astronomy

Wolf–Lundmark–Melotte

Wolf–Lundmark–Melotte 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 Wolf–Lundmark–Melotte rather than just read about it. In short: The Wolf–Lundmark–Melotte Galaxy (WLM) is a barred irregular galaxy discovered in 1909 by Max Wolf, located on the outer edges of the Local Group. The discovery of the nature of the galaxy was accredited to Knut Lundmark and Philibert Jacques Melotte in 1926.

Key takeaways

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

Reference excerpt

The Wolf–Lundmark–Melotte Galaxy (WLM) is a barred irregular galaxy discovered in 1909 by Max Wolf, located on the outer edges of the Local Group. The discovery of the nature of the galaxy was accredited to Knut Lundmark and Philibert Jacques Melotte in 1926. It is located in the constellation of Cetus.

Properties Wolf–Lundmark–Melotte is a rotating disk that is seen edge-on. It is relatively isolated from the rest of the Local Group, and does not seem to show much evidence of interaction. However, the rotation curve of Wolf–Lundmark–Melotte is asymmetrical, in that the receding side and approaching side of the galaxy are rotating in different ways. Although isolated, Wolf–Lundmark–Melotte shows evidence of ram pressure stripping. It is far outside of the virial radius of the Milky Way, so it is possible that Wolf–Lundmark–Melotte is currently passing through some relatively dense medium.

Star formation In 1994, A. E. Dolphin used the Hubble Space Telescope to create a color–magnitude diagram for WLM. It showed that around half of all the star formation in this galaxy occurred during a starburst that started ~13 Gyr ago. During the starburst, the metallicity of WLM rose from [Fe/H] ~ −2.2 to [Fe/H] −1.3. There being no horizontal-branch population, Dolphin concludes that no more than ~20 M☉ per Myr of star formation occurred in the period from 12 to 15 Gyr ago. From 2.5 to 9 Gyr ago, the mean rate of star formation was 100 to 200 M☉ per Myr. Being at the edge of the Local Group has also protected WLM from interactions and mergers with other galaxies, giving it a "pristine" stellar population and state that make it particularly useful for comparative studies. WLM is currently forming stars, as evidenced by clumps of newly formed stars visible in ultraviolet light. These clumps are about 20 to 100 light-years (7 to 30 parsecs) in size. The youngest clumps are found in the southern half of the galaxy, which has more star formation. In 2015, interferometric observations from ALMA detected CO in the low metallicity dwarf galaxy WLM revealed dense cloud cores. These results suggest that the CO clouds in WLM are normal in terms of density, pressure and column density, which explains why they lie on the standard correlations. They also appear to be marginally self-bound by gravity, suggesting that they are related to star formation. Their properties are typical for parsec-size molecular cloud cores in the solar neighbourhood.

Astronomical objects

Globular cluster WLM has one known globular cluster (WLM-1) at 00h 01m 29.5s −15° 27′ 51″ that Hodge et al. (1999) determined as having an absolute magnitude of −8.8 and a metallicity of –1.5, with an age of ~15 billion years. This cluster has a luminosity that is slightly over the average for all globulars. The seeming lack of faint low-mass globular clusters cannot be explained by the weak tidal forces of the WLM system.

Star

WLM-CB1 is a massive candidate contact binary system identified in 2024 through archival time-series photometric observations conducted with the Hubble Space Telescope (HST) and the James Webb Space Telescope (JWST). It is notable as the first observed massive contact binary at a metallicity significantly lower than that of the Small Magellanic Cloud (SMC), with an estimated metallicity of [Fe/H] ≈ -1.85 (or 0.14 Z⊙). It is located at 00h 02m 00.23s −15° 31′ 05.20″. The Primary companion (WLM-CB1a) has a mass of 16+2−3 M⊙ and has a radius of 5.9 R⊙ and the Secondary component (WLM-CB1b) has a mass of 7+5−3 M⊙ and has a radius of 3.9 R⊙.

References in popular culture In E. E. Smith's Lensman novels, the "Second Galaxy" is identified as "Lundmark's Nebula". However, some believe the "Second Galaxy" may not be the Wolf–Lundmark–Melotte galaxy, since the first chapter of the first novel in the series (Triplanetary) and the series-establishing material appearing at the beginning of subsequent novels states that the "Second Galaxy" and the "First Galaxy" (the Milky Way) collided and passed through each other "edge-on" during the "planet-forming era"—implying that the "Lundmark's Nebula" of the series must necessarily be obscured from view by the Milky Way; however, according to others, it could have passed through at an angle and thus be identified with the galaxy described in this article; some have stated that this is the galaxy that E.E. Smith was thinking of when he wrote the series. However, the distance to Lundmark's nebula is defined quite precisely in Gray Lensman as approximately 24 million parsecs, much larger than the distance to Wolf–Lundmark–Melotte (approximately 930,000 parsecs). Additionally, in Second Stage Lensmen multiple references are made to the spiral arms of Lundmark's Nebula. Wolf–Lundmark–Melotte does not possess such structures. At the time of writing of these books, the name of Lundmark was associated with such classifications and Smith may have elected to use this as a "believable" name for an entirely fictional galaxy. At the time the Lensman series was written, most astronomers favored the tidal theory of Solar System formation, which required that planets be formed by the close approach of another star. In order to produce the massive numbers of planets necessary to evolve into galactic civilizations in both the Milky Way and Lundmark's Nebula, as portrayed in the Lensman series, E.E. Smith thought it would have been necessary for another galaxy to have passed through the Milky Way to produce the large number of close encounters necessary to form so many planets. The Doctor Who novel Synthespians™ by Craig Hinton refers to the New Earth Republic of the 101st Century and beyond, which spearheads a programme of colonisation, sending sleeper ships to the Wolf-Lundmark-Melotte galaxy and Andromeda.

References

External links Media related to WLM galaxy at Wikimedia Commons

Illustrations

Worked examples

Example 1 — a first encounter with Wolf–Lundmark–Melotte

Start with the simplest possible case. Write down what Wolf–Lundmark–Melotte 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 Wolf–Lundmark–Melotte 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 Wolf–Lundmark–Melotte 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 Wolf–Lundmark–Melotte

In research: Wolf–Lundmark–Melotte 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 Wolf–Lundmark–Melotte 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: Wolf–Lundmark–Melotte is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1909, Cetus (constellation), Irregular galaxies, so understanding it makes those chapters shorter.
In everyday life: Look for Wolf–Lundmark–Melotte 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 Wolf–Lundmark–Melotte in 20 minutes

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

Frequently asked questions

What is Wolf–Lundmark–Melotte in simple terms?

Why does Wolf–Lundmark–Melotte 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 Wolf–Lundmark–Melotte?

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 Wolf–Lundmark–Melotte.