astronomy

NGC 4650A

NGC 4650A 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 4650A rather than just read about it. In short: NGC 4650A is a lenticular galaxy of the rare polar-ring type, located in the southern constellation of Centaurus. It has an apparent visual magnitude of 13.3 and spans an angular size of 1.6′ × 0.8′.

Key takeaways

NGC 4650A 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 4650A to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 4650A from memory before moving on to harder problems.

Reference excerpt

NGC 4650A is a lenticular galaxy of the rare polar-ring type, located in the southern constellation of Centaurus. It has an apparent visual magnitude of 13.3 and spans an angular size of 1.6′ × 0.8′. This galaxy is located at an estimated distance of 130 million light-years (39.8 Mpc) and is receding with a heliocentric radial velocity of 2,908.5 km/s. It should not be confused with the nearby spiral galaxy NGC 4650; the physical distance between both galaxies is only about 6 times the optical radius of NGC 4650. NGC 4650A lies in a chain of five galaxies in the Centaurus Cluster.

Observations Early studies of this galaxy beginning in 1967 identified it as peculiar, although it was not included in Halton Arp's Atlas of Peculiar Galaxies. It has the appearance of having two very different components. In the middle is what resembles an elliptical galaxy with an axial ratio of around 3, which would give it a morphological classification of E6–7. Its major axis is aligned along a NW-SE direction. Oriented at nearly right angles to this central component is a fainter, S-shaped feature resembling a spiral or ring galaxy seen almost edge-on. The elliptical central nucleus does not appear to be especially active. During the 1990s, attempts were made to model the dark matter distribution around the galaxy, with only partial success. A more extensive mapping of the neutral hydrogen distribution was made in 1997. The observed shapes and motions suggested that the polar disk most likely possessed two spiral arms, which produce the S-shape seen in images. The total flux suggested a neutral hydrogen mass of 8×109 M☉. Imaging of the central S0 (lenticular) feature by the Hubble Space Telescope showed a complex pattern of dust lanes extending inward toward the nucleus, while the outer portions of the S0 showed an aging stellar population that had ceased new star formation some 3–5 billion years ago. The outer polar galaxy displays a complex shape that shows warping. Gas is accumulating to form a ring that encircles the central S0 at a radius of 3 thousand light-years (1 kpc). The inner disk is inclined about 63°, then flattens out with increasing radius, forming what appears to be two star-forming spiral arms. Most of the light from the polar feature is coming from stars less than a billion years old. The youngest detected stars are 6.5 Myr old. Measurements of the motions of stars in NGC 4650A showed a consistent rotation pattern in the polar ring. The rotation curve is flat, providing more support for a disk structure rather than a ring. There is no counter-rotating streams of stars. Both the structure and shape of NGC 4650A support the idea of a merger of two separate galaxies. The central component appears to be an oblate spheroid supported by rotation. Careful examination of the central part of the disk shows that the stellar motions extend right to the middle, with the two components co-existing with separate rotations.

Supernova On April 29, 1990, Oscar Pizarro discovered a supernova in the polar ring of NGC 4650A, positioned 13.4″ east and 44.9″ south of the galactic nucleus. This identification was made from a photographic plate taken April 27 with the ESO Schmidt telescope at La Silla Observatory. Given the identifier SN 1990I, this event was later classified as a Type Ib supernova. Based on light curve data, SN 1990I was estimated to have begun April 11 and reached peak light on April 29.

References

Illustrations

Worked examples

Example 1 — a first encounter with NGC 4650A

Start with the simplest possible case. Write down what NGC 4650A 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 4650A 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 4650A 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 4650A

In research: NGC 4650A 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 4650A 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 4650A is common in secondary-school and first-year university syllabi. It links to neighbouring topics Centaurus, Lenticular galaxies, NGC objects, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 4650A 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 4650A in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 4650A 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 4650A out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 4650A in simple terms?

Why does NGC 4650A 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 4650A?

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 4650A.