Gaia continues the search for the ultimate celestial map

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Work: Gaia is providing fundamental insights into the nature of the Milky Way

The European Gaia telescope has released its latest batch of data as it seeks to gather the largest catalog of light sources in the sky.

It’s becoming a discovery machine like no other.

Distant, bright stars, asteroids and galaxies – anything that can be visibly located is having its vital statistics measured by the observatory.

Gaia has already mapped the positions of nearly two billion objects. Now, he can reveal more about his makeup.

“Essentially, previously, we could say very accurately where they are; now we can tell what they are,” Professor Nick Walton, from the University of Cambridge and a member of the Gaia science team, told BBC News.

The European Space Agency (ESA) Gaia satellite was launched in 2013 and placed one million miles from Earth.

It looks a bit like a spinning top hat. And as it spins, the telescope uses its British-built billion-pixel camera to track everything that shines or moves – with surprising accuracy.

This is especially important when trying to measure distances to objects, which Gaia achieves by tracking how these targets oscillate slightly across the sky as they circle the Sun – an elegant form of trigonometry that has now been practiced on 1.8 billion stars, or very close to, our Milky Way galaxy.

Calculating distances to stars

Calculating distances to stars

  • As the Earth revolves around the Sun, relatively close stars appear to move against “fixed” stars that are even further away.

  • Since we know the Sun-Earth distance, we can use the parallax angle to calculate the distance to the target star

  • But these angles are very small — less than an arcsecond for the closest stars, or 0.05% of the diameter of the full moon.

  • Gaia is making repeat observations to reduce measurement errors by up to seven micro-arcseconds for the brightest stars.

  • Parallaxes are used to anchor other more indirect techniques in the ‘ladder’ deployed to measure the farthest distances.

In the previous version of data, in December 2020, Gaia also revealed basic brightness and color information for these stars.

The new data dump also reveals spectroscopy information.

Spectroscopy cuts the light coming from stars into its constituent colors to reveal the chemistry, temperature, mass, age and velocity of the targets under study.

And for an important subset of stars — about 33 million — it allowed Gaia’s scientists to determine how quickly these objects are approaching or moving away from Earth.

element map

Elements in stars: The color indicates stellar metallicity. Redder stars are richer in “metals”

Combined with its previously established motion across the sky, this means that we now have its full three-dimensional behavior.

This information will give researchers even sharper insights into how the Milky Way is structured and evolving – from the past to the future.

Gaia data transport now includes:

  • two billion light sources – mostly stars, but also many Solar System objects and some beyond the Milky Way

  • spectroscopic detail revealing temperature, chemistry, mass and age for hundreds of millions of objects

  • 1.9 million quasars – distant galaxies where a voracious central black hole is fueling light emission

  • 156,000 asteroids – critical to understanding their origin and possibility of them passing close to Earth

And with some of these 3D stars also mapped into the nearby Andromeda Galaxy, we should have a better idea of ​​how and precisely when their mass will merge with the Milky Way – something to be expected in the next billions of years.

One of the most surprising findings of the new data is the recognition that Gaia can do so-called asteroseismology. This is the study of the subtle surface resonances of stars, which allow scientists to extract information such as a star’s size and age.

“Earthquakes teach us a lot about stars, especially their inner workings. Gaia is opening a gold mine for asteroseismology of massive stars,” said Professor Conny Aerts, from KU Leuven, Belgium.

radial speeds

Gaia can see stars moving away from us (light areas) and towards us (dark areas)

Whenever Gaia releases its latest dataset (and this is the third full release), it is immediately explored by astronomy groups around the world.

Some of these teams have academic papers ready for publication and only need Gaia numbers to complete their projects.

For competing groups, it will be a race to see who can post first.

Hot topics will include the search for high-speed stars, which move at hundreds of kilometers per second.

“The most likely scenario for how these stars are getting such high speeds is that they must be close to our galactic center, which has the physics to produce these accelerations,” said Esa’s Gaia project scientist Timo Prusti.

“Until now, these stars have been more like candidates, because Gaia’s accuracy wasn’t enough [to fully understand them]but I’m sure astronomers will be ready with their queries to attack the new Gaia data.”

Other hot topics ready to be explored include whether stars are enriched in elements heavier than hydrogen and helium, or depleted.

Low “metallicity” stars are the most fascinating because they are likely very old, perhaps in the first group that came together to form the Milky Way.

Dust in the Milky Way

Mapping dust: The galactic plane is the dustiest (black-red); less dust above and below (blue)

The Gaia telescope mission may have launched just over eight years ago, but Monday’s data release represents only the first 34 months of its science operations.

Another five years of collected data still needs to be fully processed.

And with the expectation that Gaia will continue scouring the sky until 2025, it could be the end of the decade or even the early 2030s before all of its information is placed in the public domain.

“What do you get out of that extra time? Well, it takes away the uncertainty. But the main advantage is increasing your sensitivity to things that are changing,” Professor Gerry Gilmore, from the University of Cambridge, told BBC News.

“In particular, this is true for the oscillations of stars that tell us that there are planets moving around them.

“If you only have a year’s worth of data, you can only find planets very, very close to their stars.

“But after 10 years of observations, you will find planets far from their parent star, actually families of planets.”

By the end of its mission, Gaia could have identified tens of thousands of planets in the Milky Way.

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