The study of dwarf galaxy groups helps to understand the formation of larger galaxies and dark matter

A group of dwarf galaxies (Image courtesy Sloan Digital Sky Survey)
A group of dwarf galaxies (Image courtesy Sloan Digital Sky Survey)

An article published in the journal “Nature Astronomy” describes the discovery of seven groups of dwarf galaxies that show the conditions for starting the merger process that will lead to form galaxies like the Milky Way. A team of researchers led by Sabrina Stierwalt of the National Radio Astronomy Observatory (NRAO) identified seven groups starting from data of the TiNy Titans (TNT) survey then carried out specific studies.

It was speculated for some time that ordinary galaxies were the result of the merger of dwarf galaxies in a cosmological model called Lambda-CDM (Cold Dark Matter) paradigm but so far it wasn’t possible to test it. One of the problems was the far from complete cataloging of dwarf galaxies and their possible companions. In some cases it was possible to observe mergers involving dwarf galaxies such as in the study of DDO 68 but not enough to prove that that model was correct.

This new research started by selecting seven isolated groups of dwarf galaxies from the TiNy Titans (TNT) survey also using spectroscopic data of another survey, the Sloan Digital Sky Survey (SDSS). The Magellan telescope in Chile, the Apache Point Observatory in New Mexico, and the Gemini telescope in Hawaii were used to confirm them spectroscopically. In essence, there was a systematic research that led to their selection.

The result was the study of seven groups of dwarf galaxies that are interacting with each other in different ways from a gravitational point of view. There are cases where it some kind of galactic cannibalism could be happening in which a dwarf galaxy absorbs a much smaller one.

These dwarf galaxies also are an interesting source of study about dark matter because they tend to have much more of it than larger galaxies. The result is an overall force of gravity greater than you would expect from the matter we can see, enough to hold together the galaxy clusters.

The observations of these dwarf galaxies are also made easier by the fact that they’re older and therefore have less “debris” such as gas and dust that may overshadow their emissions. One hypothesis is that dark matter particles emit gamma rays following some interactions and in these galaxies researchers can try to detect them. In the end, studying these dwarf galaxies allows to obtain new information about various cosmological research.

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