Ar-Rehman

Early universe was full of hydrogen as per Astronomers : It looks they've discovered it

Astronomers have discovered tens of thousands of massive hydrogen gas halos surrounding ancient galaxies, offering new insights into the rapid growth of galaxies in the early universe. They have identified tens of thousands of massive hydrogen gas halos surrounding ancient galaxies, some as far back as 11.3 billion years ago. These halos, crucial to understanding galaxy formation, were largely unknown until the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) expanded their discovery by more than tenfold. This discovery could transform our understanding of the early universe, shedding light on the essential role hydrogen played in the rapid growth of galaxies during the Cosmic Noon period. An enormous halo of hydrogen gas found in Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) data and superimposed over its location as seen in deep imaging from the James Webb Space Telescope (JWST). Present 11.3 billion years ago, this system glows from the combined light of many galaxies within it, with the brightest region represented in red. Using data from HETDEX, astronomers have increased the known number of these haloes by more than a factor of ten, from roughly 3,000 to over 33,000.

The Eberly Telescope Dark Energy Experiment (HETDEX) has discovered tens of thousands of gigantic hydrogen gas halos, called "Lyman-alpha nebulae," surrounding galaxies 10 billion to 12 billion years ago. Known as Cosmic Noon, this is an epoch in the early universe when galaxies were growing their fastest. To spur this growth, they would have needed access to vast reservoirs of hydrogen gas, a key building block for stars. However, until recently, astronomers had only found a handful of these essential structures. The universe’s early days are still shrouded in mystery, but new findings from the HETDEX team are providing unprecedented insights into the cosmic landscape. What were once thought to be rare and extreme examples of hydrogen gas halos are now known to be much more common than previously thought. “We’ve been analyzing the same handful of objects for the past 20 or so years,” said Erin Mentuch Cooper, HETDEX data manager and lead author of the study. “HETDEX is letting us find many more of these halos and measure their shapes and sizes. It has really allowed us to create an amazing statistical catalog.” A new study has now increased the known number of hydrogen gas halos by a factor of 10: from roughly 3,000 to over 33,000. This confirms suspicions that they are not rare curiosities. The study also increases the range of known sizes, providing a more representative sample for astronomers to study as they continue to tease out the origin and evolution of the first galaxies.

This surge in discovery marks a new era in the study of the early universe, offering astronomers a more representative sample to work with as they explore the origins of galaxies and stars. Images from Subaru/HSC-r band, and JWST filters F115W, F150W, F277W, and F444W reveal that multiple low-mass galaxies accompany the LAN. Hydrogen gas halos, also known as Lyman-alpha nebulae, have long been difficult to detect due to their faint glow. Unlike other cosmic objects, hydrogen doesn’t emit its own light. However, when it is near a highly energetic galaxy or a group of galaxies, ultraviolet radiation from the stars can cause the hydrogen gas to glow, making it visible to advanced instruments. Detecting these halos has historically been challenging, with astronomers only able to identify the brightest and most extreme examples. HETDEX team used a unique approach to scan a vast area of the sky, uncovering many more of these faint structures. With the power of the Hobby-Eberly Telescope and its ability to observe large portions of the sky, they have unveiled thousands of previously hidden hydrogen halos, offering a more complete picture of the early universe. Observations from HETDEX are starting to fill in this gap. Using the Hobby-Eberly Telescope at McDonald Observatory, it is charting the position of over one million galaxies in its quest to understand dark energy.

"We've captured nearly half a petabyte of data on not only these galaxies but the regions in between," said Karl Gebhardt, HETDEX principal investigator, chair of The University of Texas at Austin's astronomy department, and co-author on the paper. "Our observations cover a region of the sky measuring over 2,000 full moons. The scope is enormous and unprecedented." Hydrogen gas is notoriously hard to detect because it doesn't generate its own light. However, if it's near an object that's throwing off a lot of energy, say, a galaxy or group of galaxies full of UV-emitting stars, that energy can cause the hydrogen to glow. To detect this, you need to dedicate a lot of time to precise instruments, which are often in high demand. "The Hobby-Eberly Telescope is one of the largest in the world," added Dustin Davis, a postdoctoral fellow at UT Austin, a HETDEX scientist, and co-author on the study. "And the instrument HETDEX uses produces 100,000 spectra in each observation. So, we have huge amounts of data and there are all kinds of neat, fun, weird things waiting for us to find." While previous astronomical surveys have found some of these halos, their instruments were only able to pick up on the brightest, most extreme examples. And targeted observations of early galaxies are usually so zoomed in that they cut off all but the smallest halos. As a result, everything in between the little guys and the big honkers has remained elusive.

One of the driving forces behind this discovery is the sheer scale of data collected by HETDEX. The telescope’s unique capabilities have allowed the team to examine over one million galaxies, uncovering their surrounding hydrogen halos. The newly revealed halos measure from tens of thousands to hundreds of thousands of light years across. Some are as simple as a football-shaped cloud surrounding a single galaxy. Others are sprawling, irregular blobs containing multiple galaxies. "Those are the fun ones," said Mentuch Cooper. "They look like giant amoebas with tendrils extending into space." To find them, the team selected the 70,000 brightest of the over 1.6 million early galaxies which have been identified by HETDEX so far. With the help of supercomputers at the Texas Advanced Computing Center, they looked to see how many of these showed evidence of a surrounding halo: a compact central region of hydrogen and a thinner cloud extending beyond it. Nearly half did. What's more, this fraction is likely an underestimate, explained Mentuch Cooper. "We suspect the faintest systems simply aren't bright enough to fully reveal how large they are."

HETDEX’s ability to capture 100,000 spectra in a single observation has made it a powerful tool for studying the universe at a depth never before possible. As the HETDEX team delved deeper into the data, they discovered that the newly identified hydrogen halos come in a variety of shapes and sizes. These cosmic “amoebas” represent the dynamic and diverse nature of the early universe. Their irregular shapes and vast sizes, some halos spanning hundreds of thousands of light years, offer a new way to study the evolution of galaxies and their surrounding environments. By analyzing these shapes, astronomers can begin to piece together the mechanisms that drove galaxy growth during the universe’s formative years. The team hopes their discovery will help others study the early universe: how its structures evolved, the distribution of matter, the movement of objects, and more. With 33,000 halos to study, the problem will no longer be where to find them, but which one to choose. "There are various models for galaxies in this epoch that largely work and seem to make sense, but there are gaps and holes," explained Davis. "Now we can focus in on individual halos and see at a greater detail the physics and mechanics of what's going on. And then we can fix or throw out the models and try again."

The discovery of over 33,000 hydrogen gas halos is not just a significant leap in numbers; it also provides new opportunities for scientific exploration. With such an expansive dataset, astronomers are no longer limited by a lack of sample size when testing theories of galaxy formation and evolution. The research team is excited to move beyond the limitations of previous models and explore the fine details of individual halos. By studying these hydrogen halos, astronomers will be able to refine their understanding of the distribution of matter in the early universe, how galaxies formed and evolved, and the role of hydrogen in cosmic growth. With such a rich catalog of data at their disposal, scientists are poised to make new breakthroughs in the coming years about the universe.