Indian astronomers discover cosmic web filament from 11.7 billion years ago
The discovery was made possible using the Very Large Telescope (VLT) in Chile, operated by the European Southern Observatory (ESO)
A team of international scientists led by Eshita Banerjee, a PhD scholar at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune and her supervisor Sowgat Muzahid, has discovered a giant cosmic web filament stretching nearly 850,000 light-years by analyzing light emitted 11.7 billion years ago.

The discovery was made possible using the Very Large Telescope (VLT) in Chile, operated by the European Southern Observatory (ESO).
Galaxies are the fundamental building blocks of the universe. Modern galaxy evolution theories predict that galaxies are interconnected by vast, invisible streams of gas and dark matter, collectively referred to as the cosmic web. These cosmic web filaments serve as the nurseries where galaxies grow by accreting pristine gas that fuels their star formation. However, observing these filaments has been a daunting challenge because of their tenuous nature with densities 100 billion trillion times lower than our atmosphere.
“In complementary observations with the Multi-Unit Spectroscopic Explorer (MUSE) on the VLT, the team identified seven Lyman-alpha emitting galaxies at the same redshift. The number of galaxies detected in such a small volume of the universe is ten times higher than what we typically observe in surveys at this epoch,” said Banerjee.
Redshift is a measure of how much the wavelength of light from a distant object has been stretched due to the expansion of the universe. It occurs because as light travels through space, the universe itself is expanding, stretching the light to longer (redder) wavelengths.
“Moreover, their spatial distribution across the sky revealed a rare alignment, which strongly suggests the presence of a larger, underlying filamentary structure. The 10-hour-long deep observations with MUSE, one of the most sought-after instruments for astronomers, enabled us to search for and detect extended Lyman-alpha emission along the filamentary structure,”said Banerjee.
To detect this elusive structure, the researchers directed their telescope toward the high-redshift quasar Q1317–0507. By analyzing the high-resolution spectra of the quasar, they identified a neutral hydrogen-rich region, known as a partial Lyman Limit System (pLLS), at a redshift of z ~ 3.6. This region exhibited an exceptionally low proportion of heavy elements, with a metallicity 10,000 times lower than the solar neighborhood, aligning with theoretical predictions for pristine cosmic filaments.
“These nebulae are typically observed around luminous quasars, whose intense radiation illuminates the surrounding gas. However, none of the galaxies detected in this study exhibit quasar-like properties, making this discovery truly exceptional,” said Muzahid, an associate professor at IUCAA.
“While the precise mechanism(s) driving the extended Lyman-alpha emission remains unclear, we propose that recombination radiation, powered by the radiation fields of the detected galaxies, is the primary contributor,” he added.
The research was on January 29 accepted by the prestigious Astrophysical Journal Letter.