Into the Cosmos - multiple choice test

all of the lectures merged into 1

what is the Fermi Paradox

Apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations, and the lack of evidence for such civilizations. It questions why, given the vastness of the universe and the likelihood of life, we have not yet encountered any signs of extraterrestrial life.

What is 2 reasons why we haven’t seen anyone

• Suppose that intelligent life is rare, or

• The resources to sustain it are in short supply

Even with plentiful resources, civilizations might be able to annihilate themselves (e.g. nuclear war/ruining climate). Natural disasters could also limit lifetime of civilization (e.g. impacts of asteroids/comets, Supernovae, eruption of supervolcanoes, etc)

the Fermi Paradox debate will continue until

1) A thorough exploration of Galaxy (and beyond), or

2) Actual communication with an alien race

why might the fossil record on Earth be sufficent to understand how life started

There are no records of the first 0.5 – 1 billion years of life on this planet, though the following 3 billion years are recorded. We will not accurately be able to track back to when life started.

what are the two methods being used to discover our origin

– one makes guesses on how it might have happened and attempts to re-create these scenarios in the laboratory (hypothesis-driven) – the other seeks examples in nature that might provide vital clues (discovery science).

how to use the scientific view to find life in the cosmos

• We need to draw conclusions from the lifeforms that exist on our planet

• We need to speculate in a scientific manner on the probability of finding life elsewhere

• Scientific speculation creates a new hypothesis that can be tested against existing data (e.g, does life need oxygen?)

• Any new hypothesis must be tested by the best scientists on the planet and survive. Perhaps in an improved version.

• The hypothesis either makes accurate testable predictions or not!

what is the laws of Nature

• Someone proposes a hypothesis (e.g, the Moon is made of Cheese)

• If the hypothesis survives testing by a large number of different methods then it achieves the status of a law

  • These laws provide the underlying basis of scientific speculation,

  • Allows us to predict things that have not yet been observed  (e.g, other moons may also be made of cheese)

• Sometimes laws absorb previous laws (e.g, Einstein’s view of the Universe absorbed Newton’s views)

  • The longer a law has been tested, the less likely it is to be proved incorrect – but this does happen, and this is often one of the most exciting events in scientific research (e.g, particle faster than light??)

why might the scientific methods not be perfect

• To some people the scientific method appears to offer less emotional appeal than other methods, but this is a requirement of the method. - based on facts

• We are all capable of holding contradictory views on things (e.g, supporting a team even though you suspect that they are not the best team)

• The topic of this module is one that always becomes entangled with this conflict between scientific reasoning and emotional wishful thinking. We need to be careful!

what is a star?

it is a self graviating spere of gas that generates and radiates energy. it retaines its own shape

what makes a star shine

Nuclear fusion in its core generates the radiation power - generates radiation power, photons are being released and pushing the plasma out

what determines a stars lunimosity

Mass

how to stars remain in a hydrostatic equilibrium

they balance the inward gravitational collapse with the radiation outward pressure. when a star is born it starts to go inward until it is hot enough for nuclear fussion to begin which kickstarts the energy for the outward pressure

what determines a stars temperature

the mass

what is the “Hertzsprung-Russell” (HR) diagram

a diagram showing thetemperature lumonisity of stars

what do red stars typically represent on the “Hertzsprung-Russell” (HR) diagram

The red stars are dimmer and cooler

what do blue stars typically represent on the “Hertzsprung-Russell” (HR) diagram

the blue stars are brighter and hotter.

what is the main sequence for stars?

in the equilibrium. Most of the stars are in this. They spend most of the time here.

what is the Stefan-Boltzmann Law

The Stefan-Boltzmann Law states that a star's luminosity is proportional to the fourth power of its temperature. Therefore, hotter stars emit significantly more energy and appear brighter.

If the temperature goes up a little bit the luminosity will increase a lot!

The bigger = more surface = brighter

how to stars maintain their temperature

The inner parts of the stars are collapsing and then get hotter which allows for more fussion causing the star to expands more which causes it to cools down. The inner core becomes hotter and smaller but the outer layer becomes cooler and larger.

what are red giants?

Red Giants: H in core is used. Gravity compresses core (gets hotter, fusion of He into carbon (C). Outer layer expands (cools down)

 

what are white dwarfs

end products of low-mass stars: all H is used. They are not massive enough to fuse heavier elements.

Red giants can produce a nice explosion if they don’t get the next process (not a supernova) and all that remaines is the core (called a white dwarf)

what are different spectral type stars and their surface temp and radius

• O - 35,000 - 18 (BLUE)

• B - 20,000 - 7

• A - 10,000 - 2.5

• F - 6,500 - 1.5

• G (SUN) - 5,500 - 1 (YELLOW)

• K - 4,500 - 0.8

• M - 3,000 - 0.6 (RED)

What is the brightest star in the Northern Hemisohere

Sirius is a binary star system B is a white dwarf

It is 8.6 light years away

 

what is the mass of our sun

around 330,000 times Earth

what is the surface temp

around 5800K

how old is it?

4.6 billion years old

what is teh distance

150 million kmw

what are sunspots

cooler regions in solar photosphere due to intense magnetic field strength (inhibits convection)

why do stars shine?

cooler regions in solar photosphere due to intense magnetic field strength (inhibits convection) e=mc2

The basic process of nuclear fusion in stars is known as the Proton-Proton Cycle

what is the proton - proton cycle

• Two protons fuse together to produce deuterium + a positron + a neutrino

• Another proton fuses with the deuterium to produce a nucleus of 3He + a photon

• Two 3He nuclei fuse to produce a single 4He + two more protons (which can start all over again)

Mass of 4 protons is larger than mass of 1 helium atom Converted into energy! mass is lost in this process which is the energy.

what is the lifetime of the sun

10 billion years

why is temperature imporntat for proton-proton

For the proton-proton cycle to function: two positively charged objects (the protons) must come close enough together. • This is very difficult because of their identical charges, but with enough energy (i.e. speed), then the mutual electrostatic repulsion can be overcome. • For fusion to occur, protons need to get within 10-15m of each other. Can only be achieved at T >10 million K.

why is the temp generated by the fusion process vital for supporting a star

• Because stars are not solid bodies they tend to try and collapse under their own gravitational pressure.

• Small increase in temp causes an outward pressure to increase casues the star to expand and then cool down. A nice balance.

• This effect is balanced by the outflow of thermal energy (photons) from the star’s core (radiation pressure), which keeps the star at its current size until the fuel is all used up.

• This is a natural self-balancing method: if the star suddenly produces more energy, then it expands slightly. The act of expansion then causes the core to cool slightly and thereby reduces the energy output. And vice verse.

 

why do stars have different lifetimes

because they have different masses and different temperature cores. In other words, the more massive stars burn up very much quicker than objects the size of our own Sun

 

If the mass goes up a little bit the lifetime will go down a lot

what is the equation describing the relationship between stars lifetime and mass

lifetime = 1/(mass) ².5

what is the lifetime of sirius A

1 billion years (2.3 times bigger than our sun)

what is the lifetime for rigel

2 million years (10 times bigger than our sun)

what is the lifetime of procyon a

2.4 billion years (1.8 times bigger than our sun)

why is the lifetime of stars important for life in the cosmos

Since we seem to need several billion years to create life (at least in our case it took ~1 billion years to form simple cells), then some stars may simply not be suitable nurseries for life (even if they have formed planets around them)

how many O stars in the galxey?

~10,000

how many B stars in the galxey?

~50 million

how many A stars in the galxey?

~250 million

how many F stars in the galxey?

~1.2 billion

how many G stars in the galxey?

~3 billion

how many K stars in the galxey?

~5 billion

how many M stars in the galxey?

Even more M-type stars (75% of 100-400 billion stars in our Galaxy), but too hard to detect as they are faint

what type of stars are not worth searching for and why

There is probably no point searching for life around O, B, and A stars (and maybe F-type stars) as they don’t last long enough.

How do we know that stars evolve?

By comparing HR diagrams of different star clusters

What is the solar neutrino problem?

Models of the Sun predict that we need a 2-3x higher neutrino flux than the one we measure on Earth.

Explanation: The neutrinos emitted in the PP-chain are electron neutrinos, one of the 3 types of neutrinos. Neutrinos could change from one type to another, explaining the lower observed flux.

how are stars created

Stars are created from condensations in the interstellar medium (ISM).

what is ISM

matter filling interstellar space, including gas (ions, atoms, and molecules) dust and cosmic rays

what does colder temperatures mean for star formation

The colder temperatures mean less internal pressure and hence a greater chance of condensation occurring

what is necessary for gravity in a stars formation

gravity must overcome the internal pressure of the medium. This is most likely to happen in regions where the ISM is relatively dense and temperatures are relatively low.

what is a dark nebulae

interstellar clouds that contain a very high concentration of dust

The dark nebula because it is filled with dust which absorbes the backrgound light. The pik you see is the clouded light from other stars

why is dust important in star formation?

• Relatively large particles: catalyzing condenstations. It is a good building block to start the building blocks to start and create clumps of molecules and dust

• It absorbs most of the wavelengths (make it dark and cold) important to have low temp as allows things to overcome internal pressures

• Shielding inner regions from 'harmful' radiation. Where the beginings of the stars are forming they are being shielded which is important

what are three examples of dark nebulae

• elephant’s trunk

• pillars of creation (in eagle nebula)

• horsehead nebula (in orion)

what happens to newly born stars?

once they are able to have nuclear fussion they create stellar winds which blow away the internal gas and dust, creates a clear circle around the star.

Do nebula’s have high density

Within these nebulae the densities are up to 10,000-106 particles per cubic centimetre. (c.f., normal ISM densities are about 1 particle/cm3, air@sea level:1019 molecules/cm3 , high-vacuum chamber in lab:1010 particles/cm3 )

Do nebula’s have low temperature

• Temperatures are low (roughly 10K) compared to ten times more in most interstellar regions (remember room temperature is 293K).

• Most interstellar regions are around 100K)

  

what is the typical size and mass of a nebula

s 3-10 light years across and contains ~1000 solar masses of material.

what is the typical content percentage of a nebula

74% hydrogen 25% helium 1% other elements

How do star’s form?

A dense portion of the nebula starts to contract under its own gravity:

Usually these large clumps of material will have some small rotation, which will speed up as the material collapses in order to conserve angular momentum.

The nebula starts shrinking causing the dense portions to contract under its own gravity. The contraction can be triggered by nearby shockwave such as a supernova explosion. OR unless if it has a large enough mass by itself it will just start to contract anyway. They then have some small rotation. Smaller objects have faster spinning. So the faster they start shrinking they will have faster rotations.

The cloud fragments collapse under their own gravity and form protostars. They are stars that are already getting warmer and hotter on the inside but are not hot enough to turn hydrogen into helium.

 

They start to collapse and create a rotating object, the rotation helps to create symmetry and becomes a flat disk around the protostar. Eventually when nuclear fusion starts and the inner temp is high enough 10 million kelvin. Then the star creates the stellar winds. It starts to push any gas material off from around it. Once the stellar winds kick in the final mass of the star is being set. There is a little disk and little objects within that still has the ability to grow

 

 

what can sometimes trigger a nebula to contract

nearby shock waves from exploding older stars, or simply contracting because of their own densities

what happens to objects formed in the star building process that are not big enough

not massive enough to reach the internal heat so they keep shrinking and shrinking and don’t have the radiation pressure to stop it from shrinking

how are planets formed

Planetesimals and protostar are formed from the same cloud at approx. the same time

They break eachother apart. The star dust disk is where the different type of planets are forming

 

 

In the same nebula there are multiple starts form, in the little clumps to form their individual solar systems. Planes are very common

what does this image show?

a star with stellar fussion and most likely nuclear fussion turned on

how does a protostar go to the main sequence

rapudly. they become hotter or smaler depending on their mass

 

6% of its time it moves towards the main sequence. The more massive stars are more pequiler. Out sun spends 10 billion years on the main sequence, 1.5% spent getting to it. They become bluer and hotter until they get to the equilibrium

 

why is the stability of stars important fo life in cosmos

• Even though it is pretty stable while on the MS, changes can and DO take place. 

• E.g, our Sun has become 40% more luminous and 6% larger over last 4.6 billion yrs. (Reminder: age of Earth is 4.6 billion yrs

• Therefore, we must be aware that current conditions do not reflect the circumstances when life first came into existence

• Note: the Sun will keep increasing its size & luminosity, and it is predicted that conditions on Earth are going to be unbearable for life in approx. one billion years from now

 

1 billion years will be too warm and too hot for life to sustain as the sun will be too bright. There will be no way we will be able to sustain life!!!

does the stellar stability effect a planet

yes, ice time effects life and glacier acitivity is driven by sunposts

what is the last phase of stellar evolution

it depends on how large it is.

• A red giant star that is 8 times lower than our sun just create regular red giants.

  • The colapsing layers will create a white dwarf

• A red giant that is 8 times our sun the outwer layers will be blown away ad then the outwer layers will be blown away in a supernova and a contracting core will be left as a nutron star or the more massive stars will become a black hole.

   

what is the red giant phase

all stars go though the red giant. massive stars form red supergiants.

As the star reaches the end of burning up all the hydrogen in its core the fusion process moves further away from the core. This has the effect of causing the core to collapse and, ironically, the increasing pressure raises the temperature of the star core (i.e. stars becomes brighter).
The outwer layers are pushed away, many many times the originla size and cool down ans so the observed temp is cool and red, so see a star that looks cool but much much brighter due to its internal core.

what happens when a red giants core increases

The central temperature can increase from 10 to 100 million K, resulting that the outer layers of the star (envelop) undergo a tremendous expansion to many times their original size (and observed surface temperature decreases as result of this expansion). What we see: A much brighter star with a cooler (red) surface

Note: we expect our own Sun to expand out as far as the Earth, i.e. roughly 100 times larger than at present.

what happens when the red giant’s outer layer expands

The expanding outer layers: Will cause the inner planets (in our solar system) to be immersed in a stellar atmosphere at a temperature of 3500K, resulting in catastrophic consequences for anything on the planet. Even the massive outer planets will have their thick gaseous atmospheres blown away.

what are red supergiants?

when massive stars Reach the end of burning up all the hydrogen in their cores, the fusion process moves further away from the core. The core collapses, raising its temperature, and turns on the next phase of nuclear fusion. This process of shrinking, increasing T, and turning on next step of fusion continues all the way up to fusing Fe in its core. Red supergiants W

how did our solar system form?

As the Sun was forming, the surrounding spinning disk contained the ingredients that would be used to create the planets

After ~100,000 yrs, accretion onto the Sun has finished: ➢ Sun has reached its final mass and switched on as a star ➢ Disk turbulence becomes less intense and dust settles into the central plane of the disk

This process of sedimentation happens fairly fast (few 1000 yrs) and is used to define the “Age Zero*” of the solar system (when nuclear fusion takes over contribution to luminosity).

*This point in time can be determined from the age of carbonaceous chondrites in meteorites, and is found to be 4.6 billion yrs ago.

Planetesimals continue to collide and grow. e) Over the course of a hundred million years or so, planetesimals form a few large planets that travel in roughly circular orbits

what elements does the soalr disk consist of?

98.5% gas (Cosmic Abundance: 99% H & He, 1% rest) • 1.5% dust (mostly carbon, but also iron & silica)

what two things affect where and how planets form

• turbulence in disk

• temperature in disk

how does turbulence effect how and wehre panets form

Turbulence:

• Too turbulent: particles move too fast and bounce off each other Less turbulent: greater chance that particles collide and stick together

• Less turbulent: greater chance that particles collide and stick together

 

 

Less turbulance means dust can stick togehr. More turbulance means that dust will bounce off of eachother.

 

how does disk temperature affect how and wehre planets form

• At Age Zero (~4.6 billion yrs ago), the temperature distribution in the disk is critical in deciding which materials will be used to form which type of planets

• The temperature falls off roughly as 1/(distance)2 as we move away from the new star (if you go 4 times the difference the temperature falls 16th)

• The critical point is the “ice line” (or frost line). Beyond this line it is so cold that hydrogen compounds (like water) condense into solid ice grains

 

The ice line moves further away from the sun. large planets need ice to form whereas for planets like earth you don't need it

how does disk temperature vary?

• In the inner zone (between 0.8 and 1.3 AU*): the dust was very hot (around 1000K) and could not contain any residual water (or material that easily evaporates)

• Between 2 and 5 AU: the temperature remained low enough (below 500K) such that volatile organic substances can stay solid (on dust grains)

• Beyond 5 AU: water no longer evaporates (T below 150K), surviving in the solid phase in empty space. This water-ice will be critical for forming the cores of the giant planets

explain this?

Each of the lines are different elements - when it starts to go from a gas state to a solid state. The lower you go there is more water ices.

 

Jupiter was formed outside of the ice line but has been pushed into inward out of the ice line

how long does the Early growth by sticking and coagulation process of forming planetesimals take

• f there were no turbulence left at all, then objects of a few kilometres diameter would form in a few tens of years through the weak action of their own gravity

• But it is likely there would be some residual turbulence, so we expect the process to actually take 1000 – 100,000 years to produce objects larger than 1 km

 

what happens after 100,000 years of formation of planetesimals

• So after 100,000 yrs, we expect the central plane to contain 100 billion objects of 1-10 km in size, still surrounded by a thicker disk of nebular gas.

• Because they are all rotating in the same direction around the Sun (with different velocities), they undergo many gentle collisions. They gradually agglomerate into larger masses.

how do larger planets form?

• Based upon the local temperature, the chemical nature of these km-sized objects evolves as we move away from the centre:

• The inner ones are rocky in nature with sufficient local gravity to retain any passing dust, but not to capture any gas.

• In contrast, the outer planetesimals contain large amounts of water-ice and rapidly reach much greater masses. This much greater mass allows them develop a gravitational field strong enough to capture and retain an immense gaseous atmosphere.

Inner planets are not known to have gassy layers due to them having rocky in nature and have a gravity to retain dust

what happens around 1 million yerars of planetesmel formation

• the inner zone contains about 20 objects the size of our Moon, plus millions of smaller objects

• the outer zone contains only a few large objects because they have swept up all of the smaller objects

 

At this point the nature of the accumulation process changes:

• these 20 objects are sufficiently massive to start influencing the orbits of other bodies around them.

how does agglomeration happen of planets?

• Massive objects will attract smaller objects from far, inducing a larger number of collisions and hence speeding up the accumulation of larger objects (can see on our moon there was a lot of collisions happening on it)

• Smaller objects that avoid an initial collision but undergo a grazing pass, are deflected into more elliptical orbits. When these objects finally do collide, they have a much greater relative motion, and fragmentation rather than conglomeration could occur

this results in an increase the growth of the more massive objects, while the smaller objects growth is either slowed down or destroyed due to fragmentation

what are the main ingredients of our planets

what are the gas giants in our solar system

jupiter, neptune, uranus and saturn

what are the rocky planets in our solar system

mercury, venus, earth and mars

what are the properties of a gas giant

• Composed primarily of hydrogen & helium

• Low densities

• Rapid rotation

• Deep atmospheres

• Rings

• Lots of moons

why do gas giants have a solid core?

A solid core with a mass greater than 10 Earth masses is critical for the formation of the gas giants

• This can only happen beyond the “ice line” in a solar system.

  • Having formed such a core, the gravitational field is sufficiently strong to attract and keep large amounts of hydrogen gas – a major difference to the terrestrial planets.

• Because they are so large their gravitational field allows for them to attract and keep the gas

why doe gas giants have large masses?

so they can retain the mass

what is jupiters total mass

317 times bigger than the earth

what is saturn total mass

94 times the earth

what is uranus total mass

14 and a half times the earth

what is neptune total mass

17 times the earth

what are the properties of rocky planets

•  Composed primarily of rock & metals - because they were the only materials that were avaliabe for their core.

• High densities

• Slow rotation - although their size is small they have slow rotation

• Solid surfaces

• No rings

• No or few moons

what is the mystery with mar’s moons

It's believed that mars does not have moons but it captured two asteroids as it is very near to the asteroid belt

does mars have seasons?

yes

how was the moon formed

a planetoid crashed into earth and a bit of earth and that planet formed the moon. Life on earth may have not been possible without it.