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NGC 4622

NGC 4622 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 NGC 4622 rather than just read about it. In short: NGC 4622, also known as the Backward Galaxy, is a face-on unbarred spiral galaxy with a very prominent ring structure located in the constellation Centaurus. The galaxy is a member of the Centaurus Cluster.

NGC 4622 — main illustration
NGC 4622 — illustration

Key takeaways

  • NGC 4622 belongs to astronomy; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect NGC 4622 to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of NGC 4622 from memory before moving on to harder problems.

Reference excerpt

NGC 4622, also known as the Backward Galaxy, is a face-on unbarred spiral galaxy with a very prominent ring structure located in the constellation Centaurus. The galaxy is a member of the Centaurus Cluster.

Spiral structure

The spiral galaxy NGC 4622 lies approximately 111 million light-years away from Earth in the constellation Centaurus. NGC 4622 is an example of a galaxy with leading spiral arms. Each spiral arm winds away from the center of the galaxy and ends at an outermost tip that "points" in a certain direction (away from the arm). Spiral arms were thought to always trail, meaning that the outermost tip of every spiral arm points away from the direction of the disk's orbital rotation. This is true of the inner spiral arm of NGC 4622 but not of its outer spiral arms. The outer arms of NGC 4622 are instead leading spiral arms, meaning the tips of the spiral arms point towards the direction of disk rotation. This may be the result of a gravitational interaction between NGC 4622 and another galaxy or the result of a merger between NGC 4622 and a smaller object. NGC 4622 also has a single inner trailing spiral arm. Although it was originally suspected that the inner spiral arm was a leading arm, the observations that established that the outer arms were leading also established that the inner arm was trailing. These results were met with skepticism in part because they contradicted conventional wisdom with one quote being "so you're the backward astronomers who found the backward galaxy." Astronomical objections centered on the fact that dust reddening and cloud silhouettes were used to determine that the outer arms lead. The galaxy disk is tilted only 19 degrees from face-on making near to far-side effects of dust hard to discern and because clumpy dust clouds might be concentrated on one side of the disk, creating misleading results.

In response, new research determined NGC 4622's spiral arm sense with a method independent of the previous work. The Fourier component method reveals two new weak arms in the inner disk winding opposite the outer strong clockwise pair. Thus the galaxy must have a pair of arms winding in the opposite direction from most galaxies. Analysis of a color-age star formation angle sequence of the Fourier components establishes that the strong outer pair is the leading pair. A Fourier component image of the arm pairs is shown with one of the pair of arms marked for the newly discovered inner CCW pair (black dots) as well as one of the already known (CW) outer pair (white dots).

Supernovae Two supernovae have been observed in NGC 4622:

SN 2001jx (type unknown, mag. 17.5) was captured on an image taken by the Hubble Space Telescope on 25 May 2001. It was discovered by R. Buta and G. G. Byrd of the University of Alabama, as well as T. Freeman of Bevill State Community College. The type of supernova was not determined. SN 2019so (Type Ia-91bg-like, mag. 18.535) was discovered by ATLAS on 14 January 2019.

Group and cluster According to AM Garcia, NGC 4622 is a member of the NGC 4709 group which consists of at least 42 galaxies including NGC 4616, NGC 4622B (also called PGC 42852), NGC 4679 and NGC 4709. The NGC 4709 group is part of the Centaurus Cluster.

See also Messier 64 – a spiral galaxy with its gas disk orbiting opposite the disk of stars

References

External links Media related to NGC 4622 at Wikimedia Commons Hubble Heritage site: Pictures and description SKY-MAP.ORG : NGC 4622

Illustrations

NGC 4622 illustration
NGC 4622: Based only on their shape, one would expect from observations of other spiral galaxies that the outermost spiral arms (blue and blue-green) move by rotating counterclockwise around the center of the galaxy. This is not the case; the outermost spiral arms rotate clockwise, just like the inner spiral arm and the rest of the galaxy's disk. Additionally, the "trailing" inner spiral arm (green) and the "leading" outer spiral arms (blue and blue-green) curl around the galaxy in opposite directions (although both move clockwise around the galaxy's center).
Based only on their shape, one would expect from observations of other spiral galaxies that the outermost spiral arms (blue and blue-green) move by rotating counterclockwise around the center of the galaxy. This is not the case; the outermost spiral arms rotate clockwise, just like the inner spiral arm and the rest of the galaxy's disk. Additionally, the "trailing" inner spiral arm (green) and the "leading" outer spiral arms (blue and blue-green) curl around the galaxy in opposite directions (although both move clockwise around the galaxy's center).
NGC 4622: A simulation of the NGC 4622 arm pairs, exhibiting the Fourier transform m = 2
A simulation of the NGC 4622 arm pairs, exhibiting the Fourier transform m = 2

Worked examples

Example 1 — a first encounter with NGC 4622

Start with the simplest possible case. Write down what NGC 4622 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 NGC 4622 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 NGC 4622 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 NGC 4622

In research
NGC 4622 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 NGC 4622 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
NGC 4622 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Centaurus, Centaurus Cluster, NGC objects, so understanding it makes those chapters shorter.
In everyday life
Look for NGC 4622 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 NGC 4622 in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what NGC 4622 means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain NGC 4622 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 4622 in simple terms?

NGC 4622, also known as the Backward Galaxy, is a face-on unbarred spiral galaxy with a very prominent ring structure located in the constellation Centaurus. The galaxy is a member of the Centaurus Cluster.

Why does NGC 4622 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 NGC 4622?

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 NGC 4622.

Tags

  • Centaurus
  • Centaurus Cluster
  • NGC objects
  • Principal Galaxies Catalogue objects
  • Ring galaxies
  • Unbarred spiral galaxies

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