Astronomers have produced one of the most accurate, comprehensive cosmic maps ever made, revealing a brilliant “sea of light” that permeated the early universe.
Unlike other universal maps, this 3D representation is composed of light emitted by a single element: hydrogen, the simplest and most abundant element in the universe, which emits large amounts of a specific wavelength of light when it is excited by energy from nearby stars.
The new research, described in an article published on March 3 in the The Astrophysical Journalis part of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), a sky survey that aims to shed light on how dark energy and gravity shapes the universe. The researchers can now compare their simulations with this new data, collected with the Hobby-Eberly Telescope at the McDonald Observatory in Texas, to assess how cosmological models differ from observations.
An exciting way to see the baby universe
When hydrogen atoms are bombarded by stellar radiation, they are excited and emit Lyman-alpha light, a specific wavelength in the ultraviolet part of electromagnetic spectrum.
Massive, bright galaxies are easier to spot, but fainter galactic structures and the vast interstellar gas clouds that form stars and galaxies have been largely undiscovered – until now.
To reveal the sea of light that permeated the new cosmos, the researchers used a technique called line intensity mapping, which focuses on the telltale wavelengths, or signature spectral emissions, given off by different elements. Astronomers can therefore use line mapping to map the concentration and distribution of the specific elements throughout the cosmos, forming a map of the luminous galaxies and glowing gas clouds illuminated by excited hydrogen atoms.
Cosmology is about zooming out
When you study individually galaxiesstars or other discrete celestial objects, astronomers analyze their properties by zooming in. However, cosmology requires zooming out. Consequently, the HETDEX survey does not observe individual galaxies, but rather the combined light from each object in a particular region of the sky. As a result, astronomers can collect integrated data from a multitude of galaxies and intergalactic gas clouds simultaneously.
“Imagine you’re in an airplane and looking down,” co-author of the study Julian Muñoza theoretical cosmologist at the University of Texas at Austin, said in a statement. “The ‘traditional’ way of doing galaxy surveys is like mapping only the brightest cities: you learn where the big population centers are, but you miss everyone who lives in the suburbs and small towns. Intensity mapping is like seeing the same scene through a tinted airplane window: you get a blurrier image, but you catch all the light and not just the brightest points.”
In the quest to understand dark energy and map more than 1 million bright galaxies, HETDEX “has collected more than 600 million spectra over an area equivalent to more than 2,000 full moons, creating an unprecedented data set,” the researchers said in another statement.
A golden age of cosmic mapping
The mapping method made possible by HETDEX offers another way to investigate the driving forces of cosmology and how mass is distributed throughout the universe.
“These new 3D maps allow us to study how galaxies cluster together,” study co-author Karl Gebhardta professor of astrophysics at the University of Texas at Austin, told LiveScience via email. “The culprit that causes galaxies to come together is gravity. So by studying the clustering properties, we understand the properties of gravity and how much mass there is,” Gebhardt explained.
Viewing galactic structures as a collective is invaluable for measuring large-scale density fluctuations across the cosmos to explore the influence of dark energythe mysterious entity that appears to be accelerating the expansion of the universe.
Unsurprisingly, it is difficult to detect the signals from ancient galaxies, “but excluding the weak signal from everything else – faint foreground galaxies, noise from the detector, artifacts produced by the analysis techniques, scattered light sources such as the Moon, weak absorption/emission lines from the Earth’s atmosphere,” the study, he himself co-authored. Robin Ciardulloa professor of astronomy and astrophysics at Penn State and the observatory director for HETDEX, told LiveScience via email.
The next step is to improve noise reduction techniques and separate the desired signals from the many astronomical and terrestrial contaminants. The researchers can then use fainter sources and lower-mass objects as traces of cosmic evolution to more robustly constrain gravity models.
“The Hobby-Eberly is a groundbreaking telescope,” said Muñoz. “And with new, complementary instruments coming online, we are entering a golden age for mapping the cosmos.”
