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Trapezium Cluster

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The Trapezium Cluster is a tight open cluster of stars. It is located in the heart of the Orion Nebula. This cluster sits within the constellation of Orion. Astronomers also call it Theta1 Orionis. This group of stars is important because it helps illuminate its surroundings. The stars provide much of the light for the nebula.

Trapezium cluster optical and infrared comparison
Trapezium cluster optical and infrared comparison

The cluster formed directly out of its parent nebula. This makes the Trapezium a relatively young stellar group. The five brightest stars are extremely massive. They are between 15 and 30 solar masses in size. This means they are much larger than our Sun. These bright stars stay within a diameter of 1.5 light-years of each other.

Trapezium cluster optical and infrared comparison
Trapezium cluster optical and infrared comparison

Astronomers identify the cluster by a specific asterism. An asterism is a recognizable pattern of stars. The Trapezium is named for four relatively bright stars. These are often labeled A, B, C, and D. They are listed in order of increasing right ascension. The brightest star in this group is C, or Theta1 Orionis C. It has an apparent magnitude of 5.13.

Galileo Trapezium Notebook
Galileo Trapezium Notebook

History shows how our view of the cluster has changed. Galileo Galilei discovered the cluster long ago. On February 4, 1617, he sketched three of the stars. These were stars A, C, and D. He did not mention the surrounding nebulosity, which is the gas cloud known as M42. Galileo believed a better telescope would resolve the glow into more stars. He thought the diffuse light was just a limitation of his equipment.

Galileo Trapezium Notebook
Galileo Trapezium Notebook

More stars were found as technology improved. Observers identified a fourth component, star B, in 1673. By 1888, scientists had discovered a total of eight components. Many of these stars are actually binaries. A binary is a system where two stars orbit one another. Amateur astronomers can resolve six stars under good seeing conditions. Infrared images are even better for studying this area. Infrared light can penetrate the surrounding clouds of dust.

Trapezium cluster optical and infrared comparison
Trapezium cluster optical and infrared comparison

Detailed observations reveal much about how stars grow. About half of the stars in the cluster have circumstellar disks. These are disks of material that circle a star. These disks are currently dwindling in size. This process is likely a precursor to planetary formation. Scientists have also identified brown dwarfs in the cluster. They have also found low-mass runaway stars in this region.

Trapezium cluster optical and infrared comparison
Trapezium cluster optical and infrared comparison

The Trapezium may be part of a much larger system. It might be a sub-component of the Orion Nebula Cluster. That larger grouping contains about 2,000 stars. Those stars are spread within a diameter of 20 light-years. Some researchers suggest a mysterious object exists here. A 2012 paper suggests an intermediate-mass black hole might be present. This black hole could be more than 100 times the mass of the Sun. Such a massive object could explain the large velocity dispersion of the stars. This dispersion refers to how much the stars move within the cluster.

Trapezium cluster optical and infrared comparison
Trapezium cluster optical and infrared comparison
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File:Trapezium cluster optical and infrared comparison.jpg
Trapezium cluster optical and infrared...
File:Galileo Trapezium Notebook.png
Galileo Trapezium Notebook.png
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