Using observations from Chile, astronomers have logged nearly 50 extremely faint dwarf systems — including so-called "ghost galaxies" — around three larger galaxies, adding new data to a major unresolved problem in cosmology, according to Phys.org.
Here's what to know
The survey, led by INAF (the Italian National Institute for Astrophysics), identified dwarf companions around NGC 5068, NGC 5084, and NGC 5087.
Those hosts are, respectively, a spiral, a lenticular, and an elliptical galaxy at distances of roughly 17 million, 80 million, and 100 million light-years.
Researchers made the detections with the VST (VLT Survey Telescope), a device at an Italian facility run by INAF at ESO's Paranal Observatory in Chile; the study appeared in the journal Astronomy & Astrophysics.
Most known examples have been found much closer to Earth, especially around the Milky Way in the Local Group, because galaxies with about a billion suns of mass or less are so faint.
Looking outside that nearby region is meant to show whether the unusual patterns reported around the Milky Way and neighboring galaxies are specific to our corner of the universe or reflect a broader issue in theories of galaxy formation.
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More background
The findings matter because dwarf galaxies have long highlighted a gap between observation and the standard cosmological model, the main framework scientists use to explain how the universe evolved.
The best-known version of that conflict was the "missing satellite galaxies" problem, in which simulations produced more small companions around large galaxies than telescopes were finding.
The picture has become less straightforward, with some analyses arguing that observations may instead contain more satellite galaxies than the simulations do.
Another sticking point is geometry.
Rather than appearing in all directions, dwarf satellites around systems like the Milky Way are often seen in a thin, flattened plane.
Whether that kind of layout is compatible with existing theory remains unsettled.
What's being done?
Scientists are continuing to push observations deeper and farther, searching for faint objects that earlier surveys may have missed.
The low brightness of dwarf galaxies can make them effectively invisible even when they are relatively nearby on cosmic scales.
The new catalog around these three host galaxies gives astronomers more data points beyond the Local Group, helping them test whether the apparent over- or undercounting of dwarf satellites is widespread. It also gives researchers more examples to compare across different kinds of host galaxies.
Identifying more of these faint companions lets astronomers test simulations and determine whether the universe is behaving as expected — or whether the models themselves need updating.
The discovery does not settle the debate — but by bringing dozens of dim dwarf galaxies into view far beyond our cosmic backyard, it gives scientists fresh insights into a mystery that is still unfolding.
Where can I learn more?
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