The nebula has been named RaJav by its discoverers at CEFCA. It lies about 11 billion light-years away and belongs to the rare class of Enormous Lyman-Alpha Nebulae (ELANe) of which only a few others are known. Measurements from some of the 56 filters used by JPCam, the camera of the JST250 telescope, have made it possible to confirm and demonstrate the association of this nebula with two quasars. Quasars are the bright cores of distant galaxies and they are powered by supermassive black holes.

The discovery, led by Rahna Payyasseri Thanduparackal (CEFCA), was prompted by another finding: the faint quasar known as JPAS-9600-10844, detected in the first data release of the J-PAS survey. The RaJav nebula forms a luminous bridge connecting this newly identified faint quasar with another, brighter one (SDSS J162029.07+433451.1), both revealed through J-PAS data. The Lyman-Alpha Nebulae are giant clouds of hydrogen gas, often hundreds of thousands of light-years across, found around young galaxies billions of light-years away. The J-PAS data confirm the extraordinary nature of RaJav: it is exceptionally bright for its size. RaJav is about 413,000 light-years across, or roughly four times the diameter of the Milky Way’s stellar disk.

The J-PAS observations suggest that the vast glow of the RaJav nebula is mainly powered by two mechanisms: The first is photoionization - a process in which intense radiation from nearby quasars energizes the surrounding hydrogen gas, stripping away electrons and causing the gas to emit light. The second is quasar outflows - immense winds of gas and energy driven by supermassive black holes at the centers of these quasars. Together, these forces light up enormous regions of space, revealing how galaxies interacted with its environment in the early universe. The survey also detected extended emission from ionized carbon (C IV), showing that the RaJav nebula contains metal-rich gas.

The study uses as reference the well-known Fabulous nebula and compares its dimensions with those of RaJav. Given RaJav’s exceptional luminosity, it could be the largest known nebula of this kind. Further, deeper observations will be needed to confirm its full extent.

First Discoveries from an 8,000-square-degree Map

Detecting Lyman-alpha nebulae in the distant universe is extremely challenging because their light is faint and spread out in diffuse structures. Typically, only deep observations with large telescopes can reveal them. Remarkably, however, the J-PAS survey was able to detect the massive structures of these gigantic nebula.

Until now, these nebulae have been detected mainly through pre-selection in very limited fields of view. This suggests that the current census of such objects is incomplete and biased—highlighting the potential of J-PAS. This survey, conducted from the OAJ, provides a complete mapping of the sky visible from Javalambre, enabling a deeper and more comprehensive view of the Universe by observing every point in the sky through 56 distinct filters. Covering 8,000 square degrees, it will make it possible to perform systematic searches for these nebulae and to understand their role in galaxy formation.

ELANe are often found at the intersections of filaments marking the nodes of the cosmic web, the large-scale structure of the Universe. Their size, rarity, and association with dense environments make them powerful tools for studying galaxy formation, gas accretion, and the structure of the early Universe.

What Is Lyman-Alpha (Lyman-α) Emission?

Lyman-alpha emission is a special kind of light produced by hydrogen, the most common element in the universe. It is produced when an electron inside a hydrogen atom jumps from a higher energy level down to its lowest level, releasing a photon of ultraviolet light called Lyman-alpha.

Astronomers can’t see this light with their eyes because it’s in the ultraviolet part of the spectrum, but telescopes designed for this purpose can detect it, even from billions of light-years away. As the Universe expands, this ultraviolet light is stretched to longer, redder wavelengths, a phenomenon known as redshift. Consequently, J-PAS can detect this emission in the optical range, even though it was originally emitted more than 10.5 billion years ago.

When we observe Lyman-alpha emission coming from space, it usually means there’s a lot of excited hydrogen gas, often around young galaxies, quasars, or star-forming regions in the early universe.

This research is funded through the Collaboration Agreement with the Government of Aragon for the implementation of I+D+i actions under the Astrophysics and High-Energy Physics Programme, within the framework of the Complementary Plans (PPCC) included in the Recovery, Transformation and Resilience Plan (PRTR), supported by Next Generation EU funds. It is also part of the recognized Aragon Research Group (E16_23R).

The research has been supported by two Research and Development Projects (PID): Spatially Resolved Structure of Galaxies (PID2021-124918NA-C43) and Ecosystems: Mass- and Environmental-driven Evolution (PID2021-124918NB-C44), both funded by the Ministry of Science, Innovation and Universities and the Spanish State Research Agency (MCIN/AEI/10.13039/501100011033/FEDER, EU).

It has also received support from grant CNS2023-14539 (funded by MCIN/AEI/10.13039/501100011033 and by the European Union Next Generation EU/PRTR).