The Trapezium or Orion Trapezium Cluster, also known by its

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

of Theta¹ Orionis (θ¹ Orionis), is a tight

open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

s in the heart of the

Orion Nebula The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula in the Milky Way situated south of Orion's Belt in the Orion (constellation), constellation of Orion, and is known as the middle "star" in the "sword" of Orion. It ...

, in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

of Orion. It was discovered by

Galileo Galilei Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642), commonly referred to as Galileo Galilei ( , , ) or mononymously as Galileo, was an Italian astronomer, physicist and engineer, sometimes described as a poly ...

. On 4 February 1617 he sketched three of the stars ( A, C and D), but missed the surrounding nebulosity.Galileo Galilei: Siderius Nuncius,

Venice Venice ( ; ; , formerly ) is a city in northeastern Italy and the capital of the Veneto Regions of Italy, region. It is built on a group of 118 islands that are separated by expanses of open water and by canals; portions of the city are li ...

, 1610. English Translation published at Bard College, Hudson, New York, October 9, 2003 English Translatio

Original Latin versio

/ref>Tom Pope and Jim Mosher: Galilean telescope homepage" March 17, 2006 , "Some have expressed puzzlement that in his text Galileo does not mention the nebulosity (known in modern nomenclature as M42) enveloping these stars. ... Galileo believed, as he explains in ''Sidereus Nuncius'', that what looks nebulous to the eye is resolved into stars by his telescope; what looks nebulous through his telescope could presumably also be resolved into stars by a still larger and more powerful telescope. Hence, a diffuse glow would be, more than anything, an indication of the limitations of his telescope and not particularly worthy of special note."Tom Pope and Jim Mosher: Page on Galileo's February 4, 1617 notebook drawing of the Trapezium region, May 2, 2006 "Perhaps significantly, Galileo makes no mention of having noticed the now well-known gas cloud, M42, surrounding the Trapezium stars

A fourth component ( Theta1 Orionis B, B) was identified by several observers in 1673, and several more components were discovered later like E, for a total of eight by 1888. Subsequently, several of the stars were determined to be binaries. Telescopes of amateur astronomers from about

aperture In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...

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 to 30

solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

es in size. They are within a diameter of 1.5

light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...

s 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

The Trapezium is most readily identifiable by the asterism of four relatively bright stars for which it is named. The four are often identified as A, B, C and D in order of increasing

right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the equinox (celestial coordinates), March equinox to the (hour circle of the) point in questio ...

. The brightest of the four stars is C, or Theta¹ Orionis C, with an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

of 5.13. Both A and B have been identified as

eclipsing binaries A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

Infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

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 exhibit circumstellar disks that are dwindling, a likely precursor to planetary formation. In addition,

brown dwarf Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main sequence, main-sequence stars. Their mass is approximately 13 to 80 Jupiter mass, times that of Jupiter ()not big en ...

s and low-mass

runaway stars In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as ...

have been identified.

Possible black hole

A 2012 paper suggests an

intermediate-mass black hole An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range of one hundred to one hundred thousand (102–105) solar masses: significantly higher than stellar black holes but lower than the hundred thousand to more than ...

with a mass more than 100 times that of the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

may be present within the Trapezium, something that could explain the large

velocity dispersion In astronomy, the velocity dispersion (''σ'') is the statistical dispersion of velocities about the mean velocity for a group of astronomical objects, such as an open cluster, globular cluster, galaxy, galaxy cluster, or supercluster. By measu ...

of the stars of the cluster. File:GRAVITY discovers new double star in Orion Trapezium Cluster.jpg, One of the components of the cluster (Theta¹ Orionis F, lower left) is a double star. File:Chandra X-ray View of Orion.jpg, The

Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources ...

view of the Orion Nebula File:TrapeziumStars.jpg, Trapezium star identification File:Glowing region Trapezium stars.jpg, Hubble detail of a region west of the Trapezium, showing arcs and bubbles formed when

stellar wind A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...

s collide with existing interstellar material File:Trapezium Labeled.jpg, A wider shot of the core details showing the trapezium in context of the surrounding nebulae File:Great Nebula in Orion Labeled.jpg, Core detail of the nebula with all the stars identified

List of stars

References

External links

Chandra Observatory Uncovers Hot Stars In The Making
MIT Press Release, 2000. *

Astronomy Picture of the Day Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include ...

In the Center of the Trapezium
2003 March 2
Observing the Trapezium
{{DEFAULTSORT:Trapezium Cluster Open clusters Orion (constellation) Orion molecular cloud complex Orionis, Theta1 Asterisms (astronomy) BD-05 1315 Orionis, 41

Identification

Possible black hole

List of stars

References

Further reading

External links