SPACE — Astronomers may have discovered a galaxy composed entirely of dark matter, with no stars. This object has long been predicted in cosmology.
Astronomers observed plumes of gas found around the spiral galaxy M94. The clump of gas may be a starless dark matter galaxy.
Reporting from BBC Skythis blob is of interest to astronomers because it could be the first example of a type of object that has long been predicted by leading cosmological theories: small galaxies with gas, dark matter and no stars.
Star formation in a galaxy occurs if it overcomes gravitational limitations to reach a certain density. If this limit cannot be crossed, then star formation will not occur.
How could this starless galaxy, which is entirely dark matter, be discovered?
A team of Chinese astronomers used the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) in southwest China. This telescope is similar to the recently decommissioned Arecibo telescope in Puerto Rico.
During their observations, they detected radio waves with a wavelength of 21cm. This wavelength corresponds to hydrogen, which comes from a point in the sky less than one degree from M94, in the constellation Canes Venatici.
If the emissions do come from hydrogen, they appear to be moving away from us at about the same speed as more massive galaxies. It is very possible that these wavelengths are part of the same cosmic group.
Lots of gas, but no stars
The galaxy without stars and all the dark matter called Cloud-9 could be a satellite of the spiral galaxy M94. The discovery, which the team calls ‘Cloud-9’, may be the satellite galaxy M94. However, if so then it is a strange galaxy.
The deepest imaging available so far shows no sign of starlight at a position consistent with a radio source.
Modeling in this paper shows that assuming no stars are found, its mass could be 5 billion times that of the Sun.
This number is relatively small for a galaxy, although it is not unprecedented. The material inside is a little more spread out than expected.
According to scientists, these objects may have a different distribution of dark matter than ‘normal’ galaxies of the same size. There may also be more galaxies than previously thought.
2023-11-05 03:50:00
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