124 terms

Midterm #2

Why does the Hubble Space Telescope obtain higher resolution images than most ground-based telescopes?
Because it is above Earth's atmosphere
Diffraction Limit
Limit on a telescope's angular resolution
How much greater is the light-collecting area of a 6-meter telescope than a 3-meter telescope?
4 times
What causes the twinkling of stars?
The motion of air in our atmosphere
True or false? The lens in your eye forms an upside-down image of the world.
True or false? Sunspots are cooler than the surrounding region of the Sun's surface.
How does the sun primarily generate energy?
Nuclear fission
Hydrogen fusion in the Sun requires a temperature (in Kelvin) of...
millions of degrees
What was wrong with Kelvin and Hemholtz's idea that the Sun stayed hot because of gravitational contraction?
It predicted that the Sun could last only about 25 million years, which is far less than the age of Earth
When an atom loses an electron, it becomes...
Which electron energy level transitions have the highest energy?
Those that travel the greatest distance
Which electron energy level transitions have the longest wavelength?
Those that travel the shortest distance
Compared to an atom as a whole, an atomic nucleus is...
Very tiny but contains most of the mass
True or false? Electrons orbit an atomic nucleus like planets orbit the Sun.
True or false? The energy levels for electrons vary from on element to another.
What particles are found in the nucleus of an atom?
Protons and neutrons
Material that transmits light well
A positive and a negative charge will _________ each other.
How much electrical charge does an atom/ion with 6 protons, 6 neutrons, and 4 electrons have?
A positive charge of 2
Atomic Number
The number of protons
Atomic Mass Number
The number of protons + neutrons
A gas heated to millions of degrees would emit what kind of light?
When light reflects off an object, what is the relation between the angle of incidence and the angle of reflection?
Angle of incidence = angle of reflection
At extremely high temperatures (e.g., millions of degrees), which of the following best describes the phase of matter?
A plasma consisting of positively charged ions and free electrons
If you heat a gas so that collisions are continually bumping electrons to higher energy levels, when the electrons fall back to lower energy levels the gas produces...
An emission line spectrum
What happens in the convection zone of the Sun?
Energy generated in the solar core travels upward, transported by the rising of hot gas and falling of cool gas called convection
What happens in the radiation zone of the Sun?
Energy moves outward primarily in the form of photons of light
True or false? A 10-solar-mass star is about ten times more luminous than a 1-solar-mass star.
On a Hertzsprung-Russell diagram, where on the main sequence would we find stars that have the greatest mass?
Upper left
List the spectral types from highest temp/most massive to lowest temp/least massive
O, B, A, F, G, K, M
How do temperature and luminosity of low mass stars compare to that of high mass stars?
Low mass stars are cooler and less luminous than high mass stars
At the center of the Sun, fusion converts hydrogen into...
Helium, energy, and nutrients
How do scientists estimate the central temperature of the Sun?
Mathematical models
Which subatomic particle is the most massive?
List the layers of the Sun from innermost to outermost
Core, radiation zone, convection zone, photosphere, chromosphere, corona
Rank the layers of the Sun based on their density, from highest to lowest
Core, radiation zone, convection zone, photosphere, chromosphere, corona
Rank the following layers of the Sun based on the pressure within them, from highest to lowest
Core, radiation zone, convection zone, photosphere, chromosphere, corona
Which layers of the Sun can be seen with a telescope?
Photosphere, chromosphere, corona, solar wind
During solar maximum...
-sunspots are most numerous on the Sun
-solar flares are most common
-auroras are most likely in Earth's skies
-orbiting satellites are at most risk
How often do solar maximums and minimums occur?
Solar maximums occur about every 11 years, solar minimums occur about every 5 or 6 years after a maximum
What do we need to measure in order to determine a star's luminosity?
Apparent brightness and distance
According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?
Its apparent brightness will decrease by a factor of 9
Visual Binary
A binary system in which both stars can be revealed through a telescope (can measure period and orbital radius)
Eclipsing Binary
A binary system in which two stars orbiting each other eclipse each other and appear as only one star (can measure period only)
Spectroscopic Binary
A binary system whose binary nature can be revealed by measuring their periodic Doppler shifts (can measure period and velocity)
On a Hertzsprung-Russell diagram, where would we find stars that have the largest radii?
Upper right
On a Hertzsprung-Russell diagram, where would we find stars that are cool and dim?
Lower right
Radiation Pressure
Pressure exerted by photons of light, prevents stars of extremely large mass from forming
When does a star become a main-sequence star?
When the rate of hydrogen fusion within the star's core is high enough to maintain gravitational equilibrium
For every star with a mass greater than 10 solar masses, about how many stars are there with masses less than a solar mass?
What happens to the core of a high-mass star after it runs out of hydrogen?
It shrinks and heats up
Do stars with high or lower masses live longer?
Lower masses
The helium fusion process results in the production of what element?
True or false? Our Sun will end its life in a planetary nebula and become a white dwarf.
How many helium nuclei fuse together when making carbon?
What are stages of life for a low mass star?
Protostar, main sequence, red giant, white dwarf
Degeneracy Pressure
A type of pressure unrelated to an object's temperature, which arises when electrons or neutrons are packed so tightly that it supports core against the crush of gravity
True or false? In any star cluster, stars with lower masses greatly outnumber those with higher masses.
True or false? Photographs of many young stars show long jets of material apparently being ejected from their poles.
When does a protostar become a true star?
When nuclear fusion begins in the core
Thermal Pressure
The ordinary pressure in a gas arising from motions of particles that can be attributed to the object's temperature, depends on density and temp
By mass, the interstellar medium in our region of the Milky Way consists of...
70% Hydrogen, 28% Helium, 2% heavier elements
How long does the protostellar stage last for a star like our Sun?
30 million years
What is the typical density and temperature of molecular clouds?
300 molecules per cubic centimeter, 10-30 Kelvin
What happens after a helium flash?
The core quickly heats up and expands
What would happen to a protostar that formed without any rotation at all?
It would not have any planets
What happens when a star can no longer fuse H to He in its core?
The core shrinks and heats up
What happens when the star's core runs out of He?
He fuses in a shell around the core
What happens to a white dwarf when it accretes enough matter to reach the 1.4 MSun limit?
It explodes into a supernova
How does the radius of the event horizon change when you add mass to a black hole?
It increases
What is the upper limit to the mass of a white dwarf?
1.4 solar masses
True or false? All massive-star supernovae leave behind black holes as remnants.
Black hole
An object from which the escape velocity exceeds the speed of light
True or false? Brown dwarfs, white dwarfs, and neutrons stars are all kept from collapsing by degeneracy pressure.
What kind of pressure supports a white dwarf?
Electron degeneracy pressure
A rapidly rotating neutron star
If we can't see black holes, how do we know that they exist?
Studying its gravitational interaction with other objects
The center of the black hole where gravity crushes all matter to a single, tiny, dense point
True or false? The remnant left behind from a white-dwarf supernova is a neutron star.
False, nothing is left behind
What kind of star is most likely to become a white-dwarf supernova?
A white dwarf star with a red giant binary companion
Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?
Different spectra and light curve
What are the two types of supernovae?
1. High mass star (no need for companion)
2. White dwarf as a "vampire companion" to another star
Neutron Star
Ball of neutrons left behind by a massive-star supernova
Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4-solar-mass limit?
The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy
What is the neutron star limit?
3 solar masses
What would stars be like if hydrogen had the smallest mass per nuclear particle?
Nuclear fusion would not occur in stars of any mass
Which of these elements (calcium, uranium, oxygen) had to be made in a supernova explosion?
What are the characteristics of a high mass star?
-end life as a supernova
-have higher fusion rate during main sequence life
-late in life fuse carbon into heavier elements
What are the characteristics of a low mass star?
-the Sun is an example
-have longer lifetimes
-final corpse is a white dwarf
-end life as a planetary nebula
Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission?
Why do scientists think that our solar system must have formed sometime after nearby supernovae explosions?
Existence of heavier elements
True or false? The most massive stars generate energy at the end of their lives by fusing iron in their cores.
What is the heaviest element produced by stars or in supernovae?
Where does nuclear fusion occur in the Sun?
The core
What's the phase of matter in the Sun
Plasma (gas in which atoms are ionized because of high temp)
How does the energy produced at the core of the Sun get transferred to the surface?
1. Radiation - photons carry energy from core to convection zone
2. Convection - hot gas rises, cool gas sinks
What is the average surface temp of the Sun?
6000 K
What are the axes of the HR diagram and where are red giants located?
x: surface temp
y: luminosity
red giants: upper right
What is the apparent magnitude of the faintest star visible to the naked eye?
6 (The higher the magnitude, the fainter the star)
How old is the Sun?
4.5 billion years old (Sun is mid-life star)
How did nuclear fusion reaction in the Sun start initially?
Gravitational contraction - contraction of cloud released gravitational potential energy which caused interior temp and pressure to rise, igniting nuclear fusion
How does the apparent brightness of a star change with distance?
When you double the distance, apparent brightness decreases by a factor of 4
What is the Sun made of?
Hydrogen and Helium
The total amount of power that a star emits into space per second
Apparent Brightness
The brightness of a star as it appears to our eyes (L/4pi*r2)
How do the apparent magnitude and the absolute magnitude of a star relate to each other?
-Apparent magnitude: apparent brightness of an object in the sky
-Absolute magnitude: how bright a star appears if placed 32.6 light years away
What is the diameter of the mirrors for the world's largest optical telescope?
10 meters (30 feet)
Particle with same mass as ordinary particles but whose electrical charge is opposite (opposite of electron is positron)
What do massive-star supernovae leave behind?
Neutron star or black hole
Iron is at the end of the line for nuclear fusion processes in stars. How and where are heavier elements made?
Energy released in supernova explosion enable heavier elements to form
What is the greatest mass a newborn star can have?
100-150 solar masses
You can say that we are all "star stuff;" why is that?
Heavier elements that give us life came from remnants of stars
What's the typical size and mass of a white dwarf?
size= earth
mass= sun (1 solar mass)
What's the Chandrasekhar limit and what's the significance of it?
White Dwarf Limit - white dwarfs cannot exceed 1.4 solar masses, electron degeneracy pressure can no longer resist gravity and thus it collapses
How does a white dwarf supernova happen?
White dwarf reaches 1.4 solar masses (through accretion) and explodes into a supernova
What's the typical size of a neutron star?
Small City (radius= 10km)
How much would a teaspoonful of white dwarf material weigh on Earth? How much would a teaspoonful of neutron star material weigh?
White dwarf: a few tons
Neutron star: greater than Mt. Everest
What is the size (radius) of the event horizon of a stellar mass black hole?
A small city
Do black holes really emit nothing?
No, they emit Hawking radiation
Dramatic brightening of a star that lasts for a few weeks and then subsides. Occurs when a burst of H fusion ignites in a shell on the surface of an accreting white dwarf in a binary system.
What happens if the Sun suddenly gets turned into a black hole?
Planets will keep orbiting black hole, but there will be no more light
How are the size and mass of a white dwarf related?
The greater the mass, the smaller the white dwarf
What are the two types of black holes?
1. Stellar mass bh (few solar masses)
2. Supermassive bh (millions of solar masses) - at the center of most galaxies
What would happen if you go too close to a black hole's event horizon?
-stellar mass: tidal force stretch you to death
-supermassive: tidal force gentler, so may survive but can never come out