"Cloud-9": Failed dwarf galaxy of dark matter and without stars
With "Cloud-9", a cosmic object has likely been discovered that has so far only been theoretically described: a small gas cloud with a lot of dark matter.
The "Cloud-9" (marked in pink and yellow) reconstructed from data from the Very Large Array (VLA) radio interferometer
(Image: NASA, ESA. G. Anand (STScI), and A. Benitez-Llambay (Univ. of Milan-Bicocca); Image processing: J. DePasquale (STScI))
An international research group has discovered a new type of cosmic object with the Hubble Space Telescope, which the research leader describes as an original building block of a failed galaxy. It is a cloud of dark matter and hydrogen gas but without stars, which has been nicknamed “Cloud-9.” It has a diameter of 4900 light-years and consists of one million solar masses of gas but five billion solar masses of dark matter. Its existence suggests that there are numerous other relatively small structures in the universe that are dominated by dark matter and which we have not been able to detect so far. There may be others in our vicinity as well.
Confirmation only, thanks to Hubble
(Image:Â NASA, ESA. G. Anand (STScI), and A. Benitez-Llambay (Univ. of Milan-Bicocca); Image processing: J. DePasquale (STScI))
The first detection of the object was made three years ago with the giant radio telescope FAST (Five-hundred-meter Aperture Spherical Telescope) in China, explains the European Space Agency ESA. The nickname “Cloud-9” (“Wolke 9”) has no special meaning; it was simply the ninth gas cloud found in the vicinity of the galaxy Messier 94. However, until verification with Hubble, it could simply be assumed that it was a faint dwarf galaxy whose stars could not be resolved with ground-based telescopes. Only the space telescope confirmed that there are indeed none.
The researchers, led by Alejandro Benitez-Llambay from the University of Milan-Bicocca, explain that the cloud is likely an object that has so far only been theoretically described and has been named “RELHIC.” Such a “Reionization-Limited H I Cloud” therefore consists of hydrogen gas from the early universe, but not enough to initiate star formation. The discovery thus not only provides insight into the still mysterious dark matter but also into the early universe and the processes of star and galaxy formation. “In science, we usually learn more from failures than from successes,” says Benitez-Llambay.
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Dark matter is currently one of the most important topics in physics and astronomy; allegedly, there was a first experimental detection. However, its existence was postulated based on astronomical observations where stellar movements were measured that could not be sufficiently explained by known matter and its gravity. Overall, there should be five times more dark matter in the cosmos than classical matter. Even more is attributed to the equally mysterious dark energy. Currently, the particles that could constitute it are being searched for in various ways. The research work on “Cloud-9” has been published in The Astrophysical Journal Letters.
(mho)
