Lone, starless cloud may be a 'dark' galaxy

Key Points:

• Astronomers using China's FAST radio telescope have discovered an isolated hydrogen cloud, J1351+0039, with no visible stars or galaxy nearby, making it a strong candidate for a "dark galaxy" containing about 500,000 solar masses of neutral hydrogen.
• The cloud is isolated from large galaxies by at least 100 kpc and shows no signs of tidal interactions, with a total mass around 130 million solar masses, most of which is attributed to dark matter.
• J1351+0039 exhibits weak rotation and is primarily supported by the pressure of randomly moving gas rather than rotational forces, consistent with theoretical predictions for reionization-limited H I clouds (RELHICs) or starless dark galaxies.
• Deep optical surveys found no stellar counterpart, but the possibility of an ultra-faint galaxy cannot be ruled out without further observations using space telescopes like JWST or Hubble.
• Unlike previous dark galaxy candidates found near massive galaxies, J1351+0039's complete isolation makes it the most compelling example of an isolated RELHIC discovered so far.