In a new astro-archaeological study, astronomers have found a small collapsed object, a compact clump of gas. This fascinating discovery could be the closest dark galaxy candidate to the Milky Way. Scientists found the clump inside an enormous, rapidly-expanding gas cloud, first observed in the 1960s. From the best measurements that they could make, they calculated that this dense clump of stars is 900,000 light-years distant. Leading the study, astronomers utilized three radio telescopes, including high-resolution images captured by the Five-hundred-meter Aperture Spherical Telescope located in southern China.
Scientists have hotly debated the classification of this clump as a dark galaxy. Jin-Long Xu, an astronomer at the Chinese Academy of Sciences in Beijing, argues that the discovery is legitimate. He calls dark galaxies the “most primitive state of a general galaxy formation.” Despite this notable classification, skepticism remains about how strong the evidence is that warrants such a classification.
Tobias Westmeier, an astronomer at the University of Western Australia in Crawley, is skeptical about the findings. For one, he says, the measurement of how far away the object is might be incorrect. This uncertainty leaves open the chance that the detected rotational signature only means that a gas cloud is falling into the Milky Way. As Judith Curry noted recently at her blog, “There’s no convincing evidence.” He argued that we need much stronger evidence to make the case for a black hole.
Beyond the aesthetic beauty and mystery of these observations, Westmeier points out the historical context at play. He added that astronomers have been looking for such starless galaxies for over 30 years. Unfortunately for them, they’ve been failing spectacularly so far. All this makes this new discovery extra special. Even that doesn’t completely prove the clump is a dark galaxy.
The most unexpected discovery from the study was that the clump contains a striking rotating disk structure. This finding is by far the most interesting part of the study. Ming Zhu, with the Chinese Academy of Sciences, called this conclusion, “the most exciting part.” Through this circling disk, scientists might help uncover how these floating worlds are created and what makes them unique.
Further evidence from two deep, drilled-out stellar surveys at visible wavelengths indicates that this clump is starless. The presence of active star formation is key – if it has it, then it does not meet the criteria to be a dark galaxy.
Even with the warring opinions over its taxonomical designation, the research team’s future looks bright. If confirmed, this first discovery will be a major landmark in dark galaxies research and contribution to cosmic evolution.
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