astronomy

Messier 32

Messier 32 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 Messier 32 rather than just read about it. In short: Messier 32 (also known as M32 and NGC 221) is a dwarf "early-type" galaxy about 2,490,000 light-years (760,000 pc) from the Solar System, appearing in the constellation Andromeda. M32 is a satellite galaxy of the Andromeda Galaxy (M31) and was discovered by Guillaume Le Gentil in 1749.

Key takeaways

Messier 32 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Messier 32 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 32 from memory before moving on to harder problems.

Reference excerpt

Messier 32 (also known as M32 and NGC 221) is a dwarf "early-type" galaxy about 2,490,000 light-years (760,000 pc) from the Solar System, appearing in the constellation Andromeda. M32 is a satellite galaxy of the Andromeda Galaxy (M31) and was discovered by Guillaume Le Gentil in 1749. The galaxy is a prototype of the relatively rare compact elliptical (cE) class. Half the stars are concentrated within the inner core, which has an effective radius of 330 light-years (100 pc). Densities in the central stellar cusp increase steeply, exceeding 3×107 M☉ pc−3 (30 million solar masses per cubic parsec) at the smallest sub-radii resolved by Hubble Space Telescope, and the half-light radius of this central star cluster is around 6 pc (20 light-years). Like more ordinary elliptical galaxies, M32 contains mostly old faint red and yellow stars with practically no dust or gas and consequently no current star formation. It does, however, show hints of star formation in the relatively recent past.

Origins

The structure and stellar content of M32 are difficult to explain by traditional galaxy formation models. Theoretical arguments and some simulations suggest a scenario in which the strong tidal field of M31 can transform a spiral galaxy or a lenticular galaxy into a compact elliptical. As a small disk galaxy falls into the central parts of M31, much of its outer layers will be stripped away. The central bulge of the small galaxy is much less affected and retains its morphology. Gravitational tidal effects may also drive gas inward and trigger a star burst in the core of the small galaxy, resulting in the high density of M32 observed today. There is evidence that M32 has a faint outer disk, and as such is not a typical elliptical galaxy. Newer simulations find that an off-centre impact by M32 around 800 million years ago explains the present-day warp in M31's disk. However, this feature only occurs during the first orbital passage, whereas it takes many orbits for tides to transform a normal dwarf into M32. The observed colours and stellar populations of M32's outskirts do not match the stellar halo of M31, indicating that tidal losses from M32 are not their source. Taken together, these circumstances may suggest that M32 already began in its compact state, and has retained most of its own stars. At least one similar cE galaxy has been discovered in isolation, without any massive companion to thresh it. Another hypothesis is that M32 is in fact the largest remnant of a former spiral galaxy, M32p, which was then the third largest member of the Local Group. According to this simulation, M31 (Andromeda) and M32p merged about two billion years ago, which could explain both the unusual makeup of the current M31 stellar halo, and the structure and content of M32.

Distance measurements At least two techniques have been used to measure distances to M32. The infrared surface brightness fluctuations distance measurement technique estimates distances to spiral galaxies based on the graininess of the appearance of their bulges. The distance measured to M32 using this technique is 2.46 ± 0.09 million light-years (755 ± 28 kpc). However, M32 is close enough that the tip of the red giant branch (TRGB) method may be used to estimate its distance. The estimated distance to M32 using this technique is 2.51 ± 0.13 million light-years (770 ± 40 kpc). For several additional reasons, M32 is thought to be in the foreground of M31, rather than behind. Its stars and planetary nebulae do not appear obscured or reddened by foreground gas or dust. Gravitational microlensing of M31 by a star in M32 was observed at the end of November 2000 in one event (with peak on 2 December 2000).

Black hole

M32 contains a supermassive black hole. Its mass has been estimated to lie between 1.5 and 5 million solar masses. A centrally located faint radio and X-ray source (now named M32* in analogy to Sgr A*) is attributed to gas accretion onto the black hole.

See also List of Messier objects List of Andromeda's satellite galaxies List of galaxies

References

External links

"StarDate: M32 Fact Sheet" "SEDS: Elliptical Galaxy M32" Merrifield, Michael. "M32 – Dwarf Elliptical". Deep Sky Videos. Brady Haran. Messier 32 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Illustrations

Worked examples

Example 1 — a first encounter with Messier 32

Start with the simplest possible case. Write down what Messier 32 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 Messier 32 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 Messier 32 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 Messier 32

In research: Messier 32 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 Messier 32 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: Messier 32 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Andromeda (constellation), Andromeda Subgroup, Arp objects, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 32 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 Messier 32 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 32 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 Messier 32 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 32 in simple terms?

Why does Messier 32 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 Messier 32?

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 Messier 32.