After a feverish wait, astronomers around the world have an ocean of new information to throw themselves into. This afternoon in Europe, the European Space Agency’s (ESA) Gaia mission published its first fully 3D map of the Milky Way.

The data haul includes the positions of nearly 1.7 billion stars, and the distance, colours, velocities and directions of motion of about 1.3 billion of them. Together they form an unprecedented live movie of the sky, covering a volume of space 1,000 larger than previous surveys have (see ‘Gaia’s gold’). “In my professional opinion, this is crazy awesome,” says Megan Bedell of the Center for Computational Astrophysics in New York, one of the many astronomers who will conduct studies based on the data set. “I think the whole community is eager to dive in.”

Within hours of the catalogue going online, 3,000 users from around the world had already started downloading the data, ESA said in a tweet.

“We’re very curious to see what the community will do with it,” says Anthony Brown, an astronomer at the Leiden Observatory in the Netherlands who chairs Gaia’s data-processing collaboration.

At an event to present the Gaia catalogue at the Royal Astronomical Society in London, astronomer Gerry Gilmore of the University of Cambridge, UK, presented a striking video that extrapolated on the Gaia data to simulate the future motion of millions of stars. “Everything moves,” he said.

The 2-tonne, €1-billion Gaia mission launched in late 2013 and began collecting scientific data in July 2014. From a vantage point beyond our planet, Gaia tracks Earth in its orbit around the Sun. It makes repeated measurements to estimate the distances of stars — and other celestial objects — using a technique called parallax (see ‘The parallax effect’).

As well as making its 551-gigabyte database available today, the Gaia team also released a number of scientific papers. The main goal of these was to describe quality checks the researchers did on the data and demonstrate how it can be used: the mission’s policy is to make the catalogue immediately available to the broader community, rather than reserve it for the team’s own science studies first.

Still, the Gaia papers also described a wealth of original findings, said Floor van Leeuwen, another senior Gaia scientist from Cambridge who was at the press briefing. For example, he showed how Gaia proved for the first time that certain star clusters puff up at the same time as large stars sink to their centres. “We weren’t allowed to make discoveries, but we couldn’t avoid making them,” he said.

One of those findings has implications far beyond the Milky Way. Some astronomers are especially eager to see Gaia’s measurements of certain types of variable star that are used as ‘standard candles’ of cosmology. Knowing the precise distances of stars of this type in the Milky Way makes them useful as yardsticks for measuring distances to galaxies much farther away. In particular, astronomers use standard candles to estimate how fast the Universe is expanding, but in recent years their measurement has been in apparent contradiction — or “tension”, as scientists say — with predictions based on maps of the cosmic microwave background, the afterglow of the Big Bang. A preliminary look at the Gaia data shows that the measurements of the standard candles are now more precise, Gimore said at the press briefing. But, he adds, “at face value, the tension is still there”.

Dozens of preprints are likely to appear in the next few days, Gilmore says, as teams around the world download Gaia data and run them through algorithms they have been honing for years in preparation. For example, researchers will be able to test models for how the Galaxy formed through mergers of smaller galaxies; measure the distribution of dark matter; and refine their theories for how stars evolve as they burn through their reserves of nuclear fuel.

Denis Erkal, an astronomer at the University of Surrey in Guildford, UK, and his collaborators plan to use Gaia data to weigh the Large Magellanic Cloud, the largest of the dwarf galaxies orbiting the Milky Way. They will do so by measuring tidal motions in our Galaxy’s stars that are caused by the dwarf galaxy — a bit like weighing the Moon by measuring its effects on Earth’s oceans.

Gaia had released a preliminary catalogue in 2016, but at that time it did not have enough data yet to directly measure the distances of many stars. Further data releases will contain more and more information and will enable entirely new kinds of studies (the next one is in 2020). Some researchers expect to discover tens of thousands of exoplanets by watching stars wobble under their planets’ gravitational pull — but the probe must collect several years’ more data for these motions to become apparent. Others will inspect similar wobbles in search of evidence of the passage of gravitational waves. In addition to tracking stars, the probe has monitored asteroids and will help scientists to monitor bodies in the Solar System that might look on their way to hitting might be on a collision trajectory with Earth.

A technical glitch in February temporarily sent Gaia into ‘safe mode’, but the probe is in overall good health, says project scientist Timo Prusti at ESA’s European Space Research and Technology Centre in Noordwijk, the Netherlands. If nothing breaks down and if ESA continues extending the mission, Gaia has enough fuel to keep operating until 2024, for a total of ten years, he says.