astronomy

Twin Quasar

Twin Quasar 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 Twin Quasar rather than just read about it. In short: The Twin Quasar (also known as Twin QSO, Double Quasar, SBS 0957+561, TXS 0957+561, Q0957+561 or QSO 0957+561 A/B), discovered in 1979, was the first identified gravitationally lensed quasar, It is a single quasar that appears in images as two identical quasars as a consequence of gravitational lensing. Quasar The Twin Quasar is a single quasar whose appearance is distorted by the gravity of a galaxy along the line…

Key takeaways

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

Reference excerpt

The Twin Quasar (also known as Twin QSO, Double Quasar, SBS 0957+561, TXS 0957+561, Q0957+561 or QSO 0957+561 A/B), discovered in 1979, was the first identified gravitationally lensed quasar, It is a single quasar that appears in images as two identical quasars as a consequence of gravitational lensing.

Quasar The Twin Quasar is a single quasar whose appearance is distorted by the gravity of a galaxy along the line of sight from Earth. This gravitational lensing effect is a result of the warping of space-time by the nearby galaxy, as described by general relativity. The single quasar thus appears as two separate images, separated by 6 arcseconds. Both images have an apparent magnitude of 17, with the A component having 16.7 and the B component having 16.5. There is a 417 ± 3-day time lag between the two images. The Twin Quasar lies at redshift z = 1.41 (8.7 billion ly), while the lensing galaxy lies at redshift z = 0.355 (3.7 billion ly). The lensing galaxy with apparent dimension of 0.42×0.22 arcminutes lies almost in line with the B image, lying 1 arcsecond off. The quasar lies 10 arcminutes north of NGC 3079, in the constellation Ursa Major. The astronomical data services SIMBAD and NASA/IPAC Extragalactic Database (NED) list several other names for this system.

Lens The lensing galaxy, YGKOW G1 (sometimes called G1 or Q0957+561 G1), is a giant elliptical (type cD) lying within a cluster of galaxies that also contributed to the lensing.

History The quasars QSO 0957+561A/B were discovered in early 1979 by an Anglo-American team around Dennis Walsh, Robert Carswell and Ray Weymann, with the aid of the 2.1 m Telescope at Kitt Peak National Observatory in Arizona, United States. The team noticed that the two quasars were unusually close to each other, and that their redshift and visible light spectrum were very similar to each other. They published their suggestion of "the possibility that they are two images of the same object formed by a gravitational lens". The Twin Quasar was one of the first directly observable effects of gravitational lensing, which was described in 1936 by Albert Einstein as a consequence of his 1916 general theory of relativity, though in that 1936 paper he also predicted "Of course, there is no hope of observing this phenomenon directly." Critics identified a difference in appearance between the two quasars in radio frequency images. In mid-1979, a team led by David Roberts at the Very Large Array (VLA) near Socorro, New Mexico, discovered a relativistic jet emerging from quasar A with no corresponding equivalent in quasar B. Furthermore, the distance between the two images, 6 arcseconds, was too great to have been produced by the gravitational effect of the galaxy G1, a galaxy identified near quasar B. In 1980, Peter J. Young and collaborators discovered that galaxy G1 is part of a galaxy cluster which increases the gravitational deflection and can explain the observed distance between the images. Finally, a team led by Marc V. Gorenstein observed essentially identical relativistic jets on very small scales from both A and B in 1983 using Very Long Baseline Interferometry (VLBI). Subsequent, more detailed VLBI observations demonstrated the expected (parity reversed) magnification of the image B jet with respect to image A jet. The difference between the large-scale radio images is attributed to the special geometry needed for gravitational lensing, which is satisfied by the quasar but not by all of the extended jet emission seen by the VLA near image A. Slight spectral differences between quasar A and quasar B can be explained by different densities of the intergalactic medium in the light paths, resulting in differing extinction. 30 years of observation made it clear that image A of the quasar reaches earth about 14 months earlier than the corresponding image B, resulting in a difference of path length of 1.1 ly.

Possible planet In 1996, a team at Harvard-Smithsonian Center for Astrophysics led by Rudy E. Schild discovered an anomalous fluctuation in one image's light curve, which they speculated was caused by a planet approximately three Earth masses in size within the lensing galaxy. This conjecture cannot be proven because the chance alignment that led to its discovery will never happen again. If it could be confirmed, however, it would make it the most distant known planet, 4 billion ly away.

Candidate magnetospheric eternally collapsing object In 2006, R. E. Schild suggested that the accreting object at the heart of Q0957+561 is not a supermassive black hole, as is generally believed for all quasars, but a magnetospheric eternally collapsing object. Schild's team at the Harvard-Smithsonian Center for Astrophysics asserted that "this quasar appears to be dynamically dominated by a magnetic field internally anchored to its central, rotating supermassive compact object" (R. E. Schild).

See also Cloverleaf quasar Cosmic string Gravitational lens Hypothetical astronomical object

References

External links Q0957+561: Die historisch erste Linse mit Quasar – The University of Cologne. Q0957+561 – CCD image based on 45-min total exposure – March 2007. Q0957+561 A,B. Simbad

Illustrations

Worked examples

Example 1 — a first encounter with Twin Quasar

Start with the simplest possible case. Write down what Twin Quasar 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 Twin Quasar 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 Twin Quasar 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 Twin Quasar

In research: Twin Quasar 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 Twin Quasar 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: Twin Quasar is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1979, Exoplanet candidates, Gravitational lensing, so understanding it makes those chapters shorter.
In everyday life: Look for Twin Quasar 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 Twin Quasar in 20 minutes

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

Frequently asked questions

What is Twin Quasar in simple terms?

Why does Twin Quasar 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 Twin Quasar?

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 Twin Quasar.