BSC provides supercomputing power and programming models for Gaia space mission

• The third release of the results of the European Space Agency Gaia mission presents the largest collection of astrophysical data on the Milky Way
• For the first time, it includes data on low-resolution and radial velocity spectroscopy
• Data on binary stars surpass the scientific work carried out during the last two centuries

The new Gaia data catalogue includes information on the population of asteroids of the Solar System which is key for studying the origins of this planetary system

The largest collection of astrophysical data for stars of the Milky Way, a catalogue of binary stars that surpasses all the scientific work from the past two centuries and the first low-resolution and radial velocity spectroscopy studies carried out to date: these are some of the scientific findings of the third catalogue release of the Gaia mission, published by the European Space Agency (ESA) on Monday, June 13.

Since its beginning, Gaia has counted on the participation of a team of astronomers and engineers of the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institute of Space Studies of Catalonia (IEEC), led by researchers Carme Jordi, Xavier Luri and Francesca Figueras, from the Department of Quantum Physics and Astrophysics (UB-ICCUB-IEEC).

The Barcelona Supercomputing Center-Centro Nacional de Supercomputación (BSC-CNS) has contributed to Gaia since its beginning, providing millions of hours of supercomputing in the MareNostrum supercomputer and programming models.

Specifically, since the beginning of the project, BSC has contributed almost 58 million hours, and for this third release of data, it has contributed almost 33 million hours.

On the other hand, the PyCOMPSs programming model and the dislib machine learning library developed by the BSC's Workflows and Distributed Computing group have been used in the software developed by the Gaia team to search for new open star clusters.

The BSC user support team has collaborated in data storage and transfer to other processing centres involved in the project.

This new data release, which includes a total of 1.8 billion stars of the Milky Way, provides the international astronomic collective with an unprecedented perspective of stellar characteristics and their life cycle, as well as the structure and evolution of the Galaxy. The published data of the Gaia Data Release 3 (DR3) were collected during thirty-four months, between July 25, 2014 and May 28, 2017.

Since the launch of Gaia in 2013, data sets have been released in 2016 and 2018, as well as a subgroup of the third data set in 2020. For the moment, the Gaia mission exceeds the 2,850 days of sky observation, it has collected 100 terabytes of data and has documented 200-billion-star transits in its focal plane.

Gaia Mission: the most accurate map of our galaxy

Gaia is the ESA’s emblematic mission launched in December 2013 to create the most accurate and complete multi-dimensional map of our galaxy —the Milky Way—, with data on the position, speed and direction of motion, brightness, temperature and composition of nearly two billion galactic and extragalactic objects. This information will allow astronomers to rebuild the past and future evolution of the Galaxy over billions of years.

The largest low-resolution spectroscopy study ever

The Gaia satellite, located 1.5 million away from the Earth in the opposite direction to the Sun in the Lagrange L2 point, has surveyed the sky through two telescopes which have provided scientific data to calculate the position, distance, speeds and physical features of nearly 2 billion stars.

One of the first scientific indications of the dataset now published are the light spectra of 220 million stars, which can be used to determine brightness, temperature, mass and chemical compositions with precision. As noted by Professor Carme Jordi, “for the first time, we can separate in detail the light we receive from the stars and that from other objects observed by Gaia”. The expert adds that “this separation provides us with knowledge on the physical properties such as temperature, brightness and chemical composition, which is essential information for determining the age of the stars and deduce their origins”.

Gaia DR3 includes the radial velocity of 33 million stars, a volume of information five times higher to the one the second data set of the mission provided in 2018. The radial velocity is the speed to which the objects distance from us or get closer, a parameter that is brought by the third dimension of speed in the Gaia map of our galaxy.

As Professor Xavier Luri says, “the number of measurements is, by far, larger than the total measures of radial velocity conducted from Earth in all history. This is already a radical change in data availability”. Luri also notes that “having the third motion component (the other two are provided by astrometry, through the own motions measured by Gaia) enables us to make a complete analysis of the kinematics of the stars. Overall, the volume, quality and completeness of data opens new perspectives for understanding the kinematics and dynamics of our galaxy”.

The largest catalogue of binary stars to date

Another novelty of the dataset is that it has the largest catalogue of binary stars of the Milky Way to date. With positions, distances, orbits and masses of more than 800,000 systems, this catalogue is key for understanding the stellar evolution. Moreover, Gaia DR3 has essential information for studying the origins of the Solar System. Specifically, data on 156,000 asteroids of this solar system, information of great precision which combines compositions and orbits.

The great volume of data Gaia offers to the international astronomic collective provides unprecedented views on the understanding of the characteristics of the stars and their life cycle, as well as on the study of the structure and evolution of the Milky Way. The data now presented include information on the stars with a brightness which varies over time, in addition to objects from the Solar System —asteroids and planetary moons— and galaxies and quasars beyond the Galaxy in which we find ourselves.

“As seen in previous data releases, the most unexpected and surprising findings will arrive during the following weeks, as soon as we distinguishing the secrets these data have; these data have been open to the professional community and amateurs since the beginning”, notes lecturer Francesca Figueras. “We are watching millions of eclipsing binary stars moving and beating, as well as thousands of pulsating cepheids, stellar populations that trace the distance of the universe. We also capture the non-radial pulsations of variable stars in rapid rotation, small tsunamis in its surface. These are only some examples, I cannot imagine the euphoria and passion Henrietta Swan Leavitt would feel now”.

A scientific collaboration since the beginning of the space mission

The role of the UB-ICCUB-IEEC team focused on the scientific and technological design of the project, the development of the data processing system and on the production of simulated data. A part of the software for data processing sent by the satellite has been developed by the UB-ICCUB-IEEC team and is carried out by the MareNostrum computer, from the Barcelona Supercomputing Center-Centro Nacional de Supercomputación (BSC-CNS).

The team members work on the scientific exploitation of data, in fields such as the study of the spiral structure of the Galaxy; identification of past interactions of the Milky Way with near galaxies, which are essential for knowing its evolution to present times; open clusters, including the identification of unknown clusters to date; and the study of the Magellanic Clouds, two small galaxies orbiting in our galaxy.

“With each each new release, the data accuracy and its volume improve. In the upcoming years, we will have, for instance, 150 million high-resolution spectra with more accurate distance and motions. The results we will obtain from the analysis of these data are unpredictable, but they will allow us, among other things, to better understand the evolution of the Galaxy, or its structure”, notes lecturer Eduard Massana.

The Gaia team at ICCUB (UB-IEEC), led by Professor Jordi Torra at the beginning of the mission, was awarded in 2013 the Barcelona City Award in the category of Experimental Sciences and Technology. Some of its members are part of the Gaia Science Team (GST), ESA’s scientific advisory body. Fuel consumption leads to the prediction that Gaia is expected to operate until 2025, and that the final catalogue will not come out before 2030.

This article was first published on 13 June by Barcelona Supercomputing Center.