Astronomers were hit Thursday (Dec. 3) with a huge wave of data from the European Space Agency's Gaia space observatory.
Those researchers can now explore the best-yet map of the Milky Way, with detailed information on the positions, distances and motion of 1.8 billion cosmic objects, to help us better understand our place in the universe.
"Gaia data is like a tsunami rolling through astrophysics," said Martin Barstow, head of the physics and astronomy department at the University of Leicester, who is part of Gaia's data processing team. He was speaking at a virtual news conference held Thursday, at which another Gaia researcher, Giorgia Busso of the Leiden Observatory in the Netherlands, also told reporters that this data has produced "a revolution" in many fields of astrophysics, from the study of galactic dynamics like stellar evolution to the study of nearby objects like asteroids in the solar system.
Gaia launched in December 2013 to map the galaxy in unprecedented detail. The $1 billion spacecraft orbits the Lagrange-2, or L2, point, a spot about 1 million miles (1.5 million kilometers) away from Earth, where the gravitational forces between our planet and the sun are balanced and the view of the sky is unobstructed. Gaia can measure about 100,000 stars each minute, or 850 million objects each day, and can scan the whole sky about once every two months.
The latest trove of data improves upon the precision and scope of the two previous Gaia data sets, which were released in 2016 and 2018. For example, compared to the 2018 data, which included measurements for 1.7 billion objects, the 2020 data improves by a factor of two the accuracy of the data points for proper motion, or the apparent change in the position of a star as viewed from our solar system.
"It really gives us an insight into how the Milky Way lives," Nicholas Walton, an astronomer at the University of Cambridge who is part of Gaia's science team, said at the same science and news conference. "We're talking about billions of stars, which really gives us the ability to probe at a meaningful level the whole population of the Milky Way, similar to what you'd want to do with studying people."
Walton said the cosmic census would be like having trackers on every person in the U.K. to map their location and monitor their health. "If everyone's got a tracker, we could tell you if they're sweating or not. It's a bit like that with the stars here: We can tell you which ones are sweating, which ones are active, which ones are dormant, which ones are going to die, which ones are going to explode."
Data from Gaia has already been used across a wide range of applications over the past four years. The mission has helped researchers find the corpse of a galaxy that the Milky Way cannibalized 10 billion years ago, spot 20 hypervelocity stars unexpectedly zooming toward the galactic center, and identify about 1,000 nearby stars where hypothetical extraterrestrials would be able to see signs of life on Earth.
Closer to home, the spacecraft has allowed scientists to find previously unknown asteroids, and its precise data even allowed NASA to make a crucial, last-minute adjustment to the path of its New Horizons probe in 2018 to successfully swing past the icy rock Arrokoth, the most distant and primitive object in the solar system ever visited by a spacecraft.
So far, some 1,600 studies have been published based on Gaia data, Barstow said. More will surely result from the newly released material, now available on ESA's website, and by the time the briefing for scientists and reporters ended, Walton said he expected a lot of scientists were already poring over it: "I think a lot of astronomers would have left this broadcast to go work on the data."
Some of the new Gaia data has already been used to make discoveries. One group of researchers led by scientists at the Dresden University of Technology measured how our solar system is accelerating inside the Milky Way, using as reference points Gaia's 1.6 million newly observed quasars, which are so far away they appear fixed in space, like galactic lighthouses.
The solar system was measured to be very slightly accelerating, as predicted by theorists, toward the galactic center. Busso said this barely perceptible acceleration only became observable in this newly released Gaia data because "the precision of the measurements increased hugely."
These super precise tests of the way masses are distributed and accelerated are essential for "probing the limits of fundamental physics," Gerry Gilmore, an astronomer at the University of Cambridge and a Gaia scientist, said during the event. Such measurements might help scientists understand the nature of the dark matter that we know is lurking throughout the universe.
"Even our own sun is moving so fast that our whole Milky Way would fly apart if it wasn't held together by the dark matter, and we've got no idea what the dark matter is," Gilmore said. "The hope is that by continuing experiments along the line that we're doing — and making them more precise, and doing them on different scales — we'll be able to see if there are different types of dark matter."
The third Gaia data set was set to be released in 2022, but the mission scientists decided to release preliminary data now so astronomers could use it sooner, with at least two more data sets to be released in the coming years. The spacecraft will operate until at least 2022, but its mission may be extended until 2025.
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