Unit 3 (Chapters 8-11) Flashcards
What are the three layers of the sun?
Photosphere - the visible surface of the sun made up of low density gas that produces most of Earth’s light.
Chromosphere - the bight gases just above the photosphere
Corona: the faint outer atmosphere of the sun that extends beyond 20 solar radii and is made up of extremely low density gas that reaches almost 2 million degrees K or more at it’s outer reaches
What is granulation?
Granulation is the dark edged regions of granules that produce a mottled pattern on the photosphere.
Granules can be 1000km accross but only last 10-20 minutes before sinking and being replaced by new granules.
Granulation is the result of convection currents below the photosphere (convection is when hot material rises and cool material sinks.
What are super granules?
Super granules are regions about 2x the size of earth’s diameter and are made up of about 300 granules. They tend to last 1-2 days and are produced by larger gas currents that begin deeper under the photosphere.
What is the thickness of the chromosphere? How bright is the chromosphere?
What is the chromosphere made up of? And what is the temperature distribution of the chromosphere?
The chromosphere has an irregular thickness that is usually thicker than the diameter of the earth.
It is much fainter than the photosphere and only visible during a solar eclipse.
Is made up of low density excited gas.
Gets hotter closer to the surface where the surface of the chromosphere produces x-rays.
What are spicules?
They are flame like jets of gas extending up into the chromosphere. They look like flames but are actually cooler gas from the lower chromosphere extending upward into the hotter regions.
They can last 5-15 minutes
Describe the role of magnetic fields in the sun.
The sun has a magnetic carpet of looped magnetic feilds which extends up through the photosphere.
Because the gas in the chromosphere and corona is ionized and low density, it becomes accelerated by the movement of he magnetic fields. When the magnetic loops are disturbed by the turbulence below them, they in turn disturb the gas in the chromosphere and corona, heating it and making it hotter than the photosphere.
What is solar wind?
Solar wind is areas in the magnetic field that are open and allow gas to flow out and away from the sun. These winds are considered part of the corona. These winds cause the sun to lose 1 million tons (less than 10^-14 of its total mass) each year
When solar wind collides with material in interstellar space it is called Heliopause.
What is the sun’s primary composition?
Mostly Hydrogen (92.6%) with helium (7.3%). Carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, and iron make up less than 0.1%.
What are sun spots?
Sun spots are intense magnetic fields which appear as dark spots on the sun’s photosphere. Thjey are relatively cool and appear in groups that disappear over the course of a few weeks-months.
The centre of the sunspot is called the umbra and the outer region is called the penumbra
These sun spots follow an 11 year cycle where they gradually increase to over 100 spots and then decrease in number, sometimes reaching 0. They also follow a cycle of location, starting at higher latitudes and slowly moving towards the equator. The intensity of cycles can vary over time.
They are caused by a strong local magnetic force.
What is the Dynamo Effect?
This is the process where highly ionized gas conducting electricity is moved by convection and gets converted into magnetic field energy.
This effect leads to the sun’s magnetic fields being produced at the bottom of the convection currents, deep below the photosphere and then slowing moving outward.
What is differential rotation?
This is when different parts of the body have different rotational periods. The sun has differential rotation because it is made up of gas so it does not have to rotate as one unit. As such, depending on depth and latitude, some areas of the sun have shorter or longer rotational periods.
What is the Babcock Model? How does it relate to sun spots?
This model suggests that the sun’s magnetic cycle can be understood as the repeated tangling and untangling of the solar magnetic field caused by differential rotation. The Meridional flow is a refinement of this model.
it also suggests that sun spots occur in pairs as tubes of concentrated magnetic energy burst through the sun’s surface.
What are prominences and what are different types?
A prominence is ionized gas trapped in a magenitc arch rising through the chromosphere/photosphere and into the lower corona.
Different types:
- Filaments: prominences seen from above
- Quiescent prominences: ones that hang in the lower corona for days
- Eruptive prominences: ones that only last a few hours.
What happens when two prominences (or arches) connect with eachother?
These reconnection events cause powerful eruptions called flares which then can cause solar winds which, when they reach earth, can cause power surges, disruption of navigation services, and auroras.
If the reconnection event is significant enough, it can release enough energy to blow out a large portion of the ionized gas away from the corona. These are called Coronal Mass Ejections.
What powers the sun?
Nuclear reactions in the sun’s core power the sun. The energy released by the nuclear reactions keeps the interior hot and the gas ionized. Specifically the sun use nuclear fusion (combing smaller nuclei together into larger nuclei).
Describe the nuclear fusion which takes place in the sun
4 hydrogen nuclei are fused through a proton-proton chain (one proton at a time) to form 1 helium.
- 2 hydrogen protons bind together and one proton transforms into a neutron and 2 particles: a positiron (+electron), and a neutrino (subatomic particle with low mass and high velicity). Combined, this forms a deuterium.
- the deuterium absorbs another proton resulting in it emmiting a gamma-ray photon and becoming a light weight helium nuclues
- two light weight helium combine to form a regular helium.
The mass combination results in a loss of mass which is then concerted to energy. This energy is in the form of gamma rays and neutrinos)
What is the coulomb force and how does the sun overcome it?
Coulomb force is the electrostatic force that causes positivley charged nuclei to repel eachother. To over come this, atoms must collide violently with each other and that can only happen in gas that is very hot so the atoms move fast, and is also very dense. This is why nuclear fusion only takes place in the sun’s core.
What are the two different zones of the sun?
The Radiative zone: the inner part of the sun where energy radiates outward
The convection zone: the outer zone of the sun where hot blobs of gas rise and cool blobs sink to form circulating gas.
What is stellar parallax?
Stellar parallax is the apparent change in a spars position because the observer’s position has changed due to the orbit of the earth.
The parallax measured in arc seconds can be used to calculate the distance of the star.
What are two factors which affect the apparent brightness of a star? What is luminosity and absolute visual magnitude?
Apparent brightness is affected by: How much light the star emits AND How far away the star is.
Luminosity is the total energy output of a star (includes visible and non-visible light)
Absolute visual magnitude is the apparent magnitude of a star at 10parasecs. (only considers visible light)
How do other stars compare to the sun?
Stellar composition is similar between the sun and other stars
How are stars classified by temperature?
Star temperature is classfied into spectral types with have a spectral sequence of O B A F G K M where O is the hottest and M is the coldest.
Each spectral type is divided into 10 subtypes (0-9)
There are also classifications for dwafs which are cooler than M.
L dwarf, T dwarfs, and Y dwarfs (cooler than 500 K.)
How do you read an H-R diagram and what are the classifications?
H-R diagram sorts stars according to size using temperature on the horizontal axis and luminosity on the vertical axis.
Includes the following classifications
- Main sequence: hot main sequence are more luminous than cool main sequence
- Giants: Cooler but larger so more luminous
- Supergiants: largest radius, temp varies but high luminosity
- Red dwarf: small, cool, low luminosity
- White dwarf: very small, high temp, low luminosity
How is luminosity and size classified ?
Luminosity sequence
Ia = luminous supergiants
Ib = supergiants
II: luminous giants
III: Giants
IV: low luminosity giants (subgiants)
V: Main sequence/dwarfs
VI: low luminosity main sequence/sub dwarfs
What is spectroscopic parallax?
This is when you find a stars distance based on spectral type, luminosity class, and apparent magnitude.
The spectral type tells you the horizontal location on the HR diagram. Luminosity class gives you approximate vertical position. Plotting these two points gives you absolute magnitude which can then be used in a formula with apparent magnitude to determine distance.
What are binary stars? What are the three types?
Binary stars are pairs of stars that orbit each other.
Types:
- Visual binary systems: stars are visibly separate and their orbit can be physically observed
- Spectroscopic Binary Systems: stars are too close together, they can only be discerned through the spectral light
- Eclipsing binary systems: a spectroscopic binary system whose orbit is nearly on the edge to earth so they eclipse each other as they orbit and you can see the difference in brightness when one star is eclipsed.
How can binary stars be used to calculate star mass?
The orbital period and size of the orbit tells you the amount of gravitational force being exerted on the stars which in turn tells you about the star’s mass.
What is the most common type of star?
Red dwarfs with low luminosity
Most of the stars we can actually see are not typical but rather just more visible because they are so luminous.
What pattern does mass and luminosity follow in main sequence stars?
Main sequence stars follow a mass-luminosity relation where high mass = high luminosity. This ONLY works in main sequence stars.
What is the denisty of Main squence, giants, supergiants and dwarfs
Main sequence stars have similar density to the sun
Giants are low density
Supergiants are extremely low density
White dwarfs are extremely dense
What is Interstellar Medium and what is Nebula?
What are different types of nebulae?
Interstellar Medium is the gas and dust between stars.
Nebulae are clouds of gas and dust scattered throughout the sky. There are three types:
1. Emission Nebula: when a hot star excites the gas near it to produce an emission spectrum. This ISM forms B1 or hotter stars. This ISM has a density of 100-10000 atoms/m^3
2. Reflection Nebula: this nebula scatters starlight due to its dust content. the spectrum for this star is the same as the star’s light being reflected.
3. Dark nebula: dense clouds of gas and dust which block the view of more distant stars. They have irregular shapes which suggests that there a breezes and currents in the ISM
2.
What is the composition of ISM?
Mostly hydrogen, some helium, and 2% other heavier elements .
The ISM is 99% gas and 1% dust with the dust being made up of:
- Carbon
-Silica
- Iron
- ice/organic components
What is Interstellar Reddening?
This is when far away stars appear more red than they should because the blue shorter wavelengths are scattered more readily by the ISM so a larger portion of red wavelengths reach earth.
What is the temperature of ISM?
VERY COLD, 100K (280F) or lower
What are the 4 components of ISM?
- Cool Clouds (H-I clouds): density of 100 atoms/cm^3, is non-ionized, is 100K in temp, and often 50-150 parasec (pc) in size.
- Intercloud medium: hot low density gas that fills the space between cool clouds. Temperature is a few 1000k, density 0.1atom/cm^3), partially ionized. Has the same pressure as cool clouds so they co-exist without encroaching on each others region.
- Molecular clouds: Clouds of gas and dust with densities ranging from 100-1000atoms/cm^3. Molecules form inside these clouds because they are protected from UV rays by the dust. Usually are only a few hundred solar masses BUT giant molecular clouds can be up to 1 million solar masses (Giant molecular clouds are where stars form).
- Coronal Gas: has high temperature and low density. Temp = 10^6K but a density of 10^-4 particles/cm^3. they are the same pressure as cool clouds so they do not encroach on their region. Form from the death of a star and can force cool gas to compress and form stars.
What are the proportions of ISM?
about 50% intercloud medium, 20% cool clouds, 20% molecular clouds, and 10% coronal clouds.
What 4 factors must line up in order for gravity to compress molecular clouds in the start of star formation?
- Thermal Energy: thermal energy causes clouds to expand and gravity must be stronger than this outward force
- Magnetic fields: magnetic fields in ISM act as an internal spring to stop the gas from contracting, gravity must be stronger than this.
- Rotation: as the rotating gas contracts, it rotates fast and can counteract the gravity, resisting contraction.
- Turbulence: the turbulent, twisting distorted nature of the gas is caused by a strong current that the gravity has to overpower.
What is a dense core in a giant molecular cloud?
A dense core is when regions in the giant molecular cloud begin to contract.
They are caused by shock waves (which are common) and dense cores are dense enough that gravity becomes able to overcome the 4 factors which normally prevent it from compressing the cloud.
What is Free fall collapse?
This is when the dense cores contract, gravity draws the atoms towards the centre. As the atoms fall they gain speed and collide with each other, randomizing their movement. This rapid random movement creates thermal energy which begins to heat the cloud.
It is through this process that gravitational energy is converted to thermal energy. (the reverse can also happen where atoms move more, they lose speed, and the gas cools.)
What is a protostar? How is a cocoon nebula related?
A protostar is a forming star that is compressed enough to be opaque at all wavelengths but not hot or compressed enough to generate energy by nuclear fusion.
Cocoon nebula is the cold dusty gas that surrounds the contracting protostar and absorbs the protostar’s radiation.
How does star mass relate to it’s rate of contraction?
The more massive the star, the stronger its gravity and therefore the more rapid it contracts. For example, the sun took about 30 million years to get from cloud to main sequence where as a 30 solar mass star would only take 30 000 years
What are young stellar objects? What are Birth Lines?
Young Stellar object is a star late in the stages of formation. The birth line is the location on an H R diagram where the protostar becomes detectable at visible wavelengths.
What are protostellar disks?
these are rapidly spinning cores in the cloud that flatten like a spinning pizza dough. The angular momentum leads to gas being added to the centre allowing the protostar to grow.
These disks cause bipolar flow which push into ISM and produce glowing globs called Herbig-Haro objects.
What is an association?
An association is a widely distributed star cluster that is not dense enough to be permanently held together by its own gravity so the stars wander.
What is Hydrostatic Equilibrium?
This is a balance created by the gravity of the star working to make it contract and the internal pressure working to make it expand.
What is an alternative source of nuclear fusion energy for stars besides hydrogen to helium?
CNO cycle where carbon is converted to nitrogen and then to oxygen and then to helium.
This cycle is often used in O and B stars.
