astronomy

Melnick 34

Melnick 34 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 Melnick 34 rather than just read about it. In short: Melnick 34 (abbreviated to Mk34), also called BAT99-116, is a binary Wolf–Rayet star near R136 in the 30 Doradus complex (also known as the Tarantula Nebula) in the Large Magellanic Cloud. Both components are amongst the most massive and most luminous stars known, and the system is the most massive known binary system.

Key takeaways

Melnick 34 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Melnick 34 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Melnick 34 from memory before moving on to harder problems.

Reference excerpt

Melnick 34 (abbreviated to Mk34), also called BAT99-116, is a binary Wolf–Rayet star near R136 in the 30 Doradus complex (also known as the Tarantula Nebula) in the Large Magellanic Cloud. Both components are amongst the most massive and most luminous stars known, and the system is the most massive known binary system.

Binary

Melnick 34 is a binary star with an orbital period of 155 days. It shows high x-ray luminosity characteristic of colliding-wind binaries, and periodic variations in luminosity, spectral absorption, and the x-ray brightness. The orbit has been calculated based on spectroscopic observations with the Very Large Telescope. The two components have identical spectral types of WN5h and the spectral lines of each vary every 155 days, indicating projected orbital motions with speeds of 130 km/s and 141 km/s respectively. The similar orbital speeds show that the two components have similar masses; the secondary has a mass 92% of the primary, assuming an inclination near 50°. The inclination of 50° best matches the orbital properties of the two stars to their observed properties. The primary is designated A and the secondary B. The orbit is moderately eccentric, with a periastron separation of about 0.9 AU.

Physical characteristics

The two components of Mk34 have identical spectral classes of WN5h, having spectra with prominent emission lines of highly-ionised helium, nitrogen, and carbon. The h suffix indicates that the spectrum also contains lines of hydrogen which are not usually seen in Wolf-Rayet spectra. The strength of the helium emission lines in the spectrum shows that the outer layers of the star consist of 35% helium. The WN5 spectral class indicates an extremely high photospheric temperature. Modelling the profiles of several spectral lines gives an effective temperature of 53,000 K for each star. The primary star has a bolometric luminosity of about 2,000,000 L☉ and a radius of about 19 R☉, while the secondary has a luminosity of about 1,600,000 L☉ and a radius of about 18 R☉. The masses of the two components inferred from their spectra are about 148 M☉ and 135 M☉ respectively. The masses determined from the orbit of the stars depends strongly on the inclination of the orbit, which is poorly known. The best match with the observed masses is found for orbits with an inclination near 50°. The emission line spectra of the two stars in the Mk34 system are caused by strong mass loss which produces a dense stellar wind. Both stars have a stellar wind with a velocity of about 2500 km/s causing each star to lose more than the mass of the sun every 10,000 years, a billion times stronger than the sun's wind.

Evolution Although Wolf-Rayet stars are typically old stars that have lost their outer layers of hydrogen, some are very young massive stars which still contain hydrogen. Both stars in the Mk34 system are very young, and the helium, carbon, and nitrogen fusion products in their spectra are produced by the strong convection that occurs in massive main sequence stars and by rotational mixing. The stars are rotating at about 240 km/s and 250 km/s respectively. Modelling the evolution of the stars gives ages of about 500,000 years, with current masses of about 139 M☉ and 127 M☉ respectively, and initial masses of 144 M☉ and 131 M☉ respectively. These are similar to the masses deduced from observation. The stars are expected to have a hydrogen-burning lifetime of about 2.2 Myr, and are not expected to experience significant mass exchange during their evolution. Both stars should reach core collapse with masses too high to produce a normal supernova. Instead they are likely to produce a weak supernova followed by collapse to a black hole, or directly collapse to a black hole with no visible explosion.

References

Further reading Crowther, Paul A.; Caballero-Nieves, S. M.; Bostroem, K. A.; Maíz Apellániz, J.; Schneider, F. R. N.; Walborn, N. R.; Angus, C. R.; Brott, I.; Bonanos, A.; De Koter, A.; De Mink, S. E.; Evans, C. J.; Gräfener, G.; Herrero, A.; Howarth, I. D.; Langer, N.; Lennon, D. J.; Puls, J.; Sana, H.; Vink, J. S. (2016). "The R136 star cluster dissected with Hubble Space Telescope/STIS. I. Far-ultraviolet spectroscopic census and the origin of He II λ1640 in young star clusters". Monthly Notices of the Royal Astronomical Society. 458 (1): 624–659. arXiv:1603.04994. Bibcode:2016MNRAS.458..624C. doi:10.1093/mnras/stw273. Hainich, R.; Rühling, U.; Todt, H.; Oskinova, L. M.; Liermann, A.; Gräfener, G.; Foellmi, C.; Schnurr, O.; Hamann, W. -R. (2014). "The Wolf-Rayet stars in the Large Magellanic Cloud". Astronomy & Astrophysics. 565: A27. arXiv:1401.5474. Bibcode:2014A&A...565A..27H. doi:10.1051/0004-6361/201322696. S2CID 55123954. Groh, J. H.; Meynet, G.; Georgy, C.; Ekström, S. (2013). "Fundamental properties of core-collapse supernova and GRB progenitors: Predicting the look of massive stars before death". Astronomy & Astrophysics. 558: A131. arXiv:1308.4681. Bibcode:2013A&A...558A.131G. doi:10.1051/0004-6361/201321906. S2CID 84177572.

External links ESA/Hubble image

Illustrations

Worked examples

Example 1 — a first encounter with Melnick 34

Start with the simplest possible case. Write down what Melnick 34 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 Melnick 34 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 Melnick 34 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 Melnick 34

In research: Melnick 34 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 Melnick 34 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: Melnick 34 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Dorado, Spectroscopic binaries, Stars in the Large Magellanic Cloud, so understanding it makes those chapters shorter.
In everyday life: Look for Melnick 34 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 Melnick 34 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Melnick 34 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 Melnick 34 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Melnick 34 in simple terms?

Why does Melnick 34 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 Melnick 34?

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 Melnick 34.