How to Weigh a Black Hole More Preciselysimilarity 0.65
- Spindle Black Hole: The Shadow Changes Shapesimilarity 0.61
- A White Hole in the Lens: What the Telescope Will Seesimilarity 0.61
- Black Holes Without Singularities: Almost Indistinguishablesimilarity 0.60
- A Bright Spot in a Black Hole's Shadowsimilarity 0.60
- Black hole in a dark matter cocoonsimilarity 0.60
The closest work in the archive sits at 0.65 by meaning — the usual level for our corpus.
Original abstract
as written by the authors arXiv:2606.01699v1
We investigate the observational differences between the Ellis--Bronnikov (EB) wormhole and the Schwarzschild black hole (BH) by performing general relativistic radiative transfer (GRRT) simulations. We consider a spherically symmetric steady-state accretion flow and perform GRRT simulations incorporating synchrotron emission. For both the EB wormhole and the Schwarzschild BH, the simulated images consist of a central shadow region and a bright photon ring. We find that both the shadow region and the photon ring of the EB wormhole are brighter than those of the Schwarzschild BH. These differences arise from the absence of an event horizon in the EB wormhole, allowing the emission from the accreting matter around and beyond the throat to contribute to the observed intensity. We also compare the simulated images with the Event Horizon Telescope (EHT) observations of M87* and find that both the EB wormhole and the Schwarzschild BH are in reasonable agreement with the current EHT results.
The Ellis-Bronnikov wormhole was discovered independently by H. Ellis and K. Bronnikov in 1973 as a solution with a phantom scalar field. Interestingly, its mass in the other asymptotic region is negative, and the throat is located at R=0.
The idea of wormholes as portals to other universes is widely known from the film Interstellar, where characters travel through a wormhole created by a super-advanced civilization. Although the Ellis-Bronnikov model is unstable without additional fields, it illustrates the real scientific basis for such hypothetical objects.
Key numbers
- Total flux: 0.5 Jy
- M87* ring diameter: 42 μas
- EB shadow diameter: ~45 μas
- Photon ring radius: 6.21M
- Central depression: 2.8