As telescopes have become more advanced and powerful, astronomers have been able to find galaxies that are getting farther away. These are some of the oldest galaxies to form in our universe and which began to drift away from us as the universe expanded. In fact, the further away they are, the faster the galaxy is moving away from us. Interestingly, we can estimate how fast galaxies are moving, and thus, when galaxies form based on how the “redshift” emission appears. This is similar to a phenomenon called the “Doppler effect”, in which objects moving away from the observer emit light that appears to shift towards a longer wavelength (hence the term “redshift”) at the observer.
The Atacama Large Millimeter/submillimeter Array (ALMA) telescope located in the center of the Atacama Desert in Chile is perfect for observing such redshifts in galactic emission. Recently, an international research team included Professor Akio Inoue and graduate student Tsuyoshi Tokuoka from Waseda University, Japan, Dr Takuya Hashimoto from the University of Tsukuba, Japan, Professor Richard S. Ellis from University College London, and Dr Nicolas Laporte A. A researcher at the University of Cambridge, England, observed a redshift in the emission of a distant galaxy, MACS1149-JD1 (hereinafter JD1), which led them to some interesting conclusions. “In addition to the discovery of high redshift, i.e. very distant galaxies, studying the internal motions of gas and stars provides impetus for understanding the process of galaxy formation as close as possible to the universe,” explains Ellis. The results of their study were published in Astrophysics Journal Letter.
The formation of galaxies begins with the accumulation of gas and continues with the formation of stars from that gas. Over time, star formation expands from the center outward, the galactic disk expands, and galaxies acquire a certain shape. As stars continue to form, new stars form in the rotating disk while older stars remain in the center. By studying the ages of stellar bodies and the movement of stars and gas in galaxies, it is possible to determine which stage of evolution the galaxy has reached.
After making a series of observations over a two-month period, the astronomers managed to measure small differences in the “redshift” from site to site within the galaxy and found that JD1 met the criteria for a spin-dominated galaxy. Next, they modeled the galaxy as a rotating disk and found that it reproduced the observations well. The calculated rotational speed is about 50 kilometers per second, which is compared to the rotational speed of the Milky Way disk of 220 kilometers per second. The team also measured JD1’s diameter at just 3,000 light-years, which is much smaller than the diameter of the Milky Way at 100,000 light-years.
The significance of their results is that JD1 is by far the most distant and, therefore, the oldest source to date of containing a disk of gas and a rotating star. Combined with similar measurements of nearby systems in the research literature, this allowed the team to determine the gradual evolution of the rotating galaxy over more than 95% of our cosmic history.
Furthermore, the estimated mass of the galaxy’s rotational speed is in line with previous estimates of stellar mass from the galactic spectral signature, and mostly comes from “mature” stars that formed about 300 million years ago. “This suggests that the star cluster in JD1 formed in the early era of the cosmic epoch,” said Hashimoto.
“JD1’s rotational speed is much slower than later galaxies and our own and it is likely that JD1 is in the early stages of spinning development,” Inoue said. With the recently launched James Webb Space Telescope, astronomers now plan to find young and old stars in galaxies to verify and update galaxy formation scenarios.
New discoveries are definitely on the horizon!