astronomy

NGC 7424

NGC 7424 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 7424 rather than just read about it. In short: NGC 7424 is a barred spiral galaxy located 37.5 million light-years away in the southern constellation Grus (the Crane). Its size (about 100,000 light-years) makes it similar to our own galaxy, the Milky Way.

Key takeaways

NGC 7424 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 7424 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 7424 from memory before moving on to harder problems.

Reference excerpt

NGC 7424 is a barred spiral galaxy located 37.5 million light-years away in the southern constellation Grus (the Crane). Its size (about 100,000 light-years) makes it similar to our own galaxy, the Milky Way. It is called a "grand design" galaxy because of its well defined spiral arms. Two supernovae and two ultraluminous X-ray sources have been discovered in NGC 7424.

Characteristics NGC 7424 is intermediate between normal spirals (SA) and strongly barred galaxies (SB). Other features include the presence of a central ring-like structure and a relatively low core brightness relative to the arms. The redder color of the prominent bar indicates an older population of stars while the bright blue color of the loose arms indicates the presence of ionised hydrogen and clusters of massive young stars. NGC 7424 is listed as a member of the IC 1459 Grus Group of galaxies, but is suspected of being a "field galaxy"; that is, not gravitationally bound to any group.

Supernovae Two supernovae have been observed in NGC 7424:

SN 2001ig was a rare Type IIb supernova discovered by Australian amateur Robert Evans on the outer edge of NGC 7424 on 10 December 2001. Type IIb supernovae (SNe) initially exhibit spectral lines of hydrogen (like typical Type II's), but these disappear after a short time to be replaced by lines of oxygen, calcium and magnesium (like typical Type Ib's and Ic's). SN 2017bzb (Type II, mag. 13) was discovered by New Zealand astronomer Stuart Parker on 7 March, 2017.

In 2006, Anglo-Australian Observatory astronomer Stuart Ryder et al. found what they argued could be the binary companion to SN 2001ig using the Gemini Observatory. It is a massive A or F class star that had an eccentric orbit around the progenitor, a Wolf-Rayet star. They believe that the companion periodically stripped the outer hydrogen-rich envelope of the progenitor, accounting for the observed spectral changes. Princeton University fellow Alicia Soderberg et al. also believe that the progenitor was a Wolf-Rayet star, but suggest that the periodic mass loss was a result of the intense stellar wind these stars produce. In a paper published in March 2018, Ryder et al. announced that the surviving companion had been observed with the Hubble Space Telescope in the ultraviolet. This is the first time a companion to a Type IIb supernova has been imaged.

Ultraluminous X-ray sources In May and June 2002, Roberto Soria and his colleagues at the Harvard-Smithsonian Center for Astrophysics discovered two Ultraluminous X-ray sources (ULXs) with the Chandra X-ray Observatory. ULXs are objects that emit tremendous amounts of X-rays (> 1032 watts or 1039 erg/s), assuming they radiate isotropically (the same in all directions). This amount is larger than currently understood stellar processes (including supernovae) but smaller than the amount of X-rays emitted by active galactic nuclei, which accounts for their alternate name, Intermediate-luminosity X-ray Objects (IXOs). The source designated ULX1 was found in a relatively empty interarm region, far from any bright clusters or star-forming complexes, and showed a 75% increase in X-ray luminosity over the course of 20 days. ULX2 was found in an exceptionally bright young stellar complex, and showed an order of magnitude increase over the same time period.

References

External links Media related to NGC 7424 at Wikimedia Commons

Illustrations

Worked examples

Example 1 — a first encounter with NGC 7424

Start with the simplest possible case. Write down what NGC 7424 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 7424 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 7424 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 7424

In research: NGC 7424 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 7424 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 7424 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Barred spiral galaxies, Grus (constellation), NGC objects, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 7424 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 7424 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 7424 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 7424 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 7424 in simple terms?

Why does NGC 7424 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 7424?

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 7424.