Black holes are some of the most mysterious objects in the universe. They have such strong gravity that nothing, not even light, can escape once it crosses the event horizon. For many years, black holes existed only in scientific theories. Today, thanks to powerful telescopes, scientists can actually take images of them and study how they behave.
A new study by Deng and his research team looks at an exciting question: Could hidden extra dimensions change the appearance of black holes? Their research suggests that if extra dimensions exist, they could slightly change how light moves around a black hole. These small changes may be visible in future black hole images.
 |
| 230 GHz intensity |
Black Holes and Einstein's Theory
Our current understanding of black holes comes from Albert Einstein's General Theory of Relativity. According to this theory, gravity bends space and time. A black hole is created when a huge amount of matter is packed into a very small space, producing an extremely strong gravitational pull.
General Relativity has successfully explained many observations of black holes. The first image of a black hole, released in 2019 by the Event Horizon Telescope (EHT), matched Einstein's predictions very well. Later, scientists also captured an image of Sagittarius A*, the supermassive black hole at the center of our Milky Way galaxy.
Even though these discoveries confirmed Einstein's theory, scientists continue searching for tiny differences that could reveal new physics.
What Is the Braneworld Theory?
Some scientists believe our universe may have more than the four dimensions we know—three dimensions of space and one dimension of time.
One popular idea is called the Randall-Sundrum braneworld model. According to this theory, our universe is like a four-dimensional surface floating inside a much larger universe with extra hidden dimensions.
We cannot see these extra dimensions directly, but they may still affect gravity. If that is true, black holes could look slightly different from the ones predicted by Einstein's theory.
What Is Tidal Charge?
The researchers focused on something called tidal charge.
This is not the same as electric charge.
Electric charge comes from particles like electrons and protons. Tidal charge is different because it comes from the effect of hidden extra dimensions on gravity.
Tidal charge can change the shape of a black hole's event horizon, the path of light around it, and the appearance of the black hole's shadow.
Finding signs of tidal charge would give scientists an important clue that extra dimensions may really exist.
Following Light Around a Black Hole
The research team used powerful computer simulations to study how light travels around rotating black holes.
Normally, light moves in straight lines. But near a black hole, gravity is so strong that light bends around it. This bending of light is called gravitational lensing.
The scientists used a technique called ray tracing, which follows the path of millions of light rays. This allowed them to create detailed images of black holes surrounded by hot gas called an accretion disk.
The glowing gas in the accretion disk produces the bright ring seen around the black hole.
The Observer's Angle Makes a Big Difference
One of the most important discoveries was that the viewing angle changes the black hole image.
When someone looks almost directly at the black hole, the bright rings of light appear nearly round. Smaller secondary images remain hidden inside the main bright ring.
But when the observer views the black hole from the side, the image becomes very different.
The bright rings separate from each other, and the black hole looks much more uneven and stretched.
This means that where we observe a black hole from is just as important as the black hole itself.
Spin Changes the Shape
Most black holes rotate.
The speed of this rotation is called the spin.
The researchers found that the spin has a strong effect on the black hole's shadow. Faster spinning black holes produce more distorted shadows.
The tidal charge also changes the shadow, but its effect is smaller than the effect of spin.
Together, the spin and tidal charge decide how the black hole image looks.
Studying the Color of Light
The scientists also studied how the color of light changes near a black hole.
As light escapes the strong gravity, its frequency changes.
If the light gains energy, it becomes blueshifted.
If it loses energy, it becomes redshifted.
To make their study more realistic, the researchers included gas that is falling into the black hole after passing the Innermost Stable Circular Orbit (ISCO). Earlier studies often ignored this falling gas.
The team found that the observer's viewing angle has the biggest effect on these color changes.
For black holes where the disk rotates in the same direction as the black hole, one side of the image becomes mostly blue while the other side becomes mostly red.
If the disk rotates in the opposite direction, the colors are reversed.
Comparing Two Radio Frequencies
The team also created images at two different radio frequencies: 230 GHz and 86 GHz.
These frequencies are commonly used to study black holes with radio telescopes.
The researchers found that images taken at 86 GHz are brighter than those taken at 230 GHz.
Both the total brightness and the brightest parts of the image were stronger at 86 GHz.
However, the important features, such as the black hole shadow and the bright photon ring, remained visible at both frequencies.
This means that observing black holes at different frequencies can help scientists understand both the black hole and the hot gas surrounding it.
 |
| 86 GHz intensity |
Why Negative Tidal Charge Is Important
The researchers also studied negative tidal charge, which has attracted interest in recent years.
Some earlier studies suggest that a small negative tidal charge is still possible based on observations of black holes like M87* and Sagittarius A*.
Although there is no proof that negative tidal charge exists, the new study shows how it would change the brightness, color, and shape of black hole images.
These predictions give astronomers something to look for in future observations.
What Does This Mean for Future Research?
Today's telescopes are already giving us amazing pictures of black holes, but future telescopes will produce even sharper images.
As technology improves, scientists may be able to measure very small differences in the shape, brightness, and color of black hole images.
If these observations match the predictions made by Deng and his team, they could provide evidence that extra dimensions influence gravity.
That would be one of the biggest discoveries in modern physics.
Conclusion
Deng and his team have shown that black hole images may contain hidden clues about the structure of our universe. By combining advanced mathematics with computer simulations, they found that the appearance of a rotating black hole depends on its spin, tidal charge, viewing angle, and the frequency used to observe it.
Their results show that extra dimensions, if they exist, could leave small but measurable signatures in black hole images. Future observations with more powerful telescopes may be able to detect these signatures and help scientists test ideas that go beyond Einstein's theory.
Although many questions remain unanswered, this research brings us one step closer to understanding gravity, black holes, and the true nature of the universe.
Reference: Wen-Hao Deng, Sen Guo, Qing-Quan Jiang, Kai Lin, Pei Wang, "Optical Images of the Braneworld Black Hole Surrounded by an Optically Thin Accretion Disk", Arxiv, 2026. https://arxiv.org/abs/2607.29121
Comments
Post a Comment