astronomy

Irregular galaxy

Irregular galaxy is a astronomy 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 Irregular galaxy rather than just read about it. In short: An Irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy. Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arm structure.

Key takeaways

Irregular galaxy belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Irregular galaxy to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Irregular galaxy from memory before moving on to harder problems.

Reference excerpt

An Irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy. Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arm structure. Other galaxies have an axis of symmetry for their blue-light distribution, which cannot be found in the sporadic organization of irregular galaxies. This absence of structure in an irregular galaxy leads to little density waves in these galaxies. This makes irregular galaxies prime areas to study star formation without the effects of density waves. Collectively they are thought to make up about a quarter of all galaxies. A large chunk of the Local Group is made up of irregular galaxies, most being distant and classified as dwarf irregulars. Irregulars are broken down into two more subcategories along with dwarf. Some irregular galaxies were once spiral or elliptical galaxies but were deformed by an uneven external gravitational force, or may be young galaxies between spiral and elliptical status. Irregular galaxies may contain abundant amounts of gas and dust. This is not necessarily true for dwarf irregulars. Irregular galaxies may also be formed in galaxy collisions. Irregular galaxies are commonly small, about one tenth the mass of the Milky Way galaxy, though there are also unusual cases of large irregulars like UGC 6697. Due to their small sizes, they are prone to environmental effects like colliding with large galaxies and intergalactic clouds.

Types There are three major types of irregular galaxies:

An Irr-I galaxy (Irr I) is an irregular galaxy that features some structure but not enough to place it cleanly into the Hubble sequence. Subtypes with some spiral structure are called Sm galaxies Subtypes without spiral structure are called Im galaxies. An Irr-II galaxy (Irr II) is an irregular galaxy that does not appear to feature any structure that can place it into the Hubble sequence, and is often shaped via collision or merger.

A dI-galaxy (or dIrr) is a dwarf irregular galaxy. Irregular galaxies with luminosities below 10 8 L ⊙ {\displaystyle 10^{8}L_{\odot }} fall into the dwarf irregular galaxy category. This type of galaxy is now thought to be important to understand the overall evolution of galaxies, as they tend to have a low level of metallicity and relatively high levels of gas, and are thought to be similar to the earliest galaxies that populated the Universe. They may represent a local (and therefore more recent) version of the faint blue galaxies known to exist in deep field galaxy surveys. These types of irregular galaxies also have high amounts of dark matter. Irregular galaxies are considered late-type along with spiral galaxies as opposed to early type elliptical galaxies. Some of the irregular galaxies, especially of the Magellanic type, are small spiral galaxies that are being distorted by the gravity of a larger neighbor.

Magellanic Clouds The Magellanic Cloud galaxies were once classified as irregular galaxies. The Large Magellanic Cloud has since been re-classified as type SBm (barred Magellanic spiral). The Small Magellanic Cloud remains classified as an irregular galaxy of type Im under current galaxy morphological classification, although it does contain a bar structure.

Star formation Star formation in irregular galaxies is both common and varied, with some having rates comparable to spiral galaxies. The processes of star formation are the same as in other types of galaxies. However, the origins of star formation in irregular galaxies are perhaps more influenced by the random movement of gas, as well as the effects of massive stars and the unusually common giant HII regions on the interstellar medium. This is because they lack the density waves believed to contribute to star formation in spiral galaxies.

Notable Examples

See also Blueberry galaxy – Small and very active galaxies. Dwarf galaxy Dwarf elliptical galaxy Peculiar galaxy Galaxy morphological classification

References

External links

Illustrations

Worked examples

Example 1 — a first encounter with Irregular galaxy

Start with the simplest possible case. Write down what Irregular galaxy claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, 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 Irregular galaxy 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 Irregular galaxy 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 Irregular galaxy

In research: Irregular galaxy appears in astronomy 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 Irregular galaxy 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: Irregular galaxy is common in secondary-school and first-year university syllabi. It links to neighbouring topics Irregular galaxies, Morphological types of galaxy, so understanding it makes those chapters shorter.
In everyday life: Look for Irregular galaxy 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 Irregular galaxy in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Irregular galaxy means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Irregular galaxy out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Irregular galaxy in simple terms?

Why does Irregular galaxy matter?

Because it connects several astronomy 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 Irregular galaxy?

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 Irregular galaxy.