Astronomers have barely scratched the surface of mapping the almost endless stars and galaxies in the heavens. Researchers at the University of Texas at Austin have now used supercomputers to reveal the locations of more than 200,000 new astronomical objects. Their goal is to map even more and use this knowledge to predict the ultimate fate of the universe.
The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) has been scanning the dark skies of the Davis Mountains in West Texas since 2017, aiming to capture spectroscopic data on Lyman-alpha light from neutral hydrogen emission in galaxies 10 billion light-years away.These galaxies emit a characteristic wavelength of light from hydrogen that signals to astronomers intense new star formation.
The HETDEX collaboration involves a large team including astronomers, engineers, technicians, and graduate students from six academic institutions in the United States and Germany.
Scientists have cataloged astronomical objects for the first time – mapping over 51,863 Lyman-alpha emitting galaxies at high redshift; 123,891 star-forming galaxies at lower redshift; 5,274 low-redshift non-emission line galaxies; and 4,976 active galactic nuclei (AGN)—bright spots that signal the presence of black holes.
An article describing the catalog is published in February 2023 in The Astrophysical Journal. “We’ve just exploded in terms of the number of redshifts cataloged for the first time,” said study co-author Erin Mentuch Cooper, a scientist at the University of Texas at Austin (UT Austin). Cooper is the data manager for the HETDEX project.
Gebhardt is a project scientist and principal investigator of HETDEX. “The HETDEX catalog is a goldmine of astronomical exploration. That’s what I love about it,” said study co-author Karl Gebhardt, the Herman and Joan Suit Professor of Astronomy in the College of Natural Sciences, UT Austin.
A star’s redshift tells astronomers how fast a star is moving away from Earth because its frequency, similar to its color, decreases as it moves away, much like a train’s horn as it passes by.
The faster a star moves away, the further away it is. This relationship between speed and distance, called Hubble’s law, can determine the position of a galaxy and allows astronomers to create a 3D map of more than 200,000 stars and galaxies with HETDEX.
HETDEX tiles the sky, collecting 35,000 spectra
HETDEX is unique from previous large sky surveys in that it is an untargeted survey that covers the sky and collects spectra from 35,000 optical cables of the Visible Integral Field Replicable Unit Spectrograph (VIRUS).
VIRUS takes starlight from distant galaxies and splits the light into individual colors like a prism. HETDEX tiles the sky, collecting 35,000 spectra in a moon-sized swath of sky and moving from place to place. It collects around 500-600 hours of observations each year for its survey data.
“TACC has worked hard with us to streamline our system and it works just fantastic. On TACC’s systems we can process years of data in a few days, maybe a week. And we do it multiple times because we’re constantly tweaking and improving our methods,” added Gebhardt.
HETDEX used Maverick and Stampede2 supercomputers from the Texas Advanced Computing Center, a leading academic supercomputing center at UT Austin. Stampede2 is funded by the National Science Foundation as a shared resource for thousands of scientists across the US. They helped process and analyze about 60 terabytes of image data in TACC’s Corral system.
Holy grail for HETDEX is an accurate measure of the universe’s expansion
The science generated from HETDEX adds to the bigger picture of understanding the expansion of the entire universe, which is unexpectedly growing much faster than expected based on precise observations of supernovae that act as a cosmic benchmark from 2019 from the Hubble Space Telescope.
The holy grail for HETDEX is an accurate measure of the universe’s expansion rate 10 billion years ago, revealed by the physics model of dark energy.
Astronomers are at odds over how to explain the current rate of expansion. Understanding it might require a modification in the theory of gravity or a change in the basic theory of the big bang. It could be the handiwork of an undiscovered particle.
The exact value of the expansion rate at the beginning of the universe can be compared to the expansion rate today. This comparison may determine whether the universe will continue to expand forever or one day collapse in on itself many billions of years from now.
“The whole point of the HETDEX project is to measure the expansion of the universe,” Gebhardt said.
“This new catalog adds valuable data in the final answer to the ‘millionth galaxy’ question, which is something the HETDEX Collaboration is working very hard on in the coming year. But there’s a bigger picture, and that’s what we’re giving back to the community.” not only to scientists from around the world, but also to the entire community. We wouldn’t be able to do this work without the supercomputing resources and experts at TACC, because the computing power allows us to do a lot of data analysis and continue to improve the process.”
