• Researchers at the Institute of Particle and Cosmos Physics of the Complutense University of Madrid (IPARCOS-UCM) have taken a decisive step forward in understanding supermassive black holes. Their work explains why the jets of these cosmic giants, when observed from Earth, can hide their most energetic core due to a visual trick caused by our perspective

 

Madrid, May 28, 2026.- Supermassive black holes, hidden at the centers of almost all large galaxies, act as cosmic engines that influence how these galaxies form and evolve. When they feed on gas and dust, they become Active Galactic Nuclei (AGN), some of the brightest objects in the universe. However, when looking at the sky, astronomers see a "zoo" of different cosmic beasts: quasars, radio galaxies, and blazars.

The traditional paradigm, known as the AGN Unification Scheme, suggests that all these objects are actually the same type of central engine observed from different angles. If the powerful jet of matter and light (plasma) is highly tilted relative to our line of sight, we observe it as a radio galaxy; if it is nearly aligned pointing toward Earth, the radiation is amplified as it travels at extreme speeds, appearing as a brilliant blazar.

However, a challenge has persisted for decades: understanding why, even within this family, some blazars and quasars display such different energy signals and light patterns from one another.

Now, a team from IPARCOS at UCM has discovered that part of these differences is due to a perspective effect they have dubbed "geometric masking". In a series of papers recently published in the journal Astronomy & Astrophysics, the team proposes that a blazar's jet is not uniform but is composed of two distinct parts:

• A wider, softer sheath of light (the "mask").
• A much more energetic inner core (the "spine").

When the jet points directly at Earth, the "mask" shines so brightly that it hides the true high-energy core. It is like looking straight into a very intense light: the glare prevents you from seeing the structure behind it. Only when it stops pointing directly at us can we better distinguish the internal source.

"After analyzing up to 18 years of gamma-ray data from the Fermi Large Area Telescope (Fermi-LAT), we have demonstrated this effect by studying the behavior of two of these objects," explains Elena Madero, an undergraduate Physics student. Both blazars show light changes that fit with a slow wobbling motion of their jet (like a spinning top), revealing that the extreme energy emission is only visible when the overall brightness drops to its lowest point and we are no longer blinded by the "mask."

"What is traditionally interpreted as a state of rest, or low total brightness, does not necessarily imply lower physical activity. It may simply be the moment when the orientation of the jet stops blinding us, allowing its most energetic component to become visible," notes Adithiya Dinesh, a PhD student.

The finding has profound implications for cosmology. "If we confirm this effect in more sources, we will have to rewrite part of what we thought we knew about how black holes regulate galaxy formation," concludes Alberto Domínguez, the lead researcher of the study. In this way, extreme particle acceleration would occur more often than previously thought, sometimes remaining hidden by a simple perspective effect.

This work also highlights the direct involvement of young researchers, such as Elena Madero and Adithiya Dinesh, who have played a key role in analyzing these results at the IPARCOS Institute.

 

^{Artist’s impression of a supermassive black hole and its particle jet. The image distinguishes the two regions proposed in the study: the high-energy central 'spine' (light blue beam) and the outer 'sheath' or envelope (purple area), which can blind or dazzle us depending on the perspective.}

 

_References

^{Madero & A. Domínguez, 2026, Astronomy & Astrophysics, 707, L18. DOI: 10.1051/0004-6361/202659239}

^{Domínguez, A. Dinesh & E. Madero, 2026, Astronomy & Astrophysics, 709, A206. DOI: 10.1051/0004-6361/202659728}

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^IPARCOS

^{The Institute of Particle and Cosmos Physics (IPARCOS) at UCM researches the fundamental constituents of matter and the laws governing the universe, from the subatomic to the cosmological scale, actively participating in international collaborations and training new generations of scientists.}

^{Press Contact: Alberto Domínguez, alberto.d@ucm.es}

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