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Local Sheet

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The Local Sheet is a massive galaxy filament in our cosmic neighborhood. It is an extragalactic region where many galaxies move together. This shared motion is known as a peculiar velocity. The Milky Way and the members of our Local Group are part of this sheet. Most bright galaxies near us belong to this specific structure.

Local Group and nearest galaxies
Local Group and nearest galaxies

The sheet is a thin part of the larger Local Volume. It also exists within the Virgo Supercluster, which is a much larger collection of galaxies.

To understand the sheet, we must look at its unique shape and size. The Local Sheet is a very thin, flat structure. It has a diameter of about 10 million light-years. However, it is only about 1 million light-years thick. This shape makes it look like a wall or a thin layer. This wall forms one boundary of the Local Void. The Local Void is a vast, empty region of space.

Council of giants (front view)
Council of giants (front view)

This void is estimated to be 150 million light-years across.

The movement of galaxies in the Local Sheet is caused by two main forces. First, the gravity of the Virgo Cluster pulls on them. This creates a peculiar motion toward that massive cluster. Second, galaxies move away from the center of the Local Void. This void is an expanding region of space with very few galaxies. This expansion pushes the galaxies outward at a velocity of about 240 kilometers per second. These two forces combine to create the specific motion we observe in the sheet.

There is a famous group of galaxies within the sheet called the Council of Giants. This is a ring of twelve large galaxies. The ring surrounds our own Local Group. It has a radius of about 10 million light-years. The center of this ring is located 15 million light-years from the Sun.

Council of giants (front view)
Council of giants (front view)

Most of these galaxies are spirals. Specifically, ten of the twelve are spiral galaxies. The remaining two are elliptical galaxies. These two ellipticals are named Maffei 1 and Centaurus A. They sit on opposite sides of our Local Group.

We can see specific details about the galaxies in this Council. For example, the Sculptor Galaxy is 11 million light-years away. The galaxy M81 is about 12 million light-years from us. Centaurus A is an elliptical galaxy located 11 million light-years away. Each galaxy has a different stellar mass. This mass is often measured using a logarithm of its mass in solar masses. These diverse galaxies help scientists understand the structure of our local space.

Astronomers first identified this region in 1987. An astronomer named Brent Tully and his colleague Richard Fisher described it. They published their findings in a book called The Nearby Galaxies Atlas. In that book, they originally called the region Cloud 14. The region is also known as the Coma–Sculptor Cloud. There is some debate about the exact names used. Tully believes the Local Sheet is only the co-moving part of the Coma-Sculptor Cloud. This means it is the part where galaxies move together. However, other researchers like McCall consider the two terms to be the same thing.

The Local Sheet is different from other galaxy clusters like the Virgo Cluster. Most galaxies in the sheet are late-type galaxies. In contrast, more than half of the giant galaxies in the Virgo Cluster are early-type galaxies. The sheet is also tilted at an angle of 8 degrees from the Local Supercluster. This orientation is important for mapping the universe. Scientists use the Supergalactic coordinate system to track these positions. This system uses the Local Sheet and the Supergalactic Plane as its base.

Local Group and nearest galaxies
Local Group and nearest galaxies
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File:Council of giants (front view).png
Council of giants (front view).png
File:Local Group and nearest galaxies.jpg
Local Group and nearest galaxies.jpg
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