Ultra-diffuse galaxies or UDGs are cosmic structure formations that are composed of dwarf galaxies. The said group of cosmic bodies is unique, as they have stars that are not too close compared to a typical galaxy.
In ultra-diffuse galaxies, stellar objects are often scattered throughout their perimeter, all with massive spaces between them. In addition, these stars exhibit low surface brightness to the point that they are undetectable through astronomical instruments available today.
Ultra-diffuse Galaxies: Dwarf, Isolated, and Quenched
Ultra-diffuse galaxies are still a puzzle to experts. Obvious questions about the UDGs are why the stellar bodies are abnormally apart from each other and why they are hard to detect.
The main interest of the experts is in the dark matter halos of the ultra-diffuse galaxies. The invisible energy cloak that holds galaxies from the outside may be the key to the unusual structure of UDGs.
University of California's Department of Physics and Astronomy expert Laura Sales and their international team conducted a study on the unusual structure of ultra-diffuse galaxies.
In the research, they developed a detailed simulation to chart every possible UDGs they can gather. Part of the subjects they have searched for are galaxies in the densest regions of the universe that cannot produce stellar bodies.
Sales said in a PhysOrg report that they detected unusual features that contradict the initial theories on UDGs. In addition, researchers traced the cosmic evolution of these galaxies that are also isolated to find out more about their development phases and their true origin in the form of backsplash orbits.
Quenched galaxies are usually identified from isolated space in the universe where no other galaxies are present. Moreover, the backsplash orbits that the experts referred to are objects that are identical to an isolated galaxy when formed.
These types of galaxies were originally made from objects that look like comets identical to those that propel near the sun, inside the solar system, and outside to the farthest reach of the universe.
Formation of Ultra-Diffuse Galaxies
Sales said that both isolated and satellite galaxies are quite different from the casual galaxies, as they have an evolution formed through a different league of physics. The backsplash galaxies that were previously part of a system are often isolated from the system itself.
Dwarf galaxies are categorized based on the number of stellar bodies present in them. For a system to be known as a dwarf galaxy, it must contain 100 million to a few billion stars.
On the other hand, Milky Way contains a population of stars that were estimated from 200 billion to 400 billion stars. Ultra-diffuse galaxies are categorized as dwarf galaxies, but not all dwarf galaxies are UDGs. Despite the smaller stellar population of UDGs, they are usually the size of our galaxy.
TNG50 is the simulation approach utilized by experts to track the origins of the UDGs. Based on their findings, the UDGs were initially separate satellites from different systems but ended up in today's isolated, elliptical orbit.
In addition, it was determined that the overall ultra-diffuse galaxies contain 25% quenched types. More quenched UDGs are expected to show in future studies of the unique galaxies.
The study was published in the journal Nature Astronomy, titled "Quiescent Ultra-Diffuse Galaxies in the Field Originating From Backsplash Orbits."
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