1.4 Making Matter Flashcards
What is antimatter?
Antimatter has the same mass as ordinary matter (that we call baryonic matter) but has opposite properties, including charge
For every particle of ordinary matter, there is..
What is antimatter?
a corresponding antimatter particle with the same mass and opposite charge
WHAT HAPPENS WHEN ANTIMATTER AND BARYONIC MATTER INTERACT?
…they annihilate each other and produce energy in the form of gamma rays
WHY IS ANTIMATTER IMPORTANT?
Medical imaging, where positron-emitting isotopes are used in positron emission tomography (PET) scanners to detect and monitor diseases such as cancer.
WHEN DID MATTER AND ANTIMATTER FORM?
In the extremely hot conditions of the early universe, fractions of a second after the Big Bang, matter and antimatter were created through a process known as pair production
WHEN CAN PAIR PRODUCTION OCCUR?
- …when high-energy photons transform into particles and their corresponding antiparticles, such as an electron and a positron
- In this manner, as the Big Bang theory predicts, equal quantities of baryonic matter and antimatter were produced
WHAT HAPPENED AFTER THE UNIVERSE COOLED?
Antimatter/Baryonic Matter
- However, as the universe cooled,** the temperature dropped below the threshold required for pair production**.
- The baryonic matter and antimatter that had been created continued to annihilate each other (Figure 2-right), which should have destroyed both forms of matter.
- This is called THE BARYON ASYMMETRY PROBLEM
HOW DID THE DROP IN UNIVERSAL TEMP. AFFECT THE PROPORTION OF BARYONIC TO ANTIMATTER?
- MORE baryonic matter (unknown as to why)
- It is possible that just a little more matter was produced than antimatter.
- If this is the case, then the imbalance, about one particle in a billion difference, allowed for the survival of some baryonic matter, which ultimately formed the building blocks of all the visible material we see in stars, planets, and galaxies.
ONE SECOND AFTER THE BIG BANG:
Which elements formed during the big bang?
Protons and neutrons (nucleons) formed from quarks
WHAT WAS THE FIRST ATOMIC NUCLEI TO FORM?
Which elements formed during the big bang?
The first atomic “nuclei” to form would have been protons, basically hydrogen (also called protium 1H) nuclei
3 MINUTES AFTER THE BIG BANG:
Which elements formed during the big bang?
- Around 3 minutes after the Big Bang, the universe had cooled sufficiently for protons and neutrons to combine to form heavier atomic nuclei via nucleosynthesis
- By the time of nucleosynthesis, protons were still moving fast enough to overcome the repulsion of the electromagnetic force and get close enough to each other to allow the strong nuclear force to capture and bind the protons together
At times earlier than 3 minutes
Which elements formed during the big bang?
- Nucleons were moving too rapidly for the strong nuclear force to capture them.
- In this dense soup of high-energy particles, nuclei of atoms with atomic masses greater than protium (1H) were formed
- Only rare collisions could produce any atomic nuclei beyond hydrogen and helium nuclei
- As a result, the early universe was mostly composed of Hydrogen and Helium atoms at recombination
If the universe was mostly hydrogen and helium following the Big Bang and the universe was expanding and cooling, how can we…
- “cook” the rest of the heavier elements beyond boron? (RE: rare collisions could produce any atomic nuclei beyond hydrogen and helium nuclei; Boron is the highest atomic # so far)
- Remember, it was only in the very early history of the universe that temperatures were hot enough (and particles moving fast enough) for atomic nuclei to fuse and create atoms heavier than hydrogen
To cook heavier elements, we need to turn our attention to…
…the life and death of stars
How is a star born from Baryonic matter?
- Following the Big Bang, most baryonic matter was hydrogen and helium.
- Irregularities in the distribution of this matter would cause certain areas to gravitationally attract more hydrogen and helium, forming concentrations of gas that would continue to collapse under gravity.
- Eventually, temperatures and pressures at the centre of these masses would become so great that hydrogen would be fused into helium with an associated release of energy (nuclear fusion).
- At this point, a star was born!
- However, different types of stars have different types of lives and deaths and can “cook” a different range of elements.
How hot is the sun in comparison to earth?
Temperature in the Sun’s core is about 15.7 million °K, 260 billion times Earth’s atmospheric pressure.
What happens at the sun’s high temperature?
Electrons are stripped from atoms to form a soup of subatomic particles, a plasma
At these temperatures, hydrogen-1 (1H) is fused into helium-4 (4He) in three steps:
- Stage 1: Two protons combine, one converts into a neutron to form a nucleus of the heavy isotope of hydrogen (2H, deuterium)
- Stage 2: The deuterium nucleus combines with another proton (1H) to form the light helium isotope known as helium-3 (3He)
- Stage 3: Two helium-3 nuclei combine to form helium-4 (4He), releasing two protons.
SUMMARY: hydrogen-1 (1H) fused into helium-4 (4He)
WHY? WHAT EQUATION APPLIES?
- OVERALL: four protons are converted into one helium nucleus; energy is released at each stage,
- WHY? The nuclei formed have slightly less mass than the particles that form them
- SUMMARIZED BY: E=mc2
GRAVITATIONAL EQUILLIBRIUM:
- The energy produced by nuclear fusion in the core of a star, like our Sun, counteracts the force of gravity that tends to collapse the star.
- INSIDE VS OUTSIDE PUSH
HOW DOES GRAVITATIONAL EQUILLIBRIUM WORK?
- When the core runs out of hydrogen, it contracts due to gravity since there’s no longer enough energy being produced to resist this force.
- This contraction causes an increase in temperature, eventually reaching levels where helium fusion begins, forming heavier elements like carbon, oxygen, and neon.
- This renewed fusion process generates more energy, which again balances out the force of gravity, stabilizing the star for a time.
What would be the result of a much bigger (8x) start than the sun?
HYDROGEN FUSION PHASE
Higher mass stars
- Due to their mass, their cores are at much higher pressures and temperatures.
- AS A RESULT: Rather than yellow, these stars tend to shine towards the blue end of the visible spectrum
- The higher temperatures also mean that these stars burn through their hydrogen fuel much faster
Helium fusing and beyond
Higher mass stars
- As hydrogen fuel is used, helium builds up in the core, like ash in a fireplace.
- Once the hydrogen has been used up, the core contracts and heats up, enabling it to fuse the helium “ash” into carbon + continue the fusion process.
- As the helium is used up, the core contracts and heats again, allowing the star to fuse the carbon “ash” into neon, sodium, and magnesium.
- This process continues to iron, each contraction allowing for the fusion of heavier elements from the ash of the previous fusion step (Table 2). Each successive fusion step in the core happens faster than the previous step.
Contraction Result: “Onion Skin”
Higher mass stars
- The heat produced by each contraction produces a series of nested spherical “onion skin” fusion shells outside of the core.
- As you move away from the star’s core, there are shells of decreasing temperature where fusion progresses using nuclei of progressively lower mass
