Successful start of DESI Instrument to reveal dark energy mysteries


The circular surface, superimposed on the image of Andromeda Galaxy (M31), represents the instrument DESI, covering a portion of more than three square degrees in the sky. The represented spectrum in the sky corresponds to a distant quasar of 11 billion years ago. Image: DESI - Legacy Imaging Surveys collaboration.

The circular surface, superimposed on the image of Andromeda Galaxy (M31), represents the instrument DESI, covering a portion of more than three square degrees in the sky. The represented spectrum in the sky corresponds to a distant quasar of 11 billion years ago. Image: DESI – Legacy Imaging Surveys collaboration.

Today is the official beginning of a 5-year research to map the universe and reveal the mysteries of the dark energy using the Dark Energy Spectroscopic Instrument (DESI). Based in the Kitt Peak National Observatory (Arizona, United States), this instrument will take and study the light of tens of millions of galaxies and other distant objects of the Universe.

Recording the light of 30 million galaxies will help scientists in the DESI project to build a 3D map of the Universe with unprecedented details. The data will enable scientists to better understand the repulsive gravity force associated with dark energy that drives the acceleration of the expansion of the Universe across vast cosmic distances.

“DESI will enable us to observe ten times more galaxies than previous maps and to study the evolution of the Universe from 11 million years ago to the present day”, notes researcher Héctor Gil Marín, from the Institute of Cosmos Sciences of the UB (ICCUB) and the Institute of Space Studies of Catalonia (IEEC), who co-directs the first analysis of galaxy maps. The DESI telescope gathers light, or spectra, from galaxies and quasars, which enable the obtaining of its recessional velocity. “We know the farther the object is from us, the greater its recessional velocity is, this will enable us to build a 3D map of the Universe”, says Gil Marín.

The scientific program will enable researchers to tackle two main issues: what dark energy is and the degree in which gravity force follows the laws of general relativity, which build the base of how we understand the cosmos.

The formal beginning of the DESI mapping occurs after a 4-month period of tests, during which the instrumentation has captured up to four million galaxy spectra ─more than the total of all the previous spectroscopic mappings. The instrument includes new optics that increase the field of view of the telescope and includes 5,000 robotically controlled optical fibers, able to obtain spectra from 5,000 astronomical objects.

The gathered spectra by DESI are components of light, corresponding to the colors of the rainbow. The characteristics, which include the wavelength, provide data such as the chemical composition of the observed astronomical objects or the relative distance and velocity.

While the Universe expands, galaxies move away from each other and their light moves to longer wavelengths (redder). The farther the galaxy is, the greater the red movement of the spectrum is. When measuring this, the DESI researchers will create a 3D map of the Universe. A detailed distribution of the galaxies in the map is expected to yield insights on the knowledge on the influence and nature of dark energy.

“Knowing the properties of dark matter is the main objective in DESI”, notes Licia Verde, ICREA professor at ICCUB. “We know that nowadays 70% of the energy content of the Universe is formed by dark matter, but we know very little about its properties”. Dark matter determines the rate of expansion of the Universe. “While the DESI instrument looks out at space and time, we can observe the Universe in different periods simultaneously, and when comparing them, we can find out about the evolution of the content of energy as the Universe ages”, concludes the researcher.

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