The National Astronomical Observatory announces the results of the "GALAXY CRUISE" project, in which the general public could participate, in a published paper.

Publication Date: October 11, 2023, 19:14

The National Astronomical Observatory of Japan (NAOJ) announced on October 10th the first research findings from its citizen astronomy project, "GALAXY CRUISE". The project combines high-resolution images from the Subaru Telescope with the high classification accuracy of citizen astronomers to reveal that various activities within galaxies increase when they collide and merge.

The research was conducted by a team led by Associate Professor Kenyu Tanaka (the "Captain" of GALAXY CRUISE) at the NAOJ Hawaii Observatory, along with citizen astronomers who participated in the project. The details of the study were published in the English academic journal "Publications of the Astronomical Society of Japan".

The aim of GALAXY CRUISE is to unravel the mysteries of the various colors and shapes of galaxies that fill the universe. The first season of the project, which lasted for two and a half years, resulted in a catalog of classification results (approximately 2 million cases) that has been made public, and the scientific analysis results have been published.

The universe is filled with galaxies of various shapes and colors, such as spiral galaxies, elliptical galaxies, and irregular galaxies. It is believed that collisions and mergers between galaxies play a significant role in this diversity. However, our observational understanding of what happens when galaxies merge has been limited, mainly because such galaxies are rare and difficult to find.

To address this, GALAXY CRUISE was launched to leverage the power of citizen astronomers to identify colliding and merging galaxies from observational data captured by the Subaru Telescope's ultra-wide-field prime focus camera, the "Hyper Suprime-Cam" (HSC). The project began its first season in November 2019, and the current research results are based on this season (the second season is currently underway).

One might imagine that citizen astronomers are individuals with knowledge equivalent to researchers, regularly observing the night sky with their own telescopes. However, to participate in GALAXY CRUISE, all you need is a PC, tablet, or smartphone with an internet connection. Knowledge for classifying galaxies can be acquired through a training course, and once you understand the morphology of galaxies, you can participate (you will receive a boarding pass and can board the GALAXY CRUISE). Approximately 10,000 people participated in the first season, which lasted about two and a half years, and over 2 million classifications were made. This is a number that could not have been achieved by researchers alone.

Associate Professor Tanaka carefully analyzed the classification results and found that the classification accuracy of citizen astronomers was very high. For example, many cases were discovered where a clear spiral structure was visible around galaxies that had been classified as elliptical galaxies in previous studies by researchers. In other words, there were many galaxies where the classification errors of researchers could be corrected, and the classification accuracy of GALAXY CRUISE significantly exceeded that of previous studies.

The galaxies that were classified as elliptical galaxies by researchers but were reclassified as spiral galaxies by citizen astronomers this time. Thanks to the high quality of the HSC images from the Subaru Telescope, it is clear that all of them have splendid spirals, and they were reclassified. (c) National Astronomical Observatory (Source: Subaru Telescope Website)

The main targets of GALAXY CRUISE, galaxies in the process of collision and merger, also apply to this. When galaxies collide and merge, the shape of the galaxy may be distorted, or characteristic shapes may appear around the galaxy. These features are often very faint and widespread, and are often overlooked. However, images utilizing the sensitivity and resolution of the Subaru Telescope have discovered faint traces of collisions and mergers in many galaxies that had not been found before.

Furthermore, by effectively using the classifications of citizen astronomers, they were also successful in finding galaxies that are particularly in the midst of intense mergers among colliding and merging galaxies. Galaxies with greatly distorted and complex shapes are rare and difficult to find, so the classification results were achieved through a strategy of mass participation by approximately 10,000 citizen astronomers.

The scientific analysis revealed that galaxies that are colliding and merging have more active star formation activity compared to galaxies that are not. Furthermore, it was shown that supermassive black holes, which are believed to exist at the center of all galaxies, also have increased activity in colliding and merging galaxies. This tendency was particularly confirmed in galaxies with intense collisions and mergers. It is speculated that various activities are triggered within the galaxy when galaxies finally merge.

The numerous galaxies in the midst of intense mergers that were newly discovered by citizen astronomers this time. All of them are galaxies with greatly distorted shapes, and the intensity of the mergers can be inferred. (c) National Astronomical Observatory (Source: Subaru Telescope Website)

In addition, the classification results of GALAXY CRUISE were made public to researchers around the world at the same time as the announcement of this paper. It is expected that the classifications by citizen astronomers, which have been recognized for their scientific value, will be used more widely and lead to new discoveries.

Japanese astronomy has been supported not only by researchers but also by the efforts of citizen astronomers, and GALAXY CRUISE can be said to be the 21st-century version of this. The second season is currently underway, so anyone with a PC, tablet, or smartphone (a larger screen PC or tablet is recommended for checking images of colliding galaxies) that can connect to the internet can become a citizen astronomer from today.

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