astronomy

GHZ2

GHZ2 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 GHZ2 rather than just read about it. In short: GHZ2, also named GLASS-z12 (formerly known as GLASS-z13) is a Lyman-break galaxy discovered by the Grism Lens-Amplified Survey from Space (GLASS) observing program using the James Webb Space Telescope's NIRCam in July 2022. It has a spectroscopic redshift of 12.34, making it one of the most distant galaxies and astronomical objects ever discovered.

Key takeaways

GHZ2 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect GHZ2 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of GHZ2 from memory before moving on to harder problems.

Reference excerpt

GHZ2, also named GLASS-z12 (formerly known as GLASS-z13) is a Lyman-break galaxy discovered by the Grism Lens-Amplified Survey from Space (GLASS) observing program using the James Webb Space Telescope's NIRCam in July 2022. It has a spectroscopic redshift of 12.34, making it one of the most distant galaxies and astronomical objects ever discovered. According to current theory, this redshift corresponds to a time about 13.44 billion years ago, approximately 355 million years after the Big Bang, or about 2.57% of its current age.

Discovery GLASS-z12/GHZ2, was initially discovered as a robust z ≈ 12.0–12.5 candidate by Castellano et al. and Naidu et al. in the GLASS-JWST Early Release Science NIRCam field. The two discovery papers appeared on arXiv the same day. Hence these two names for this galaxy of GLASS-z12 (Naidu et al. 2022) and GHZ2 (Castellano et al. 2022a). GLASS-z12 derives its name from the GLASS survey that discovered it and its estimated photometric redshift of approximately z = 12.4+0.1−0.3. GLASS-z12 was initially announced as GLASS-z13 because it was thought to have a higher redshift of z = 13.1. This redshift value was later revised down to z = 12.4 in October 2022, resulting in the renaming of this galaxy. It was discovered alongside another galaxy, GLASS-z10, comparable to GN-z11, also one of the oldest galaxies discovered.

Spectroscopy by the Atacama Large Millimeter Array Spectroscopic observations of GLASS-z12 by the Atacama Large Millimeter Array (ALMA) in August 2022 confirmed that the galaxy has a spectroscopic redshift of 12.117±0.012, making it one of the earliest and most distant galaxies ever discovered, dating back to 360 million years after the Big Bang, 13.44 billion years ago. ALMA observations detected an emission line associated with doubly ionized oxygen (O III) at 258.7 GHz with a significance of 5σ, suggesting that there is very low dust content in GLASS-z12, if not the early universe as well. Also based on oxygen-related measurements, the age of the galaxy is confirmed. GLASS-z12 has a light-travel distance (lookback time) of 13.4 billion years. However, due to the expansion of the universe, its present proper distance is 32.718 billion light-years.

Spectroscopy by the James Webb Space Telescope This galaxy was observed again in October 2023 by the James Webb Space Telescope with the NIRSpec and MIRI spectrographs, making it the most distant redshift galaxy of z = 12.34 with full spectroscopic coverage from ultraviolet (UV) to optical.

According to current ΛCDM parameters (H0 = 67.4, Ωm = 0.315, ΩΛ = 0.685), this redshift of 12.34 corresponds to a light-travel distance (lookback time) of 13.44 billion years. However, due to the expansion of the universe, its comoving distance is 32.837 Gly.

Illustrations

Worked examples

Example 1 — a first encounter with GHZ2

Start with the simplest possible case. Write down what GHZ2 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 GHZ2 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 GHZ2 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 GHZ2

In research: GHZ2 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 GHZ2 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: GHZ2 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Discoveries by the James Webb Space Telescope, Dwarf galaxies, Sculptor (constellation), so understanding it makes those chapters shorter.
In everyday life: Look for GHZ2 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 GHZ2 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what GHZ2 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 GHZ2 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is GHZ2 in simple terms?

Why does GHZ2 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 GHZ2?

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 GHZ2.