According to a new study, galaxies from the early Universe are more like the Milky Way than previously thought. This turns the narrative on structure formation in the early Universe.
Image Credit: The University of Manchester
By making use of the James Webb Space Telescope (JWST), an international research group, including those at The University of Manchester and the University of Victoria in Canada, have found that galaxies like the Milky Way dominate the universe and are amazingly common.
These galaxies have origins extending deep into the history of the Universe, with many of them taking shape a staggering 10 billion years ago or even earlier.
The Milky Way is a normal “disk” galaxy, which has a shape similar to a pancake or compact disk, rotating about its center and consisting of spiral arms. Such galaxies are believed to be the most common in the nearby Universe and may be the kind where life could develop.
Astronomers previously thought that such galaxies were too fragile to exist in the early Universe, where galaxy mergers were highly common.
The breakthrough, recently reported in the Astrophysical Journal, determines that these “disk” galaxies are ten times more common compared to what astronomers believed based on earlier observations made with the Hubble Space Telescope.
Using the Hubble Space Telescope we thought that disk galaxies were almost non-existent until the Universe was about six billion years old, these new JWST results push the time these Milky Way-like galaxies form to almost the beginning of the Universe.
Christopher Conselice, Professor, Extragalactic Astronomy, The University of Manchester
The study entirely overturns the current knowledge of how the Universe progresses, and the researchers say that new concepts must be taken into account.
For over 30 years it was thought that these disk galaxies were rare in the early Universe due to the common violent encounters that galaxies undergo. The fact that JWST finds so many is another sign of the power of this instrument and that the structures of galaxies form earlier in the Universe, much earlier in fact than anyone had anticipated.
Leonardo Ferreira, Study Lead Author, The University of Victoria
It was once believed that disk galaxies like the Milky Way were comparatively unusual in cosmic history and that they developed once the Universe was middle-aged.
Previously, astronomers who made use of the Hubble Space Telescope assumed that galaxies consisted of mostly irregular and strange structures that matched mergers. However, the excellent capabilities of JWST now enable one to see the true structure of such galaxies.
The scientists state that this is yet one more sign that “structure” in the Universe develops much quicker than anticipated.
These JWST results show that disk galaxies like our own Milky Way, are the most common type of galaxy in the Universe. This implies that most stars exist and form within these galaxies which is changing our complete understanding of how galaxy formation occurs. These results also suggest important questions about dark matter in the early Universe which we know very little about.
Christopher Conselice, Professor, Extragalactic Astronomy, The University of Manchester
Conselice added, “Based on our results astronomers must rethink our understanding of the formation of the first galaxies and how galaxy evolution occurred over the past 10 billion years.”
Journal Reference
Ferreira, L., et al. (2023) The JWST Hubble Sequence: The Rest-frame Optical Evolution of Galaxy Structure at 1.5 < z < 6.5. The Astrophysical Journal. doi.org/10.3847/1538-4357/acec76.