Everything that has ever been observed, with all of humans’ senses and tools on Earth and beyond, only accounts for 5% of the universe. The rest is energy and matter that has eluded scientists.
Dark Matter and Dark Energy compose 95% of the universe. That means everything humans have ever sensed or measured, composes just a small fraction of what makes up the cosmos.
While scientists are uncertain about what exactly dark matter and energy are, they believe it will provide answers to some of the biggest questions about the universe.
Researchers with the University of Arizona are attempting to shine a light on those secrets, by creating the largest 3D map of the universe.
Two years into a five-year project, the team has already accomplished that goal. So far they have observed more than 20 million galaxies.
But by the time the project is completed, that map will contain 35 million.
“The most important goal of DESI is to actually push the measurement of the expansion of the universe to larger distance than we have been able to do right now and to higher accuracy," said Xiaohui Fan, a University of Arizona astronomer.
“So basically you are looking at how dark energy may change over this more than 10 billion years of cosmic history," he said.
The Dark Energy Spectroscopic Instrument, or DESI for short, is on the Nicholas U. Mayall 4 meter Telescope at Kitt Peak National Observatory near Tucson.
Parker Fagrelius has worked with the DESI team from its outset.
“So we have 5000 of these robots. Each one has two motors, and these motors are able to move a very small fiber about the size of a hair to anywhere within kind of a 12 millimeter diameter circle," she said.
Those robots are able to collect the greatest amount of data ever possible with this technology, about 150,000 celestial objects each day.
“It takes less than two minutes to move all of the fibers to align with the galaxies. Then we stare at those galaxies for about 20 minutes. We get as much light as we can, and then we move to another field on the sky," said Fagrelius.
Previously, fibers had to be plugged into plates by hand, which took much more time. Fagrelius says the new technology provides unique possibilities.
“Desi presents kind of an exciting opportunity because we'll have this huge data set that is all coming from one instrument being operated in the exact same way," she said.
Raga Pucha is a UA doctoral student using the instrument to study spectra of black holes.
Spectra are charts and graphs that show the intensity of light being emitted over a range of wavelengths. Basically the rainbows given off by these galaxies.
“So you have this 35 million spectra of galaxies just sitting there, and it's just data we just have to analyze it and then we will know a lot about the galaxies and how they grow," said Pucha.
But analyzing the data is challenging. Distance and time affect light itself as it travels through space.
Just like a siren’s pitch lowers as a fire truck drives away, light waves from cosmic objects stretch and become more red as the universe expands. This phenomenon is called redshift.
“There's like a cosmological redshift, which happens because basically the universe is expanding," said Pucha.
Researchers like Raga are able to use that data to calculate galaxy locations and movement.
“We see all of them in a combined sense when we see the spectrum. We are able to get an average redshift the galaxy is at based on how much the emission lines are shifted," Pucha said.
Space is expanding faster than the speed of light. While scientists believe Dark Energy is the culprit, Desi has been tasked with learning more about what Dark Energy is.
Fan says the instrument is testing the theories posed by Albert Einstein.
“Dark Energy was a somewhat unexpected discovery in the sense that it was a long time that predicted as a possibility through something called: Cosmological Constant. This is something that Einstein first proposed originally more than 100 years ago with his original theory of General Relativity that there could be this term that is associated with some energy in the vacuum. That as the universe expands, actually that will propel the universe to expand even faster or cause other sort of changes in the expansion of the universe," Fan said.
But getting an idea of that cosmological constant requires a lot of data.
“The higher accuracy means it can tell you whether the parameter of dark energy is consistent with this constant. And to larger distance can tell you whether dark energy is really a constant, or it's actually changing as with cosmic time. Because Desi can measure distance of galaxies and quasars more than 10 billion lightyears away," Fan said.
Observations had to pause last year when a lightning strike caused a wildfire near the observatory. But it quickly grew in size and eventually climbed Kitt Peak, damaging structures.
The instrument and the other telescopes on site were intact.
After recovery and cleaning, DESI has been up and running since September, continuing its mission.
Here’s Fagrelius again.
“There's so many scientific explorations and discoveries that can be made with this huge data set that we aren't even sure is out there yet, so that's very exciting," she said.
One such discovery was announced this year, as a mass migration of stars has been detected in our nearest galactic neighbor the Andromeda Galaxy.
Astronomer Joan Najita co-authored the study detecting the patterns.
"When we look up in the sky at night, we see the Milky Way, the Galaxy we live in, and it's we see it's made of stars. But we might wonder where do those stars come from? The answer to that question is thought to be much like the answer to the question of where the people. We think some stars were born in the galaxy where they live today and others were born abroad in another Galaxy and arrived as immigrants. That is to say that, you know, small galaxies fall into larger galaxies and waves of immigration and disperse their stars," Najita said.
While the James Webb Telescope offers pristine images of far off celestial bodies, Najita says DESI has its own benefits.
"We really want to study the whole Galaxy in order to see the expected large scale pattern which extends over the entire Galaxy. So DESI is superbly suited for this because it can study a large area of Andromeda all at once. The whole Galaxy, and it can measure the motions of 5000 stars at a time," Najita said.
"And the DESI Spectra were so great because the velocities are very good and we had a large number of stars that it was really easy to see the patterns once we knew what to look for and the fun part for us was that in terms of a discovery was that we really didn't set out to find these patterns."
