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This group of galaxies has been nicknamed the "Cheshire Cat" because of its resemblance to a smiling feline.
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Some of the cat-like features are actually distant galaxies whose light has been stretched and bent by the large amounts of mass contained in foreground galaxies.
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This is an effect called "gravitational lensing," predicted by Einstein's Theory of General Relativity.
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X-rays from Chandra show that the two "eye" galaxies and the smaller galaxies associated with them are slamming into one another in a giant galactic collision.
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Chandra Photo Album
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SDSS J103842.59+484917.7collision.
Welcome to CLEVeR
CLuster and group
Environment as
Viewed by
eROSITA
What is CLEVeR?
CLEVeR (The CLuster and group Environment as Viewed by eROSITA) is a research project exploring how black holes and stars shape the universe. Scientists know that galaxies don’t evolve in isolation—they interact with their surroundings, exchanging gas and energy. But how does this process work? And why do some galaxies stop forming stars while others continue growing?
To find out, CLEVeR uses powerful space telescopes like eROSITA, which detects X-ray light from hot gas around galaxies. By combining these X-ray observations with optical and radio data, the project aims to:
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Map the invisible gas in galaxy groups, even those as small as the Milky Way’s neighborhood.
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Study how galaxies lose or retain gas, determining what keeps them alive or causes them to fade.
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Track powerful cosmic winds from black holes, revealing how they shape their surroundings over billions of years.
By studying these hidden forces, CLEVeR is helping scientists uncover the unseen side of galaxy evolution and how the universe came to look the way it does today.
The Importance of Galaxy Groups in Astrophysics: A Journey Through Our Cosmic Neighborhood
When we look up at the night sky, we see countless stars, but beyond them lies an even grander structure: galaxies—vast collections of stars, gas, dust, and dark matter bound together by gravity. Our own Milky Way is one of these galaxies, but it doesn’t exist in isolation. Instead, it is part of a galaxy group, a small but significant gathering of galaxies that travel through the universe together.
The Local Group: Our Cosmic Home
The Milky Way is a member of the Local Group, a collection of galaxies spanning about 10 million light-years across. At its core, the Local Group is dominated by three large galaxies:
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The Milky Way – our home galaxy, hosting around 100-400 billion stars and a supermassive black hole at its center.
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The Andromeda Galaxy (M31) – the largest member of the group, about 2.5 million light-years from us, on a slow-motion collision course with the Milky Way.
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The Triangulum Galaxy (M33) – a smaller spiral galaxy, a possible satellite of Andromeda.
Surrounding these giants are dozens of dwarf galaxies, including:
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The Magellanic Clouds (Large and Small) – two of the closest and brightest satellite galaxies of the Milky Way.
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Leo I, Leo II, and Sagittarius Dwarf Galaxy – small, faint galaxies gravitationally bound to the Milky Way.
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M32 and M110 – two dwarf galaxies orbiting Andromeda.
In total, the Local Group contains more than 80 known galaxies, most of them tiny and faint compared to the larger spirals.
Why Are Galaxy Groups Important?
Galaxy groups like the Local Group are the building blocks of the cosmic structure. They are more common than massive galaxy clusters and help astronomers understand how galaxies interact, merge, and evolve over billions of years. These groups are key environments where star formation can be triggered by interactions, gas can be stripped from galaxies, and dark matter plays a fundamental role in shaping their structure.
Hot Gas and X-ray Emissions: A New Discovery
Until recently, astronomers thought that small galaxy groups like the Local Group did not contain much hot, intergalactic gas. However, a recent discovery using the eROSITA X-ray telescope has challenged this assumption.
eROSITA has detected X-ray emissions from the Local Group, revealing the presence of hot gas at temperatures of millions of degrees Kelvin. This gas likely forms a tenuous, hot atmosphere surrounding the Milky Way and Andromeda, similar to the intracluster medium found in larger galaxy clusters. This discovery is crucial because:
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It suggests that galaxy groups can retain hot gas, providing a reservoir for future star formation.
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It helps astronomers study how galaxies accrete matter from their surroundings.
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It may offer insights into the role of dark matter, which helps trap and heat this gas.
The Local Group’s Place in the Cosmic Web
The Local Group is not floating in space alone—it is part of a much larger structure known as the Cosmic Web. This vast, interconnected network of galaxies, filaments, and voids is the fundamental structure of the universe. The Local Group resides in a filament of galaxies that connects it to the Virgo Supercluster, a much larger concentration of galaxies about 60 million light-years away.
Eventually, under the influence of gravity, the Local Group and nearby galaxy groups may merge into even larger structures. In a few billion years, the Milky Way and Andromeda will collide to form a single massive galaxy, and the Local Group may become part of a future supercluster.
Final Thoughts
A key question in astrophysics is whether the Local Group is a typical galaxy group or if its location within the Cosmic Web makes it unique. To address this, the CLEVeR project will investigate how the properties of galaxy groups—such as their hot gas content, star formation history, and dark matter distribution—vary depending on their position in the Cosmic Web.
By analyzing a large number of galaxy groups across different environments, CLEVeR aims to determine whether all galaxy groups behave like the Local Group or if its characteristics are shaped by its specific location within a cosmic filament. This research will help us understand whether the gas retention, interactions, and evolutionary patterns seen in the Local Group are common across the universe or if they are influenced by the surrounding cosmic structures. Ultimately, CLEVeR will provide a new perspective on how galaxies grow and evolve within the grand architecture of the cosmos, deepening our understanding of the universe’s fundamental structure.
Our Milky Way Galaxy is not an island universe, but a member of a small cluster of galaxies called the Local Group. The Local Group contains about 3 dozen known galaxies, clumped in two subgroups around two massive spiral galaxies — the Milky Way & Andromeda. @Chandraxray
This image from the eROSITA X-ray telescope shows the energetic Universe, represented in false color (red for energies 0.3-0.6 keV, green for 0.6-1.0 keV, blue for 1.0-2.3 keV). The Milky Way plane is visible as a think layer in blue and green, while the South and Noth X-ray bubbles are visible in yellow and oragne color. Image credit: Jeremy Sanders, Hermann Brunner & the eSASS team / Max Planck Institute for Extraterrestrial Physics / Eugene Churazov & Marat Gilfanov, IKI.
Comparison of scales showing our position in the Milky Way and the Local Group (top row) and the Local Group position in the nearby part of the Cosmic Web (bottom panel + background) on top of a theoretically modelled dark matter map of the nearby universe showing high density regions in bright color and low density regions in dark (Credits: The figure is based on adaptions of images of NASA, theskylive.com, GAIA and the CLUES project)
