astronomy

Messier 74

Messier 74 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 Messier 74 rather than just read about it. In short: Messier 74 (also known as NGC 628 and Phantom Galaxy) is a large spiral galaxy in the equatorial constellation Pisces. It is about 32 million light-years away from Earth.

Key takeaways

Messier 74 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Messier 74 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 74 from memory before moving on to harder problems.

Reference excerpt

Messier 74 (also known as NGC 628 and Phantom Galaxy) is a large spiral galaxy in the equatorial constellation Pisces. It is about 32 million light-years away from Earth. The galaxy contains two clearly defined spiral arms and is therefore used as an archetypal example of a grand design spiral galaxy. The galaxy's low surface brightness makes it the most difficult Messier object for amateur astronomers to observe. Its relatively large angular (that is, apparent) size and the galaxy's face-on orientation make it an ideal object for professional astronomers who want to study spiral arm structure and spiral density waves. It is estimated that M74 hosts about 100 billion stars.

Observation history M74 was discovered by Pierre Méchain in 1780. He then communicated his discovery to Charles Messier, who listed the galaxy as M74 in his catalog of permanent celestial objects that should not be confused with transient objects in the sky. In July 2022, it was observed by the James Webb Space Telescope.

Structure M74 has two spiral arms that wind counterclockwise from the galaxy's center. The spiral arms widen as they get farther from M74's center, but one of the arms narrows at the end. The arms deviate slightly from a constant angle.

Supernovae Three supernovae have been observed in M74:

SN 2002ap (Type Ic, mag. 14.5) was discovered by Yoji Hirose on 29 January 2002. It was one of few Type Ic supernovae (which denotes hypernovae) recorded within 10 Mpc every century. This explosion has been used to test theories on the origins of others further away and theories on the emission by supernovae of gamma ray bursts. It got as bright as magnitude 12.3, making it the brightest supernova of 2002. SN 2003gd (Type II-P, mag. 13.2) was discovered by Robert Evans on 12 June 2003. Type II supernovae have known luminosities, so they can be used to accurately measure distances. The distance measured to M74 using SN 2003gd is 9.6 ± 2.8 Mpc, or 31 ± 9 million ly. For comparison, distances measured using the brightest supergiants are 7.7 ± 1.7 Mpc and 9.6 ± 2.2 Mpc. Ben Sugerman found a "light echo" – a later reflection of the explosion – associated with SN 2003gd. This is one of the few supernovae in which such a reflection has been found. This reflection appears to be from dust in a sheet-like cloud that lies in front of the supernova, and it can be used to determine the composition of the interstellar dust. SN 2013ej (Type II-P, mag. 13.5) was discovered by the Lick Observatory Supernova Search (LOSS) on 25 July 2013. It was bright as 10th magnitude when viewed from the surface of Earth, so it was visible from almost all modern telescopes in a good night sky.

In addition to these supernovae, the astronomical transient AT 2019krl was discovered by Anna Ho on 6 July 2019, and classified as either a Type IIn supernova or an LBV in outburst. Later analysis argued that it was consistent with known examples of giant LBV eruptions and SN 2008S-like objects.

Galaxy group This is the brightest member of the M74 Group, a group of 5 to 7 galaxies that also includes the peculiar spiral galaxy NGC 660 and a few irregular galaxies. Different group membership identification methods (ranging from a clear, to likely, to perhaps historic gravitational tie) identify several objects of the group in common, and a few galaxies whose exact status within such groupings is currently uncertain.

Suspected black hole In 2005 the Chandra X-ray Observatory announced its observation of an ultraluminous X-ray source (ULX) in M74, radiating more X-ray power than a neutron star, in periodic intervals of around two hours. It has an estimated mass of 10000 M☉. This is an indicator of an intermediate-mass black hole. This would be a rather uncommon class, in between in size of stellar black holes and the massive black holes theorized to be in the center of many galaxies. Such an object is believed to form from lesser ("stellar") black holes within a star cluster. The source has been given identification number CXOU J013651.1+154547.

Amateur astronomy observation Messier 74 is 1.5° east-northeast of Eta Piscium. This galaxy has the second-lowest Earth-surface brightness of any Messier object. (M101 has the lowest.) It requires a good night sky. This galaxy may be best viewed under low magnification; when highly magnified, the diffuse emission becomes more extended and appears too faint to be seen by many people. Additionally, M74 may be more easily seen when using averted vision when the eyes are fully dark adapted.

Illustrations

Worked examples

Example 1 — a first encounter with Messier 74

Start with the simplest possible case. Write down what Messier 74 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 Messier 74 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 Messier 74 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 Messier 74

In research: Messier 74 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 Messier 74 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: Messier 74 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1780, Discoveries by Pierre Méchain, IRAS catalogue objects, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 74 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 Messier 74 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 74 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 Messier 74 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 74 in simple terms?

Messier 74 (also known as NGC 628 and Phantom Galaxy) is a large spiral galaxy in the equatorial constellation Pisces. It is about 32 million light-years away from Earth.

Why does Messier 74 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 Messier 74?

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 Messier 74.