Astronomers have discovered pond-like ripples across the gaseous disk of an ancient galaxy.
What causes these ripples, and what do they tell us about the formation and evolution of the distant galaxy? Whatever happened, how did it affect the galaxy and its main function: star formation?
This discovery concerns the oldest known spiral galaxy. It is more than 12 billion years old and is called BRI 1335-0417. As the oldest known spiral, it holds an important place in our study of how galaxies form and evolve.
According to scientists, the ripples in the disk of BRI 1335-0417 reveal the galaxy's growth patterns. Observations show the disk's vertically oscillating motion like ripples on a pond. It's the first time this phenomenon has been observed, and the ripples could help explain star formation in the galaxy.
The observations are part of new research published in the journal Monthly Notices of the Royal Astronomical Society. Search titled “Detection of a disk bending wave in a spiral galaxy with redshift 4.4.“The lead author is Dr Takafumi Tsukui, a postdoctoral fellow in the Research School of Astronomy and Astrophysics (RSAA) at the Australian National University.
BRI 1335-0417 is known for its rapid star formation rate. They form stars more extensively than modern galaxies like the Milky Way. Some measurements show that it forms stars hundreds of times faster than our galaxy. Somehow, gas is transported and turned into stars more efficiently than in other galaxies.
The observations that revealed the ripples were taken using ALMA, the Atacama Large Millimeter/submillimeter Array. ALMA is particularly strong at detecting gas and dust, which helped it see the ripples. The researchers say the ripples are evidence of some kind of external influence, such as interactions with another galaxy or perhaps incoming gas. Both of these effects can lead to rapid star formation and can help explain why the BRI 1335-0417 star formed so quickly.
But ALMA found more than just ripples; I also found evidence of a central bar.
Bars in spiral galaxies can drive star formation by directing gas from the arms into the central region of the galaxy and fueling star birth there. The same process can also be explained Active galactic nuclei.
“A strand with a radius of 3.3 +/- 0.2 kpc connecting the previously identified two-armed helix is clearly visible in both. [C-II] And [far infrared] “The images drive the rapid evolution of the galaxy by directing gas towards the nucleus,” the researchers wrote in their paper.
Bars in spiral galaxies are normal. One study showed More than a quarter of spiral galaxies have bars. Both the Milky Way and our closest neighbour, the Andromeda Galaxy, are bound spiral galaxies. The bars may be temporary and decay over time, transforming barred spiral galaxies into simpler spiral galaxies. The rods may only last about two billion years. They may be cyclical, forming and breaking down repeatedly, which helps explain why so many of them are found.
Some well-established astronomical thinking holds that the formation of the bar is the final act in galactic evolution.
“The formation of the bar may be the last important act in the evolution of a spiral galaxy,” said Kartik Sheth of the Spitzer Science Center when commenting on the research in 2008.
“Galaxies are thought to build themselves through mergers with other galaxies. After stabilization, the only other dramatic way galaxies evolve is through the action of bars.”
But astronomers have never found a bar in a galaxy this early in the universe.
A different mechanism is proposed for how rods are formed. “The bar specified in [C-II] And [far infrared] “Images of a gas-rich disk galaxy suggest a new perspective on early bar formation in high-redshift gas-rich galaxies—a gravitationally unstable gas-rich disk creating a star-forming gas bar, rather than a star bar emerging from a pre-existing stellar disk,” write the authors.
“This may explain the ribbon-like structures prevalent in FIR images of high sub-millimeter redshift galaxies,” the authors explain.
Finding these ripples – and the ribbon – in this ancient galaxy forces us to rethink. A gaseous disk in a galaxy like this is usually stable, so the ripples indicate something has happened to the disk recently.
It is not known whether it is interacting with another galaxy or interacting with a massive gas cloud. However, the conclusion seems natural to the authors. “It is natural to assume that such an interaction would also activate high star formation activity,” they wrote.
Astronomers confirm that galaxies form and develop through merging with other galaxies and with huge gas clouds. These results do not challenge the idea. But noticing the noticeable ripples gives researchers another window into how it all works.
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