The universe has surprised us once again. For the first time, astronomers have obtained images capturing the corona of a supermassive black hole with unprecedented clarity. The object is called RX J1131 and lies approximately 6 billion light-years from Earth. Although the black hole itself remains invisible, the surrounding material—gas and dust falling towards it—is so hot that it glows intensely, producing what astronomers call a quasar. In this case, that extreme light comes from the superheated “corona”, a compact, energy-rich region that emits X-rays and millimetre waves.
For further context, see The Mysteries of Antarctica: What Is the True “Gravitational Hole”?, an article that explores an aspect directly related to this subject.
Recently, the team led by researcher Matus Rybak of Leiden University in the Netherlands published a study describing how it measured the size of RX J1131’s black-hole corona, observed its variability, and what this step means for understanding the extreme environments around black holes. The images and measurements were obtained using cosmic tricks—gravitational lensing and microlensing—along with old and new data from ALMA.
2. What Is a Black Hole Corona?
In the context of black holes, the term “corona” refers to a region of extremely hot, energetic matter close to the black hole, above the accretion disc—the disc of gas and dust falling towards the hole. This is a zone in which electrons are in a relativistic state, interacting with magnetic fields and X-ray radiation, and where inverse Compton scattering occurs: photons from the accretion disc gain energy and become much higher-energy photons.
The corona generates extremely energetic radiation, and although we do not see the black hole itself—the event horizon emits no light—we see the effects of the matter and energy around it. The corona’s size, shape and structure are highly important to theories of black holes, their evolution and the behaviour of accretion environments, but these details have been very difficult to measure directly until now.
3. RX J1131: The Black Hole Under Study
- Cosmic location: The quasar RX J1131 is located about 6 billion light-years away. It is a supermassive quasar, meaning that the black hole is extremely large and draws matter from a brightly lit accretion disc.
- Rotation speed: The black hole rotates at more than half the speed of light. This means that frame dragging—the relativistic effect that forces spacetime to rotate along with the black hole—is relevant, and its influence on emission from the accretion disc and the corona is considerable.
- The role of the foreground galaxy: Along the line of sight, there is a massive galaxy between RX J1131 and Earth, about 4 billion light-years away. The gravity of this galaxy bends light from the quasar and creates a gravitational-lensing phenomenon—four images of the quasar that can be observed with telescopes, including ALMA.
4. Methods and Techniques Used
a. Gravitational Lensing and Microlensing
- Gravitational lensing occurs when light from very distant objects passes through regions of large mass on its way to the observer. The gravity of that mass curves spacetime, and the light is consequently deflected, magnified or distorted.
- Gravitational microlensing is caused by stars in the foreground lensing galaxy, which act as small lenses and affect very small parts of the light source—in this case, the corona. It can cause localised changes in brightness in separate images of the lensed quasar.
b. The ALMA Observatory
- ALMA (the Atacama Large Millimeter/submillimeter Array) is one of the most sensitive and highest-resolution instruments for observing millimetre and submillimetre waves. It was used to collect older data—around a decade old—and more recent data from 2022, observing brightness variations among the quasar’s four images.
- Analysis of independent brightness fluctuations among these images made it possible to distinguish signals from the black hole’s corona, rather than only slow effects or propagation through the lensing galaxy.
c. Multiple Observations and Data Reanalysis
- Historical and new data, separated in time, were used—observations in 2022 taken one day apart—to see how brightness evolves over time.
- Reanalysing older data makes it possible to detect subtle fluctuations that were previously ignored or unnoticed.
5. Measurement Results
- The corona is estimated to extend across approximately 50 astronomical units (around 50 AU, where 1 AU is the Earth–Sun distance). This is a size comparable to that of the Solar System.
- The brightness variations among the lensed images are not synchronised: each image fluctuates independently, indicating the presence of microlensing in the lensing galaxy.
- This is the first direct measurement of the corona’s size on this scale, opening the prospect of mapping the regions immediately around the black hole and the magnetic fields involved.
6. The Significance of Magnetic Fields
- Magnetic fields play a critical role in how gas falls towards the black hole and how nearby particles are accelerated. They control the transport of angular momentum in the accretion disc, as well as the emission of high-energy radiation.
- Theoretical models predict links between the corona’s size, magnetic-field strength and millimetre-wave emission. The recent measurements make it possible to test these models.
- In addition, these observations provide a tool for tracking how quickly the black hole grows and how it interacts with the surrounding galactic environment.
7. What Comes Next
- Researchers plan to use additional data from NASA’s Chandra X-ray telescope, which has sufficient spatial resolution to capture fine fluctuations from regions close to black holes.
- The Vera C. Rubin Observatory is also involved, providing high-resolution optical imaging, monitoring of lensed-quasar systems and detection of optical fluctuations.
- Other data from a new generation of instruments—ALMA extended to lower frequency bands, X-ray observatories and new cosmic surveys—will improve the precision of mapping both the corona and its magnetic fields.
8. Comments and Views
“This is the first time such a measurement has been made,” said Matus Rybak, a senior researcher at Leiden University. “In principle, we have found a new way to look at what is happening very close to the black hole.”
The scientific community has welcomed the results as a major step. The study was published in Astronomy & Astrophysics and brings not only images, but also a new methodology for probing extreme environments.
Academics and astrophysicists emphasise that the discovery enables:
- Validation or adjustment of corona models: simulations can compare these data to determine whether the hot atmosphere above the accretion disc is distributed uniformly or has uneven structures;
- Exploration of how microlensing phenomena occur in gravitational lenses: microlensing detected in foreground galaxies usually produces variations that can be confused with intrinsic quasar fluctuations, but here the analysis clearly separates the signals;
- Long-term studies: if these systems can be monitored over time, it may be possible to observe long-term changes in the corona’s structure, the black hole’s rotation, environmental influences and more.
The discovery of the RX J1131 black-hole corona, made by combining ALMA observations, gravitational lensing and microlensing, marks a turning point in observational astronomy. The direct measurement of the corona’s size (approximately 50 AU) opens the door to understanding the extreme physics close to the black hole—from the behaviour of the radiation it emits to the way magnetic fields influence its evolution.
In the future, with new instruments and continued observations, we may gain a much better understanding of the most enigmatic cosmic bodies—black holes—and discover whether variations in coronas can be standardised or whether every black hole has its own astronomical “personality”.
