New Gaia data paint the most detailed picture of the Milky Way yet

1.6 billion stars. 11.4 million galaxies. 158,000 asteroids.

A spaceship.

The European Space Agency’s Gaia space observatory, launched in 2013, has long surpassed its goal of mapping more than a billion stars in the Milky Way (SN: 10/15/16). On June 13, the mission expanded this map into new dimensions, releasing more detailed measurements of hundreds of millions of stars, as well as – for the first time – asteroids, galaxies and the dusty medium between stars.

“Suddenly you have a flood of data,” says Laurent Eyer, an astrophysicist at the University of Geneva who worked on Gaia for years. For some topics in astronomy, the new results effectively replace any observations made previously, Eyer says. “The data is better. It is wonderful.”

Data in the new survey, collected from 2014 to 2017, is already leading to some discoveries — including the presence of surprisingly massive “starquakes” on the surfaces of thousands of stars (SN: 8/2/19). But most importantly, the publication is a new tool for astronomers, one that will help them understand how stars, planets and entire galaxies form and evolve.

Here are some of the long-standing mysteries the data could solve.

Asteroid Mishmash

The asteroid belt between Mars and Jupiter is a historical mess. After Earth and other planets formed, the remaining rocky building blocks smashed into each other, leaving jumbled fragments. But if scientists know enough about individual asteroids, they can reconstruct when and where they came from (SN: 4/13/19). And that can provide a glimpse into the earliest days of the solar system.

Using new Gaia data, astronomers recorded the positions of 156,000 asteroids as of June 13, 2022. The tracks show their orbits over the last 10 days, and the colors mark different groups of asteroids based on their position (blue, inner solar system; green, the main asteroid belt between Mars and Jupiter; orange, the Trojan asteroids near Jupiter) .DPAC/Gaia/ESA, CC BY-SA 3.0 IGO

Gaia’s massive new dataset could help solve this mystery, says Federica Spoto, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. It contains data on the chemical composition of over 60,000 asteroids – six times more than researchers had such detail before using other tools. This information can be crucial in tracing asteroids back to their harrowing origins.

“You can go back in time and try to understand the entire formation and evolution of the solar system,” says Spoto, a Gaia collaborator.This is something big that we couldn’t even think about before Gaia.”

However, asteroids are not just parts of the past; they are also dangerous. The new data could reveal asteroids that are all but impossible to see from Earth because they orbit too close to the Sun, says Thomas Burbine, a planetary scientist at Mount Holyoke College in South Hadley, Mass., who is not at the mission is involved (SN: 02/15/20). Because these asteroids would originally have come from further out (e.g. the asteroid belt), they can tell us about the rocks that are passing by Earth and can potentially hit us. “We’ll get to know our neighborhood better,” says Burbine.

Dating a star

It is notoriously difficult to measure the ages of stars (SN: 07/23/21). “Uncertainties of more than a billion years are not uncommon,” says Alessandro Savino, an astrophysicist at the University of California, Berkeley, who is not involved in Gaia. Unlike brightness or location, age is not directly visible. Astronomers have to rely on theories about the evolution of stars to predict ages from what they can measure.

If previous versions of the Gaia survey were like a photograph of stars, the new version is like switching the photograph from black and white to color. It offers a deeper look into hundreds of millions of stars by measuring their temperature, gravity and chemistry. “You think of the star as this point in space, but then they have so many properties,” says Spoto. “This is what Gaia gives you.”

While these types of measurements are far from new, they have never been collected on such a scale in the Milky Way. These data could provide a better insight into the evolution of stars. “We can improve the resolution of our clocks,” says Savino.

Milky Way Snacks

Though it may seem steady, the Milky Way is actually eating a steady diet of smaller galaxies — it’s about to eat one. But for decades, predictions about when and how these cosmic mergers will occur have been at odds with evidence from our galaxy, says Bertrand Goldman, an astrophysicist at the International Space University in Strasbourg, France, who is not involved in the publication of the Gaia data . “This has long been controversial,” Goldman says, “but I think Gaia will certainly shed some light.”

The key is being able to take apart different structures in the Milky Way and see how old they are (SN: 1.10.20). Gaia’s latest publication helps in two ways: by mapping the chemistry of stars and by measuring their motion. Previous versions of the survey described how millions of stars moved, but primarily in two dimensions. The new catalog quadruples the number of stars with full 3D trajectories from 7 million to 33 million.

This has an impact beyond our neighborhood. Most of the universe’s mass is contained in galaxies like the Milky Way, so knowing how our own galaxy works goes a long way toward understanding space at the largest scales. And the more scientists understand the parts of galaxies they can see, the more they can learn about dark matter, the mysterious substance that exerts gravity but doesn’t interact with light (SN: 06/25/21).

As astronomers mine this latest data set, they are already looking ahead to future treasure hunts. The next round is years away, but it’s expected to enable the discovery of thousands of exoplanets, provide rare measurements of black holes, and help astronomers measure how fast the universe is expanding. That’s partly because Gaia is designed to track the movement of objects in space, and it gets easier to do that over time. So Gaia’s observations can only get more powerful. “Like good wine, they age very, very well,” says Savino.

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