chapter 13
If Star A is twice as far as Star B, and they are identical in all other ways, then the brightness of Star A would be
one-fourth the brightness of Star B.
Protostars initially do not experience hydrogen fusion. How does their temperature increase?
gravitational energy from infalling material
Type Ia supernovas involve a __________.
white dwarf
The Sun lies _______ the disk of our Milky Way Galaxy.
about half of the way out in
What type of galaxy has only old stars, little dust, low density, hot gas, and no star formation?
elliptical galaxies
Luminosity (absolute brightness) of a star depends on its ___________.
temperature and radius
Where do most of the elements heavier than iron form?
in supernova explosions
Two important properties of young pulsars are
extremely rapid rotation and a strong magnetic field.
The estimated age of the Milky Way Galaxy is about ___________.
13 billion years
_____ galaxies contain mostly Population II stars; while _____ galaxies contain both Population I and Population II stars.
Elliptical; spiral
Which stars has the hottest stellar surface temperature?
B2
When do we say that a star is born?
when fusion of hydrogen atoms into helium atoms starts
remnants of a dying star?
white dwarf
neutron star
black hole
What does the Milky Way look like on the night sky?
a pale band of light scattered with stars that stretches across the sky
What type of galaxy has a mix of young and old stars, an abundant amount of gas and dust, ongoing star formation, and a definitive shape?
spiral galaxies
A binary star is a pair of stars that orbit around each other. By detecting this orbital motion, and using Kepler's laws and the law of gravitation, one can directly measure the stars' ____.
masses
After a star leaves the main sequence, ______________________.
it now fuses hydrogen into helium in a shell outside the core
A __________ happens when a single high-mass star explodes.
Type II supernova
What might you find at the center of the Milky Way?
a black hole with the mass of a few million Suns
_____ form when galaxies collide and _____.
Starburst galaxies; star formation is triggered, making them very bright
Analysis of stellar spectra shows that most stars consist of 71% ___, 27% ___, and a 2% mix of the other elements.
hydrogen; helium
When a star moves off the main sequence and becomes a red giant it is brighter because
the star moves closer to Earth.
the size of the star increases.
This event recurs and happens when one of the companions in the binary system is a white dwarf.
Nova
In general, Population I stars are ______ and Population II stars are _______.
blue; red
The blue color seen in some galaxies is an indication that star formation is occurring in those galaxies.
True