final Flashcards
which scientist discovered that the equations he had derived predicted an expanding universe, then modified his equations to eliminate this expansion?
Albert Einstein
what do cosmologists study
origin, structure and evolution of the universe
why is the universe expanding
spacetime itself is expanding, carrying the galaxies (superclusters of galaxies) with it.
which on of the following statements is a correct description of the expansion of the universe
spacetime is something real, with galaxies inside it; as spacetime expands, the galaxies( or superclusters of galaxies) are carried along by the expansion
what is the cosmological redshift
stretching of the wavelengths of photons as they travel through expanding space
the cosmological redshift of the light from very distant galaxies is caused by the
expansion of space, stretching the photon’s wavelength while the photon is traveling toward earth
what is it that keeps localized regions of space, such as things on earth, planetary systems, star clusters, and whole galaxies, from participating in the general expansion of the universe?
mutual gravitational attraction between objects in these systems
what is the cosmic microwave background radiation?
radiation left over from the Big Bang after the universe expanded and cooled
the cosmic background radiation is
low intensity radio noise, with a 3K blackbody temperature, almost uniform in intensity in all directions.
the cosmic background radiation is the
electromagnetic remnants of the explosion in which the universe was born.
good evidence for an original Big Bang that “created” our universe comes from
a background “glow” of microwaves, with blackbody temperature of about 3k
in relation to the universe, what does isotropy mean
the universe looks the same in all directions
what do we mean when we say that the universe is homogeneous
at any given time, the universe looks the same at all locations
how many fundamental forces are there in nature at the present time under normal conditons
four: strong, weak, electromagnetic and gravitational
what is the range of the electromagnetic force (the maximum distance over which it acts?
infinity
which is the four fundamental forces holds the electrons in the atom/
electromagnetic force
what is the gravitational force ( the maximum distance over which it acts)
infinity
what makes gravity the main force determining the large scale structure of the universe
while the electromagnetic force of a charged particle has an infinite range, it is usually screened and limited by the existence of charges of the opposite sign. Ordinary matter has only one sign and therefore does not screen other gravitational forces.
what are quarks
component particles making up protons and neutrons
what are the particles that make up protons and neutrons
quarks
most quasar produce their strongest emissions in which region of the electromagnetic spectrum
infrared
what is the most outstanding feature of a quasar compared with other objects in deep space
prodigious output of energy
quasars in our universe are
relatively common. Over 10000 have been identified so far
quasars all appear to be
moving away from us at very high speeds, up to about 90 of the speed of light
the specific characteristics that identify most quasars are
bright, starlike appearance with very high redshifts and hence very large distances indicating very energetic sources.
an intense radio source is found to coincide with a starlike object whose spectrum contains a pattern of intense emission lines in in the visible range that matches that of the Lyman uv hydrogen spectral lines but is very redshifted. what is this object
quasars
the extreme redshifts of quasar spectra are caused by
very high recession speeds of the sources away from the Milky Way galaxy
compared with the total output of energy from the Milky Way galaxy, what is the equivalent output of a typical quasar?
100 times brighter
seyfert galaxies are
active galaxies with bright starlike nuclei
seyfert galaxies are a distinct class of galaxies because they
have very bright, very hot starlike central cores with variable energy output
which of one of the following properties do seyfert galaxies and the Milky Way galaxy share
spiral galaxy classification
sayfert galaxies are
spiral galaxies with extremely active cores
which of the following objects is not classified as an active galaxy?
barred spiral
the central engine of an active galaxy appears to be
a supermassive black hole at the center of an accretion disk and material being projected out perpendicular to the disk in both directions.
for gravitational lensing of a distant quasar to occur, the galaxy producing the lensing must
be almost perfectly placed on a line between Earth and the quasar.
the mechanism that appears to generate two extensive regions of rado emission near active galaxies is
the double image of a single source behind the galaxy produced by gravitational lensing by the galaxy
in observation of a double quasar image produced by gravitational lensing, fluctuations on the intensity of one image appear to be delayed compared with equivalent variations on the other image.
the optical path through the gravitational lens producing one images is longer than that for the other image.
what is an Einstein ring
example of the image formed by a gravitational lens.
who developed the classification system that divides galaxies into spiral, elliptical, and irregular and classifies spirals by the size of their nuclear region and the tightness of winding of their arms
edwin hubble
what is the basic shape of a spiral galaxy
round, flat disk with long lanes of stars that curve outward from a round nuclear region of uniform brightness
which of the following terms does not name one of the four main categories of galaxies in the Hubble classification scheme
starbursts
what is the hubble classification for a spiral galaxy with a large nuclear region and tightly wound arms
sa
what is the hubble classification for a spiral galaxy with a oderately sized nuclear region and moderately wound arms
sb
what is the hubble classification for a spiral galaxy with a small nuclear region and loosely wound arms
sc
according to the hubble classification scheme, an sc galaxy has a
small central bulge and loosely wound spiral arms
a typical spiral galaxy has —– stars in a disk of diameter—ly
10 -11, 10-5
spiral galaxies are classified in terms of increasing tightness of their spiral arms as types Sa, Sb, Sc. However many spiral galaxies are aligned edge on to earth and their spiral arms cannot be seen. which other parameter that is directly related to spiral arm tightness can be easily seen edge-on and can therefore be used to provide this classification.
size of the nuclear bulge
a particular galaxy appears round , with a nuclear region of uniform brightness and an outer region that is broken up into curved but fuzzy and poorly defined lanes of stars and light gas clouds. How would this galaxy be classified
flocculent spiral
a particular galaxy appears round with a nuclear region of uniform brightness and an outer region that is broken up into long curved well defined lanes of stars and light gas clouds. How would this galaxy be classified
grand design spirals
one difficulty with the density wave theory is that
we are unsure of the mechanism that produces the energy output necessary to sustain the density wave.
according to the theory of self propagating star formation, the spiral arms of flocculent spiral galaxies are broad and poorly designed because
the spiral arm segments are defined only by the relatively short-O and B type stars.
why do the spiral arms show up so clearly in spiral galaxies
stars are spread almost uniformly over the galaxy( outside the nuclear bulge) but the brightest stars occur only in the spiral arms, where their brightness and the fact that they illuminate gas clouds make the arms stand out.
why is the Milky Way Galaxy different from most spiral galaxies
The Milky Way has at least four spiral arms, whereas most galaxies have only two.
how does the amount of dust and gas in a spiral galaxy vary with the classification of the galaxy
the most loosely wound galaxy, Sc, has the most dust and gas in its arms.
what is an SBc galaxy
galaxy with a small nuclear bulge and loosely wound arms starting from the ends of a straight bar through the nuclear bulge.
what is an elliptical galaxy
galaxy with an elliptical outline and a smooth distribution of brightness but no apparent structure.
elliptical galaxies look far less impressive than spiral galaxies because
they contain no gas and dust clouds or young hot stars
what name is give to a galaxy with a smooth distribution of brightness and a round shape
E0
which of the following statement is not a characteristic of elliptical galaxies
elliptical galaxies have a disk and a central bulge but no spiral arms
an elliptical galaxy typically contains which of the following primarily old kind of stars.
primarily old metal poor stars
an astronomer studying a galaxy finds that its spectrum shows only old, low mass, population II stars and photographs of the galaxy show little or no interstellar gas or dust. what kind of galaxy i this astronoer studying
elliptical galaxy
how are the magellanic clouds the two nearby satellite galaxies of thee milky way galaxy classified
irregular galaxies
the megellanic clouds as seen from the southern hemisphere are examples of what type of objects.
irregular galaxies
in which of the following types of galaxies is star formation no longer occuring.
elliptical galaxies
recent evidence suggests that galaxies formed
from the mergers of hundreds of smaller objects
when swirling eddies of gas rich matter in the universe collide and form a disk centered on an especially massive black hole and lot of dark matter we believe the following type of galaxy will form
normal spiral
overall through space galaxies are
concentrated on the surface of huge open spaces or voids like soap bubbles
how are galaxies spread throughout the universe
clusters of galaxies exist that are themselves often clustered into superclusters. Clusters and superclusters appear t be distributed on surfaces surrounding empty regions of space.
The Milky Way galaxy is a
member of a small cluster of galaxies
what is the local group
clusters of about 40 galaxies of which the Milky Way is one
what is a rich cluster of galaxies
cluster containing thousands of galaxies
what i a poor cluster of galaxies
a cluster containing a few dozen galaxies
collision between galaxies
can las hundreds o millions of years
what is a starburst galaxy
galaxy with an unusually large number of new born stars
globular clusters
can be formed in collision of galaxies and thus can be young if the collision occurred recently
as much as 90% of the matter in the universe may be unseen dark matter “ Where is this dark matter
Dark matter appears to be concentrated in spherical haloes around galaxies but extends several times the radius of visible matter
dark matteer in clusters of galaxies
is distributed mostly in and around the galaxies in a cluster, not in the voids between galaxies
