Stellar earthquakes, merged galaxies... the incredible findings of the new map of the Milky Way

The Milky Way over the GRANTECAN telescope, at the Roque de los Muchachos Observatory, on the island of La Palma. / iac

Science | Astronomy

Third data release from ESA's Gaia mission includes new information on almost 2 billion stars

Elena Martin Lopez

Since its launch in 2013, ESA's Gaia satellite has been mapping our galaxy from Lagrange Point 2 (L2), a prime observing site 1.5 million kilometers from Earth. The goal is to create the most accurate and complete multidimensional map of the Milky Way, in order to reconstruct its past evolution and make predictions about its future. Until now, two data sets had been published in this regard, the first in 2016 (DR1) and the second in 2018 (DR2). The third (DR3), which was made public yesterday, collects even more detailed information and surprising discoveries about almost 2 billion stars, as well as other objects inside and outside our galaxy.

It is quite an achievement, since “obtaining information from the Milky Way is very difficult, because we are inside it and the observations made from Earth are, in some way, biased by our location in space. Thanks to Gaia, however, we obtain a very precise and detailed global image", explains Rocío Guerra, Gaia's scientific operations coordinator.

DR3 data was collected between July 25, 2014 and May 28, 2017. Later dates are not included because most are not yet analyzed. "This is a very complex process that can take years and requires the collaboration of more than 450 people (including many Spaniards)," says Guerra. Once the information is organized, the scientists have produced nine studies explaining the findings and their practical potential. Here are some of them.

stellar earthquakes

Although it was not created for that purpose, one of the great discoveries made by Gaia has been to be able to detect stellar earthquakes (also called non-radial oscillations). These are small movements recorded on the surface of stars that change their size and shape, altering their luminosity. “Thanks to the fact that Gaia observes the sky so many times, we can capture the intensity with which the light of very hot, very massive and rapidly rotating stars reaches us, and infer a lot of information about their internal functioning,” says Guerra. In this case, such vibrations have been detected in thousands of stars, including some where they have rarely been seen before.

The DNA of the stars

The chemical composition of a star is like its DNA and gives us crucial information about its origin. The DR3 release presents the largest chemical map of the Milky Way to date. Thus, it has been seen that the youngest stars (such as the Sun) contain more heavy metals (iron, calcium...) than the stars of previous generations (formed mainly by hydrogen and helium), and that those stars that are more 'metallic' They are closer to the center and the plane of our galaxy than the rest.

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radial speed

Another key parameter obtained has been the radial velocity of 33 million stars, that is, the speed at which these stars approach and move away from us. A figure much higher than that obtained in the previous catalog, when this figure of 7 million stars was determined.

A galaxy within another

From the chemical composition and radial velocity, the origin of many stars has been identified, some of which come from galaxies other than our own. “Between 8 and 11 billion years ago, the Milky Way collided with the Enceladus galaxy and acquired part of its stars. Thanks to Gaia we can distinguish what they are, ”says Guerra. This means that some galaxies grow and evolve by assimilating or absorbing others.

asteroids

156,000 asteroids with very precise orbits have also been defined. "Of 60 of them, we also know their colors and chemical composition, which gives us valuable information about what the families of asteroids that populate the Solar System are like and how they were formed," says Guerra.

binary systems

In addition, more than 800,000 binary systems have been detected, that is, systems in which there is more than one star, unlike the Solar System where there is only the Sun.

extragalactic objects

While surveying the sky, Gaia also sees objects outside the Milky Way, such as quasars (supermassive black holes that accumulate matter) and other galaxies. Specifically, in DR3 1.9 million quasars and 2.9 million galaxies have been observed, from which she has obtained information such as brightness, color or shape.

Gaia's future

Gaia continues to observe the sky and it is expected that in the not too distant future she will reveal new mysteries of our galaxy. “No specific dates are known, but two more publications like this are expected. The fourth catalog will not arrive before 2025 and the fifth not before 2030," says Guerra. Both will make it possible, even more, to delve into all kinds of objects in the Milky Way, benefiting many fields of study and even the work of many other satellites.

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