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The findings of a new study suggest that astronomers may be on the verge of uncovering a hidden galaxy composed largely of dark matter. Published today in Science Advances, researchers from the Chinese National Academy of Sciences have analyzed a cloud of gas adjacent to the Milky Way, hypothesizing that it might represent a dark galaxy rather than merely a gas formation.
Understanding AC G185.0-11.5
The object in question, designated AC G185.0-11.5, is identified as part of the AC-I Complex, categorized by astronomers as a high-velocity cloud (HVC). These clouds consist of hydrogen gas that travels at speeds significantly exceeding that of the gas found in the Milky Way. They are thought to be remnants from external galaxies or material ejected from supernovae within our galaxy, eventually falling back into it.
Utilizing data from the now-defunct Arecibo Observatory and the Five-hundred-meter Aperture Spherical radio Telescope (FAST) located in Guizhou, China, the researchers focused on AC G185.0-11.5. They observed that this particular clump exhibits characteristics of a rotating disk galaxy, despite the absence of visible stars.
Galaxies that contain minimal star formation are termed dark galaxies, primarily characterized by their dark matter content. Dark matter makes up about 85 percent of the universe’s matter, while the visible matter, or baryonic matter, constitutes only 15 percent. According to Ming Zhu, an astrophysicist and co-author of the study, “We didn’t see any star formation from the available optical data, thus it is always dark.” In addition, Zhu noted that AC G185.0-11.5 seems to harbor twenty-one times more dark matter than ordinary matter.
Evidence of Rotation
The research team discovered the galaxy’s nature by analyzing the rotation patterns of material within AC-I. Zhu explained that the distinctive motion indicates that the gas is rotating in a disk-like formation and is likely underpinned by dark matter that influences this rotation.
The mass of AC G185.0-11.5 has been estimated to be equivalent to approximately 300 million solar masses, although uncertainties in the measurements exist. Researchers have also inferred that its distance from Earth is roughly 900,000 light-years, presenting a significant advancement in understanding HVC distances, which have been notoriously difficult to ascertain.
This galaxy is expansive enough to be examined by both ground-based and space telescopes. Observatories such as the James Webb Space Telescope (JWST) could potentially reveal any hidden stars, while the Very Large Array may provide additional insights into the galaxy’s disk and possible central components.
Implications for Dark Matter Research
While the findings warrant cautious optimism, historical precedents exist where some dark galaxy candidates were later found to be regular gas clouds subject to internal forces. Consequently, several uncertainties linger in the data concerning AC G185.0-11.5.
If confirmed as a dark galaxy, its closeness to the Milky Way makes it an ideal candidate for in-depth studies that could elucidate the influence of dark matter in galactic structures. Since all galaxies are believed to possess dark matter, which interacts with baryonic matter primarily through gravitational forces, examining a galaxy rich in dark matter promises to deepen our understanding of how this enigmatic substance behaves. Astronomers have gathered evidence since the 1960s that dark matter plays a crucial role in the spin dynamics of galaxies, showcasing discrepancies between expected and observed rotational speeds based on visible matter.
Thus, studying AC G185.0-11.5 could enhance our comprehension of dark matter’s characteristics and aid the ongoing search for its presence within our galaxy and others throughout the universe.
Source
www.astronomy.com