Astronomers recently reported that they discovered a "blade-thin" galaxy filament composed of hydrogen-rich galaxies about 140 million light-years from the Earth, and confirmed that the entire structure is rotating. It is considered one of the largest rotating structures ever discovered. The research, published in the Monthly Notices of the Royal Astronomical Society, is expected to provide important clues about how galaxies formed and acquired rotation in the early universe.
The "cosmic web" in the universe is composed of huge dark matter and galaxy filaments. These cosmic filaments are both structural skeletons and "highways" that transport matter and momentum to galaxies. The research team pointed out that filaments in nearby space that contain a large number of co-rotating galaxies are particularly suitable for studying how galaxies "take over" rotation and gas from larger-scale structures, and can also test existing theories about how the large-scale rotation of the universe gradually accumulates over tens of millions of light-years.
During this observation, the team discovered 14 neighboring galaxies rich in neutral hydrogen gas, which were almost aligned, forming an extremely thin filament about 5.5 million light-years long and only about 117,000 light-years wide. This "filament" is embedded in a much larger cosmic filament, which contains more than 280 galaxies and has a total length of about 50 million light-years. Observations show that the rotation direction of a considerable number of galaxies is consistent with the rotation direction of the entire filament, which is much higher than expected under random distribution. This poses a challenge to existing theories and implies that the influence of the large-scale structure of the universe on the rotation of galaxies may be stronger and last longer.
The researchers also found that the galaxies on both sides of the filament's "main ridge" showed reverse motion, indicating that the entire structure was rotating as a whole. Through the filament dynamic model calculation, they gave a rotation speed of about 110 kilometers per second, and estimated that the radius of the dense central region of the filament is about 50,000 parsecs (about 163,000 light-years). The research team vividly compared this phenomenon to a "spinning teacup" in an amusement park: each galaxy is like a rotating teacup, and the platform that carries them, the cosmic filament itself, is also rotating. This "double rotation" provides a rare window for understanding how galaxies obtain rotation from the large-scale structure in which they are located.
From its dynamical characteristics, this galactic filament appears to be still young and relatively "unperturbed." The existence of a large number of hydrogen-rich galaxies and the low amplitude of internal motion indicate that they are in a so-called "dynamically cold" state and may still be in the early stages of evolution. Since hydrogen is the raw material for star formation, hydrogen-rich galaxies often mean that these galaxies are still actively accreting or retaining the "fuel" required to form stars, and therefore provide an ideal sample for studying the early or ongoing stages of galaxy formation and evolution.
Neutral hydrogen gas is extremely sensitive to motion perturbations, so hydrogen-rich galaxies are also excellent "tracers" for tracking the flow of gas in cosmic filaments. By observing the distribution and movement of hydrogen gas, researchers can more clearly see how the gas is "transported" into the galaxy along the filaments, thereby inferring how angular momentum is transferred in the cosmic web, thereby affecting the structure, rotation and star formation efficiency of the galaxy. This result is also expected to provide a reference for future weak gravitational lensing observations in cosmology, because the inherent shape and orientation of the galaxy itself will cause "intrinsic alignment" contamination to relevant measurements, which needs to be characterized and corrected in the model.
The work used data from the MeerKAT radio telescope in South Africa, which consists of 64 interconnected radio antennas and is one of the most powerful radio telescopes operating today. The research team identified this rotating filament in the deep sky survey project called MIGHTEE, and combined the optical observations of the Dark Energy Spectroradiometer (DESI) and the Sloan Digital Sky Survey (SDSS) to confirm that it has both an overall alignment of the galaxy's rotation direction and a large-scale overall rotation. One of the leaders of the study said that this filament is like a "fossil record of the flow of the universe", helping people trace how galaxies accumulated rotation and gradually grew over the long history of the universe.