astronomy

S55 (star)

S55 (star) 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 S55 (star) rather than just read about it. In short: S55 (also known as S0–102) is a star that is located very close to the centre of the Milky Way, near the radio source Sagittarius A*, orbiting it with an orbital period of 12.8 years. This beat the record of 16 years previously set by S2.

Key takeaways

S55 (star) belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect S55 (star) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of S55 (star) from memory before moving on to harder problems.

Reference excerpt

S55 (also known as S0–102) is a star that is located very close to the centre of the Milky Way, near the radio source Sagittarius A*, orbiting it with an orbital period of 12.8 years. This beat the record of 16 years previously set by S2. The star was identified by a University of California, Los Angeles team headed by Andrea M. Ghez. At its periapsis, its speed reaches 1.7% of the speed of light. At that point it is 246 astronomical units (34 light hours, 36.7 billion km) from the centre, while the black hole radius is only a small fraction of that size (the Schwarzschild radius is about 0.082 au). It passed that point in 2022 and will be there again in 2034. In 2019 the star S62 was believed to have surpassed S55 to become be the new record holder, but further scrutiny found this star was much further from Sagittarius A* than believed, and earlier observations were consistent with star S29 instead. In 2020, further observation discovered several stars in the Sagittarius A* cluster with shorter orbital periods than S55. Its position in the sky has been monitored from 2000 to 2012 using the W. M. Keck telescope and from 2002 to 2016 with the VLT. One complete orbit has been observed. From Earth's current perspective, it travels in a clockwise direction. Having observed two stars orbiting through complete periods around the centre (S55 and S2), the gravitational potential of Sgr A* could be established. It is also possible that there is a great deal of dark matter around the orbits of these stars. Also general relativistic effects due to gravitational redshift should become observable.

References

External links University of California (4 October 2012). "Astronomers discover star racing around black hole at Milky Way center". Retrieved 6 October 2012. A. M. Ghez (4 October 2012). "Supplementary Materials for The Shortest Known Period Star Orbiting our Galaxy's Supermassive Black Hole" (PDF). Archived from the original (PDF) on 14 November 2012. Includes position measurements and images.

Worked examples

Example 1 — a first encounter with S55 (star)

Start with the simplest possible case. Write down what S55 (star) 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 S55 (star) 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 S55 (star) 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 S55 (star)

In research: S55 (star) 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 S55 (star) 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: S55 (star) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Galactic Center, Sagittarius (constellation), so understanding it makes those chapters shorter.
In everyday life: Look for S55 (star) 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 S55 (star) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what S55 (star) 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 S55 (star) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is S55 (star) in simple terms?

Why does S55 (star) 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 S55 (star)?

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 S55 (star).