
| Cosmic ghost cities: new galaxies discovered that are difficult to explain
Astronomers still don't know exactly why small, very dim galaxies stopped creating new stars in the early Universe.
Scientists have discovered three new, extremely faint dwarf galaxies that have never been seen before. They are very small and far from larger galaxies. They contain only a few hundred thousand old stars and do not have the interstellar gas needed to create new stars. This means that some event in the early Universe led to the suppression of the star formation process in these dwarf galaxies. The study is published in The Astrophysical Journal Letters, writes IFLScience.
While the Milky Way and similar large galaxies contain hundreds of billions of stars of all ages, the three new very faint dwarf galaxies contain only a few hundred thousand old stars. This means that long ago in the early Universe, something blocked the process of new star formation and removed the interstellar gas needed for their formation.
The three new dwarf galaxies, which belong to the type of the faintest, and therefore poorly detected, galaxies, are located in the constellation Sculptor and have been named Sculptor A, Sculptor B, and Sculptor C.
All three galaxies are millions of light-years away, but no larger neighbors have been detected nearby, which is a problem when it comes to explaining why these galaxies stopped forming new stars long ago in the early Universe.
Such small galaxies cannot hold the interstellar gas needed for star formation if a large galaxy is nearby. That is, if they are satellites of the latter. The gravity of the large galaxy will constantly pull this valuable gas from the dwarf galaxies, which will lead to a halt in the process of new star formation. But the detected galaxies, as already mentioned above, are located in an isolated region of space.

Astronomers have called these galaxies cosmic ghost cities, which are difficult to explain, and yet there are some assumptions about why they do not have new stars.
Scientists suggest that the reason may be a period in the history of the early universe called the epoch of reionization. A few hundred million years after the Big Bang, intense radiation from the very first stars filled the cosmos and caused the hydrogen gas in the smallest galaxies to evaporate. And this hydrogen would have become the main ingredient for the creation of new stars.
Another hypothesis suggests that some of the earliest stars in dwarf galaxies exploded as extremely powerful supernovae, and the radiation from this explosion could have blown interstellar gas out of the galaxies.
To better understand what happened to these three galaxies, scientists say they need to find more of these objects in isolated regions of space. Previously, extremely faint dwarf galaxies had only been found near the Milky Way.