Gaia Mission: Five pieces of knowledge that astronomers could extract from their latest data

By Adam McMaster and Andrew Norton for The Conversation

The European Space Agency’s (ESA) Gaia mission has just released new data. The Gaia satellite was launched in 2013, with the goal of measuring the accurate positions of a billion stars. In addition to measuring the position, speed, and brightness of stars, the satellite has collected data on a variety of objects.

There are many things to excite astronomers about. Here are five of our favorite statistics that can provide the data.

1. Secrets of the past and future of our galaxy

Everything in space moves, and the stars are no exception. The latest data release contains the largest three-dimensional map of the Milky Way ever produced, showing how the stars in our galaxy travel. The above data included the movements of the stars in two dimensions: up and down and left-right (collectively known as the movements of the stars). But the latest data also shows how fast stars move away from or toward us, which we call the radial velocities of stars.

By combining radial velocity with proper motions, we can find out how fast three-dimensional stars move as they orbit the Milky Way. This means that now we not only have the best map of where the stars in the galaxy are now, but we can follow their movements forward to see how things will change and backwards to see how things were before.

This can tell us things about the history of our galaxy, such as which stars may have come from other galaxies and merged with ours in the past. Radial velocity measurements can also help us find hidden objects, such as planets and brown dwarfs (extremely faint stars with little mass), from the small oscillations they cause when they orbit a host star.

2. Details of how stars die

Gaia not only measures the stars in our own galaxy, it also measures those in the neighboring Andromeda galaxy. The data includes something called Gaps: Gaia Andromeda’s photometric survey. A photometric survey measures the brightness of stars and how they change over time. With Gaps, Gaia has measured the brightness of each star over time in the direction of the Andromeda Galaxy.

This includes 1.2 million stars. Some of them will be stars in the foreground of the Milky Way that were in the way, but they should include about the brightest 1% of stars in the Andromeda Galaxy. This will allow us to study how the largest and brightest stars in Andromeda change brightness, telling us how they evolved and where they are in their life cycles.

This could tell us more about ancient stars reaching the end of their lives, some of which could eventually produce supernovae (huge explosions).

3. The truth about the strange expansion of the universe

Quasars, the nuclei of extremely energetic galaxies on the edge of the observable universe, are the brightest objects in the universe and the most distant objects we can see. And the new data includes measurements of 1.1 million of them. Quasars contain supermassive black holes that are trapped in a violent feeding frenzy. In addition to these confirmed quasars, Gaia has found another 6.6 million candidates for quasars.

This can greatly increase the number of known quasars, and this could be very important because they allow us to measure the distance to the farthest ends of the universe. This in turn allows us to measure how quickly the universe expands. Being able to measure it more accurately is important, because we have two contradictory measures of expansion and we don’t know which one is right: the problem is called “Hubble tension.”

4. How many asteroids have moons

Not everything Gaia studies is that far from home. The data contains 158,000 objects from our own Solar System. This includes new measurements of 156,000 known asteroids, which tell us exactly which paths they follow as they orbit the Sun.

Not only that, but Gaia’s team has shown that they are able to find moons orbiting asteroids, based on how the moons cause asteroids to oscillate. A few hundred asteroids with moons are already known, but Gaia can find asteroid moons even when the moon is too small to be seen directly. It can also measure the positions of asteroids so accurately that it sees the slight oscillation in position caused by the gravity of the moon. That says the latest data contains at least one such new moon, but there could be many more.

Gathering better data about asteroids can explain the chaos of the first solar system when the larger planets launched smaller planets and asteroids into new orbits around the Sun and led to the current solar system.

5. How stars form and operate

Our Sun is a solitary star, but many stars have companions, orbiting each other around a shared center. The new data contains the first taste of Gaia’s catalog of these multi-star systems. This is an initial list, with the full catalog coming in a later data release, but it already contains 813,000 binary (two star) systems.

Binary stars can tell us a lot about how they work and how they form. This is especially true for so-called eclipsing binary systems. These are binary systems that are randomly aligned so that the stars pass in front of each other from our point of view. Eclipse binaries are special because we can measure them to determine all the physical properties of the system, such as the masses and sizes of stars, and how far apart they are. This allows us to learn much more than we could study individual stars.

This new data will excite astrophysicists around the world, and we can’t wait to get hooked on what we can find. We may have some of these answers in the coming months, while others may take longer.

The authors are from Open University, UK

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