astronomy

PKS 2155−152

PKS 2155−152 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 PKS 2155−152 rather than just read about it. In short: PKS 2155−152 is an optically violent variable BL Lacertae object located in the southern constellation of Capricornus. It has a redshift of (z) 0.672 and it was first discovered as an astronomical radio source in 1970 by astronomers whom they designated it as OX −192.

Key takeaways

PKS 2155−152 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect PKS 2155−152 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of PKS 2155−152 from memory before moving on to harder problems.

Reference excerpt

PKS 2155−152 is an optically violent variable BL Lacertae object located in the southern constellation of Capricornus. It has a redshift of (z) 0.672 and it was first discovered as an astronomical radio source in 1970 by astronomers whom they designated it as OX −192.

Description PKS 2155−152 is radio-loud quasar with a steep radio spectrum with a bolometric luminosity of 45.67 erg s−1 and a supermassive black hole mass of 7.59 M☉. It is classified as a blazar due to its variability on the electromagnetic spectrum, showing a 3.5 magnitude outburst detected towards the end of the 19th century in 1899. Between the years 1933, 1941 and in 1948, the object had several outbursts of around 3 magnitudes. When observed in 1995, it showed a variability timescale of approximately 15.5 days. The radio structure of PKS 2155−152 is compact. An observation with Very Long Baseline Interferometry (VLBI) conducted in May 1993, found the source has a core-jet morphology, consisting of an unresolved radio core whose brightness temperature is estimated to be more than 6.7 × 1011 Kelvins. When detected with Very Long Baseline Array (VLA) it has a bright core with a jet pointing towards the southern direction. Further investigations suggested the jet may be extending south-west instead which was confirmed by Pushkarev. An X-ray jet counterpart was found in 2011 by Chandra X-ray Observatory with its X-ray emission terminating at 8 arcseconds from the core. It is confirmed that PKS 2155−152 is highly polarized. Based on results, it has polarization in both its core and inside a second jet component south-west. VLBI observations showed the core polarization was shown varying while the jet component polarization remained constant. A study involving calculating the vector sum of the two polarized components in the object via model fitting and with VLA, found a sharp drastic decrease in flux density suggesting most of the variations occurred inside the core. In January 2025, Yongyun Chen found the host galaxy of PKS 2155−152 has a logarithm star formation of 3.386 and a stellar mass of 11.97.

References

External links PKS 2155−152 on SIMBAD

Illustrations

Worked examples

Example 1 — a first encounter with PKS 2155−152

Start with the simplest possible case. Write down what PKS 2155−152 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 PKS 2155−152 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 PKS 2155−152 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 PKS 2155−152

In research: PKS 2155−152 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 PKS 2155−152 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: PKS 2155−152 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Active galaxies, Astronomical objects discovered in 1970, BL Lacertae objects, so understanding it makes those chapters shorter.
In everyday life: Look for PKS 2155−152 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 PKS 2155−152 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what PKS 2155−152 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 PKS 2155−152 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is PKS 2155−152 in simple terms?

Why does PKS 2155−152 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 PKS 2155−152?

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 PKS 2155−152.