Chapter 30: Stars Flashcards
What is a star?
A ball of gases that gives off a tremendous amount of electromagnetic energy (from thermonuclear fusion), starts vary in color
What are spectrographs?
Devices that separate light into different colors, or wavelengths
What is a spectrum?
Starlight passing through a spectrograph produces a display of colors and lines called a spectrum
What are the 3 types of spectra?
- Emission (bright-line)
- Absorption (dark-line)
- Continuous
What is a dark-line spectra? (what does it reveal?)
- All stars have this
- Bands of color crossed by dark lines where the color is diminished
- Reveals the star’s composition and tempurature
What happens to the elements in the outer layers of a star?
They absorb some of the light radiating within the star
How can scientists determine the elements that make up a star?
- By studying its spectrum
- Different elements absorb different wavelengths of light
What do the colors and lines in the spectrum of a star indicate?
The elements that make up the star
What have scientists learn though spectrum analysis?
That stars are made up of the same elements that compose Earth
What are the most common elements in stars?
1) Hydrogen (mostly)
2) Helium
3) Carbon, oxygen, nitrogen
How is the surface temperature of a star indicated?
By its color
What is the range for the temperatures of most stars?
2,800 C to 24,000 C
What are the surface temperatures of stars that are:
1) blue
2) red
3) yellow
1) 35,000 C (some as high as 50,000 C)
2) 3,000 C
3) 5,500 C
What is the range in sizes of stars?
Dwarf stars: as small as Earth
Medium-sized stars: 1,390,000 km
Giant stars: 1,000 times sun’s diameter
How big are most stars visible from Earth? (how far can we see them)
- Medium-sized (similar to our sun)
- Within 100 light years
How dense are stars?
- Many have about the same mass as the sun
- Can be very dense (and more mass than sun) but still much smaller than the sun
- Can be less dense (and less mass than sun) but have larger diameter than the sun
What is the apparent motion of a star? (caused by what, in which 2 ways, circular trails)
-Motion visible to the unaided eye
-Caused by the movement of Earth
-Curves of light record apparent motion in the northern sky
-Circular trails- stars moving counter-clockwise around a central star called Polaris (North Star)
-Circular pattern caused by the rotation of Earth on its axis
Earth’s revolution around sun- different stars visible during different seasons
-Shifts west slightly every night
What are circumpolar stars? (where are all stars circumpolar, what is one example)
- Stars always visible in night sky
- In Northern Hemisphere makes them appear to circle Polaris
- The Little Dipper (in Northern Hemisphere)
- North Pole- all stars circumpolar
What is the actual motion of a star?
- Rotate on an axis
- May revolve around another star
- Either move away from or toward our solar system
What is the Doppler effect?
- The apparent shift in the wavelength of light emitted by a light source moving toward or away from and observer
- An observed change in the frequency of a wave when the source or observer in moving
What is blue shift? Why does it occur?
- The colors in the spectrum of a star moving toward Earth are shifted slightly toward blue
- Occurs because the light waves from a star appear to have shorter wavelengths as the star moves toward Earth
What is red shift? Why does it occur?
- A star moving away from Earth has a spectrum that is shifted slightly red
- Occurs because the wavelengths of light appear to be longer
What color spectra do distant galaxies have? What does it indicate?
- Red-shifted spectra
- Indicates that they are moving away from Earth
What is the nearest star to the Earth? (how far)
- Proxima Centauri
- 4.2 light years (300,000 times the distance from Earth to sun)
What is parallax?
- The apparent shift in a star’s position when viewed from different locations
- Used by scientists to determine a star’s distance from Earth (for stars within 1,000 light years from Earth)
- As Earth orbits the sun, a nearby star will appear to shift slightly relative to stars that are farther from Earth
- Closer = larger shift
How many stars can be seen through telescopes on Earth?
3 billion
How many stars are visible from Earth without a telescope?
6,000
What does the visibility of a star depend on?
Its brightness and distance from Earth
What is a star’s apparent magnitude? (depends on what)
- The brightness of a star as it appears to us on Earth
- Depends on both how much light the star emits and how far the star is from Earth
- Lower number = appears brighter from Earth
What is a star’s absolute magnitude?
- Its true brightness
- How bright the star would appear if all the stars were at a standard, uniform distance from Earth (32.6 light years)
- Brighter the star actually is = lower number of absolute magnitude
What is a star’s luminosity?
The total amount of energy that it gives off each second
What is the Hertzsprung-Russel (H-R) diagram?
- A graph that illustrates the pattern of plotting the surface temperatures of stars against their luminosity
- Temp- horizontal (highest on the left)
- Luminosity- vertical (highest at the top)
- Describes the life cycles of stars
What is the main sequence?
- The temperature and and luminosity for most stars fall within a band that runs diagonally through the middle of the H-R diagram
- Extends from cool, dim, red stars at the lower right to hot, bright, blue stars at the upper left
- The sun is in this band
What does Newton’s law of universal gravitation state?*
- All objects in the universe attract each other through gravitational force
- This force increases as the mass of an object increases or as two objects become closer together
- Nearby particles pulled toward the area of increasing mass (gravitational pull increases)
- Nebula becomes denser
What is a protostar?
- The shrinking, spinning region of dense matter begins to flatten into a disk
- Contracts for several million years
What is plasma?
- Separate state of matter
- Gas becomes so hot- electrons stripped from their parent atoms
- Nuclei and free electrons move independently
- A hot, ionized gas that consists of an equal number of free-moving positive ions and electrons
What is stellar equilibrium and how is it achieved?
- Achieved when the inward force of gravity is balanced by the outward pressure from fusion and radiation inside the star
- Makes the star stable in size (as long as the star has an ample supply of hydrogen to fuse into helium)
What is the main-sequence stage? (how long are different size stars on this stage)
- Second and longest stage
- Energy continues to be generated in the core of the star as hydrogen fuses into helium (releases energy, stopping it from contracting)
- Star with similar mass to sun is in this stage for 10 billion years
- Larger stars (fuses hydrogen faster)- 10 million years
- Less massive- hundreds of billions of years
When will the sun’s fusion stop? What will happen then?
- 5 billion years, 10% of sun’s original hydrogen converted into helium, fusion will stop in the core
- Sun’s temp and luminosity will change, sun will move off main sequence
What is a star’s third stage?
- Almost all of its hydrogen atoms in core have fused to helium atoms
- Without hydrogen for fuel, core will contract under its gravity- increases temp of core
- Transfers energy into thin shell of hydrogen surrounding core
- Causes hydrogen fusion to continue in the shell of gas
- Radiates energy outward
- Outer shell expands greatly
What are giant stars?
- A very large and bright star whose hot core has used most of it hydrogen
- Star’s shell of gases grows cooler as it expands
- As the gases in the outer shell become cooler, they begin to glow with a reddish color
- Large surface area- very bright
- Stars that have about as much mass as the sun
- Above main sequence on H-R diagram
What are supergiants?
- Main-sequence stars that are more massive than the sun will become larger than giants in their third stage
- Top of H-R diagram
- 100+ times larger than sun
- Betelgeuse
- High luminosity, surfaces relatively cool
What is a planetary nebula? (and when does it become one)
- Fusion in the core will stop after the helium atoms have fused into carbon and oxygen
- Energy no longer available from fusion- enters final stag
- As the star’s outer gases drift away, the remaining core heats these expanding gases
- A cloud of gas that forms around a sun-like star that is dying
- May for a sphere or ring or more complex shapes (ex. a double lobe)
What is a white dwarf? How are they formed? (how long, where on H-R, size)
- Planetary nebula disperses, gravity causes the remaining matter in the star to collapse inward
- The matter collapses until it cannot be pressed any further
- A white dwarf- hot/extremely dense core of matter is leftover form old star
- Shine for billions of years before they cool completely, and become fainter
- Lower left of H-R
- Hot but dim, very small (size of Earth)
- Final stage for many stars
What is a black dwarf?
When a white dwarf no longer gives off light (process is long)
What is a nova?
- A star that suddenly becomes brighter (1,000 times brighter)
- White dwarf revolving around red giant, the gravity of dense white dwarf may capture gases form red giant
- Gases accumulate on surface, pressure builds up
- May cause large explosions- releases energy and stellar material into space
- Fades back to normal brightness within days
- May become nova several times
What is a supernova in a white dwarf star?
- Tremendous explosion- blows itself apart
- White dwarf accumulates so much mass on its surface that gravity overwhelms the outward pressure
- Star collapses, becomes so dense that the outer layers rebound and explode outward
- 1,000’s of times more violent than nova
- Completely destroys red dwarf and much of red giant
What are supernovas in massive stars?
- Part of their life cycle (don’t need secondary star to fuel them)
- After supergiant stage, these stars contract with a gravitational force that is much greater than that of small-mass stars
- Collapse- high temp and pressure, thermonuclear fusion begins again (carbon atoms- heavier elements: oxygen, magnesium, silicon)
- Continues until core is almost entirely iron
- Iron has stable structure, fusion of iron to heavier elements takes energy form star rather than giving it off
- Used its supply of fuel- core begins to collapse under own gravity
- Energy transferred from core to outer layers, explode outward with great force
What is a neutron star?
- After supernova, core may contract into very small and dense ball of neutrons
- A star that has collapsed under gravity to the point that the electrons and protons have smashed together to form neutrons
- Rotate rapidly
What are pulsars? (how do we detect them)
- A rapidly spinning neutron star that emits pulses of radio and optical energy that sweeps across space
- We detect pulses of radio waves every time the beam sweeps by Earth
What is a black hole? (how are they created)
- Some massive stars produce leftovers too massive to become stable neutron stars
- If the remaining core of a star contains more than 3 times the mass of the sun, the star may contract further under its gravity- force crushes dense star core and leaves black hole
- An object so massive and dense that even light cannot escape its gravity
How can black holes be detected?
- Observed by its effect on a companion star
- Matter from companion star pulled into black hole
- Just before matter is absorbed, it swirls around the black hole
- Gas becomes so hot that X rays are released
- Scientists try to find the mass of the object that is affecting the companion star
- Black hole only exists if the companion star’s motion shows that a massive, invisible object is nearby
What is a constellation?
- One of 88 regions into which the sky has been divided in order to describe the locations of celestial objects
- A group of stars organized in a recognizable pattern
Where do the names of stars come from?
- Latin
- Real or imaginary animals
- Ancient gods
- Legendary heroes
What are binary stars?
-Pairs of stars that revolve around each other and are held together by gravity
What is the barycenter?
- The center of mass between two stars revolving around each other in systems where two stars have similar masses
- If one star is more massive than the other, the barycenter will be closer to the more massive star
What are multiple-star systems?
- More than half of stars part of them
- Two or more stars are closely associated, they form multiple star-systems
- With more than two stars: two stars revolving around barycenter while third star revolves more slowly at a greater distance from the pair
What are clusters?
Nebulas collapse to form groups of hundreds of thousands of stars
What are globular clusters?
Have a spherical shape and can contain up to 100,000 stars
What is an open cluster?
Loosely shaped cluster and rarely contains more than a few hundred stars
What is a galaxy?
- A collection of stars, gas, and dust that is bound together by gravity
- 100,000 light years in diameter
- 200 billion stars
- Hundred of billions of galaxies in the universe
What are Cepheid variables?
- Giant stars that brighten and fade in a regular pattern
- Cycles range from 1-100 days
- Longer cycle = the brighter the star’s visual absolute magnitude is
How can scientists calculate the distance to a Cepheid variable
By comparing the Cepheid’s absolute magnitude and the Cepheid’s apparent magnitude (this distance tells them the distance to the galaxy in which the Cepheid is located)
What is a spiral galaxy? (+barred)
- Has a nucleus of bright stars and flattened arms that spiral around the nucleus
- Spiral arms consist of billions of young stars, gas, and dust
- Barred spiral galaxy: some galaxies have a straight bar of stars that runs through the center
What is an elliptical galaxy?
- Vary in shape (nearly spherical to very elongated)
- Extremely bright in the center and do not have spiral arms
- Have few young stars and contain little dust and gas
What is an irregular galaxy?
- Has no particular shape
- Usually have low total masses and are fairly rich in dust and gas
- Not very many of them
What is the Milky Way galaxy?
- Cloud-like band that stretches across the sky
- A spiral galaxy in which the sun is one of hundreds of billions of stars
- Each star orbits around the center of the Milky Way
How long does it take the sun to orbit the Milky Way?
225 billion years
What is the Local Group? Which 2 are closest?
30 galaxies within 5 million light years of the Milky Way
The Large and Small Magellanic Cloud are closest- 170 light years
What is a quasar?*
- Viewed through an optical telescope
- Appears as a point of light (like a faint star)
- Shortened term form quasi-stellar radio source
- Some project a jet of gas
- Located in the center of galaxies distant from Earth (very bright when in center)
- Emits large amount of energy in small volume at high rate (because of giant black hole)
What is cosmology?
- The study of the origin, structure, and future of the universe
- Processes that affect the universe as whole
- How the universe formed and how it will change
How did Hubble determine the speed at which the galaxies were moving away from Earth?
By examining the amount of red shift
Which galaxies did Hubble find showed the greatest red shift? (what did that mean)
Most distant galaxies- meant they were moving away from Earth the fastest
What does the big bang theory state?
- Billions of years ago, all the matter and energy in the universe was compressed into an extremely small volume
- 13.8 billion years ago it exploded and began expanding in all directions (sent all energy and matter outward)
What happened as the universe expanded (big bang theory)?
Some of the matter gathered into clumps that evolved into galaxies
What is currently happening in the universe?
-The universe is still expanding and the galaxies continue to move apart from one another
What does the expansion of space explain?
The red shift that we detect in the spectra of galaxies
What is the timeline of events in the big bang theory?*
1) .000001 second– cooled to 10 trillion degrees, inflation occurs, protons + neutrons form
2) 1 second– first hydrogen ( and helium + lithium) nuclei form
3) 3 minutes later– universe 75% hydrogen nuclei, 25% helium nuclei, less than 1% lithium
4) 300,000 years– stable atoms begin forming (limit of observable universe)
5) Few hundred million years later– first stars forms, followed soon by galaxies
What is cosmic background radiation? How was it detected?
- Low levels of energy evenly distributed throughout the universe
- Remnant of big bang
- Detected in every direction using radio telescopes
How cold is background radiation?
- 3 degrees C above absolute zero (-273)
- 270 degrees C below zero
What are cosmic background radiation “ripples”? (what might they indicate)
- On a map that shows where temperatures differ from average background temperature, ripples become apparant
- Irregularities in the cosmic background radiation, which were causes by small fluctuations in the distribution of matter in the early universe
- Ripples may indicate the first stages in the formation of the universe’s first galaxies
What does analyzing the ripples in the cosmic background radiation tell us?
- The kinds of matter that humans, the planets, the stars, and the matter between the stars are made of make up only 4% of the universe
- 23% of universe made up of dark matter
What is dark matter?
A type of matter that does not give off light but that has gravity that we can detect
What is dark energy?
- Makes up most of universe
- Composed of an unknown material
- Acts as a force that opposes gravity
- Some form of undetectable dark energy is pushing galaxies apart (and rate of expansion accelerating)
What is evidence that exists for the big bang theory?
- Background radiation
- Ripples- irregularitues in C
What is the life of a star like the sun?
1) Nebula
2) Protostar
3) Star like the sun (main sequence)
4) Red giant
5) Planetary nebula
6) White dwarf
7) Black dwarf
What is the life of a massive star?
1) Nebula
2) Protostar
3) Massive star (main sequence)
4) Red supergiant
5) Supernova
6) Neutron star
7) (Black Hole)
