New observations of nine distant galaxies taken with the Subaru Telescope show that the swarms of smaller satellite galaxies around the main galaxies have important similarities and differences compared to the satellite galaxies around the Milky Way. This shows that the Milky Way is a somewhat normal galaxy, but not completely normal. This result is important for understanding to what extent we can apply what we know about the local environment to the rest of the Universe.
Astronomers are always trying to figure out how much of what we see
in the skies is typical, and how much is unique to the local area. Just
as the ability to study planets around other stars has given us new
insights about the planets in the Solar System, astronomers can now
observe distant galaxies in detail and compare them to what we know
about the Milky Way.
Large galaxies such as the Milky Way are
surrounded by smaller satellite galaxies. More than 50 satellite
galaxies have been detected around the Milky Way, many less than
theoretically expected. Also, the Milky Way’s satellite galaxies are
found clustered together, while predictions indicate that they should be
evenly distributed.
A group led by researchers at the National
Astronomical Observatory of Japan (NAOJ) used the Subaru Telescope to
take images of nine galaxies with masses similar to the Milky Way, each
about 50 to 80 million light-years away. In these images, the group
successfully detected 93 candidates for faint, small satellite galaxies.
The number of satellites per main galaxy varied greatly but was
comparable to the number of satellite galaxies around the Milky Way,
indicating that the Milky Way is normal in terms of its number of
satellites. Also, the satellite galaxies were evenly distributed around
the main galaxies; matching predictions but not matching what we know
about the Milky Way.
Masashi Nashimoto, a research fellow at NAOJ (currently a JSPS research
fellow at the University of Tokyo), commented: "These results are
valuable information for statistically examining various issues related
to satellite galaxies. On the other hand, some objects were not clearly
identified as satellite galaxies, and we expect to identify them by
further observations."
Satellite galaxies provide clues to how
the main galaxy formed, so improving our understanding of them helps us
to understand the evolution of galaxies in general, and the Milky Way in
particular, which created the conditions where the Earth and life could
form.
These results appeared as Nashimoto et al. "The Missing Satellite Problem outside of the Local Group. II. Statistical Properties of Satellites of Milky Way-like Galaxies" in the Astrophysical Journal on August 29, 2022.
Source: Subaru Telescope
