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SN Refsdal

SN Refsdal 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 SN Refsdal rather than just read about it. In short: SN Refsdal is the first detected multiply-lensed supernova, visible within the field of the galaxy cluster MACS J1149.5+2223. It was named after Norwegian astrophysicist Sjur Refsdal, who, in 1964, first proposed using time-delayed images from a lensed supernova to study the expansion of the universe.

SN Refsdal — main illustration
SN Refsdal — illustration

Key takeaways

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

Reference excerpt

SN Refsdal is the first detected multiply-lensed supernova, visible within the field of the galaxy cluster MACS J1149.5+2223. It was named after Norwegian astrophysicist Sjur Refsdal, who, in 1964, first proposed using time-delayed images from a lensed supernova to study the expansion of the universe. The observations were made using the Hubble Space Telescope.

Einstein cross The host galaxy of SN Refsdal is at a redshift of 1.49, corresponding to a comoving distance of 14.4 billion light-years and a lookback time of 9.34 billion years. The multiple images are arranged around the elliptical galaxy at z = 0.54 in a cross-shaped pattern, also known as an "Einstein cross".

Reappearance

After the discovery of the supernova, astronomers predicted that they would be able to see it again in about one year, after the four images had faded away. This is because the initially observed four-image pattern was only one component of the lensing display. The supernova may also have appeared as a single image some 40–50 years ago elsewhere in the cluster field. The supernova reappeared at the predicted position between 14 November and 11 December 2015 (with the exact date being uncertain by approximately one month which is the interval between two consecutive Hubble observations), in excellent agreement with the blind model predictions made before the reappearance was observed. The time delay between the original quadruplet observed in 2014 and the latest appearance of the supernova in 2015 was used to infer the value of the Hubble constant. This is the first time this technique, originally suggested by Refsdal, has been applied to supernovae. Using measurements from SN Refsdal and galaxy cluster lens models, astronomers found that the Hubble constant has value H0 = 66.6+4.1−3.3 km s−1 Mpc−1.

Other multiply-lensed supernova Other reported multiply-lensed supernova are iPTF16geu, SN Requiem (SN 2016jka), SN Zwicky (SN 2022qmx), Chen et al. SN, SN H0pe, SN 2022riv, and SN Winny (SN 2025wny). Besides SN Refsdal, SN H0pe has also been used to measure the value of the Hubble constant using the relative delay in the arrival between images.

See also Einstein Cross, the gravitationally lensed quasar that gave rise to the term "Einstein cross" How One Supernova Measured The Universe

References

External links

Images of first SN Refsdal in March and reappeared in December 2015 at hubblesite.org NASA's Hubble Discovers Four Images of Same Supernova Split by Cosmic Lens - by NASA Predicted Reappearance of SN Refsdal (March 2015) The image taken by Hubble around November 2015 shows new supernovae 'SX' in multiply image system at astro.berkeley.edu. Hubble Hangout December 17 2015 discussing SN Refsdal View of Exploding Star Appears, Right on Cue National Geographic Society 17 December 2015

Illustrations

SN Refsdal illustration
SN Refsdal: The image to the left shows a part of the deep field observation of the galaxy cluster MACS J1149.5+2223 from the Frontier Fields programme. The circle indicates the predicted position of the newest appearance of the supernova. To the lower right, the Einstein cross event from late 2014 is visible. The image on the top right shows observations by Hubble from October 2015, taken at the beginning of the observation programme to detect the newest appearance of the supernova. The image on the lower right shows the discovery of the supernova on 11 December 2015, as predicted by several different models.
The image to the left shows a part of the deep field observation of the galaxy cluster MACS J1149.5+2223 from the Frontier Fields programme. The circle indicates the predicted position of the newest appearance of the supernova. To the lower right, the Einstein cross event from late 2014 is visible. The image on the top right shows observations by Hubble from October 2015, taken at the beginning of the observation programme to detect the newest appearance of the supernova. The image on the lower right shows the discovery of the supernova on 11 December 2015, as predicted by several different models.

Worked examples

Example 1 — a first encounter with SN Refsdal

Start with the simplest possible case. Write down what SN Refsdal 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 SN Refsdal 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 SN Refsdal 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 SN Refsdal

In research
SN Refsdal 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 SN Refsdal 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
SN Refsdal is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 2014, Gravitational lensing, Leo (constellation), so understanding it makes those chapters shorter.
In everyday life
Look for SN Refsdal 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 SN Refsdal in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what SN Refsdal means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain SN Refsdal out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is SN Refsdal in simple terms?

SN Refsdal is the first detected multiply-lensed supernova, visible within the field of the galaxy cluster MACS J1149.5+2223. It was named after Norwegian astrophysicist Sjur Refsdal, who, in 1964, first proposed using time-delayed images from a lensed supernova to study the expansion of the univer…

Why does SN Refsdal 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 SN Refsdal?

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 SN Refsdal.

Tags

  • Astronomical objects discovered in 2014
  • Gravitational lensing
  • Leo (constellation)
  • Type Ia supernovae

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