The Dark Energy Spectroscopic Instrument (DESI) has created the most detailed 3D cosmic map ever, which could help better understand dark energy, black holes, and the expanding Universe.
Image Credit: Artur Tomskiy/Shutterstock.com
Humanity’s increasing ability to map the Universe in three dimensions is revealing previously hidden details of galaxies and star-forming regions and could, ultimately, help solve some of cosmology’s most pressing problems.
The Universe is expanding at an accelerating rate. While scientists don’t quite know why this is, dark energy has been posited as a placeholder mechanism for this accelerating expansion.
While dark energy currently accounts for 70 percent of the Universe’s energy/matter budget, as the Universe’s accelerating expansion continues its dominance is predicted to grow.
If we are to understand what dark energy is, and what this accelerating expansion means for the future of the cosmos, at least partially, this hinges on detailed maps of distant galaxies.
A striking example of this has been provided by the Dark Energy Spectroscopic Instrument (DESI) which completed the first seven months of its survey run by creating an unprecedented 3D map of the Universe.
The 3D cosmic map was revealed by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), which manages DESI, installed at the Nicholas U. Mayall 4-meter telescope at Kitt Peak National Observatory near Tucson, Arizona. It is larger than all previous 3D surveys combines.
What is even more extraordinary about the map of galaxies created by DESI is that it is only 10 percent through its planned five-year mission. When that mission comes to its conclusion, the cosmic map built by its survey should give cosmologists a much better understanding of dark energy, the force that is driving the acceleration of the expansion of the Universe.
This initial model provides a detailed look at some of the Universe’s most powerful light sources, as well as star clusters and filaments of gas and voids within galaxies.
Understanding dark energy will not just help scientists better picture how the cosmos will continue to expand and evolve, but will also help build a better image of how it existed in the past.
How Cosmic Mapping Reveals the Imprints of Dark Energy
The key to DESI’s observational power is the incredibly detailed control over each of the 5,000 cutting-edge robots that position optical fibers on the instrument. This ensures that the positioning of these optical fibers is accurate to within 10 microns — about a tenth of the width of a human hair.
This level of accuracy allows for the collection of color images of millions of galaxies from a section of sky equivalent to a third of the night sky over Earth. This light is then broken down, and DESI can determine how much the light has been redshifted.
Redshift is the change in frequency of light that occurs when a source moves away from an observer. This shifts the wavelength of light and thus its frequency towards the “red end” of the electromagnetic spectrum.
That means that the expansion of the Universe causes the redshift of light from distant sources. The faster a light source is moving away from us the more it is redshifted, and the further away it is the faster the expansion of the Universe carries that source away.
That means that the measurement of redshift is a great way to measure the effect of dark energy, which drives that expansion. It is unsurprising then that the redshift of distant cosmic objects was responsible for both our discovery that the Universe was expanding and then the discovery that this expansion was proceeding at an accelerating rate.
Observing the redshifts of distant galaxies allows DESI to see the depth of the cosmos and chart structures like clusters and superclusters. These groupings still contain imprints or echoes of their initial formation.
DESI’s three-dimensional “CT scan” of the Universe
Video Credit: NOIRLabAstro/Youtube.com
Studying these echoes and using DESI data reveals the history of the Universe’s expansion and could reveal the Universe’s future, helping us predict if this unabated expansion will cause the cosmos to cool to the point it experiences heat death, to collapse in on itself, or just to continue expanding forever.
While DESI is not currently able to deliver enough data to begin tackling these questions, the observations it has provided thus far could help researchers better understand some of the cosmos’ most powerful events and objects.
Mapping Bright Galaxies and Black Holes
The data delivered by DESI thus far may not be enough to crack the dark energy conundrum just yet, but even this early data and the map it builds helps to develop a picture of the Universe as it was 10 billion years ago in its relative infancy.
One breakthrough this picture of a three billion or so year old Universe could bring researchers closer to is the understanding of how feeding black holes powers the emissions of bright galaxies.
Supermassive black holes are believed to lurk at the heart of most galaxies, and of all large galaxies such as the Milky Way. What is less certain is if smaller galaxies also possess their own black holes.
Black holes do not emit any light themselves and their tremendous gravitational influence creates an escape velocity that even photons traveling through a vacuum are not rapid enough to escape. Material is drawn to these tremendous spacetime events, forming what is known as an accretion disc around them that gradually “feeds” them.
In these accretion discs, the gravitational forces around the black hole create violent effects that power highly energetic emissions, as does the destructive processes that occur when material falls to the “surface” of the central black hole.
This results in a central region of a galaxy marked by powerful emissions, which researchers term active galactic nuclei, (AGN). In larger galaxies AGNs are incredibly bright - some of the most luminous objects in the Universe. Yet, in smaller galaxies, these AGNs are less powerful, making them difficult to distinguish from newborn stars.
Observations of the light spectrums collected by DESI could help researchers determine more information about AGNs in these smaller galaxies. A better understanding of the cores of smaller galaxies could, in turn, help provide a better picture of galaxies that formed when the Universe was very young and how both these and their black holes grew as the Universe evolved.
Additionally, the team at Berekely Labs says that DESI has already, in its observations of 7.5 million galaxies with redshifts observed from 2.5 million of these, revealed exotic systems and objects that astronomers have not yet been able to study in detail.
By the time its mission is completed in 2026, DESI, which saw first light in 2019, will have built a stunning detailed 3D map of 35 million galaxies, revealing details of our Universe that we can currently only theorize about.
Dark Energy Spectroscopic Instrument (DESI) Creates Largest 3D Map of the Cosmos, Berkeley Lab, [https://newscenter.lbl.gov/2022/01/13/dark-energy-spectroscopic-instrument-desi-create]s-largest-3d-map-of-the-cosmos/