astronomy

GRO J1655−40

GRO J1655−40 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 GRO J1655−40 rather than just read about it. In short: GRO J1655−40 is a binary star consisting of an evolved F-type primary star and a massive, unseen companion, which orbit each other once every 2.6 days in the constellation of Scorpius. Gas from the surface of the visible star is accreted onto the dark companion, which appears to be a stellar black hole with six times the mass of the Sun.

Key takeaways

GRO J1655−40 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect GRO J1655−40 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of GRO J1655−40 from memory before moving on to harder problems.

Reference excerpt

GRO J1655−40 is a binary star consisting of an evolved F-type primary star and a massive, unseen companion, which orbit each other once every 2.6 days in the constellation of Scorpius. Gas from the surface of the visible star is accreted onto the dark companion, which appears to be a stellar black hole with six times the mass of the Sun. The optical companion of this low-mass X-ray binary is a subgiant F star. GRO J1655−40 was discovered by the Compton Gamma Ray Observatory on July 27, 1994. An optical counterpart to the gamma ray source was identified in August of the same year, by Jerome A. Orisz, and it was found to be a variable star. Along with GRS 1915+105, GRO J1655−40 is one of at least two galactic "microquasars" that may provide a link between the supermassive black holes generally believed to power extragalactic quasars and more local accreting black hole systems. In particular, both display the radio jets characteristic of many active galactic nuclei.

The distance from the Solar System is probably about 11,000 light years, or approximately half-way from the Sun to the Galactic Center, but a closer distance of ~2800 ly is not ruled out. GRO J1655−40 and its companion are moving through the Milky Way at around 112 km/s (250,000 miles per hour), in a galactic orbit that depends on its exact distance, but is mostly interior to the "Solar circle", d~8,500 pc, and within 150 pc (~500 ly) of the galactic plane. For comparison, the Sun and other nearby stars have typical speeds on the order of 20 km/s relative to the average velocity of stars moving with the galactic disk's rotation in the solar neighborhood, which supports the idea that the black hole formed from the collapse of the core of a massive star. As the core collapsed, its outer layers exploded as a supernova. Such explosions often seem to leave the remnant system moving through the galaxy with unusually high speed. The outburst source was found to exhibit quasi-periodic oscillations (QPOs) whose frequency increases monotonically during the rising phase of the outburst and with monotonically decreasing frequency in the declining phase of the outburst. This can be easily modeled assuming propagation of an oscillating shock wave: steadily going closer to the black hole due to rise in the Keplerian component rate in the rising phase and going away from the black hole as viscosity is withdrawn in the declining phase. The shock appears to be propagating at a speed of a few meters per second.

See also List of nearest known black holes NGC 6242

References

External links "GRO J1655−40". Black Hole Encyclopedia. 2006. Archived from the original on 8 August 2007. SIMBAD, V* V1033 Sco -- High Mass X-ray Binary, "GRO J1665-40" "GRO J1655−40: NASA's Chandra Answers Black Hole Paradox". Chandra X-ray Observatory. Harvard-Smithsonian Center for Astrophysics. June 21, 2006. Retrieved 2010-04-24.

Illustrations

Worked examples

Example 1 — a first encounter with GRO J1655−40

Start with the simplest possible case. Write down what GRO J1655−40 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 GRO J1655−40 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 GRO J1655−40 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 GRO J1655−40

In research: GRO J1655−40 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 GRO J1655−40 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: GRO J1655−40 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Black hole X-ray binaries, F-type subgiants, High-mass X-ray binaries, so understanding it makes those chapters shorter.
In everyday life: Look for GRO J1655−40 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 GRO J1655−40 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GRO J1655−40 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 GRO J1655−40 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GRO J1655−40 in simple terms?

Why does GRO J1655−40 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 GRO J1655−40?

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 GRO J1655−40.