astronomy

Hulse–Taylor pulsar

Hulse–Taylor pulsar 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 Hulse–Taylor pulsar rather than just read about it. In short: The Hulse–Taylor pulsar (known as PSR B1913+16, PSR J1915+1606 or PSR 1913+16) is a binary star system composed of a neutron star and a pulsar which orbit around their common center of mass. It is the first binary pulsar ever discovered.

Key takeaways

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

Reference excerpt

The Hulse–Taylor pulsar (known as PSR B1913+16, PSR J1915+1606 or PSR 1913+16) is a binary star system composed of a neutron star and a pulsar which orbit around their common center of mass. It is the first binary pulsar ever discovered. The pulsar was discovered by Russell Alan Hulse and Joseph Hooton Taylor Jr., of the University of Massachusetts Amherst in 1974. Their discovery of the system and analysis of it earned them the 1993 Nobel Prize in Physics "for the discovery of a new type of pulsar, a discovery that has opened up new possibilities for the study of gravitation."

Discovery Using the Arecibo 305 m dish, Hulse and Taylor detected pulsed radio emissions and thus identified the source as a pulsar, a rapidly rotating, highly magnetized neutron star. The neutron star rotates on its axis 16.94 times per second; thus the pulse period is 59.03 milliseconds. After timing the radio pulses for some time, Hulse and Taylor noticed that there was a systematic variation in the arrival time of the pulses. Sometimes, the pulses were received a little sooner than expected; sometimes, later than expected. These variations changed in a smooth and repetitive manner, with a period of 7.7519 hours. They realized that such behavior is predicted if the pulsar were in a binary orbit with another star, later confirmed to be another neutron star.

Star system The pulsar and its neutron star companion both follow elliptical orbits around their common center of mass. The period of the orbital motion is 7.7519 hours, and the two neutron stars are believed to be nearly equal in mass, about 1.4 solar masses. Radio emissions have been detected from only one of the two neutron stars. The minimum separation at periastron is about 1.1 solar radii; the maximum separation at apastron is 4.8 solar radii. The orbit is inclined at about 45 degrees with respect to the plane of the sky. The orientation of periastron changes by about 4.2 degrees per year in direction of the orbital motion (relativistic precession of periastron). In January 1975, it was oriented so that periastron occurred perpendicular to the line of sight from Earth.

Use as a test of general relativity The orbit has decayed since the binary system was initially discovered, in precise agreement with the loss of energy due to gravitational waves described by Albert Einstein's general theory of relativity. The ratio of observed to predicted rate of orbital decay is calculated to be 0.997 ± 0.002. The total power of the gravitational waves emitted by this system presently is calculated to be 7.35 × 1024 watts. For comparison, this is 1.9% of the power radiated in light by the Sun. The Solar System radiates only about 5,000 watts in gravitational waves, due to the much larger distances and orbit times, particularly between the Sun and Jupiter, and the relatively small mass of the planets. With this comparatively large energy loss due to gravitational radiation, the rate of decrease of orbital period is 76.5 microseconds per year, the rate of decrease of semimajor axis is 3.5 meters per year, and the calculated lifetime to final inspiral is 300 million years. In 2004, Taylor and Joel M. Weisberg published a new analysis of the experimental data to date, concluding that the 0.2% disparity between the data and the predicted results is due to poorly known galactic constants, including the Sun's distance from the Galactic Center, the pulsar's proper motion and its distance from Earth. While there are efforts underway for better measurement of the first two quantities, they saw "little prospect for a significant improvement in knowledge of the pulsar distance," so tighter bounds will be difficult to attain. Taylor and Weisberg also mapped the pulsar's two-dimensional beam structure using the fact that the system's precession leads to varying pulse shapes. They found that the beam shape is latitudinally elongated, and pinched longitudinally near the centre, leading to an overall shape like a figure eight. In 2016, Weisberg and Huang published further results, still with a 0.16% disparity, finding that the ratio of the observed value compared to the predicted value was 0.9983 ± 0.0016. They name the main driver of this improvement, from 1.8σ to 1σ discrepancy, as being improved galactic constants published in 2014.

Characteristics Mass of companion: 1.387 M☉ Total mass of the system: 2.828378(7) M☉ Orbital period: 7.751938773864 hr Eccentricity: 0.6171334 Semi-major axis: 1,950,100 km Periastron separation: 746,600 km Apastron separation: 3,153,600 km Orbital velocity of stars at periastron (relative to center of mass): 450 km/s Orbital velocity of stars at apastron (relative to center of mass): 110 km/s

Worked examples

Example 1 — a first encounter with Hulse–Taylor pulsar

Start with the simplest possible case. Write down what Hulse–Taylor pulsar 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 Hulse–Taylor pulsar 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 Hulse–Taylor pulsar 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 Hulse–Taylor pulsar

In research: Hulse–Taylor pulsar 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 Hulse–Taylor pulsar 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: Hulse–Taylor pulsar is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aquila (constellation), Astronomical objects discovered in 1974, Double neutron star systems, so understanding it makes those chapters shorter.
In everyday life: Look for Hulse–Taylor pulsar 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 Hulse–Taylor pulsar in 20 minutes

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

Frequently asked questions

What is Hulse–Taylor pulsar in simple terms?

Why does Hulse–Taylor pulsar 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 Hulse–Taylor pulsar?

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 Hulse–Taylor pulsar.