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USP researcher participates in identifying a new Milky Way satellite galaxy
Aquarius III is a dwarf galaxy discovered and studied by an international collaboration
Victor M. Blanco Telescope, used by researchers - Photo: CTIO/NOIRLab/NSF/AURA/D. Munizaga via Wikimedia Commons/CC BY 4.0
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The Delve Survey has discovered a tiny, ultra-cold galaxy orbiting the Milky Way, an international collaboration for observing the Universe, made up of more than 80 members from different institutions. Based on stellar modeling methods and light analysis, Aquarius III, as it has been called, is expected to have a few hundred or a few thousand stars, a small number even for other satellite galaxies.
For example, the Large Magellanic Cloud (LMC) brings together an estimated 10 billion to 30 billion stars. These proportions are still tiny compared to large galaxies such as the Milky Way, containing between 100 billion and 400 billion stars.
Astronomer Guilherme Limberg, who received his doctorate at USP’s Institute of Astronomy, Geophysics, and Atmospheric Sciences (IAG), was one of the researchers involved in recognizing and confirming Aquarius III. For him, the investigation of galaxies as small as the one discovered by the group could provide clues to the processes that form the Universe and celestial bodies.
Guilherme Limberg - Photo: Personal archive
Discovering galaxies
The galaxy’s discovery underwent two stages: imaging and spectroscopic confirmation, a technique that analyzes the spectrum of electromagnetic radiation. In the first phase, the researchers used public photos from the Victor M. Blanco Telescope, located in Chile.
The equipment captures photographs of a large area of the sky with a high degree of depth – due to the exposure time of the photo. “Just like a regular camera, the longer the exposure time, the more information that record has. This is because the lens will have more time to capture the light and thus form the images,” Limberg explains.
In these photos, scientists have observed regions with a high density of light, that is, areas with a cluster of stars, and indicate possible galactic systems. They listed the galaxy candidates and moved on to the second stage: confirmation.
Identifying a star cluster is not enough to confirm the existence of a galaxy. You need dark matter. This term is used to name all the yet undiscovered particles that make up most of the Universe, responsible for the high force of attraction between galactic elements.
To confirm its status as a galaxy, the researchers used a spectrograph – a prism that breaks down light into different wavelengths. From these lines, it is possible to infer different information such as: chemical composition, orbit, distance from the Milky Way and the age of the stars.
When the observed velocities do not coincide with the velocity estimated by the visible elements, it is possible to identify the presence of something invisible that influences the mass of that system: dark matter. Spectrography has confirmed that Aquarius III is an ultra-cold satellite galaxy with low metallicity, that is, the proportion of chemical elements other than hydrogen and helium, which are abundant elements in stars. Metallicity helps astronomers to identify the age of the astronomical object being studied.
Spatial distribution of stars in an area of the sky centered by Aquarius III. The top panel shows the first indication of the existence of a galaxy. The bottom panel shows the distribution of galaxies in the background - Image: Taken from the paper
The graph shows the galaxy's distance from the Milky Way (in white) over the last 3 billion years: this distance is an approximation over time. The lines
in red and blue indicate the maximum and minimum values the trajectory could have taken. The “ideal” value is blank - Image: Taken from the paper
Celestial laboratories
The study of dwarf galaxies – characterized by their small size, low luminosity, and low mass – is a promising branch of astrophysics. These structures are excellent “laboratories” for investigating dark matter and the phenomena that form celestial bodies.
Limberg explains that dwarf galaxies represent the most fragile galactic systems, where small variations in the initial formation conditions can have major impacts. For this reason, studying smaller galaxies allows us to test the limits of cosmological models.
“The physical processes that we know and admit are important for the formation of galaxies have to be able to form both the Milky Way, with 100 billion stars, and the tiny galaxies, with a thousand stars.”
The researcher points out that every galaxy is concentrated in a halo of dark matter – an invisible and massive structure that provides enough gravity to keep its stars and gases together. What still needs to be discovered is: what is the smallest possible mass for the formation of a dark matter halo? What is the smallest possible size of a dark matter region? Galaxies such as Aquarius III can help find these answers.
Nasa, the National Science Foundation (NSF), and the Fermi National Accelerator Laboratory funded the project. The USP researcher received a fellowship grant from the São Paulo Research Foundation (Fapesp).
The paper Discovery and Spectroscopic Confirmation of Aquarius III: A Low-mass Milky Way Satellite Galaxy is available online and can be read here.
More information: guilherme.limberg@usp.br, with Guilherme Limberg
English version: Nexus Traduções
*Intern under the supervision of Fabiana Mariz
**Intern under the supervision of Moisés Dorado
Background photo: ESO/S. Brunier via Wikimedia Commons/Public Domain
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A reprodução de matérias e fotografias é livre mediante a citação do Jornal da USP e do autor. No caso dos arquivos de áudio, deverão constar dos créditos a Rádio USP e, em sendo explicitados, os autores. Para uso de arquivos de vídeo, esses créditos deverão mencionar a TV USP e, caso estejam explicitados, os autores. Fotos devem ser creditadas como USP Imagens e o nome do fotógrafo.