astronomy

Messier 84

Messier 84 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 84 rather than just read about it. In short: Messier 84 or M84, also known as NGC 4374, is a giant elliptical or lenticular galaxy in the constellation Virgo. Charles Messier discovered the object in 1781 in a systematic search for "nebulous objects" in the night sky.

Key takeaways

Messier 84 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 84 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Messier 84 from memory before moving on to harder problems.

Reference excerpt

Messier 84 or M84, also known as NGC 4374, is a giant elliptical or lenticular galaxy in the constellation Virgo. Charles Messier discovered the object in 1781 in a systematic search for "nebulous objects" in the night sky. It is the 84th object in the Messier Catalogue and in the heavily populated core of the Virgo Cluster of galaxies, part of the local supercluster. This galaxy has morphological classification E1, denoting it has flattening of about 10%. The extinction-corrected total luminosity in the visual band is about 7.64×1010 L☉. The central mass-to-light ratio is 6.5, which, to a limit, steadily increases away from the core. The visible galaxy is surrounded by a massive dark matter halo. Radio observations and Hubble Space Telescope images of M84 have revealed two jets of matter shooting out from its center as well as a disk of rapidly rotating gas and stars indicating the presence of a 1.5 ×109 M☉ supermassive black hole. It also has a few young stars and star clusters, indicating star formation at a very low rate. The number of globular clusters is 1,775±150, which is much lower than expected for an elliptical galaxy. Viewed from Earth its half-light radius, relative angular size of its 50% peak of lit zone of the sky, is 72.5″, thus just over an arcminute.

Supernovae Three supernovae have been observed in M84:

SN 1957B (Type Ia, mag. 12.5) was discovered by Howard S. Gates on 28 April 1957, and independently by Dr. Giuliano Romano on 18 May 1957. SN 1980I (Type Ia, mag. 14) was discovered by M. Rosker on 13 June 1980. Historically, this supernova has been catalogued as belonging to M84, but it may have been in either neighboring galaxy NGC 4387 or M86. SN 1991bg (Type Ia-pec, mag. 14) was discovered visually by Reiki Kushida on 9 December 1991. A precovery image showed the supernova was present, at magnitude 14.9, on 3 December 1991. This supernova has been studied extensively as a peculiar and underluminous Type Ia, and is now used as a template, with similar events being classified as Type Ia-91bg-like. This high rate of supernovae is rare for elliptical galaxies, which may indicate there is a population of stars of intermediate age in M84.

Illustrations

Worked examples

Example 1 — a first encounter with Messier 84

Start with the simplest possible case. Write down what Messier 84 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 84 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 84 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 84

In research: Messier 84 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 84 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 84 is common in secondary-school and first-year university syllabi. It links to neighbouring topics 3C objects, 4C objects, Astronomical objects discovered in 1781, so understanding it makes those chapters shorter.
In everyday life: Look for Messier 84 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 84 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Messier 84 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 84 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Messier 84 in simple terms?

Why does Messier 84 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 84?

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 84.