Scientists Discover the Most Ancient Spiral Galaxy

Scientists studying the data acquired with the Atacama Large Millimeter/submillimeter Array (ALMA) have identified a galaxy with a spiral structure that formed just 1.4 billion years after the famous Big Bang.

Scientists Discover the Most Ancient Spiral Galaxy
ALMA image of the galaxy BRI 1335-0417 at 12.4 billion years ago. ALMA detected emissions from carbon ions in the galaxy. Spiral arms are visible on both sides of the compact, bright area in the center of the galaxy. Image Credit: ALMA (ESO/NAOJ/NRAO), T. Tsukui & S. Iguchi.

This galaxy is the most ancient of its kind to be ever visualized. This latest finding of a spiral galaxy at such an early phase offers a crucial clue to solving the traditional questions of astronomy—that is, “How and when did spiral galaxies form?”

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.

Takafumi Tsukui, Study Lead Author and Graduate Student, SOKENDAI

The study has been published in the Science journal.

Humans live in the Milky Way Galaxy, which is also a spiral galaxy. Within the Universe, spiral galaxies are crucial objects and account for as much as 70% of the overall number of galaxies.

But other analyses have demonstrated that the number of spiral galaxies reduces quickly as one revisits the history of the Universe. So, when did these spiral galaxies actually form?

Tsukui, along with his supervisor Satoru Iguchi, a professor from SOKENDAI and the National Astronomical Observatory of Japan, detected a galaxy known as BRI 1335-0417 in the ALMA Science Archive.

This galaxy was in existence 12.4 billion years ago and comprised a huge amount of dust, which conceals the starlight. But this makes it hard to thoroughly examine the BRI 1335-0417 galaxy with visible light. Conversely, ALMA can identify radio emissions from carbon ions in the galaxy, allowing scientists to explore what is happening in the galaxy.

The team identified a spiral structure that expands around 15,000 light-years from the galaxy core. This structure is one-third of the size of the Milky Way. The projected overall mass of the interstellar matter and stars in the BRI 1335-0417 galaxy is approximately equal to that of the Milky Way Galaxy.

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.

Takafumi Tsukui, Study Lead Author and Graduate Student, SOKENDAI

Then the query becomes, how did this distinct spiral structure develop in just 1.4 billion years after the famous Big Bang? The investigators considered numerous potential causes and proposed that it might be due to an interaction with a tiny galaxy.

The BRI 1335-0417 galaxy is intensely forming stars and the investigators noticed that the gas in the exterior portion of the galaxy is gravitationally unstable, which is favorable to the formation of stars This scenario may probably take place when a massive amount of gas is delivered from outside, perhaps due to collisions with tinier galaxies.

The destiny of the BRI 1335-0417 galaxy is also enigmatic. Galaxies, which contain huge amounts of dust and intensely create stars in the old Universe, are assumed to be the ancestors of the massive elliptical galaxies in the current Universe.

In such a case, the BRI 1335-0417 galaxy alters its shape from a disk galaxy to an elliptical one in the days to come.

Or, in contrast to the traditional perception, the galaxy may continue to remain a spiral galaxy for an extended period. The BRI 1335-0417 galaxy will play a crucial role in the analysis of galaxy shape evolution across the extended history of the Universe.

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.

Satoru Iguchi, Professor, SOKENDAI

渦巻銀河の形成 (ver.3)

Supercomputer simulation of the formation of a spiral galaxy. Over a period of about 13.5 billion years, small galaxies merge one after another into a single giant spiral galaxy. Please note that this video was created in 2007 and is not a reproduction of the current study. Video Credit: Takaaki Takeda, Sorahiko Nukatani, Takayuki Saito, 4D2U Project, NAOJ.

Journal Reference:

Tsukui, T., et al. (2021) Spiral morphology in an intensely star-forming disk galaxy more than 12 billion years ago. Science. doi.org/10.1126/science.abe9680.

Source: https://alma-telescope.jp/en/

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