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Scientists Discover Way to Send Information into Black Holes Without Using Energy

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How Dark Matter Affects Black Holes

Black holes are some of the most mysterious and fascinating objects in the universe. They are regions in space where gravity is so strong that nothing—not even light—can escape. For a long time, scientists studied black holes mainly to test Einstein’s theory of general relativity, which explains how gravity works. But now, black holes are also being used to learn about another cosmic mystery: dark matter.

Dark matter is invisible and does not emit light, but it makes up about 27% of the universe. We cannot see it directly, yet its gravity affects stars, galaxies, and even black holes. Studying how dark matter interacts with black holes can help us understand this mysterious substance in a way that was never possible before.

Why Black Holes Are Special

Black holes are not just empty points in space. They bend spacetime around them, which affects how matter, light, and even time behave. This bending of spacetime creates unique phenomena such as the photon sphere, where light can orbit the black hole, and the black hole shadow, the dark silhouette seen against bright background light.

Modern telescopes like the Event Horizon Telescope (EHT) and instruments like the GRAVITY collaboration have already captured images of black hole shadows, including the supermassive black holes at the centers of M87 and our Milky Way (Sgr A*). These observations match Einstein’s predictions extremely well.

Because black holes are affected by everything around them, any nearby matter, including dark matter, could slightly change the size and shape of the shadow. By studying these small changes, scientists can probe the properties of dark matter in ways that were not possible before.

The Challenge of Studying Dark Matter Around Black Holes

Modeling a black hole surrounded by dark matter is not easy. Traditional approaches either assume simple Newtonian physics (ignoring full relativity) or make assumptions about dark matter’s behavior that may not be fully consistent with general relativity. These methods can lead to uncertainties and conflicting results.

To solve this problem, researchers have developed a perturbative approach. Instead of solving the full complex equations for a black hole plus dark matter system, this method treats dark matter as a small disturbance, or “perturbation,” to a known black hole solution. This allows scientists to calculate its effects in a systematic and manageable way.

How the Perturbative Method Works

The perturbative approach starts with a standard black hole model, like a Schwarzschild black hole, which is non-rotating and perfectly spherical. Then, researchers add a surrounding dark matter distribution, using realistic density models like the Hernquist profile or the Navarro–Frenk–White (NFW) profile.

Using this method, scientists calculate how the black hole’s spacetime is slightly deformed by dark matter. This allows them to find:

  • Photon-sphere radius: the distance from the black hole where light can orbit.

  • Shadow radius: the apparent size of the black hole shadow observed from far away.

These calculations can be done analytically, which means they can produce exact formulas that can be compared with real observations.

What Recent Studies Found

When this framework is applied, the results show that dark matter does affect black holes, but the effects are small. For example:

  • The shadow radius changes only slightly due to dark matter, well within the current limits set by telescopes like Keck and VLTI.

  • Calculations of the total dark matter mass within the orbit of the S2 star around the Milky Way’s central black hole show that it remains below 0.1% of the black hole’s mass, matching the observations of the GRAVITY collaboration.

These findings mean that while dark matter has an effect, it is subtle and requires very precise measurements to detect.

Why This Research Matters

The perturbative framework provides a simple and consistent way to study black holes in dark matter environments. It avoids the need for complex numerical simulations, which are time-consuming and require huge computer power.

Moreover, this approach can be extended to more realistic and complex scenarios:

  • Dense dark matter spikes or ultracompact halos could produce stronger effects, making them easier to detect.

  • Rotating black holes (Kerr black holes) would allow the study of how dark matter changes photon rings and shadow shapes.

  • Extreme mass-ratio inspirals (EMRIs), which are tiny stars or black holes orbiting supermassive black holes, could reveal small but cumulative effects of dark matter on their orbits. This is important for future gravitational wave detectors like the LISA mission.

By combining observations of shadows, orbital motion, and gravitational waves, scientists now have a multi-messenger approach to study dark matter near black holes.

Connecting Theory with Observations

Current observations, such as the black hole images from EHT, match general relativity’s predictions for vacuum black holes. This tells us that any effect from dark matter must be very small, below current measurement errors.

However, with future telescopes like the next-generation EHT (ngEHT), we may achieve much higher precision. Then, the small changes predicted by perturbative studies could be detected, opening a new way to map dark matter near black holes.

Looking Forward

This research is just the beginning. The perturbative framework can be applied to:

  • Any spherically symmetric black hole surrounded by different dark matter profiles.

  • More extreme dark matter environments, such as compact spikes or ultracompact halos.

  • Rotating black holes, which are more realistic in galaxies.

Such studies could help scientists understand not only how black holes behave but also the nature of dark matter itself. The combination of theory, observation, and future high-precision instruments could reveal the hidden structure of the universe.

Conclusion

Black holes are no longer just cosmic mysteries—they are powerful tools to study fundamental physics and the invisible universe. Using a perturbative approach, scientists can calculate how dark matter affects black hole shadows and spacetime geometry.

These small effects, once measurable with next-generation instruments, could provide new insights into dark matter, gravitational physics, and the structure of our galaxy. As observational techniques improve, black holes may help us uncover the secrets of both the visible and invisible universe, bringing us closer to solving some of the biggest mysteries of modern science.

Reference: Gabriel Gomez, "Perturbative Effects of Dark Matter Environments on Black Hole Shadows", Arxiv, 2026. https://arxiv.org/abs/2603.16402


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