Map directions

Milky Way mega-map adds depth to star movements

The Milky Way in four maps: data from the Gaia spacecraft shows the speed at which stars are approaching or moving away from us, called the radial velocity (top left); their radial velocity and proper motion, or how they move across the sky (bottom left); their chemical composition (bottom right); and interstellar dust (top right).Credit: ESA/Gaia/DPAC/CU6 (CC BY-SA 3.0 IGO)

Astronomers’ leading reference guide to the Milky Way just got a major update. The Gaia mission, a spacecraft that tracks nearly two billion stars, has released a vastly improved map, which now includes the three-dimensional movements of tens of millions of stars and thousands of asteroids, “earthquake” detections stellar and possible extrasolar planets.

The Gaia team unveiled the treasure at a press conference on June 13, along with around 50 scientific papers, and made the full database available for public download. The European Space Agency (ESA) spacecraft launched the 2-ton probe in 2013. Like an earlier database released in 2020, the latest version consists of 34 months of data collected between 2014 and 2017.

“Every day, five Gaia papers are published,” ESA Scientific Director Günther Hasinger said during an online presentation of the catalog from Noordwijk, the Netherlands. “Over the past three years, we’ve surpassed astronomy’s gold standard, the Hubble Space Telescope, and are now producing 1,600 papers 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. This causes each star’s apparent position in the sky to change by a small angle – usually millionths of a degree – that is proportional to its distance. The mission team then uses these changes and a technique called parallax to calculate the star’s distance from the Sun.

Additionally, Gaia measures the light spectrum of stars. The biggest addition to the previous catalog is the vastly increased wealth of detailed spectra, now including around 1 million stars. By measuring a Doppler shift in the spectrum – similar to how the pitch of an ambulance’s siren depends on how close or far away it is – the team calculated 30 million “radial velocity” measurements, that’s i.e. the speed at which a star is moving towards or away from the Sun. Together with Gaia’s measurements of the star’s motion across the sky and its distance, the data provides a full reconstruction of the star’s path as it orbits the Galaxy.

An important application will be to detect and study clusters of stars moving together across the Galaxy, says Tereza Jerabkova, an astronomer at the European Southern Observatory in Garching, Germany. “I think everyone in the star cluster community will jump on the new radial velocities that will allow more stars to be analyzed in 6D” – which include three dimensions for each star’s positions and three for its direction of rotation. movement.

Stellar Oscillations

The Gaia Catalog now also includes information on how individual stars “wobble”, under the gravitational pull of a massive companion object. In this way, the team identified 800,000 binary systems – objects that appear to be single stars but are actually two stars. In some cases, the attraction does not appear to come from a stellar companion but from a massive planet orbiting the star, says Alessandro Sozzetti, a member of the Gaia collaboration. “It makes us hungry,” says Sozetti, who is an exoplanet researcher at the Turin Astrophysical Observatory in Italy. With several more years of observational data, the team expects to discover thousands of exoplanets.

Gaia’s planet-hunting techniques will complement those of dedicated exoplanet missions such as Kepler and NASA’s Transiting Exoplanet Survey Satellite (TESS), says NASA Exoplanet Archive project scientist Jessie Christiansen. These missions are particularly sensitive to “hot giants” — Jupiter-like planets that orbit very close to their stars — whereas Gaia will find many giant planets orbiting further away and remaining cooler, says Christiansen, of the California Institute of Technology in Pasadena. . “Systems with cold giant planets are particularly interesting because they might look much more like our solar system, which has cold giant planets, than the systems with hot giant planets found by Kepler and TESS.”

Gaia has already accumulated four more years of observations after those in today’s catalog, and it will continue to release larger and improved datasets in the years to come. The billion-euro ($1.2 billion) mission is expected to take data until 2024, when its fuel is expected to run out.