astronomy

NGC 6240

NGC 6240 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 NGC 6240 rather than just read about it. In short: NGC 6240, also known as the Starfish Galaxy, is a nearby ultraluminous infrared galaxy (ULIRG) in the constellation Ophiuchus. It was discovered by French astronomer Édouard Stephan on 12 July 1871.

Key takeaways

NGC 6240 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect NGC 6240 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NGC 6240 from memory before moving on to harder problems.

Reference excerpt

NGC 6240, also known as the Starfish Galaxy, is a nearby ultraluminous infrared galaxy (ULIRG) in the constellation Ophiuchus. It was discovered by French astronomer Édouard Stephan on 12 July 1871. The galaxy is the remnant of a merger between three smaller galaxies. The collision between the three progenitor galaxies has resulted in a single, larger galaxy with three distinct nuclei and a highly disturbed structure, including faint extensions and loops.

Double nuclei

Star formation versus supermassive black holes The power sources of ULIRGs in general has been greatly debated. Infrared light from galaxies generally originates from dust in the interstellar medium. ULIRGs are abnormally bright in the infrared. The infrared dust emission in ULIRGs is over one trillion times more luminous than the Sun (i.e. it has an infrared luminosity of 1012 L☉). Astronomers have speculated that either intense star formation regions or active galactic nuclei (which contain supermassive black holes) may be responsible for the intense dust heating that produces this emission, although the general consensus is that both may be present in most ULIRGs. Studying the exact nature of ULIRGs has been difficult, however, because the dust in the centers of these galaxies obscures both visible and near-infrared starlight and because theoretical models of both starbursts and active galactic nuclei have demonstrated that they may look similar. Because NGC 6240 is a nearby example of such a ULIRG, astronomers have studied it intensively to understand its power source.

X-ray observations

Observations performed by Stefanie Komossa and collaborators with the Chandra X-Ray Observatory have detected strong hard X-ray emission from two of the nuclei. The intensity of this emission and the presence of emission from lowly ionized or neutral iron indicate that both of these nuclei are active galactic nuclei. Presumably, these are the black holes that were originally at the centers of the merging galaxies. Over the course of millions of years, the black holes are expected to come closer together and form a binary supermassive black hole.

Recent studies by Wolfram Kollatschny and collaborators using the MUSE instrument on board the VLT have revealed that there are in fact three, not two, supermassive black holes at the core of this remnant. Their masses are suggested to be 90 million, 710 million, and 360 million solar masses. Two of the three black holes are active. The additional SMBH implies that three original galaxies are merging instead of two.

Supernovae Four supernovae have been observed in NGC 6240:

SN 2000bg (Type IIn, mag. 17.4) was discovered by the Lick Observatory Supernova Search (LOSS) on 1 April 2000. SN 2010gp (Type Ia, mag. 17.5) was discovered by The CHilean Automatic Supernova sEarch (CHASE) on 14 July 2010. SN 2013dc (Type II-P, mag. 18.7) was discovered by Adam Block on 11 April 2013. PSN J16525760+0223367 (Type Ia, mag. 15.8) was discovered by Robert Gagliano, Jack Newton, and Tim Puckett on 23 April 2014.

Final stages A galaxy merger is a slow process lasting more than a billion years as two galaxies, under the inexorable pull of gravity, dance toward each other before finally joining together. After research done over the past few years, scientists have concluded that this galaxy has reached its last stages before colliding into one another. Photographic evidence proves that the two nuclei have been growing closer, and in that process, they have been emitting more gasses and stellar winds outward. Those winds evict about 100 solar masses in gases from the galaxy every year. This type of winds and growth of the black holes are known to occur during the last 10 to 20 million years of the merger; it is assumed that this is the amount of time left for the galaxy to finish its collision phase. After this phase, the merged galaxies will become one, becoming a post-merger object until if and when any tidal tails and plumes evaporate.

Gallery

Illustrations

Worked examples

Example 1 — a first encounter with NGC 6240

Start with the simplest possible case. Write down what NGC 6240 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 NGC 6240 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 NGC 6240 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 NGC 6240

In research: NGC 6240 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 NGC 6240 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: NGC 6240 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 1871, Discoveries by Édouard Stephan, Galaxy mergers, so understanding it makes those chapters shorter.
In everyday life: Look for NGC 6240 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 NGC 6240 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NGC 6240 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 NGC 6240 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NGC 6240 in simple terms?

NGC 6240, also known as the Starfish Galaxy, is a nearby ultraluminous infrared galaxy (ULIRG) in the constellation Ophiuchus. It was discovered by French astronomer Édouard Stephan on 12 July 1871.

Why does NGC 6240 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 NGC 6240?

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 NGC 6240.