New Gaia Data to Reveal Milky Way’s Dark Past and Future

A space telescope observing stars in the Milky Way as they appear today reveals what happened to the galaxy when it was just a few billion years old, and an upcoming data release will help astronomers to peek into an even more distant past.

The European Space Agency Mission Gaia is not a household name like the The Hubble Space Telescope or the James Webb Space Telescope. However, the mission currently produces the most scientific articles and, as Milky Way researchers would tell you, has enabled unprecedented advances in our understanding of the galaxy’s history.

Gaia works differently from Webb or Hubble. Instead of watching the universe one fascinating distant object at a time, Gaia scans the entire sky again and again. The flying saucer-shaped telescope, nestled in Point of Lagrange 2 some 930,000 miles (1.5 million kilometers) from Earth, observes 2 billion of the brightest stars in the sky, its view free from the distorting effects of earth’s atmosphere that plague observations from ground-based telescopes.

Related: 4 big Milky Way mysteries the next Gaia mission data dump could solve

Unlike Hubble and Webb, Gaia isn’t focused on capturing impressive images that reveal every detail of those distant stars and galaxies. Instead, the probe focuses on a few basic parameters: the distance of stars to Earththe speed at which stars move through space and the direction of their motion as seen on the sky plane and in three dimensions.

Because objects in space follow the laws of physics, scientists can model the trajectories of these stars billions of years in the past and in the future, revealing the events that shaped the evolution of the galaxy. A discipline known as galactic archeology has grown tremendously since the launch of Gaia in 2013, and the new data release coming Monday June 13 is expected to boost research.

“We are still trying to unravel the details of the origins of the Milky Way,” Anthony Brown, an astronomer at Leiden University in the Netherlands and chairman of the Gaia Data Processing and Analysis Consortium, told “With the new version, we should be able to do it even better, because we get new data.”

Trajectories of stars in the Milky Way over the next 400,000 years according to measurements by the European Gaia mission.

Trajectories of stars in the Milky Way over the next 400,000 years according to measurements by the European Gaia mission. (Image credit: ESA/Gaia/DPAC)

know the stars

These new data contain what astronomers call astrophysical parameters. Derived from the light spectra of observed stars (essentially the fingerprints of how stars absorb light), astrophysical parameters reveal the ages, masses, brightness levels and, in some cases, detailed chemical compositions of observed stars. .

“You really get to know the stars,” ESA Gaia project scientist Jos de Bruijne told “It’s like having a group of anonymous people and now you meet each one of them. You get to know their names, their ages and where they come from.”

The cluster of stars that astronomers are “meeting” thanks to the June 13 data release consists of half a billion individual objects, or a quarter of the stars observed by Gaia. This information will help astronomers narrow down the order of events that shaped the Milky Way and “really unravel the story of its formation,” Brown added.

Dwarf galaxies orbiting the Milky Way.

The Milky Way devours small galaxies in its orbit. (Image credit: ESA/Gaia/DPAC)

What we already know

Astronomers believe that the Milky Way began to form only about 800 million years after the big Bang and went through an intense formative period of 1 to 2 billion years, Brown said. This formative period involved numerous collisions with other galaxies, which gradually built the Milky Way into what we see today: a huge spiral galaxy encompassing 200 billion stars. (Gaia only sees about 1%.)

In previously released Gaia data, the researchers found imprints of these early collisions in the form of waves that still ripple through the galaxy, affecting the motion of stars. The most important of these collisions took place with a galaxy called Gaia Enceladus. This galaxy was about four times smaller than the Milky Way when the two crashed together about 10 billion years ago. The collision, data from Gaia revealed, gave rise to the Milky Way’s halo, the finely scattered sphere of stars enveloping the galaxy’s much more massive disk.

“At the moment, we believe that [the collision with Gaia Enceladus] was the last major merger the Milky Way experienced,” Brown said.

The Milky Way consists of a central bud, a thin disk of stars embedded in a thicker disk, which is surrounded by a stellar halo.

(Image credit: ESA)

Trace the “smallest building blocks”

Among the astronomers awaiting the release of the June 13 data is Eduardo Balbinot, a postdoctoral researcher in astrophysics at the University of Groningen in the Netherlands. Balbinot is interested in smaller collisions with what he calls the “smallest building blocks” of the galaxy: globular clustersancient star clusters devoured by the Milky Way over the eternities.

“[The globular clusters] are special, because when they dissolve in these accretion events, they are torn apart,” Balbinot said. “But they live on as cohesive clusters of stars in the sky like what we call stellar streams.”

These stellar streams have been notoriously difficult to detect, but Balbinot believes the new data from Gaia will usher in a breakthrough in this endeavor.

“There will be an additional speed component [in the new data set], the so-called radial velocity – how fast the stars are moving towards or away from us,” Balbinot said. “Gaia has measured some before, but the new sample will be 10 times larger. It’s bigger than anything before.”

In these star movements, astronomers will be able to distinguish groups of stars that move through the galaxy in synchronization. By combining this information with data on the chemical compositions of stars (stars that have arrived from other galaxies have distinct chemical profiles), astronomers will be able to peek into the galaxy’s past like never before.

“That’s one of the exciting things you can do with Gaia data,” Balbinot said. “You can find these clusters of stars that move similarly and basically reconstruct where they came from and what building block got them into the Milky Way. Then you can finally answer the question of how the Milky Way milky formed.”

What’s happening at the edge of the galaxy

Balbinot hopes the new data will allow astronomers to search for remnants of globular clusters much further from Earth than previously possible, on the very outskirts of the galaxy, where the galactic halo meets intergalactic space. .

“The new dataset will contain a small subset of data on variable stars, which are very bright, and because they are so bright, we can see them all the way to the edge of the Milky Way,” Balbinot said. . “These are essentially the most distant stars that we will ever be able to detect in our Milky Way galaxy. And that’s really exciting, because it really is uncharted territory.”

Balbinot said variable stars could reveal remnants of ancient collisions with globular clusters scattered across the galactic halo, in the form of spherical “shells.” Analysis of these shells can tell a lot about the anatomy of the events that gave rise to them billions of years ago.

“There are a lot of things you can deduce if you measure the distance of these shells,” Balbinot said. “You can reconstruct in detail how these accretion events happened, what was the orbit of the satellite [galaxy] who fell into the Milky Way and so on.”

To look forward

The last billion years have been quite peaceful for the Milky Way. The galaxy produced stars and watched them die at a steady rate while absorbing aftershocks from previous tremors.

But things will get tough again in the future. In fact, astronomers are already watching the approach of the next galactic collision: the smash-up with two dwarf galaxies orbiting the Milky Way called the Large Magellanic Cloud and the Small Magellanic Cloud.

“The Magellanic Clouds orbited the Milky Way quite recently, within the last billion years,” Brown said. “We already see them influencing the Milky Way’s gravitational force field, and if we reconstruct the past really well, we might be able to bring it all together and see when the clouds merge with the Milky Way. “

Despite the violent childhood of the Milky Way, the most cataclysmic event is yet to come: the collision with the Andromeda Galaxythe nearest large galactic neighbor.

Andromeda, currently over 2.5 million Light years from Earth, is one of the celestial objects observed by Gaia. The new data release will provide new insight into the encounter that will shake the two galaxies about 4.5 billion years from now.

With Gaia, “you can actually measure the motion of the Andromeda galaxy through line of sight pretty well,” Brown said. “It gives you more constraints on the long-term future of both galaxies.”

The Sun will be near the end of its life when its parent galaxy encounters Andromeda, so it is unlikely that humanity is still around to witness the galactic crash. The Earth, for some, will have long been uninhabitable, scorched by the increasingly hot sun.

Still, unraveling the galaxy’s past and future is a fascinating project, one that should continue for several years as Gaia produces more and more data.

The telescope will retire in 2025 when it runs out of fuel. But he’s certainly not past his prime, De Bruijne said. The consortium of 400 researchers that processes the Gaia data is further refining the algorithms used to analyze the vast amounts of measurements produced by the telescope. These algorithms allow astronomers to find finer and finer details and new types of information in the vast dataset. The June 13 release will contain, for example, the largest ever published catalog of chemical compositions of asteroids in the solar system and the largest dataset of binary star systems. Gaia’s next data release should already reveal thousands of new exoplanetsDe Bruijne said.

Follow Tereza Pultarova on Twitter @TerezaPultarova. Follow us on Twitter @Spacedotcom and on Facebook.

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