CoK 2 Flashcards
Most of the bright stars are NOT among the stars that are very close to us. Why then do they look so bright to us?
these stars are intrinsically so luminous that they can easily can be seen across great distances
most of the stars we can see with the unaided eye from earth are
more luminous than the sun
the most common kinds of stars in the galaxy have
low luminosity compared to the sun
two stars that are gravitationally associated and orbit each other are called
binary stars
if the most common type of star in our galaxy are M-type “red drawf” stars why don’t we see very many of them in the sky
red drawfs have intrinsically low luminosity so they’re faint and hard to detect
how can we tell that what appears like a single star in out telescopes is actually a binary star system
their spectra will contain the absorption line of two stars
when one of the stars is moving towards earth in its orbit, we observe
that the lines in its spectrum show a blueshift
the HR diagram plots the luminosity of stars against their
surface temperature
if a of the stars we can possibly detect could be independently plotted on an HR diagram, 90% of them would fall into the region called
the main sequence
white drawfs are very hot but are also very small compared to the main sequence stars. as a result they are located in the _________ region of the HR diagram
lower left
on the HR diagram, where would you find the most massive main sequence star
toward the upper left of the main sequence
what would be a reasonable classification for a red giant star
M2III
in order for a cold atom of hydrogen to emit a 21-cm wave, it must first be in a slightly higher energy state. what event usually kicks the hydrogen atom up to this higher state
gas atoms within the cloud collide
an HII region is
a region around a hot star where hydrogen atoms are ionized
the red color we see on a lot of phtotgraphs of nubulae comes from
hydrogen
Given the presence of dust throughout the disk of the Milky Way Galaxy, what is the best technique for learning about more distant regions of our galaxy’s disk?
Look for radiation at long wavelengths, for example in the infrared region of the spectrum.
Interstellar extinction refers to the phenomenon that foreground dust has on the appearance of background stars. In particular, dust can make stars appear ______ and ______ than they would if the foreground dust wasn’t present.
fainter; more red
the dust in the dust clouds in interstellar space consists of
pieces of ice ranging from several meters to a kilometer in diameter
a Herbig-Haro (HH) object is
where a jet from a star in the process of being born collides with and lights up a nearby cloud of interstellar matter.
Astronomers identify the “birth” of a real star (as opposed to the activities of a protostar) with what activity in the star?
When nuclear fusion reactions begin inside its core.
when does a protostar “arrive” on the main sequence and “switch on” to become a star?
when it begins fuding hydrogen into helium in its core
why do all stars spend most of their lives on the main sequence
stars fuse hydrogen on the main sequence and every star is mostly made of hydrogen
As a star’s core contracts, it gets hotter. What happens to the star’s outer layers?
they expand and cool
When does a star “leave” the main sequence and begin its post-main sequence evolution?
when the core fuses the last of its hydrogen into helium
As a star becomes a giant, its outer layers are expanding. Where does the energy for expanding these layers come from?
from the fusion of hydrogen into helium in a shell surrounding the core
when the outer layers of a star like the sun expand, and it becomes a giant, which way does it move on the HR diagram
toward the upper right
what happens whne the core of a star reahes a temp of 100 million K
three helium nuclei begin fusing carbon
mass of the sun during its lifetime
the sun will lose a significant amount of mass during and after its red giant phase
Why is it easier for red giants to lose mass than main sequence stars?
red giants are so big, the gravity at their surface is less
why is the lifetime of planetary nebulae so short
because planetary nubulae expand too far from their white drawf and no longer be ionized
Planetary nebulae are rich in “metals” such as carbon, nitrogen, oxygen, and even neon. What eventually becomes of this gas?
It dissipates into the interstellar medium and seeds the next generation of stars with “metals”.
Compared to a main sequence star, a white dwarf will always
be smaller in radius
When a low-mass star (M < 8M⊙) finally dies, it leaves behind
white drawf
Which star will leave behind the white dwarf with the smallest radius?
A 2M⊙ star.
Even though high mass (> 8 M⊙) stars have far more hydrogen than low mass stars, they run out of their fuel faster and leave the main sequence much sooner. Why is this?
They fuse their hydrogen fuel hotter and faster than low-mass stars
Iron fusion cannot support a star because iron
absorbs energy when it undergoes fusion.
What prevents the core of a massive star (~ 8 - 20 M⊙) from ultimately collapsing into a black hole?
neutron degeneracy pressure
A Type II supernova is also known as
a core-collapse supernova
What percentage of the energy in a Type II supernova is released in the form of electromagnetic radiation?
1%
Heavy elements are returned to the interstellar medium by ______
- strong stellar winds during the second red giant, or asymptotic giant branch, phase.
- planetary nebulae.
- supernovae
A neutron star will be detected from Earth as a pulsar by its regular radio pulses only if Earth lies
almost directly in line with the magnetic axis of the neutron star at some time during its rotation.
The synchrotron emission in pulsars comes from _____.
charged particles forced to accelerate by moving along curved paths within a magnetic field
The long duration gamma ray bursts likely come from ___ while the short duration GRBs are likely _____
core collapse supernovae with a black hole remnant; merging neutron stars
Supernova remnants are the result of shocked gases exploded from a massive progenitor star. Although these gases emit light at all wavelengths, which of these are the most energetic?
x-rays
