Explained | What is the Gaia space mission and what has it revealed about the Milky Way?

New data released by the European Space Agency’s Gaia mission has revealed the startling phenomenon of ‘starquakes’, massive tsunami-like movements on the surface of stars

New data released by the European Space Agency’s Gaia mission has revealed the startling phenomenon of ‘starquakes’, massive tsunami-like movements on the surface of stars

The story so far: The third set of data released by the European Space Agency Gaia stellar mapping probecovering nearly 1.8 billion stars in the Milky Way galaxy, revealed an unexpected phenomenon called “starquakes,” which are similar to earthquake-like motions but on the surface of stars.

The data also revealed the largest chemical map of the entire Milky Way, showing the DNA of millions of stars, which includes their age, mass, chemical composition, color, temperature and metal content. In addition, the new data also made discoveries about binary star systems, quasars, asteroids and exoplanets.

Scientists, in the years to come, will interpret several terabytes of data to make discoveries about astronomical phenomena. The second set of data in 2018 allowed astronomers to show that the Milky Way merged with another galaxy in a violent collision around 10 billion years ago.

milky way anatomy

Structure of the Milky Way.  Photo: European Space Agency

Structure of the Milky Way. Photo: European Space Agency

The Milky Way, our home galaxy, is just one of approximately one hundred to two hundred billion galaxies of varying shapes and sizes in the universe. About 13 billion years old, the Milky Way is a barred spiral galaxy composed of 100 to 200 billion stars, with the sun as the local star.

The galaxy is shaped like a flattened disk spread over 100,000 light-years with spiral arms. The majority of stars are located in the disc, scattered in a mixture of gas and cosmic dust. The Milky Way has a central bulge where about 10 billion of its oldest stars are concentrated. The sun is positioned between the center and the periphery of the galaxy.

Outside the bulge and disk exists a halo of isolated stars and ancient star clusters, and farther beyond is an even larger halo of invisible dark matter.

The Milky Way is part of a local group of galaxies, including Andromeda, its nearest large galaxy, and nearly 60 smaller galaxies.

What is the Gaia mission?

Specificities of the Gaia mission.  Photo: European Space Agency

Specificities of the Gaia mission. Photo: European Space Agency

Gaia is an ongoing astronomical observation mission launched in December 2013 by the European Space Agency (ESA) with the aim of creating the most accurate and comprehensive 3D map of the Milky Way by probing 1% or one billion of the 100 billion stars in the galaxy. According to the ESA, “this information allows astronomers to reconstruct the past and future evolution of the galaxy over billions of years”.

The Gaia spacecraft took off from Kourou, French Guiana in 2013 on a Soyuz rocket and began scientific screening in 2014. The almost hat-shaped spacecraft is equipped with two optical telescopes and the world’s largest digital camera. space or the billion pixel camera, with more than 100 electronic detectors. This camera is precise enough to capture the diameter of a human hair at a distance of up to 1,000 km.

The spacecraft is strategically stationed 1.5 million km from Earth, in the opposite direction of the sun, in an orbit around the gravitational parking point in space called Lagrange 2 or L2.

It is from here that Gaia plots the precise positions, movements, speed, brightness, temperature, and composition of stars in the galaxy and other celestial objects beyond.

Gaia's Three Screening Techniques.  Photo: European Space Agency

Gaia’s Three Screening Techniques. Photo: European Space Agency

In order to study stars and objects, Gaia is also equipped with tracking and imaging systems that use three techniques: astrometry, photometry and spectroscopy. Astrometry is the science that measures the motion and position of stars in the plane of the sky, photometry studies the color, luminosity, and other properties derived from stars, and spectroscopy measures the radial velocity or motion of stars towards or away from us by studying stellar spectra or the fingerprints of stars. Spectra are obtained by passing light from a star through a prism which breaks it down into a spectrum of colors.

Gaia’s predecessor, ESA’s Hipparcos mission, had mapped the precise positions of 100,000 stars and could look 1,600 light-years away. Gaia, meanwhile, can trace departures and objects up to 30,000 light-years away.

Gaia makes millions of observations in a single day and this raw data observed by the spacecraft is transformed into meaningful scientific information by the Gaia Data Processing and Analysis Consortium (DPAC), a group of 400 scientists.

The release of Gaia data was planned in four tranches: the first two datasets were released in 2016 and 2018 respectively, the third is the current one, and the final data will be released in 2030 after Gaia finishes mapping the sky. in 2025.

What did the new data reveal?

Specificities of the new data collected by Gaia.  Photo: European Space Agency

Specificities of the new data collected by Gaia. Photo: European Space Agency

The newly released dataset was collected by the Gaia probe between 2014 and 2017 and contains improved information on nearly two billion celestial objects, including stars in the Milky Way, objects outside the galaxy and those inside our solar system. It contains the largest three-dimensional star map of the Milky Way. The map shows the chemical compositions as well as the past and future motions of the stars.

Starquakes: One of the most startling findings, which the ESA said Gaia was not designed to observe, was that of more than 100,000 “starquakes” – which can be likened to tsunamis or vibrations massive on the surface of stars that can change their shape. Such starquakes have also been detected on the surface of stars which should not have such large-scale vibrations according to existing astronomical theories.

“Starquakes teaches us a lot about stars, including their inner workings. Gaia opens a gold mine for the ‘asteroseismology’ of massive stars,” said Belgian scientist Conny Aerts, who is part of the Gaia collaboration.

Quasars: Quasars are extraordinarily active and bright galactic nuclei powered by supermassive black holes. They are the brightest objects in the universe and are visible along its far edges. The new data from Gaia revealed measurements of more than one million confirmed quasars and data for 6.6 million candidate quasars. This is an increase from the previous dataset which gave positions of half a million confirmed quasars. The discovery of new quasars is significant because it makes it possible to measure the most distant reaches of our universe.

Stellar DNA: The data shows the chemical constituents, colors, brightness, speed, temperatures and positions of millions of stars. The chemical composition of stars also reveals the elements they contain. Only light elements (hydrogen and helium) were formed during the Big Bang. Heavier elements, which scientists call metals, are built up inside stars, and when they die, new stars are formed with the metals dispersed by the dead stars. The chemical composition can thus be used to determine which stars were born in another galaxy and then migrated to the Milky Way. According to the ESA, astronomers hope to use the data to better understand how stars are born and die, and how the Milky Way has evolved over billions of years.

Previous data from Gaia had revealed the proper positions or 2D motions of stars (how they move vertically and horizontally across the plane of the sky), but the new set shows the radial velocity of 33 million stars, that is- i.e. how fast these stars are approaching or receding. on our side. . This can not only help scientists understand the trajectory of stars, but also their original location.

Binary stars: Binary star systems are two stars that orbit around a common center. The new data revealed the position, distance, orbits and masses of more than 8,00,000 binary star systems. Scientists can extract from this data the mass of individual stars in the binary system, how the stars work, and even find out if one of the two stars is an exoplanet, a planet that exists outside of our solar system and generally orbits around Earth. ‘a star.

Asteroids and galaxies: The data provided a catalog of more than 156,000 asteroids in our solar system, which includes their mass, composition, color and luminosity (from which details about their shape and rotation can be derived). Besides mapping the Milky Way, the data also found the magnitudes of 2.9 million other galaxies, including how their stars formed, how far apart they are and when they came into existence.

(With agency contributions)

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