The Milky Way is our home galaxy and the only known place in the universe –so far– where life exists. There are approximately 100 billion stars in our Milky Way galaxy and hundreds of billions of estimated planets. Many of them could even support life as we know it. To date, we have confirmed just over 5,000 alien worlds, while more than 8,000 are awaiting confirmation.
While we continue exploring our galaxy, it is important to search for other galaxies and see what they are like. Are distant galaxies similar to the Milky Way, and if they are, how so? Is their shape similar to that of our own galaxy? These are very important questions scientists need to know because answering some of them could lead us to the discovery of solar systems that could host planets like the Earth.
Comparing the Milky Way
Nine distant galaxies observed with the Subaru Telescope suggest that the Milky Way is a fairly normal galaxy but still kind of out of place. Researchers found that the satellite galaxies that orbit the main galaxies share many similarities but also differ from those that orbit the Milky Way.
Our understanding of the local environment can be applied to the rest of the universe, which is what makes this result valuable. Observations of the sky are always being analyzed by astronomers to determine what is typical and what is unique to the region. Scientists can now examine distant galaxies in detail and compare them to what we know about our Milky Way, just as the ability to study planets around other stars has provided insight into the planets of the Solar System.
There are smaller satellite galaxies surrounding large galaxies like the Milky Way. The Milky Way has been found to be surrounded by approximately 50 satellite galaxies, far fewer than theoretically predicted. The satellite galaxies of the Milky Way are also clustered together, despite predictions that they should be distributed evenly.
Our Galaxy is a bit odd
Using the Subaru Telescope, researchers from the Japanese National Astronomical Observatory (NAOJ) surveyed nine galaxies between 50 and 80 million light-years away that have masses similar to the Milky Way. Ninety-three candidate satellite galaxies were detected in these images. Despite wide variation in satellite numbers, the Milky Way was comparable to other satellite galaxies in terms of satellite number, indicating normal satellite density for the Milky Way. Satellite galaxies were evenly distributed around the main galaxies; this was in line with predictions but not with what we know about the Milky Way.
As the researchers contend in their study, despite the significant differences in luminosity functions between host galaxies and satellite galaxies, satellite galaxies have similar luminosity functions to Milky Way satellites. Satellites tend to be more numerous on hosts with more mass. Several of the physical properties of the satellites are also similar to those of the Milky Way satellites, such as their size-luminosity relation. There is a difference in the spatial distribution of satellite galaxies; those outside of the Local Group show no signs of concentration or alignment, while those around the Milky Way exhibit a prominent alignment.
In a statement, Masashi Nashimoto, a NAOJ researcher (and current JSPS researcher at the University of Tokyo), commented: “These results provide valuable information that can be used to analyze satellite galaxies statistically.” Nevertheless, some objects were unclearly identified as satellite galaxies, so we hope to identify them through further observations.” Developing a better understanding of satellite galaxies will help us learn more about the evolution of galaxies, especially of the Milky Way, the galaxy that produced Earth and life.
The study detailing the discovery was published in the Astrophysical Journal.
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