Spiral galaxies have distinct internal structures, including a stellar bulge, disk, and spiral arms. It is unknown when in cosmic history these structures formed.
While analyzing data obtained from ALMA, scientists from the Natural Institutes of Natural Sciences discovered an ancient galaxy that has a spiral morphology by only 1.4 billion years after the Big Bang. As scientists noted, this is the most ancient galaxy of its kind ever observed.
Takafumi Tsukui, a graduate student at SOKENDAI and the lead author of the research paper, said, “I was excited because I had never seen such clear evidence of a rotating disk, spiral structure, and centralized mass structure in a distant galaxy in any previous literature. The quality of the ALMA data was so good that I was able to see so much detail that I thought it was a nearby galaxy.”
Our home galaxy, i.e., Milky Way, is a spiral galaxy. Almost 70% of the galaxies in the Universe are spiral. Previous studies have shown that the proportion of spiral galaxies decreases rapidly as we look back through the history of the Universe.
So, when were the spiral galaxies formed?
Scientists noticed a galaxy called BRI 1335-0417 in the ALMA Science Archive. Existed almost 12.4 billion years ago, the galaxy hosted a large amount of dust, obscuring the starlight. This makes it challenging to study this galaxy in detail with visible light.
Because ALMA can detect radio emissions from carbon ions in the galaxy, scientists can investigate what is going on in the galaxy.
They found that the spiral structure of the galaxy extending 15,000 light-years from its center. It is one-third of the size of the Milky Way Galaxy and has a total mass of stars. The interstellar matter in BRI 1335-0417 is roughly equal to that of the Milky Way.
Tsukui said, “As BRI 1335-0417 is a very distant object, we might not be able to see the true edge of the galaxy in this observation. For a galaxy that existed in the early Universe, BRI 1335-0417 was a giant.”
Here, a question arises: how was this distinct spiral structure formed in only 1.4 billion years after the Big Bang?
To figure out the answer, scientists considered several possible causes and suggested that it could be due to an interaction with a small galaxy.
As the galaxy is actively forming stars, scientists found that the gas in the outer part of the galaxy is gravitationally unstable, which is conducive to star formation.
Scientists noted, “BRI 1335-0417 will play an important role in the study of galaxy shape evolution over the long history of the Universe.”
Iguchi said, “Our Solar System is located in one of the spiral arms of the Milky Way. Tracing the roots of spiral structure will provide us with clues to the environment in which the Solar System was born. I hope that this research will further advance our understanding of the formation history of galaxies.”
- Takafumi Tsukui et al. Spiral morphology in an intensely star-forming disk galaxy more than 12 billion years ago. DOI: 10.1126/science.abe9680