The most detailed map of our galaxy just keeps getting better

Astronomers’ leading reference guide to the Milky Way has just received a major update. The Gaia mission, which studies almost two billion stars, has published a vastly improved map that includes the three-dimensional movements of tens of millions of stars and thousands of asteroids, as well as detections of stellar “earthquakes” and possible exoplanets.

The Gaia team presented the findings, along with some 50 scientific papers, at a press conference on June 13, making the entire database publicly available. The European Space Agency (ESA) launched the 2-tonne spacecraft in 2013. Like the previous database, published in 2020, this latest version consists of 34 months of data collected between 2014 and 2017.

‘Five Gaia papers are published every day,’ stressed ESA’s Scientific Director, Günther Hasinger, from Noordwijk, during an online presentation of the catalogue. “In the last three years we have surpassed the gold standard of astronomy, the Hubble Space Telescope, and now we generate 1,600 articles a year.”

detailed spectra

Gaia orbits the Sun at a fixed distance from Earth. Over the course of a year, he makes repeated measurements of the same stars from slightly different perspectives. Between these measurements, each star’s apparent position in the sky changes by a tiny angle (usually millionths of a degree) that is proportional to its distance. The mission team uses these variations and a technique called parallax to calculate the distance between the star and the Sun.

In addition, Gaia measures the spectra of starlight. The most significant addition to the previous catalog is a much larger number of detailed spectra, now available for around a million stars. By measuring the Doppler shift of the spectrum (the same effect whereby an ambulance siren has a different pitch depending on whether the vehicle is coming toward us or away from us) the team has calculated 30 million values ​​of “radial velocity,” the The speed at which a star approaches the Sun or recedes from it. Together with Gaia’s measurements of the star’s motion across the sky and its distance, the data provides a complete reconstruction of the star’s path around the galaxy.

An important application will be detecting and studying star clusters that move together through the galaxy, says Tereza Jerabkova, an astronomer at the European Southern Observatory in Garching. “I think that all scientists working with star clusters will jump on the new radial velocities, which will allow more stars to be analyzed in 6D” (three dimensions for the position of each star and three for its direction of movement).

stellar wobbles

Gaia’s new catalog also includes information about how some stars ‘wobble’ due to the gravitational pull of another massive object. In this way, the team has identified 800,000 binary systems, which appear to be a single star but are actually made up of two.

In some cases, the attraction does not seem to come from a companion star, but from a massive planet orbiting the star, says Alessandro Sozzetti, a member of the Gaia collaboration. “This ‘whets our appetite’,” says Sozzetti, who researches exoplanets at the Turin Astrophysical Observatory. With several more years of observational data, the team hopes to discover thousands of extrasolar planets.

Gaia’s planet-hunting techniques will complement those of other specialized missions, such as the Kepler telescope or NASA’s Transiting Exoplanet Survey Satellite (TESS), says Jessie Christiansen, project scientist for the space administration’s Exoplanet Archive. American. Those missions are especially sensitive to “hot giants” (Jupiter-like planets that orbit very close to their stars), while Gaia will discover many giant planets that spin farther away and stay cooler, says Christiansen, who works at the California Institute of Technology. “Systems with cool giant planets are especially interesting, because they could be much more similar to our solar system than the systems with hot giants that Kepler and TESS have found.”

Gaia has already accumulated another four years of observations after those included in the new catalogue, and will continue to publish larger and more precise data sets in the years to come. The mission, with a cost of 1,000 million euros, will collect data until 2024, when it will run out of fuel.

Davide Castellvecchi

More information in Spanish and links to documentation and multimedia material on the ESA website.

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