astronomy

Stephan's Quintet

Stephan's Quintet 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 Stephan's Quintet rather than just read about it. In short: Stephan's Quintet is a visual grouping of five galaxies of which four form the first compact galaxy group ever discovered. The group, visible in the constellation Pegasus, was discovered by Édouard Stephan in 1877 at the Marseille Observatory.

Key takeaways

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

Reference excerpt

Stephan's Quintet is a visual grouping of five galaxies of which four form the first compact galaxy group ever discovered. The group, visible in the constellation Pegasus, was discovered by Édouard Stephan in 1877 at the Marseille Observatory. The group is the most studied of all the compact galaxy groups. The brightest member of the visual grouping (and the only non-member of the true group) is NGC 7320, which has extensive H II regions, identified as red blobs, where active star formation is occurring. Four of the five galaxies in Stephan's Quintet form a physical association, a true galaxy group, Hickson Compact Group 92, and will likely merge with each other. Radio observations in the early 1970s revealed a filament of emission between the galaxies in the group. This same region is also detected in the faint glow of ionized atoms seen in the visible part of the spectrum as a green arc. Space telescopes have provided new insight into the nature of the filament, which is now believed to be a shock-wave in the intergalactic gas, caused by one galaxy (NGC 7318B) falling into the center of the group at several million kilometres per hour. Stephan's Quintet was selected as one of the five cosmic objects observed by the James Webb Space Telescope as part of the release of its first official science images.

Emissions

X-rays

As NGC 7318B collides with gas in the group, a huge shock wave bigger than the Milky Way spreads throughout the medium between the galaxies, heating some of the gas to temperatures of millions of degrees where they emit X-rays detectable with the NASA Chandra X-ray Observatory.

Molecular hydrogen emission The NASA Spitzer Space Telescope, which detects infrared radiation, discovered a very powerful molecular hydrogen signal from the shock wave between the galaxies. This emission is one of the most turbulent formations of molecular hydrogen ever seen, and the strongest emission originates near the center of the green area in the visible light picture discussed earlier. This phenomenon was discovered by an international team led by scientists at the California Institute of Technology and including scientists from Australia, Germany and China. The detection of molecular hydrogen from the collision was initially unexpected because the hydrogen molecule is very fragile and is easily destroyed in shock waves of the kind expected in Stephan's Quintet. However, one solution is that when a shock front moves through a cloudy medium like the center of the group, millions of smaller shocks are produced in a turbulent layer, and this can allow molecular hydrogen to survive.

Redshift NGC 7320 indicates a small redshift (790 km/s) while the other four exhibit large redshifts (near 6,600 km/s). Since galactic redshift is proportional to distance, NGC 7320 is only a foreground projection and is ~39 million light-years from Earth, making it a possible member of the NGC 7331 group, versus the 210–340 million light-years of the other four. NGC 7319 has a type 2 Seyfert nucleus.

A sixth galaxy, NGC 7320C, probably belongs to the Hickson association: it has a redshift similar to the Hickson galaxies, and a tidal tail appears to connect it with NGC 7319.

Infrared Using its Mid Infrared Instrument (MIRI), the James Webb Space Telescope shows details shrouded by dust in visible light including large shock waves and tidal tails in four of the five galaxies, and previously hidden areas of star formation. These new details will contribute to insights on galaxy evolution.

Members

In popular culture The angelic figures at the beginning of the 1946 holiday film It's a Wonderful Life are based on images of Stephan's Quintet.

See also Wild's Triplet Zwicky's Triplet NGC 7331 Group (Deer Lick Group, about half a degree northeast of Stephan's Quintet) Robert's Quartet Seyfert's Sextet Copeland Septet

References

External links

GALEX: Stephan's Quintet and NGC 7331 Star Clusters Born in the Wreckage of Cosmic Collisions News Release at ESA/Hubble Stephan's Quintet NightSkyInfo.com : Stephan's Quintet What's Behind Stephan's Quintet? Peter Edmonds, Chandra Blog, 21 July 2009 Astronomy Picture of the Day on Stephan's Quintet: 13 Nov 2000 12 Aug 2003 11 Sep 2009 NASA’s James Webb Space Telescope reveals never-before-seen details of the galaxy group called “Stephan’s Quintet.”

Stephan's Quintet on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Illustrations

Worked examples

Example 1 — a first encounter with Stephan's Quintet

Start with the simplest possible case. Write down what Stephan's Quintet 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 Stephan's Quintet 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 Stephan's Quintet 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 Stephan's Quintet

In research: Stephan's Quintet 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 Stephan's Quintet 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: Stephan's Quintet is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1877, Discoveries by Édouard Stephan, Hickson Compact Groups, so understanding it makes those chapters shorter.
In everyday life: Look for Stephan's Quintet 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 Stephan's Quintet in 20 minutes

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

Frequently asked questions

What is Stephan's Quintet in simple terms?

Why does Stephan's Quintet 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 Stephan's Quintet?

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 Stephan's Quintet.