Astronomers from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) have discovered colossal hydrogen halos, known as Lyman-alpha nebulae, surrounding over 30,000 galaxies dating back 10 to 12 billion years. This groundbreaking finding indicates that the essential materials for galaxy formation were far more plentiful than previously believed.
A giant halo of hydrogen gas, as revealed by HETDEX data and captured in deep imaging from the NASA/ESA/CSA James Webb Space Telescope. This ancient star system, 11.3 billion years old, radiates from the collective light of its myriad galaxies, with the brightest areas highlighted in red. Image credit: Erin Mentuch Cooper, HETDEX/NASA/ESA/CSA/STScI.
Hydrogen gas presents a unique challenge to astronomers, as it doesn’t emit light independently.
However, when located near energy-emitting objects—like galaxies packed with stars radiating UV light—hydrogen can glow due to this energy.
Detecting hydrogen halos demands significant time and precision, as the specialized instruments needed are often in high demand.
Previous astronomical surveys have identified some of these halos but typically focused only on the most luminous and extreme examples.
Furthermore, targeted observations of early galaxies are often too zoomed in, leading to the omission of larger halos.
HETDEX’s observations are actively filling this observational gap. This research uses the Hobby-Eberly Telescope at McDonald Observatory to map over 1 million galaxies and deepen our understanding of dark energy.
“We collected nearly half a petabyte of data, not just on these galaxies, but also on the intergalactic space,” stated Dr. Karl Gebhardt, the principal investigator of HETDEX and chair of the astronomy department at the University of Texas at Austin.
“Our observations encompass a sky area capable of hosting more than 2,000 full moons. The extent is extraordinary and unprecedented.”
“The Hobby-Eberly Telescope ranks among the largest telescopes worldwide,” Dr. Dustin Davis, a HETDEX scientist and postdoctoral fellow at UT Austin, remarked.
“HETDEX’s instruments yield 100,000 spectra per observation, providing a vast quantity of data and a treasure trove of exciting discoveries on the horizon.”
To locate hydrogen halos, astronomers examined the brightest 70,000 of the 1.6 million early galaxies cataloged by HETDEX.
Utilizing supercomputers at the Texas Advanced Computing Center, they assessed how many showed signs of surrounding halos.
According to the research team, these halos can span tens to hundreds of thousands of light-years across.
Some appear as simple, football-shaped clouds enveloping individual galaxies, while others take on irregular forms housing multiple galaxies.
“These formations are intriguing,” said Erin Mentaci-Cooper, HETDEX data manager and researcher at UT Austin.
“They resemble giant amoebas with tentacles extending into the cosmos.”
Results of this study were published on March 11, 2026, in a paper in the Astrophysical Journal.
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Erin Mentouch Cooper et al. 2026. Lyα Nebula in HETDEX: The largest statistical census connecting Lyα halos and blobs across cosmic noon. APJ 1000, 38; doi: 10.3847/1538-4357/ae44f3
Source: www.sci.news
