This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Astronomers have found two clouds of hydrogen near the Whirlpool galaxy that appear to contain almost no stars. The clouds, discovered with China's FAST radio telescope, each contain roughly 3 million times the mass of the sun in hydrogen but have no detectable optical counterpart.
Their properties are outlined in a new paper published in the Astronomy & Astrophysics journal on Aug. 4. According to the standard Lambda Cold Dark Matter (LCDM) model of the universe, structure forms hierarchically: Small dark-matter halos form first, then merge to build larger halos and galaxies. But not every dark-matter halo is expected to become a galaxy because several processes can suppress star formation at sufficiently low masses.
If a halo's gravitational potential is weak, stars may not form. If the gas is not dense and cold enough, it cannot collapse into stars. Gas may be heated by the ultraviolet (UV) background, which is made up of diffuse radiation from quasars and stars throughout the universe.
This leads to a population of dark-matter halos containing neutral hydrogen gas but few or no stars. In this work, led by Qingze Chen of the National Astronomical Observatories, Chinese Academy of Sciences, researchers tested this idea: a small dark-matter halo that retained some gas after cosmic reionization but whose gas never became cold and dense enough to form stars because it was heated by UV radiation. They call it the reionization-limited H I cloud, or RELHIC.
To be classified as a RELHIC, a surviving hydrogen cloud should be compact, roughly spherical, show narrow spectral lines with velocities around 20 kilometers per second (km/s), and have no stellar component detected at optical wavelengths. LCDM predicts a huge population of low-mass dark-matter halos. So far, only a handful of such starless clouds have been identified.
The researchers searched for 21-cm radio wavelength signals—telltale signatures of neutral hydrogen (H I). They used H I observations from the Five-hundred-meter Aperture Spherical Telescope (FAST), specifically the FEASTS survey. They analyzed 55 galaxies in the FEASTS sample to identify objects meeting the conditions for hydrogen clouds.
Extract — continue reading at the source.
