astronomy

R136a2

R136a2 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 R136a2 rather than just read about it. In short: R136a2 (RMC 136a2) is a Wolf-Rayet star residing near the center of the R136, the central concentration of stars of the large NGC 2070 open cluster in the Tarantula Nebula, a massive H II region in the Large Magellanic Cloud which is a nearby satellite galaxy of the Milky Way. It has one of the highest confirmed masses and luminosities of any known star, at about 195 M☉ and =5.25 million L☉ respectively.

Key takeaways

R136a2 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect R136a2 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of R136a2 from memory before moving on to harder problems.

Reference excerpt

R136a2 (RMC 136a2) is a Wolf-Rayet star residing near the center of the R136, the central concentration of stars of the large NGC 2070 open cluster in the Tarantula Nebula, a massive H II region in the Large Magellanic Cloud which is a nearby satellite galaxy of the Milky Way. It has one of the highest confirmed masses and luminosities of any known star, at about 195 M☉ and =5.25 million L☉ respectively.

Discovery In 1960, a group of astronomers working at the Radcliffe Observatory in Pretoria made systematic measurements of the brightness and spectra of bright stars in the Large Magellanic Cloud. Among the objects cataloged was RMC 136, (Radcliffe Observatory Magellanic Cloud Catalogue, Catalog number 136) the central "star" of 30 Doradus. Subsequent observations showed that R136 was located in the center of a giant H II region that was a center of intense star formation in the immediate vicinity of the observed stars. In the early 1980s, R136a was first resolved using speckle interferometry into 8 components. R136a2 was marginally the second brightest found within 1 arc-second at the centre of the R136 cluster. Previous estimates that the brightness of the central region would require as many as 30 hot O class stars within half a parsec at the centre of the cluster had led to speculation that a star several thousand times the mass of the sun was the more likely explanation. Instead it was eventually found that it consisted of a few extremely luminous stars accompanied by a larger number of hot O stars.

Distance

Determining a precise distance to R136a2 is challenging due to many factors. At the immense distance to the LMC, the parallax method is beyond the limits of current technology. Most estimates assume that R136 is at the same distance as the Large Magellanic Cloud. The most accurate distance to the LMC is 49.97 kpc, derived from a comparison of the angular and linear dimensions of eclipsing binary stars.

Properties Like all Wolf-Rayet stars, R136a2 is undergoing severe mass loss by a fast stellar wind. The star loses 4.6×10−5 solar masses per year through a stellar wind with a speed of 2,400 km/s. The high mass of the star compresses and heats the core and promotes rapid hydrogen fusion predominantly through the CNO process, leading to a luminosity of 5,129,000 L☉. The fusion rate is so great that in 10 seconds R136a2 produces more energy than the Sun does in a year. The star is currently evolving towards hotter temperatures, and is predicted to have started its life with a mass over 500 M☉. Although the star is one of the most massive known it has a radius of 34.7 R☉ and a volume of 41,800 suns, far smaller than the largest stars such as VY Canis Majoris. Because of the high temperature, it emits most of its energy in the ultraviolet region of the electromagnetic spectrum, and the visual brightness is only 114,000 times the sun (MV −7.80).

Fate

It is thought that stars this massive can never lose enough mass to avoid a catastrophic end with the collapse of a large iron core. The result will be a supernova, hypernova, gamma-ray burst, or perhaps almost no visible explosion, and leaving behind a black hole. The exact details depend heavily on the timing and amount of mass loss, with current models not fully reproducing the distribution of stars and supernovae that we observe. The most massive stars in the local universe are expected to progress to hydrogen-free Wolf Rayet stars before their cores collapse, producing a Type Ib or Ic supernova and leaving behind a black hole. Gamma ray bursts are only expected under unusual conditions, or for less massive stars.

References

External links http://www.eso.org/public/news/eso1030/

Illustrations

Worked examples

Example 1 — a first encounter with R136a2

Start with the simplest possible case. Write down what R136a2 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 R136a2 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 R136a2 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 R136a2

In research: R136a2 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 R136a2 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: R136a2 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1985, Dorado, Stars in the Large Magellanic Cloud, so understanding it makes those chapters shorter.
In everyday life: Look for R136a2 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 R136a2 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what R136a2 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 R136a2 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is R136a2 in simple terms?

Why does R136a2 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 R136a2?

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 R136a2.