▎ WuXi AppTec content team editor
13.8 billion years ago, a big bang opened the curtain on the universe. What have each galaxy experienced in this long history of cosmic evolution? Where will the universe go in the future? To answer these questions, astronomers first need to grasp the distribution of all galaxies.
At the end of the last century, the Sloan Digital Sky Survey (SDSS) ushered in a new era of cosmology. The 20-year-old optical sky survey project has produced a three-dimensional map of the universe that is more than 10 billion years old and has greatly improved our understanding of the evolution of the universe.
Now, a new sky survey project called the Dark Energy Spectrometer (DESI) has been launched. This multi-team international cooperation project, including the National Astronomical Observatory of the Chinese Academy of Sciences, will take over the mission of SDSS to explore the history, present and future of the universe in greater depth and detail.
▲ A three-dimensional map of the universe from DESI, the earth is in the lower left of the picture, and each point represents a galaxy (Image source: D. Schlegel/Berkeley Lab using data from DESI）
Today, the DESI team unveiled the first results of the project. Running for just 7 months, the data broke the existing record and painted the largest and most detailed three-dimensional map of the universe in history with more than 7.5 million galaxies. DeSI plans to survey more than one-third of the sky areas during a 5-year observation cycle. Ultimately, DESI expects to acquire data on more than 35 million galaxies.
The DESI project was proposed more than 10 years ago, and construction of the telescope began in 2015. The 4-meter-diameter Mayall Telescope is located at the famous Kitt Peak Observatory in Arizona, USA. Despite the impact of the COVID-19 pandemic, DESI officially began scientific observations in May 2021.
▲ Desi's observation tool is the 4-meter diameter astronomical telescope (Image source: KPNO/NOIRLab/NSF/AURA/P. Marenfeld)
DESI's main objective is to collect detailed chromatographic photographs of tens of millions of galaxies in more than one-third of the celestial region. DESI's observations can determine the redshifts that these lights undergo. As the universe continues to expand, these rays of light are elongated toward the infrared band as they travel to Earth. It is this redshift that allows DESI to see deep into the universe.
The greater the redshift of a galaxy in its spectrum, the farther it is from us in general. According to this three-dimensional map of the universe, scientists can classify galaxies as galaxy clusters or superclusters. These structures carry "echoes" from the early universe from which astronomers can speculate about the expansion history of the universe based on DESI data.
Understanding this history of inflation is crucial. After the Big Bang, the universe continued to expand. It stands to reason that due to the gravitational pull between galaxies, the expansion of the universe should be slower and slower. But in fact, the current universe is accelerating and expanding, and the driving force for this phenomenon is dark energy, a mysterious energy that accounts for 70% of the total mass of the universe.
However, dark energy did not have such a huge impact at the beginning of the birth of the universe. Previous research has speculated that the universe began to expand at an accelerated pace about 6 billion years ago. From a sufficiently detailed map of the distribution of galaxies, scientists can infer the nature of dark energy. Not only will this allow us to read the history of the universe, but it will also help us predict the end outcome of the universe: will it expand eternally; or will it eventually collapse and return to the situation before the Big Bang; or will the universe eventually be torn apart?
Comparison of cosmic maps drawn from SDSS (left) and DESI's first data (right) (Image source: DESI COLLABORATION TEAM)
Of course, the answer to these ultimate questions will not be possible until at least five years of DESI observations are completed. But before that, according to DESI phased data, scientists are also expected to uncover the answers to many mysteries of the universe. For example, how some galaxies with a history of more than 10 billion years were born and how they evolved in the early days; how intermediate-mass black holes behave in small galaxies; how distant quasars evolved as one of the brightest objects in the universe...
For more than 4 years, the telescope will continue to receive signals from the distant universe. It won't find us other civilizations in the universe, but DESI will bring us more new discoveries to this wonderful history of nearly 14 billion years.
Resources:
[1] Dark Energy Spectroscopic Instrument (DESI) creates largest 3d map of the cosmos. Retrieved Jan. 13, 2022, from https://www.eurekalert.org/news-releases/939891
[2] NAOC helps to create the largest 3-D map of the cosmos. Retrieved Jan. 13, 2022, from https://www.eurekalert.org/news-releases/939962
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