Gaia: a new era for astronomy

Gai­­a second data release was published on the 25th of April 2018. Since then, astronomers at iREx and from all around the world have been hard at work, intently trying to uncover the secrets hidden in this gold mine of information. Completely unparalleled in quality and quantity, this data set has done nothing less than opening the door to a new era of astronomy.

The Gaia mission

The Gaia space telescope is a cutting-edge instrument that was launched in December 2013 by the European Space Agency (ESA). The scientific objectives of the missions are numerous : better understanding the  formation and evolution of our galaxy, studying the stars that it encompasses, cataloging and characterizing asteroids and comets in our Solar System, and also finding thousands of exoplanets around nearby stars using astrometry. To accomplish these science goals, Gaia measures the position, velocity, and brightness of about 1.7 billion stars, about 10 000 times more than its predecessor Hipparcos, another european telescope that operated in the early 90s.

The second release of data

The Gaia data is published in different releases and is accessible to everyone. The first release, “DR1” (for data release 1), has already allowed for many scientific advancements (see for example the projects led by iREx researchers Neil Cook in 2017 and Jonathan Gagné in 2018) since its release in September 2016.

Map of the Milky Way produced from measurements of approximately 1.7 billion stars. (Credit: ESA/Gaia/DPAC)

With the second data release (“DR”) having been made public in April 2018, astronomers now have access to brightness and position measurements of all the 1.7 billion Gaia targets. This sample represents about 1% of all the stars in our galaxy and has thus permitted a three-dimensional map of the Milky Way of an unprecedented precision to be generated. Additionally, distances and proper motions (apparent displacements in the sky) of most sources (1.3 billion), as well as radial velocities (that is, velocities in our direction) of 7 millions of the brightest stars are now available.

Jonathan Gagné, a researcher that will be joining iREx in July 2018 after a post-doctoral position at the Carnegie Institution for Science in Washington DC, is particularly enthusiastic about this new data set. « This is the first time in my career that I don’t have to wait for telescope time to get the data I need for my projects. There is so much data here that I could work day and night for years just analyzing it! », he said in an interview at Les années lumière, on Radio-Canada (in French).

He and Lison Malo, another iREx researcher, have both spent their PhDs identifying stars, brown dwarfs, and even less massive objects that are part of nearby young star associations. Being still warm, and thus brighter, these close, young stars and brown dwarfs are ideal targets for finding orbiting planets using the imaging method. « Before, we had to estimate the velocity and distance of a candidate member, or obtain telescope observations to measure these quantities one by one. Now, the Gaia catalog offers these measurements for millions of targets. It’s unprecedented! », explains Malo.

The very day of the data publication, April 25 2018, Jonathan Gagné was part of a group of sixty or so astrophysicists at the Center for Computational Astrophysics of the Flatiron Institute, in New York. They went to work as soon as the data was made available at 6 in the morning. Gagné even submitted a short article that same day: « In 2014 we announced the discovery of J1207-3900, a very faint new member of the young TW Hya association, » explains Gagné. « Gaia has now precisely measured its distance and confirmed that it indeed belongs to this 5-10 million year old star association. We have thus learnt that we are indeed dealing with a “planemo”, an object that has the mass of a planet but that is isolated in space without a host star. »

In another article published a few weeks later, Gagné and his colleagues announced the identification of 900 new members in 27 young associations, many of these being very low-mass and hard to identify members. “With Gaia it is possible that we find even more new members of known associations, and also that we find new associations!” adds Gagné.

Étienne Artigau, another iREx researcher, also shares the enthusiasm of his colleagues. « The first thing I did when the data was released was to go check the distances of all my favorite objects, namely the stars and brown dwarfs that I studied over the course of my career, » he says. « I was pleasantly able to confirm many of the results that I had published over the years! For example, our colleague Lison Malo had estimated a distance between 140 and 173 light years for the star GU Psc, around which we detected an exoplanet in 2014. Gaia measured 155 light years. The allowed us to confirm that it indeed belongs to the young association AB Doradus, which allows us to constrain the system’s age and thus be even more sure that the companion GU Psc b is indeed a planet! »

Many projects made possible with the second data release

The identification of young association members is far from being the only scientific objective that will profit from the Gaia data release. Here are some other example of projects led by iREx members:

• Mariya Krasteva, a Trottier summer intern, will use the proper motions catalogued by Gaia to create a tool  to retrieve information for stars around which the TESS spacecraft will find exoplanets. This will accelerate the planet confirmation and analysis process.
• Lauren Weiss, a postdoctoral Trottier researcher, is also part of the California Kepler Survey (CKS) team. Since the Gaia data release, her team has published an update on their catalogue of the radii of the stars hosting the planets detected by the Kepler space telescope. This then allows the size of these planets to be known with an unprecedented accuracy. Weiss particularly focuses on planetary systems containing more than one known planet. The new data allows her to see in even more details if these multi-planet systems show any discrepancies to single planet systems.

In the future…

We are still awaiting two more data releases before the nominal end of the Gaia mission in 2022. The third release, expected for 2020, will yield more precisely the position and the brightness of the 1.7 billion stars, and the velocity for many more stars than in DR2, while the fourth and last release will make possible the identification of exoplanets.

« The data from Gaia will have a profound impact on astrophysics as we know it for decades to come » confirms Jonathan Gagné. « In addition to all the results we expect to get from this incredible instrument, we are certain that there are also many surprises waiting for us. »

More information

• Gaia measures the distance to stars using the parallax method, which consists of measuring the position of a star relative to very distant background stars at different moments in Earth’s orbit around the Sun.
• Gaia also measures how fast, and in which direction, a star is moving. It does this by measuring a star’s proper motion, meaning its apparent motion in the sky, and by measuring its radial velocity, meaning its speed in the direction of the Earth.

The parallax method. The position of the stars against the background is different from one time of the year to the other. This change allows to measure the parallax, the angle between the Earth, the star and the Sun. It’s then simple trigonometry to compute the distance to the star, since the distance between the Earth and the Sun is a well-known quantity. (Credit: ESA/ATG medialab)

Proper motion (in red) and radial velocity (in blue) allow to measure the amplitude and direction of the real velocity of the star (in purple). (Credit: ESA/ATG medialab)