After 45 years as a versatile research telescope, the giant Mayall 4-meter telescope at Kitt Peak National Observatory is undergoing a major reconfiguration that will allow it to generate a 3-D map of the universe and probe the mysterious physics of dark energy that is thought to power the expansion of the universe.
To complete this lofty goal, installation of a powerful new instrument, called the Dark Energy Spectroscopic Instrument, or DESI, started Monday on the Mayall and will last over a year. DESI will then spend the next five years collecting the spectra — the separation of the components of light often seen as a rainbow — of about 30 million galaxies.
Cosmologists and astronomers who study the universe on a large scale hope to tease out the details of how the expansion rate of the universe changed over time.
It was thought that because the universe began as a result of the “Big Bang” that after a while, gravity would contract all matter in the universe into a big crunch. But astronomers were surprised to discover the universe actually expanded at a constant rate for a long time, then, a few billion years ago, that expansion began to accelerate, said Arjun Dey, project scientist for DESI.
“We don’t understand why that happened,” Dey said. “Right now, we have a crude measure of how expansion took place and DESI will help measure that on a finer time scale.”
Dark energy is the name given to the phenomenon, but what it is and how it works is still unknown.
Mayall’s primary, 4-meter mirror that gathers incoming light from space will remain a part of the telescope.
DESI will be replacing the Mayall’s smaller, secondary mirror and camera — which weigh as much as a school bus — that sit at the top end of the telescope, said Kitt Peak director Lori Allen in a statement. In mid-June, a crane will hoist the old equipment out of the narrow slit in the dome and store it within the building in preparation for accepting the new DESI instruments.
The Mayall was chosen to support the weight of DESI’s 9 tons because “it was engineered like a battleship,” and has a wide view of the sky, unlike many other large telescopes, Dey said.
The state-of-the-art technology of DESI will allow it to use 5,000 robotic fingers to rapidly point fiber optic cables at 5,000 pre-programmed galaxies, feed the light through cables snaking down the side of the telescope into devices that will separate the light into spectra to be recorded by cameras. The robotic fingers will point at new galaxies every 20 minutes.
“You can learn a lot from imaging,” said Katy Garmany, astronomer emeritus at the National Optical Astronomy Observatory, referring to the picture of space we often imagine, “but you really get into the astrophysics with spectra.”
Spectra allow cosmologists to determine the speed at which galaxies are rushing away from each other. By looking further into space, astronomers are also looking further back in time, like paleontologists studying strata of long-buried earth, in an effort to read the history of the universe and track its changing expansion rate.
“For the last few years, we’ve been doing a preliminary project, basically mapping the sky so we can decide what we want to look at with DESI,” Garmany said.
Photographs of galaxies taken during the preliminary project are available to the public now. Spectra collected by DESI will also be open for other researchers or anyone else interested after an 18-month proprietary period for DESI collaborators.
Guided public tours of the Mayall 4-meter telescope will remain available as installation of DESI allows, which will be most of the time.
Kitt Peak is located about 55 miles southwest of Tucson on the Tohono O’odham Nation. Check Kitt Peak National Observatory’s website before heading out for a tour.
DESI is managed by the Lawrence Berkeley National Laboratory for the U.S. Department of Energy and includes more than 200 collaborators from about 40 national and international institutions.