Lecture 1, 25-04-2023
Oort cloud à huge sphere of le0over material.
Kuiper Belt à disc shaped ring of le0over material.
AU à astronomical unit à distance from sun to earth is 1
Our solar system consists of:
- Sun
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
Av. Distance 0 0.39 0.72 1 1.5 5.2 9.55 19.22 30.11
(AU)
Radius (km) 695,700- 2440 6052 6378 3396 71492 60268 25559 24766
696,342
Mass (1024 kg) 1,988,500 0.33 4.87 5.97 0.64 1898 568.5 86.83 102.4
Density core- 162.2 - 1.4 5.43 5.2 5.52 3.94 1.31 0.69 1.32 1.64
avg (g-cm3)
RotaTon eq. ±25; 58.65 243.02 1 1.03 0.41 0.44 0.72 60.2
period (earth poles 34.4 (9.8 hr) (10.2 hr)
days)
RevoluTon - 87.97 224.7 365.26 686.98 11.86 29.46 84 164.8
period (earth
years)
Surface temp 15×106 - 452 726 281 210 120-150 100-270 60 (52-150) 48
(K) 3800 (100-700) (310-260) (310-150)
Gravity 274 3.7 8.87 9.78 3.71 24.97 10.44 8.69 11.15
The majority of asteroids can be found between mars and Jupiter.
Planets:
- Orbit the sun
- Have sufficient mass to assume a spherical shape
- Cleared neighbourhood around orbits
Dwarf planets:
- Orbit the sun
- Less massive than planets
- Spherically shaped
- Didn’t clear neighbourhood around orbits
Satellites and moons orbit other solar system bodies.
,Small solar-system bodies (asteroids/comets):
- Orbit the sun
- Too liele mass to become spherical
- Didn’t clear neighbourhood around orbits
- Neither planet, nor dwarf planet, nor satellite
Planetary properTes:
1. Orbit
2. Mass, distribuTon of mass
3. Size
4. RotaTon rate and direcTon
5. Shape
6. Temperature
7. MagneTc field
8. Surface composiTon
9. Surface structure
10. Atmospheric structure and composiTon
Lecture 2a, 02-05-2023
Our solar system was “born” in a dense molecular cloud as a result of gravitaTonal collapse.
The 3 stellar populaTons:
- PopulaTon 3: first stars that formed a0er the universe started expanding, extremely massive and hot
with hardly any metals (only H and He). The universe did not exist yet because the elements needed
weren’t present.
- PopulaTon 2: metal poor stars. Metals present are le0overs from (supernovae of) populaTon 3 stars.
- PopulaTon 1: metal rich “young” stars like our sun. contain le0overs from populaTon 2 and 3 stars.
H & He are the most important and abundant elements in the universe.
The milky way consists of:
- A central black hole
- Molecular clouds
- Spiral arms
- Star-forming regions
- GalacTc bulge
- The sun
- Interstellar medium (ISM) à
the maeer and radiaTon that exist in
the space between the star systems in
a galaxy.
Molecular clouds:
- They only form <1% of the total volume of the ISM
- Contain 50% of the gas inside our solar system’s orbit
- Mean densiTes of 100-1000s molecules per cm3
- Mean temperatures of 10-30K (relaTvely cold)
- Very dense cores
• Small cores: 0.1-10M☉ (means Tmes the mass of the sun)
• Large cores: 105-106M☉
- Star forming cores: 104-106 molecules/cm3, ~10K
- Predominantly H2 and He
, The life cycle of stars:
Start in star-forming nebula
When low mass:
- Becomes a brown dwarf
- Then it becomes a star
- Red giant
- Planetary nebula
- White dwarf
When high mass:
- Massive star
- Red super giant
- Supernova
- Black hole or neutron star
Star formaTon:
- There are massive gas clouds in the universe à gravitaTon pulls the gas inwards, but the gas
pressure pushes the gas outwards.
- Jeans mass: the criTcal mass that needs to be exceeded for gravitaTonal pull to overcome gas
pressure à when exceeded the cloud will further collapse.
- The core is densest near the centre, thus collapse proceeds from the inside out.
- Infall conTnues unTl the reservoir of cloud material is exhausted or strong stellar wind reverses the
flow.
- Even the slowest rotaTng core has more angular momentum than the final star would be able to
handle without breaking up.
- If the core rotates too fast, it may break up into two or more sub-clouds that orbit each other.
- IniTally, gas and dust with low angular momentum relaTve to the centre falls towards the centre
forming a protostar.
- In the case of mulTple cores binary or mulTple star systems are formed.
- RotaTon of the cloud will prevent maeer with high angular momentum to collapse into the centre
due to centrifugal forces à the material starts forming a disk around the protostar(s).
- It is expected that all single and binary/mulTple star systems are surrounded by a disk.
- As the (sub)cloud contracts, all its energy is confined to a smaller volume, and it heats up (protostar).
- The majority of the iniTal mass then resides in the (proto)star(s), most of the angular momentum is
taken up by the disk.
Hydrogen fusion:
- Cloud keeps contracTng and keeps heaTng up, kineTc energy due to contracTon enables nuclear
fusion to start.
- Heat generated by nuclear fusion acts as a force that offsets the gravitaTonal contracTon.
- The bigger the star, the stronger the gravity and the more heat is required to keep it from
contracTng.
4 H atoms can form 1 He atom with an excess of mass that gets converted into energy (Einstein).
Oort cloud à huge sphere of le0over material.
Kuiper Belt à disc shaped ring of le0over material.
AU à astronomical unit à distance from sun to earth is 1
Our solar system consists of:
- Sun
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
Av. Distance 0 0.39 0.72 1 1.5 5.2 9.55 19.22 30.11
(AU)
Radius (km) 695,700- 2440 6052 6378 3396 71492 60268 25559 24766
696,342
Mass (1024 kg) 1,988,500 0.33 4.87 5.97 0.64 1898 568.5 86.83 102.4
Density core- 162.2 - 1.4 5.43 5.2 5.52 3.94 1.31 0.69 1.32 1.64
avg (g-cm3)
RotaTon eq. ±25; 58.65 243.02 1 1.03 0.41 0.44 0.72 60.2
period (earth poles 34.4 (9.8 hr) (10.2 hr)
days)
RevoluTon - 87.97 224.7 365.26 686.98 11.86 29.46 84 164.8
period (earth
years)
Surface temp 15×106 - 452 726 281 210 120-150 100-270 60 (52-150) 48
(K) 3800 (100-700) (310-260) (310-150)
Gravity 274 3.7 8.87 9.78 3.71 24.97 10.44 8.69 11.15
The majority of asteroids can be found between mars and Jupiter.
Planets:
- Orbit the sun
- Have sufficient mass to assume a spherical shape
- Cleared neighbourhood around orbits
Dwarf planets:
- Orbit the sun
- Less massive than planets
- Spherically shaped
- Didn’t clear neighbourhood around orbits
Satellites and moons orbit other solar system bodies.
,Small solar-system bodies (asteroids/comets):
- Orbit the sun
- Too liele mass to become spherical
- Didn’t clear neighbourhood around orbits
- Neither planet, nor dwarf planet, nor satellite
Planetary properTes:
1. Orbit
2. Mass, distribuTon of mass
3. Size
4. RotaTon rate and direcTon
5. Shape
6. Temperature
7. MagneTc field
8. Surface composiTon
9. Surface structure
10. Atmospheric structure and composiTon
Lecture 2a, 02-05-2023
Our solar system was “born” in a dense molecular cloud as a result of gravitaTonal collapse.
The 3 stellar populaTons:
- PopulaTon 3: first stars that formed a0er the universe started expanding, extremely massive and hot
with hardly any metals (only H and He). The universe did not exist yet because the elements needed
weren’t present.
- PopulaTon 2: metal poor stars. Metals present are le0overs from (supernovae of) populaTon 3 stars.
- PopulaTon 1: metal rich “young” stars like our sun. contain le0overs from populaTon 2 and 3 stars.
H & He are the most important and abundant elements in the universe.
The milky way consists of:
- A central black hole
- Molecular clouds
- Spiral arms
- Star-forming regions
- GalacTc bulge
- The sun
- Interstellar medium (ISM) à
the maeer and radiaTon that exist in
the space between the star systems in
a galaxy.
Molecular clouds:
- They only form <1% of the total volume of the ISM
- Contain 50% of the gas inside our solar system’s orbit
- Mean densiTes of 100-1000s molecules per cm3
- Mean temperatures of 10-30K (relaTvely cold)
- Very dense cores
• Small cores: 0.1-10M☉ (means Tmes the mass of the sun)
• Large cores: 105-106M☉
- Star forming cores: 104-106 molecules/cm3, ~10K
- Predominantly H2 and He
, The life cycle of stars:
Start in star-forming nebula
When low mass:
- Becomes a brown dwarf
- Then it becomes a star
- Red giant
- Planetary nebula
- White dwarf
When high mass:
- Massive star
- Red super giant
- Supernova
- Black hole or neutron star
Star formaTon:
- There are massive gas clouds in the universe à gravitaTon pulls the gas inwards, but the gas
pressure pushes the gas outwards.
- Jeans mass: the criTcal mass that needs to be exceeded for gravitaTonal pull to overcome gas
pressure à when exceeded the cloud will further collapse.
- The core is densest near the centre, thus collapse proceeds from the inside out.
- Infall conTnues unTl the reservoir of cloud material is exhausted or strong stellar wind reverses the
flow.
- Even the slowest rotaTng core has more angular momentum than the final star would be able to
handle without breaking up.
- If the core rotates too fast, it may break up into two or more sub-clouds that orbit each other.
- IniTally, gas and dust with low angular momentum relaTve to the centre falls towards the centre
forming a protostar.
- In the case of mulTple cores binary or mulTple star systems are formed.
- RotaTon of the cloud will prevent maeer with high angular momentum to collapse into the centre
due to centrifugal forces à the material starts forming a disk around the protostar(s).
- It is expected that all single and binary/mulTple star systems are surrounded by a disk.
- As the (sub)cloud contracts, all its energy is confined to a smaller volume, and it heats up (protostar).
- The majority of the iniTal mass then resides in the (proto)star(s), most of the angular momentum is
taken up by the disk.
Hydrogen fusion:
- Cloud keeps contracTng and keeps heaTng up, kineTc energy due to contracTon enables nuclear
fusion to start.
- Heat generated by nuclear fusion acts as a force that offsets the gravitaTonal contracTon.
- The bigger the star, the stronger the gravity and the more heat is required to keep it from
contracTng.
4 H atoms can form 1 He atom with an excess of mass that gets converted into energy (Einstein).
