This isn’t a photograph of the Milky Method. It’s the map of 1.eight billion stars from Gaia’s largest new information launch


In 2013, the European Space Agency (ESA) launched the Gaia mission in space, a next-generation observatory that will collect data on the positions, distances and proper movements of stars over the next five years. The resulting data will be used to create the largest 3D space catalog ever, with a total of 1 billion stars, planets, comets, asteroids, quasars and other celestial objects.

Since the mission began, ESA has released three early releases of Gaia data, each of which has resulted in new research and more detailed maps of our galaxy. Based on the third version of mission data, known as Early Data Release 3 (Gaia EDR3), astronomers have created a map of the entire sky that includes updated data on celestial objects and manages to capture the overall brightness and color of stars in our galaxy.

The EDR3 was published on December 3, 2020 and contains data on the position and brightness of more than 1.8 billion stars, the parallax and proper motion of almost 1.5 billion stars, and the color of more than 1.5 billion stars. It also contains data on more than 1.6 million extra-galactic light sources, including stars, globular clusters, and more distant galaxies.

Density map of the galaxy based on EDR3 with no additional color. Photo credit: ESA / Gaia / DPAC / A. Moitinho and M. Barros

New cards

Compared to the previous version (Gaia DR2), which was released in April 2018, this means an increase of more than 100 million sources. In addition, the latest version included improvements in general accuracy and precision measurements. With this updated data, astronomers were able to create a map that shows not only the brightness but also the density of our galaxy.

While the lighter regions correspond to denser concentrations of bright stars, the darker regions are parts of the sky in which there are fewer and weaker stars. All over the galactic plane are dark spots created by foreground clouds of interstellar gas and dust that absorb light from more distant stars. The bright horizontal structure corresponds to the flattened disk of the Milky Way (also known as the plane of the galaxy) viewed from the edge.

Many of them are clouds that hide star nurseries, diffuse nebulae in the interstellar medium in which new stars are born. Across the galactic plane there are regions of dark spots that correspond to foreground clouds of interstellar gas and dust that absorb light from stars further away. And of course there is the bright “bulge” in the middle, the dense concentration of stars and gas that represents the galactic center.

Then there are the many spherical and open clusters that appear as bright spots on the picture, some of which are galaxies beyond our own. The two bright objects at the bottom right of the image are the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), the two dwarf galaxies that orbit the Milky Way (and are expected to merge with it in a few billion years). .

The color of the stars was reproduced by combining the total amount of light collected by Gaia with all of the blue and red light recorded from each patch of the sky. This is another improvement that the EDR3 offers, namely the presence of color information for around 1.5 billion sources (200 million more than DR2).

Galactic collisions

Another breakthrough from this latest data release was the way astronomers were able to track populations of older and younger stars all the way to the galactic anti-center (the extreme edge of the galaxy). This enabled astronomers to see how previous mergers affected the structure of the Milky Way disk and create computer models that predicted how they would get larger over time.

The data showed that in the outer regions of the disk there is a slow moving component of stars above the plane moving down and a fast moving component below the plane moving up. This pattern took astronomers completely by surprise, and in the recent past has reinforced the case for a near-collision between the Milky Way and Sagittarius’ dwarf galaxy.

This dwarf galaxy, which contains tens of millions of stars, is located about 70,000 light-years from Earth and orbits the Milky Way around its poles. This satellite galaxy is currently being cannibalized by the Milky Way, a process that has brought it close to our galaxy a number of times in the past. With each pass, the gravitational influence of this galaxy was sufficient to disturb some stars in the disk of our galaxy.

Gaia’s star movement for the next 400,000 years. Photo credits: ESA / Gaia / DPAC, CC BY-SA 3.0 IGO./A. Brown, S. Jordan, T. Roegiers, X. Luria, E. Masana, T. Prusti, and A. Moitinho

The ESA’s data processing and analysis consortium (DPAC), a Europe-wide team of experts and software developers, has already detected a subtle ripple in the Milky Way. They attributed this to earlier collisions between Sagittarius and the Milky Way between 300 and 900 million years ago. These latest data support this based on the movement of stars in the galaxy’s disk.

Teresa Antoja, Marie-Curie-Sk? Odowska Fellow at the Institute of Cosmos Sciences at the University of Barcelona, ​​worked with DPAC colleagues on this analysis. “The movement patterns in the disk stars are different from what we previously believed in,” she said recently in an ESA press release. “It could be a good candidate for all of these disorders, as some simulations by other authors show.”

The movement of the stars

In addition, researchers from the University of Helsinki created an animation showing the correct motions of 40,000 randomly selected stars over the next 1.6 million years. As it progresses, the stars seem to move from the left side of the galaxy and gather to the right, which is due to the movement of the solar system. Similarly, the apparent movements of quasars helped constrain the absolute motion of the solar system.

“The knowledge Gaia has acquired will affect the precision of satellite navigation in the future,” said Professor Markku Poutanen of the Finnish Geospatial Research Institute (FGI). “The satellite positions and the Earth’s orientation in space are determined in a frame of reference that is linked to the directions of the quasars. The precision and the state of the art of the reference frame are decisive for the precision in navigation. “

As Prof. Karri Muinonen from Helsinki University and a research professor at FGI explained:

“In the animation, short and long paths describe changes in the star positions with 80,000 years. The former mainly relate to distant stars, while the latter are exclusively related to the nearby stars. From time to time short distances become long and long distances become short. This is also related to the changing distances of the stars. “

“This shows the average movement of the solar system in relation to the surrounding stars. From a Finnish point of view, it is fascinating that the movement documented by Gaia coincides with the pioneering research into the movement of the solar system of Friedrich Wilhelm August Argelander (1799-1875) at the Helsinki Observatory in the 19th century. “

Argelander was a member of the Helsinki University Observatory, known at the time as the Imperial Alexander University. While was the first astronomer to calculate the movement and direction of the solar system around the center of the Milky Way. These observations were made while Argelander was at the Turku Observatory from 1827 to 1831, along with the exact positions of 560 stars.

Additional research conducted by DPAC has measured how the solar system’s motion accelerates over time. Using the observed movement of extremely distant galaxies, they estimated that the solar system was accelerating at a rate of 0.23 nm / s2 (relative to the rest of the universe), an increase of about 115 km per year.

Star count

The EDR3 data also made it possible to conduct a new census of stars known as the Gaia Catalog of Nearby Stars, which contains 331,312 objects (an estimated 92% of stars) within 326 light years of the solar system. This is the first census since the Gliese catalog of nearby stars was created in 1957. It initially contained only 915 objects, which were updated to 3,803 objects in 1991 and were limited to a distance of 82 light years.

In other words, the New Gaia census shows 100 times the number of objects four times the distance. It also provides location, motion and brightness measurements that are orders of magnitude more accurate than the Gliese catalog. How Muinonen described the data mining process:

“We are responsible for the daily calculation of the orbits for asteroids discovered by Gaia. Ground-based follow-up observations are organized based on these calculations. Before the data is published, we take part in the validation of Gaia observations of asteroid positions, brightnesses and spectra.

“Our research with Gaia data focuses on asteroid orbits, periods of rotation and polar orientations, masses, shapes, and surface structure and composition properties. When calculating the collision probabilities for near-Earth asteroids, the accuracy of reference frames plays a central role. “

As Timo Prusti, the Gaia project scientist, added:

“Gaia EDR3 is the result of an enormous effort by everyone involved in the Gaia mission. It is an extraordinarily large data set, and I look forward to the many discoveries that astronomers from around the world will make with this resource. And we’re not done yet; More great data will follow as Gaia continues to take measurements from orbit. “

These and other new discoveries are just the latest breakthroughs in data that Gaia has collected over the past seven years. EDR3 is the first of a two-part version, which will be followed by the publication of full data version 3 (DR3). Due to the pandemic, the date has been postponed, but it is currently expected to take place in the first half of 2022.

On October 1, at a meeting of ESA’s Science Program Committee (SPC), the Gaia mission was extended again – this time to December 31, 2022. Until the mid-term review and confirmation by the SPC, the mission can even use all the data it provides , it is clear that ESA wants to keep this mission going!

Further reading: ESA, ESA (2), University of Helsinki

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