Using the ALMA telescope, a team of astronomers found a slowly rotating galaxy in the early Universe. This galaxy stands out as the youngest galaxy with a measured rotation ever found and rotates much more slowly than present-day galaxies.
All galaxies spin, often at incredible speeds. For example, the Milky Way galaxy has a rotational speed of over 200 kilometers per second. But astronomers don’t yet know how galaxies reach these speeds. For now, the only way to understand this seems to be to take measurements of galaxies throughout cosmic time and create a map of galactic evolution.
A team of astronomers at Tokyo Waseda University recently used ALMA (Atacama Large Millimeter/submillimeter Array) in Chile to observe an extremely distant galaxy. This galaxy, MACS1149-JD1, is so far away that it has a low luminosity that cannot be normally observed.
However, light from this galaxy passes through a giant galaxy cluster, and gravitational lensing from this cluster makes MACS1149-JD1 appear larger. Astronomers can use this magnification to see the galaxy.
MACS1149-JD1 existed when the Universe was only 500 million years old, meaning it is among the youngest known galaxies. The team used ALMA to study O III, or doubly ionized oxygen, in the galaxy’s disk.
They then developed a model of the size and rotational speed of the galaxy’s disk to compare with the observations.
They reported their results in a paper recently published in The Astrophysical Journal Letters.
The team found that MACS1149-JD1 is only 3,000 light-years across. That means it’s much smaller than the Milky Way galaxy, which is 100,000 light-years across. They also found that MACS1149-JD1 rotates at only 50 kilometers per second, which is more than a quarter slower than the Milky Way’s rotation speed.
“JD1’s spin rate is much slower than that found in later galaxies and our [Milky Way] Galaxy, and JD1 is likely to be in the early stages of developing a spin,” says Akio K. Inoue, one of the paper’s authors at Waseda University.
These results suggest that galaxies start small and spin slowly at first. They then accumulate more matter over billions of years and increase their rotational speed.
The team hopes to use the James Webb Space Telescope to further investigate galaxy rotation rates throughout cosmic time.
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