Astronomers have just completed the largest high-resolution three-dimensional map of the universe, including more than 47 million galaxies and other massive objects. The map could help solve the mystery of dark energy, the enigmatic stuff that dominates the cosmos.
Scientists know that dark energy is an all-pervasive something that drives the universe’s accelerating expansion. But despite the ubiquity and immensity of dark energy’s large-scale effects, no one yet knows what it actually is. Many experts suspect dark energy is simply what’s known as the “cosmological constant,” a fudge factor that Albert Einstein added to the equations of his general theory of relativity. The cosmological constant represents the energy density of “empty” space and keeps the universe in a stable state of expansion. But this explanation is only one possibility for dark energy’s true nature.
The new map was constructed by research teams using the Dark Energy Spectroscopic Instrument (DESI), which is mounted on a telescope in Arizona and has surveyed huge patches of the night sky over a five-year period. The international project is led by the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).
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DESI’s first three years of data suggested that dark energy’s influence on the cosmos might change over time—challenging some fundamental assumptions about the nature of the universe. “Ultimately, we are doing this for all humanity, to better understand our Universe and its eventual fate,” said Stéphanie Juneau, an associate astronomer at the National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab) and a member of the DESI collaboration, in a statement.
“After finding hints that dark energy might deviate from a [cosmological] constant, potentially altering that fate, this moment feels like sitting on the edge of my seat as we analyze the new map to see whether those hints will be confirmed. I’m also very intrigued by the many other discoveries that await in this new dataset,” she said.
The largest ever 3D map of the universe, created by the now completed five-year DESI survey. Each dot represents a galaxy. Earth is the middle point.
DESI Collaboration and DESI Member Institutions/DOE/KPNO/NOIRLab/NSF/AURA/R. Proctor (image); M. Zamani/NSF NOIRLab (image processing)
DESI’s data includes six times as many galaxies and other cosmic objects as all previous measurements combined, according to NOIRLab. Now attention is turning to processing and analyzing all those data: the collaboration expects to have more definitive dark energy results in 2027. And although its five-year survey is complete, DESI is not done; through 2028, the project will continue observations and grow its map by another 20 percent. This next stage will focus on areas of the sky that are more tricky to observe, as well as some celestial regions where more distant and fainter objects may yet lurk.
“DESI’s five-year survey has been spectacularly successful,” said Michael Levi, director of DESI and a scientist at Berkeley Lab, in a statement. “We’re going to celebrate completion of the original survey and then get started on the work of churning through the data, because we’re all curious about what new surprises are waiting for us.”