astronomy

GW151226

GW151226 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 GW151226 rather than just read about it. In short: GW151226 was a gravitational wave signal detected by the LIGO observatory on 25 December 2015 local time (26 Dec 2015 UTC). On 15 June 2016, the LIGO and Virgo collaborations announced that they had verified the signal, making it the second such signal confirmed, after GW150914, which had been announced four months earlier the same year, and the third gravitational wave signal detected.

Key takeaways

GW151226 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect GW151226 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of GW151226 from memory before moving on to harder problems.

Reference excerpt

GW151226 was a gravitational wave signal detected by the LIGO observatory on 25 December 2015 local time (26 Dec 2015 UTC). On 15 June 2016, the LIGO and Virgo collaborations announced that they had verified the signal, making it the second such signal confirmed, after GW150914, which had been announced four months earlier the same year, and the third gravitational wave signal detected.

Event detection

The signal was detected by LIGO at 03:38:53 UTC, with the Hanford detector picking it up 1.1 milliseconds after the Livingston detector (since the axis between the two was not parallel to the wave front); it was identified by a low-latency search within 70s of its arrival at the detectors.

Astrophysical origin Analysis indicated the signal resulted from the coalescence of two black holes with 14.2+8.3−3.7 and 7.5+2.3−2.3 times the mass of the Sun, at a distance of 440+180−190 megaparsecs (1.4 billion light years) from Earth. The resulting merged black hole had 20.8+6.1−1.7 solar masses, one solar mass having been radiated away. In both of the first two black hole mergers analyzed, the mass converted to gravitational waves was roughly 4.6% of the initial total. In this second detection, LIGO Scientific Collaboration and Virgo scientists also determined that at least one of the premerger black holes was spinning at more than 20% of the maximum spin rate allowed by general relativity. The final black hole was spinning with 0.74+0.06−0.06 times its maximum possible angular momentum. The black holes were smaller than in the first detection event, which led to different timing for the final orbits and allowed LIGO to see more of the last stages before the black holes merged—55 cycles (27 orbits) over one second, with frequency increasing from 35 to 450 Hz, compared with only ten cycles over 0.2 second in the first event. The location/direction in the sky is poorly constrained. The signal was first seen at Livingston with delay of 1.1 (±0.3) ms later at LIGO Hanford.

Implications The GW151226 event suggests that there is a large population of binary black holes in the Universe that will produce frequent mergers. The measured gravitational wave is completely consistent with the predictions of general relativity for strong gravitational fields. The theory's strong-field predictions had not been directly tested before the two LIGO events. General relativity passed this most stringent test for the second time.

Illustrations

Worked examples

Example 1 — a first encounter with GW151226

Start with the simplest possible case. Write down what GW151226 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 GW151226 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 GW151226 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 GW151226

In research: GW151226 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 GW151226 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: GW151226 is common in secondary-school and first-year university syllabi. It links to neighbouring topics 2015 in outer space, 2015 in science, 2016 in outer space, so understanding it makes those chapters shorter.
In everyday life: Look for GW151226 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 GW151226 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GW151226 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 GW151226 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GW151226 in simple terms?

Why does GW151226 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 GW151226?

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 GW151226.