Chapter 15: Problem 39
Unenriched Stars. Suppose you discovered a star made purely of hydrogen and helium. How old do you think it would be? Explain.
Short Answer
Expert verified
An unenriched star made only of hydrogen and helium would likely be very ancient, possibly from the first generation of stars.
Step by step solution
01
Understanding Stellar Composition
Stars primarily consist of hydrogen and helium, the two lightest and simplest elements in the universe. Heavier elements are usually created through nuclear fusion within stars or during supernovae from older stars.
02
Identify Element Enrichment Mechanism
Stars that are enriched with heavy elements are typically younger stars because the universe initially had only hydrogen and helium after the Big Bang. Other, heavier elements (‘metals’) were formed later, inside stars.
03
Evaluating Unenriched Star Characteristics
A star made purely of hydrogen and helium is considered to have little to no 'metallicity.' This indicates it is a very old star, as it formed before heavier elements became more common in the interstellar medium due to stellar nucleosynthesis.
04
Determine Origin Time Period
The first stars, known as Population III stars, were formed in the early universe from the original hydrogen and helium available after the Big Bang. Any current star with only these elements is likely to be a remnant from this earliest stellar generation.
Unlock Step-by-Step Solutions & Ace Your Exams!
-
Full Textbook Solutions
Get detailed explanations and key concepts
-
Unlimited Al creation
Al flashcards, explanations, exams and more...
-
Ads-free access
To over 500 millions flashcards
-
Money-back guarantee
We refund you if you fail your exam.
Over 30 million students worldwide already upgrade their learning with Vaia!
Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Stellar Nucleosynthesis
Stellar nucleosynthesis is the process by which elements are formed within stars. Stars are like cosmic factories, where new elements are forged through nuclear fusion. During this process, lighter elements such as hydrogen and helium are fused into heavier elements like carbon, oxygen, and iron. This happens under extreme temperatures and pressures at the core of the stars.
Stars have different life stages, and the types of elements they produce can change as they burn through their fuel.
Stars have different life stages, and the types of elements they produce can change as they burn through their fuel.
- Small stars may create elements up to carbon and oxygen.
- Larger stars, often called supergiants, can forge even heavier elements.
Element Enrichment
Element enrichment refers to the process by which the chemical composition of the universe changes over time. Initially, after the Big Bang, only the lightest elements existed - primarily hydrogen and helium. Through stellar nucleosynthesis, stars create heavier elements, often referred to as 'metals' by astronomers.
Every generation of stars contributes to this enrichment process:
Every generation of stars contributes to this enrichment process:
- When stars end their life and explode as supernovae, they spread these heavier elements into the surrounding space.
- These enriched materials eventually become part of the molecular clouds from which new stars form.
Big Bang Nucleosynthesis
Big Bang nucleosynthesis refers to the formation of the first elements in the universe, occurring only a few minutes after the Big Bang when temperatures and pressures were incredibly high. This primordial nucleosynthesis produced the lightest elements, mainly hydrogen, helium, and small amounts of lithium and beryllium.
- Hydrogen and helium make up almost all of the ordinary matter in the universe today, reflecting their abundance from this period.
- Due to the rapid cooling of the universe, heavier elements beyond lithium were not formed at this time.
Metallicity in Stars
Metallicity in stars is a crucial concept in astrophysics that refers to the proportion of elements heavier than hydrogen and helium within a star. Astronomers denote all elements heavier than helium as 'metals'.
When we find a star with low metallicity today, it may be incredibly old, possibly tracing back to the early universe when the first stars formed. This gives us a window into the past, showing us conditions in the universe shortly after the Big Bang.
- Stars with high metallicity contain a larger variety of heavy elements.
- Low metallicity stars are considered more primitive, as they formed from material that had not been significantly enriched by previous generations of stars.
When we find a star with low metallicity today, it may be incredibly old, possibly tracing back to the early universe when the first stars formed. This gives us a window into the past, showing us conditions in the universe shortly after the Big Bang.