astronomy

Galaxy harassment

Galaxy harassment 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 Galaxy harassment rather than just read about it. In short: Galaxy harassment is a form of galaxy interaction in which one or more galaxies interact with each frequently, or are influenced by external gravitational forces of a large galaxy cluster without a direct collision, usually in the form of a flyby. The processes of galaxy harassment can change the morphology of the galaxy, including the triggering of starbursts or morphological changes in the galaxy's structure.

Key takeaways

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

Reference excerpt

Galaxy harassment is a form of galaxy interaction in which one or more galaxies interact with each frequently, or are influenced by external gravitational forces of a large galaxy cluster without a direct collision, usually in the form of a flyby. The processes of galaxy harassment can change the morphology of the galaxy, including the triggering of starbursts or morphological changes in the galaxy's structure. Galaxy harassment is different from galactic mergers, where galaxies directly collide and subsequently merge into a singular large galaxy, leaving behind detectable streams of debris. These debris streams could also provide fuel for quasars in host galaxies.

Effects The mechanisms of galaxy harassment are not significant towards the outskirts of the galaxy cluster due to the smaller number of galaxies that exist. However, towards the center of the cluster, galaxy harassment becomes a significant process altering the morphology of a galaxy. In fact, galaxy harassment drives the morphological evolution of galaxies in clusters. Galaxies towards the outskirts of the galaxy cluster that experience harassment tend to loss only <6% of the total stellar mass while galaxies towards the center of the cluster can loss up to 50% of their total stellar mass. The inclination of a disk galaxy can reduce the mass loss of a galaxy, yet amplify the thickening of the galaxies disk. An example of the effects of galaxy harassment can be seen when comparing distant galaxy clusters past redshift distance z=0.4 to modern galaxy cluster we can see. Galaxy protoclusters at high distances are filled with small spiral galaxies showing signs of multiple phases of starburst activity but over time, galaxy harassment has transformed many of them into spheroidal galaxies.

Globular clusters Galaxy harassment can also affect the globular clusters (GCs) surrounding galaxies. They are strongly effected by the remaining dark matter left after a harassment. Only when dark matter around the galaxy falls to 15% do globular clusters start to get stripped and quickly separate from galaxies. When dark matter falls to just <3%, the galaxy is close to disruption.

Examples

There are several examples of galaxies that have experienced galaxy harassment. One example is NGC 4254, also known as Messier 99. It is a spiral galaxy located in the Virgo cluster that is believed to have been harassed by another galaxy. This caused the galaxy to experience turbulence and alter the fine scale structure of the galaxies interstellar medium (ISM) suggesting that harassment effects more than just the morphology of the galaxy. Another example of a galaxy that was harassed is the Cartwheel galaxy, a lenticular galaxy with a noticeable ring around it, making it also a ring galaxy. Its features were formed from a high speed collision with another smaller galaxy transforming it from a Milky Way like galaxy to its current shape.

See also Comet Galaxy, a galaxy being stripped by the tidal forces of Abell 2667 Interacting galaxy Ram pressure, gravitational force by larger structures Tadpole Galaxy, a galaxy with a visible debris stream Tidal stripping, gravitational process where matter is pulled from a galaxy

References

Illustrations

Worked examples

Example 1 — a first encounter with Galaxy harassment

Start with the simplest possible case. Write down what Galaxy harassment 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 Galaxy harassment 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 Galaxy harassment 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 Galaxy harassment

In research: Galaxy harassment 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 Galaxy harassment 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: Galaxy harassment is common in secondary-school and first-year university syllabi. It links to neighbouring topics Interacting galaxies, so understanding it makes those chapters shorter.
In everyday life: Look for Galaxy harassment 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 Galaxy harassment in 20 minutes

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

Frequently asked questions

What is Galaxy harassment in simple terms?

Why does Galaxy harassment 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 Galaxy harassment?

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 Galaxy harassment.