Trapezium Cluster

This article is about the open cluster. For other uses, see Trapezium.

Trapezium
Trapezium in optical (left) and infrared light (right) from Hubble. NASA photo.
Observation data (J2000 epoch)
Constellation	Orion
Right ascension	05h 35.4m
Declination	−05° 27′
Distance	1,344±20 ly (412 pc)
Apparent magnitude (V)	4.0
Apparent dimensions (V)	47 (seconds of arc)
Physical characteristics
Mass	? M☉
Radius	10 ly
Estimated age	3 × 105 years

The Trapezium or Orion Trapezium Cluster, also known by its Bayer designation of Theta¹ Orionis, is a tight open cluster of stars in the heart of the Orion Nebula, in the constellation of Orion. It was discovered by Galileo Galilei. On February 4, 1617 he sketched three of the stars (A, C, D), but missed the surrounding nebulosity. The fourth component (B) was identified by several observers in 1673, and several more components were discovered later, for a total of eight by 1888. Subsequently several of the stars were determined to be binaries. Telescopes of amateur astronomers from about 5 inch aperture can resolve six stars under good seeing conditions.

The Trapezium is a relatively young cluster that has formed directly out of the parent nebula. The five brightest stars are on the order of 15-30 solar masses in size. They are within a diameter of 1.5 light-years of each other and are responsible for much of the illumination of the surrounding nebula. The Trapezium may be a sub-component of the larger Orion Nebula Cluster, a grouping of about 2,000 stars within a diameter of 20 light-years.

Identification

It is most readily identifiable by the asterism of four relatively bright stars. The four are often identified as A, B, C, and D in order of increasing right ascension. The brightest of the four stars is C, or Theta¹ Orionis C, with an apparent magnitude of 5.13. Both A and B have been identified as eclipsing binaries.

Infrared images of the Trapezium are better able to penetrate the surrounding clouds of dust, and have located many more stellar components. About half the stars within the cluster have been found to contain evaporating circumstellar disks, a likely precursor to planetary formation. In addition, brown dwarfs and low-mass runaway stars have been identified.

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  The Chandra X-ray Observatory view of the Orion Nebula.

• TrapeziumStars.jpg

  Trapezium star identification

• Glowing region Trapezium stars.jpg

  This glowing region reveals arcs and bubbles formed when stellar winds - streams of charged particles ejected by the Trapezium stars - collide with material.

• Trapezium Labeled.jpg

  A wider shot of the core details showing the trapezium in context of the surrounding nebulae

• 

  Core detail of the nebula with all the stars identified.

Possible black hole

A 2012 paper suggests an intermediate mass black hole with a mass >100 times larger than that of the Sun may be present within the Trapezium, something that could explain the large velocity dispersion of the stars of the cluster.

External links

• Chandra Observatory Uncovers Hot Stars In The Making, MIT Press Release, 2000.
• A detailed description of the Trapezium Cluster
• Astronomy Picture of the Day - In the Center of the Trapezium 2003 March 2

• Observing the Trapezium