astronomy

NGC 7172

NGC 7172 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 7172 rather than just read about it. In short: NGC 7172 is a spiral galaxy located in the constellation Piscis Austrinus. It is located at a distance of about 110 million light years from Earth, which, given its apparent dimensions, means that NGC 7172 is about 100,000 light years across.

Key takeaways

NGC 7172 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 7172 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 7172 from memory before moving on to harder problems.

Reference excerpt

NGC 7172 is a spiral galaxy located in the constellation Piscis Austrinus. It is located at a distance of about 110 million light years from Earth, which, given its apparent dimensions, means that NGC 7172 is about 100,000 light years across. It was discovered by John Herschel on September 23, 1834.

Characteristics NGC 7172 is a spiral galaxy that is seen edge-on. A thick dark dust lane runs across the galaxy, obscuring the nucleus of the galaxy. The galaxy appears in deep photographs to be tidally distorted, and a diffuse tail is extending towards the north-west.

Nucleus The nucleus of NGC 7172 was originally considered to be normal, but later observations revealed that it emitted X-rays and was a powerful infrared source, which exhibited variation. These findings indicated that NGC 7172 has an active galactic nucleus which is obstructed in optical wavelengths. The nucleus was classified as a type 2 Seyfert galaxy in the optical, but observations in other wavelengths suggest it is type 1 Seyfert galaxy. The source of activity of the nucleus is an accretion disk around a supermassive black hole. The mass of the supermassive black hole in the centre of NGC 7172 is estimated to be 5.5×107 M☉ based on the MBH–σ⋆ relation or (1.03±0.35)×107 M☉ based on the X-ray scaling method. NGC 7172 has been found to exhibit variability in X-rays. As observed by the Advanced Satellite for Cosmology and Astrophysics (ASCA), the galaxy exhibited short term variability of about 30% in the time scale of hours, which is common for Seyfert I galaxies. It also exhibits long term variability, as it dimmed three to four times between 1995 and 1996. This was also observed by BeppoSAX. The FeKα line appeared constant when observed with BeppoSAX, but appeared to variate by a factor of two by ASCA, and thus it is associated with an accretion disk. The hard X-ray spectrum appears similar to that of a Seyfert I galaxy, indicating that the nucleus is seen though a Compton-thin absorber. In infrared observations of the nucleus dominates the spectrum of the active nucleus, with 3.4-μm carbonaceous dust absorption detected, but no 3.3-μm PAH emission, indicating that the nucleus is obstructed. A strong obsurption feature is observed, probably the 9.7-μm silicate dust absorption line. X-rays and mid-infrared have similar absorption columns. It is possible that an outflow towards the southwest is detected in radiowaves.

Nearby galaxies NGC 7172 is part of the Hickson Compact Group 90. NGC 7172 lies 6 arcminutes north of the core of the compact group, which is comprised by the elliptical galaxies NGC 7173, and NGC 7176, and disturbed spiral galaxy NGC 7174; these three galaxies lie within 6 arcminutes from each other. The compact group is surrounded by a more loose group, with 19 galaxies of similar redshift within 1.5 degrees from the core group. Garcia identified as members of this group the galaxies NGC 7154, ESO 404- 12, NGC 7163, ESO 466- 36, ESO 466- 46, ESO 404- 27, NGC 7187, IC 5156, ESO 404- 39, and ESO 466- 51. Other nearby galaxies include NGC 7135 and its group, NGC 7204, and NGC 7208.

See also NGC 4388 - a similar active galaxy

References

External links

NGC 7172 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images NGC 7172 on SIMBAD

Illustrations

Worked examples

Example 1 — a first encounter with NGC 7172

Start with the simplest possible case. Write down what NGC 7172 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 7172 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 7172 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 7172

In research: NGC 7172 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 7172 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 7172 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1834, Discoveries by John Herschel, NGC objects, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 7172 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 7172 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 7172 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 NGC 7172 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 7172 in simple terms?

Why does NGC 7172 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 7172?

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 7172.