Ultradiffuse galaxies are so called because of their extremely low luminosity. Baryon distribution -
A dark matter halo is a halo of invisiblesubstance that permeates and surrounds a galaxy or a cluster of them. Although dark matter (which makes up 85% of the Universe) has never been detected in a laboratory, physicists are confident that it exists. In a new study, scientists tried to figure out why the dark matter halo is so “strange.”
Dark matter halo in rare galaxies
Ultradiffuse galaxies are much less massivecompared to the Milky Way. However, they contain a lot of gas, and its mass is much higher than the total stellar mass. This is different from what astronomers observe in the Milky Way. Ultradiffuse galaxies are also large in size.
NGC 1052-DF2 is an ultradiffuse galaxy. Photo: ESA/Hubble
About the distribution of dark matter in these galaxiescan be judged by the movement of gas particles. Surprisingly, the presence of baryonic matter itself, predominantly in the form of gas, is (almost) enough to explain the measured speed of gas particles. It also leaves little room for dark matter in the inner regions, where most of the stars and gas are found.
Why is it weird?
This is what surprises scientists:in the case of ordinary galaxies, whose masses are similar to the masses of ultradiffuse ones, the opposite is true. There, dark matter predominates over baryonic matter. To somehow explain this result, the study authors concluded that dark matter halos should be in lower “concentration.” In simple words, they contain much less mass in the inner regions compared to with ordinary galaxies. In this sense, the dark matter halos of ultradiffuse galaxies are “strange,” scientists explain.
It would seem that such halos with a low concentrationare so rare that ultradiffuse galaxies should not exist at all. However, after studying data from modern numerical simulations of cosmic structure formation, scientists found that the population of low-concentration haloes is much higher than expected.
How did the study go?
During the work, experts in the field of gas dynamicsgalaxies discovered that ultra-diffuse galaxies rotate more slowly than ordinary galaxies with the same masses. Scientists interpreted data from measurements of the movement of gas in them and concluded about the distribution of dark matter.
NGC1052-DF2, red giant stars highlighted. Photo: Hubble
In addition, physicists analyzed the datamodeling the formation of space structures. As a result, they identified dark matter halos that have the same properties as ultradiffuse galaxies.
Why is this work important?
Astrophysicists have many questions thatconcern the formation and evolution of recently discovered galaxies. For example, these ultra-diffuse objects contain a lot of gas, but it is not clear how it does not “weather” during formation. In addition, the authors of the new work showed that these objects may be younger than ordinary galaxies. The formation of ultradiffuses has not been sufficiently studied, and additional work is required.
What makes ultradiffuse galaxies like this?What's interesting is their unusual properties. They have only recently been discovered, but they will help us understand how clusters of stars form and perhaps even the nature of dark matter.
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