The largest 3D map of the cosmos may alter the ultimate fate of the universe
Scientists are on the edge of their seats as they analyze this remarkable new map, not only to better understand the fate of our universe, but also for what other discoveries it may hold!
After five years of surveying the sky, an international team has assembled the largest three-dimensional map of the cosmos, which may reveal that the expansion of the universe — once thought to be constant — has been evolving over time.
Since May of 2021, a telescope located high atop Kitt Peak, in the mountains southwest of Tucson, Arizona, has been scanning the cosmos with DESI, the Dark Energy Spectroscopic Instrument, recording the locations of millions of galaxies and quasars.
The results of this immense survey now form the largest high-resolution 3D map of our universe ever constructed.
DESI's new map of the cosmos, composed of two 3D cones, with Earth at the centre point between them. The dark areas to either side are harder-to-observe regions of the universe, which the team will attempt to fill over the next two years. (DESI Collaboration and DESI Member Institutions/DOE/KPNO/NOIRLab/NSF/AURA/R. Proctor. Image Processing: M. Zamani (NSF NOIRLab))
Click here for a zoomable version of the above graphic.
When the survey began, the team estimated that DESI would map out a total of around 34 million galaxies and quasars. However, even finishing early, it actually recorded the distance, speed, and chemical composition of over 47 million galaxies and quasars, along with an additional 20 million stars from our own galaxy.
"The Dark Energy Spectroscopic Instrument has truly exceeded all expectations, delivering an unprecedented 3D map of the Universe that will revolutionize our understanding of dark energy," Kathy Turner, the Program Manager for the Cosmic Frontier in the US Department of Energy's Office of High Energy Physics, said in a NOIRLab press release.
"From its inception, we envisioned a project that would push the boundaries of cosmology, and to see it come to such a spectacularly successful completion for its initial survey, ahead of schedule and with such rich data, is incredibly rewarding," Turner added. "The dedication and ingenuity of the entire DESI collaboration have made this world-leading science a reality, and I am immensely proud of the groundbreaking results we are already seeing and the discoveries yet to come as we continue to explore the mysteries of our cosmos."
DESI is a remarkable instrument, composed of 5,000 fibre-optic 'eyes', all of which adjust position in a coordinated 'dance' with those around them, to collect and feed the light from distant stars and galaxies into an array of 10 spectrographs attached to the telescope. These spectrographs then split the light into its component colours, revealing each object's distance, speed, and what elements it is composed of.
Watch below: See a small patch of DESI's array of eyes at work
By observing for longer and longer periods in overlapping fields of view, the instrument was able to peer farther and farther back in time, mapping out the positions of galaxies when the cosmos was younger than it is now. This has allowed the team to observe how dark energy has been driving the expansion of the universe over the past 11 billion years, which has revealed something very intriguing.
The Hubble Tension
Nearly a century ago, astronomer Edwin Hubble published a paper that showed that all the galaxies in the universe we could observe were moving away from us, and the farther away any particular galaxy was, the faster it was receding. The source of the expansion was named "Dark Energy," since there was (and still is) no indication of exactly what is driving it.
The Hubble Telescope, launched roughly 47 years after its namesake's death, showed that his results were correct, and made extremely accurate measurements of the rate of expansion, at 70-76 kilometers per second per megaparsec.
The evolution of the Universe across space and time, starting with the Big Bang and the Cosmic Microwave Background (left), up until the present day, 13.7 billion years later. (ESA)
However, other astronomers taking measurements of the Cosmic Microwave Background (CMB) — the light from the Big Bang stretched out over 13.7 billion years — showed a rate of expansion, equal to around 60-68 kilometers per second per megaparsec.
This discrepancy between these two rates has been called The Hubble Tension, and scientists still aren't sure what causes it.
A solution?
Both values for the rate of the expansion of the universe have been taken as constants. However, what if the answer to the problem is that the rate of expansion isn't constant?
The first three years of mapped-out data from DESI showed hints that this may be the case. With the addition of the last two years of additional observations, and another two more to be gathered between now and 2028, that hint may vanish, or it could grow even stronger.
This is important because the exact balance between dark energy's push and the amount of matter in the cosmos is what controls whether the universe continues to expand until all the stars are exhausted, whether it will reverse course and eventually collapse into a Big Crunch, or something else.
A small portion of DESI's year-five map in which the large-scale structure of the Universe, created by gravity, is visible. Each dot represents a galaxy. The denser areas indicate regions where galaxies and galaxy clusters have clumped together to form the strands of the cosmic web. Also seen are large voids between the filaments. (DESI Collaboration and DESI Member Institutions/DOE/KPNO/NOIRLab/NSF/AURA/R. Proctor. Image Processing: M. Zamani (NSF NOIRLab))
Up until now, it appeared as though the cosmos would continue to expand indefinitely. However, if we see stronger evidence for an evolving rate of expansion, it could represent a fundamental shift in the ultimate fate of the universe.
"It's impossible to capture everything that went into making DESI such a successful experiment. From instrument builders and software engineers to technicians, observatory staff, and scientists — including many early-career researchers — it truly took a village," says Stephanie Juneau, a Canadian astronomer from Ste-Victoire, Québec, who is the representative for DESI at NOIRLab.
"Ultimately, we are doing this for all humanity, to better understand our Universe and its eventual fate," Juneau said. "After finding hints that dark energy might deviate from a 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."