chemistry

Orion molecular cloud complex

Orion molecular cloud complex is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Orion molecular cloud complex rather than just read about it. In short: The Orion molecular cloud complex (or, simply, the Orion complex) is a star-forming region with stellar ages ranging up to 12 Myr. Two giant molecular clouds are a part of it, Orion A and Orion B.

Key takeaways

Orion molecular cloud complex belongs to chemistry; place it in that map before memorising details.
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Connect Orion molecular cloud complex to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Orion molecular cloud complex from memory before moving on to harder problems.

Reference excerpt

The Orion molecular cloud complex (or, simply, the Orion complex) is a star-forming region with stellar ages ranging up to 12 Myr. Two giant molecular clouds are a part of it, Orion A and Orion B. The stars currently forming within the complex are located within these clouds. A number of other somewhat older stars no longer associated with the molecular gas are also part of the complex, most notably the Orion's Belt (Orion OB1b), as well as the dispersed population north of it (Orion OB1a). Near the head of Orion there is also a population of young stars that is centered on Meissa. The complex is between 1 000 and 1 400 light-years away, and hundreds of light-years across. The Orion complex is one of the most active regions of nearby stellar formation visible in the night sky, and is home to both protoplanetary discs and very young stars. Much of it is bright in infrared wavelengths due to the heat-intensive processes involved in stellar formation, though the complex contains dark nebulae, emission nebulae, reflection nebulae, and H II regions. The presence of ripples on the surface of Orion's molecular clouds was discovered in 2010. The ripples are a result of the expansion of the nebulae gas over pre-existing molecular gas. The Orion complex includes a large group of bright nebulae and dark clouds in the Orion constellation. Several nebulae can be observed through binoculars and small telescopes, and some parts (such as the Orion Nebula) are visible to the naked eye.

Nebulae within the complex

The following is a list of notable regions within the larger complex:

Orion A molecular cloud The Orion Nebula, also known as M42 (part of Orion's Sword) M43, which is part of the Orion Nebula Sh2-279 (part of Orion's Sword) NGC 1980 (part of Orion's Sword) Orion Molecular Clouds Orion molecular cloud 1 (OMC-1) with the Becklin–Neugebauer Object and the Kleinmann–Low Nebula Orion molecular cloud 2 (OMC-2) Orion molecular cloud 3 (OMC-3) Orion molecular cloud 4 (OMC-4) NGC 1981 NGC 1999 HH 222 (also known as Waterfall Nebula), above NGC 1999 HH 34 a Herbig–Haro object with symmetric bow shocks LDN 1641 HH 1/2, the first recognized Herbig–Haro objects Orion B molecular cloud Flame Nebula (NGC 2024) IC 434, which contains the Horsehead Nebula The Horsehead Nebula (Barnard 33) M78, a reflection nebula (NGC 2068) McNeil's Nebula is a variable nebula discovered in 2004 near M78 Orion East Cloud (LDN 1621 + LDN 1622) HH 24-26 this group contains three Herbig–Haro objects HH 111 one of the most well-known Herbig–Haro objects Orion OB1 association Orion's Belt Sigma Ori cluster 25 Ori cluster Lambda Orionis molecular ring (Sh2-264) Lambda Ori cluster Barnard 30 Barnard 35 (Angelfish nebula) Orion-Eridanus superbubble Barnard's Loop (Sh2-276) IC 2118 Eridanus Loop Arc A Arc B Arc C A more complete list can be found for example in Maddalena et al. (1986) Table 1

Individual components

Orion A The giant molecular cloud Orion A is the most active star-forming region in the local neighbourhood of the Sun. In the last few million years about 3000 young stellar objects were formed in this region, including about 190 protostars and about 2600 pre-main sequence stars. The Orion A cloud has a mass in the order of 105 M☉. The stars in Orion A do not have the same distance to us. The "head" of the cloud, which also contains the Orion Nebula is about 1300 light-years (400 parsecs) away from the Sun. The "tail" however is up to 1530 light-years (470 parsecs) away from the Sun. The Orion A cloud is therefore longer than the projected length of 130 light-years (40 parsecs) and has a true length of 290 light-years (90 parsecs).

Orion Molecular Clouds

The Orion Molecular Clouds (OMC 1 to OMC 4) are molecular clouds located behind the Orion Nebula. Most of the light from the OMCs are blocked by material from the Orion Nebula, but some features like the Kleinmann-Low Nebula and the Becklin-Neugebauer object can be seen in the infrared. The clouds can be seen in the far-infrared and in radio wavelengths. The Trapezium Cluster has a small angular separation from the Kleinmann-Low Nebula, but the Trapezium Cluster is located inside the Orion Nebula, which is closer towards Earth.

Orion B Orion B is about 1370 light-years (420 parsecs) from Earth. It has a size of about 1.5 kpc² and a mass in the order of 105 M☉. It contains several star forming regions with the star cluster inside the Flame Nebula being the largest cluster.

Orion OB1 association

The Orion OB1 association represents different stellar populations that are superimposed along our line of sight. The oldest group with 8–10 million years is Orion OB1a, northwest of Orion's Belt, and the youngest group with less than 2 million years is Orion OB1d, which contains the Orion Nebula cluster and NGC 2024.

Lambda Orionis molecular ring

The Lambda Orionis ring is a large molecular ring, centered around Lambda Orioinis (Meissa). It was suggested that this ring formed after a supernova occurred inside the central star-forming region that once surrounded the Lambda Orionis Cluster, dispersing the material into the ring seen today. Star-formation is still continuing in regions of the ring.

Superbubble

Parts of the Orion-Eridanus superbubble were first seen as Barnard's Loop in Hydrogen-alpha images that warp around the eastern portion of Orion. The other part of the superbubble that is seen in H-alpha is the Eridanus Loop. The walls of the entire bubble are seen in far-infrared and HI. Some features of the Eridanus Loop might be as close as 590 light-years (180 parsecs) to the Sun.

Gallery

See also Runaway star Rho Ophiuchi cloud complex Taurus molecular cloud Perseus molecular cloud Scorpius–Centaurus association

References

External links Orion Cloud Complex SEDS website ESO: Hidden Secrets of Orion’s Clouds incl. Photos & Animations

Illustrations

Worked examples

Example 1 — a first encounter with Orion molecular cloud complex

Start with the simplest possible case. Write down what Orion molecular cloud complex claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Orion molecular cloud complex before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Orion molecular cloud complex ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Orion molecular cloud complex

In research: Orion molecular cloud complex appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Orion molecular cloud complex in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Orion molecular cloud complex is common in secondary-school and first-year university syllabi. It links to neighbouring topics Molecular clouds, Orion (constellation), Orion molecular cloud complex, so understanding it makes those chapters shorter.
In everyday life: Look for Orion molecular cloud complex outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Orion molecular cloud complex in 20 minutes

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Frequently asked questions

What is Orion molecular cloud complex in simple terms?

The Orion molecular cloud complex (or, simply, the Orion complex) is a star-forming region with stellar ages ranging up to 12 Myr. Two giant molecular clouds are a part of it, Orion A and Orion B.

Why does Orion molecular cloud complex matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Orion molecular cloud complex?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Orion molecular cloud complex.