astronomy

NGC 2974

NGC 2974 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 2974 rather than just read about it. In short: NGC 2974 (also catalogued as NGC 2652) is a lenticular galaxy located in the constellation Sextans. It is located at a distance of circa 90 million light years from Earth, which, given its apparent dimensions, means that NGC 2974 is about 90,000 light years across.

Key takeaways

NGC 2974 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 2974 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 2974 from memory before moving on to harder problems.

Reference excerpt

NGC 2974 (also catalogued as NGC 2652) is a lenticular galaxy located in the constellation Sextans. It is located at a distance of circa 90 million light years from Earth, which, given its apparent dimensions, means that NGC 2974 is about 90,000 light years across. It was discovered by William Herschel on January 6, 1785. NGC 2974 is located in the sky about 2 and a half degrees south-south east of Iota Hydrae and more than 6 degrees northeast of Alphard. A 10th magnitude star lies next to the galaxy, thus making it a challenging object at low magnifications. NGC 2974 is part of the Herschel 400 Catalogue.

Characteristics

NGC 2974 has been categorised by Gérard de Vaucouleurs as an elliptical galaxy, however there is evidence the galaxy has a disk. A rotating disk of neutral hydrogen with axis similar to that of the optical isophotes of the galaxy was detected in 1988 by Kim et al. They estimated the total HI mass to be 8×108 M☉. The galaxy in ultraviolet, as observed by GALEX, features an outer ring structure that holds about 1% of the total stellar mass of the galaxy and has a population of young stars. The radius of the ring is about 60 arcseconds, while one more, partial, ring has been detected in large radii. The galaxy also features multiple shells, which indicate that it has accreted material, probably by the merger of smaller galaxies. More detailed observations of the galaxy in HI by the Very Large Array revealed that the HI disk is in fact a ring. The observations also made it possible to measure the rotation curve of HI. The rotation curve rises quickly to a maximal velocity and then declines slowly until it flattens out at a lower velocity. This rotation curve is typical of galaxies with concentrated light distribution and could indicate that while the central part is dominated by visible mass, the outer parts are dominated by dark matter. The mass-to-light ratio is 4.3 M☉/L☉I at one effective radius and increases to 8.5 M☉/L☉I at 5 effective radii, where dark matter comprises at least 55 per cent of the total mass. Observations of the central area of the galaxy by Hubble Space Telescope revealed the presence of two gaseous spiral features, extending for about 200 parsecs. The kinematics of the central area show significant deviations from circular motions and they have been interpreted as the signature of a bar which is about 540 parsecs in diameter. The bar, although too weak to be detected in visual light is considered strong enough to channel material towards the central parsecs of the nucleus. Observations by SAURON (Spectrographic Areal Unit for Research on Optical Nebulae) confirmed the presence of the inner bar, while it was noted that it is possible that a large-scale bar exists too. The current star formation activity and morphological evolution of NGC 2974 has been attributed to the large bar. A ring observation in O III images may be associated with the inner bar or a nuclear ring. The nucleus of the galaxy has been found to be active and it has been categorised as a type 2 Seyfert galaxy. The most accepted theory for the energy source of active galactic nuclei is the presence of an accretion disk around a supermassive black hole. The mass of the black hole in the centre of NGC 2974 is estimated to be between 140 and 210 million (108.23±0.09) M☉ based on the stellar velocity dispersion.

Nearby galaxies NGC 2974 is the largest and brightest galaxy in the NGC 2974 group. Other members of the group include the galaxies MCG -01-25-024, UGCA 173, and UGCA 175. Other nearby galaxies include NGC 2967 and UGC 5228 with their groups.

References

External links

NGC 2974 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images NGC 2974 on SIMBAD

Illustrations

Worked examples

Example 1 — a first encounter with NGC 2974

Start with the simplest possible case. Write down what NGC 2974 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 2974 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 2974 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 2974

In research: NGC 2974 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 2974 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 2974 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1785, Discoveries by William Herschel, Lenticular galaxies, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 2974 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 2974 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 2974 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 2974 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 2974 in simple terms?

Why does NGC 2974 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 2974?

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 2974.