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236 Cards in this Set

  • Front
  • Back
The interstellar medium is made up of matter in the form of _______ and _______.
gas and dust
To scatter a beam of radiation most effectively, a particle must be _______ in size to the wavelength of the radiation.
It takes a star like the Sun a total of about _______ million years to form.
More massive stars evolve more _______.
Why do stars tend to form in groups?
large interstellar clouds are very massive. they fragment into clouds, which will turn into stars. clusters form rather than single
What are brown dwarfs?
when cloud fragment has insufficent mass to form a star. hydrogen fusion never occurs so object radiates excess energy
While a star is on the main sequence, _______ is slowly consumed in the core and _______ builds up.

A typical white dwarf has the following properties: about half a solar mass, fairly _______ surface temperature, small size, and _______ luminosity.

As time goes by, the temperature and the luminosity of a white dwarf both _______.
In a binary consisting of a white dwarf and a main-sequence or giant companion, matter leaving the companion forms an _______ disk around the dwarf.
A nova explosion is due to _______ fusion on the _______
hydrogen, surface
When a proton and an electron are forced together, they combine to form a _______ and a _______.
nuetron nuetrino
Why is the depletion of hydrogen in the core of a star such an important event?
Without hydrogen into helium occuring in the core, the core no longer has an energy source. Gravity is then able to collapse the core, forcing major chnages in the entire structure of a star
`Under what circumstances will a binary star produce a nova?
The primary factor as to whether stars in a binary will affect one another's evoltuion is the seperation of two stars. If seperated by a few AU, most stars will never expand to a sufficently large size to ever affect each otehr. closer than his and interaction is inevitable
What evidence do we have that many supernovae have occurred in our Galaxy?
After a supernova, it ejects vast cloud of gas called a supernova remnant. SR can last thousands of years.
Why do the cores of massive stars evolve into iron and not heavier elements?
Iron, the core of most massive stars, cannot release and fuse energy core collapse under gravity; high energy break up iron nuclei. reminder of star explodes as supernova
Globular clusters generally contain between a few hundred and a few thousand stars.
a. True b. False
In the vicinity of the Sun, there is about as much mass in the form of interstellar matter as in the form of stars. a. True b. False
Interstellar matter is evenly distributed throughout the entire Milky Way Galaxy.
a. True b. False
. A nova is a sudden outburst of light coming from an old main-sequence star.
a. True b. False
A planetary nebula is the disk of matter around a star that will eventually form a planetary system. a. True b. False
All the red dwarf stars that ever formed are still on the main sequence today.
a. True b. False
High-mass stars can fuse carbon in their cores. a. True b. False
Low-mass stars are conventionally taken to have masses of less than about eight solar masses. a. True b. False
No neutron star remains after the explosion of a _______ supernova.
Type I (carbon detonation)
A typical neutron star is about _______ km in diameter.
Neutron stars may be characterized as having _______ rotation rates and _______ magnetic fields.

X-ray bursters result when material from a binary companion accretes onto a _______ star.
Colliding neutron stars would be expected to release a lot of energy in the form of _______.
gamma rays
. According to the general theory of relativity, space is warped, or curved, by _______.
Photons _______ energy as they escape from a gravitational field.
The region of extremely high density at the center of a black hole is called a _______.
What would happen to a person standing on the surface of a neutron star?
a human being would weigh one million tons
Why aren’t all neutron stars seen as pulsars?
orientation doesn't allow their radiation to pass in direction of earth
Use your knowledge of escape speed to explain why black holes are said to be "black."
light itself cannot escape from black holes. escape velocity depends on mass of radius of object
What is an event horizon?
place in black hole when escape veloctiy equals speed of light
Although visible light cannot escape from a black hole, high-energy radiation, such as gamma rays, can escape. a. True b. False
As a result of their high mass and small size, neutron stars have only a weak gravitational pull at their surface. a. True b. False
If the Sun were suddenly to turn into a black hole, Earths orbit would immediately change. a. True b. False
. If you could touch it, the surface of a black hole, the event horizon, would be very hard. a. True b. False
Loosely speaking, a black hole is an object whose escape speed equals or exceeds the speed of light. a. True b. False
Newly formed neutron stars have extremely strong magnetic fields. a. True b. False
Nothing can travel faster than the speed of light. a. True b. False
The density of a typical neutron star is about 100,000 times denser than a white dwarf.
a. True b. False
9. The laws of physics break down near the center of a black hole. a. True b. False
One difficulty in studying our Galaxy in its entirety is that the Sun lies within the _______.
galatic disk
The highly flattened, circular part of the Galaxy is called the Galactic _______.
The roughly spherical region of faint old stars in which the rest of the Galaxy is embedded is the Galactic _______.
The _______ of Cepheids and RR Lyrae stars are observed to vary in a periodic fashion.
According to the period–luminosity relationship, the longer the pulsation period of a Cepheid, the _______ its luminosity.
The Sun lies roughly _______ pc from the Galactic center.
Rotational speeds in the outer part of the Galaxy are _______ than would be expected on the basis of observed stars and gas, indicating the presence of _______.

darker matter
How are Cepheid variables used in determining distances?
determining period of variation find aps: mag to apparent magnitude to disance
Roughly how far out into space can we use Cepheids to measure distance?
few million parsecs
Why can’t we study the central regions of the Galaxy using optical telescopes?
gravity is observed through thick interstellar clouds
What does the rotation curve of our Galaxy tell us about its total mass?
gravity rotates at different rates
What evidence is there for dark matter in the Galaxy?
rotation curve of the galaxy
A million-solar-mass black hole could account for the unusual properties of the Galactic center. a. True b. False
Cepheid variables can be used to determine the distances to the nearest galaxies.
a. True b. False
Dark matter is now known to be due to large numbers of black holes. a. T b. F
Most of the mass of our Galaxy exists in the form of dark matter. a. True b. False
a. True
The Galactic center has been extensively studied at visible and ultraviolet wavelengths. a. True b. False
The Galactic disk contains only old stars. a. True b. False
Why are infrared and radio telescopes the instruments of choice for study of the galactic center?
a. Dust in the plane of the Milky Way obscures observations at other wavelengths.
b. Radio and infrared telescopes are bigger than optical ones and hence can see farther.
c. These types of telescopes are cheaper to build and operate than optical ones.
d. There are more radio and infrared telescopes than optical ones in the world.
e. The galactic central region only radiates energy in the radio-frequency and infrared bands
a. Dust in the plane of the Milky Way obscures observations at other wavelengths.
The Milky Way Galaxy, the Andromeda Galaxy, and about 20 others form a small cluster known as the _______.
local group
In the Tully—Fisher relation, a galaxy’s luminosity is found to be related to the _______ of its spectral lines.
Galaxy clusters are themselves clustered, forming _______.
More than 90 percent of the mass in galaxy clusters exists in the form of _______.
dark matter
Hubble’s law is a correlation between the redshifts and the _______ of galaxies.
. Describe the four rungs in the distance-measurement ladder used to determine the distance to a galaxy lying 5 Mpc away.
radar, triangulation, spectral parallax and pulsating variable
Describe the contents of the Local Group. How much space does it occupy compared with the volume of the Milky Way Galaxy?
20 galaxies, 3 big
How does the Tully—Fisher relation allow astronomers to measure the distances to galaxies?
correlation to galaxy's luminosity and its rotational velocity
What is the Virgo Cluster?
nearest rich cluster, contains 2500 galaxies
Why do astronomers believe that galaxy clusters contain more mass than we can see?
gravity hides mass
What is Hubble’s law?
galaxies are determined to have redshift spectra, which means they all receed from us
How is Hubble’s law used by astronomers to measure distances to galaxies?
trivial recessional velocity of galaxy
What are voids? What is the distribution of galactic matter on very large (more than 100 Mpc) scales?
roughly spherical regions that contain no galaxy
Distant galaxies appear to be much larger than those nearby. a. True b. False
Elliptical galaxies do not contain a flattened disk. a. True b. False
Hubbles law can be used to determine distances to the farthest objects in the universe.
a. True b. False
Irregular galaxies, although small, have lots of star formation taking place in them.
a. True b. False
Most ellipticals contain only old stars. a. True b. False
Most galaxies appear to be receding from the Milky Way Galaxy. a. True b. False
What are the two objects observable from Earth's southern hemisphere that are known as the Magellanic Clouds?

a. They are supernova remnants that give us a measure of the distances to the nearest galaxies.
b. They are the most distant irregular galaxies that can be observed.
c. They are dwarf irregular galaxies of a few billion stars each that orbit the Milky Way
d. They are giant elliptical galaxies in the Virgo Cluster.
e. They are distant members of the local supercluster, near the Ursa Major group.
c. They are dwarf irregular galaxies of a few billion stars each that orbit the Milky Way
How are the orbits of stars within most elliptical galaxies arranged?

a. They tend to rotate around the short axis of the elliptical and have high values of orbital eccentricity.
b. They tend to rotate around the long axis of the galaxy and be quite circular.
c. They tend to rotate around the long axis of the elliptical, and to have high values of orbital eccentricity.
d. They tend to rotate around the short axis of the galaxy, and to be quite circular.
e. The move in random directions with respect to the galaxy itself, with a variety of orbital sizes and eccentricity values.
e. The move in random directions with respect to the galaxy itself, with a variety of orbital sizes and eccentricity values.
Active galaxies generally emit most of their radiation at _______ wavelengths.
A Seyfert galaxy looks like a normal spiral, but with a very bright galactic _______.
For all types of active galaxies, the original source of the tremendous energy emitted is the galactic _______.
The amount of mass that must be consumed by a supermassive black hole to provide the energy for an active galaxy is about _______ per _______.
10 solar masses per year
Quasar spectra were understood when it was discovered that their radiation is _______ by an unexpectedly large amount.
The distance to a quasar in light-years is not simply equal to the time in years since the quasar emitted the light we see because of the _______ of the universe.
The fact that a typical quasar would consume an entire galaxy’s worth of mass in 10 billion years suggests that quasar lifetimes are relatively _______.
The image of a distant quasar can be split into several images by gravitational lensing, produced by a foreground _______ along the line of sight.
Name two basic differences between normal galaxies and active galaxies.
active galaxies emit more radiation
Describe some of the basic properties of Seyfert galaxies.
emit radiation from central region called a galatic nucleus
Briefly describe the leading model for the central engine of an active galaxy.
massive blackhole surrounding accretion disk
How do astronomers know that the energy-producing region of an active galaxy must be very small?
shows energy producing regions of active galaxies to be small
How do we know that quasars are extremely luminous?
appear as redshift yer indicate enormous distance
What evidence do we have that quasars represent an early stage of galactic evolution?
If many galaxies were once quasars, what has happened to the energy sources at their centers?
with less energy about quasars it dies down
Active galaxies can emit thousands of times more energy than our own Galaxy.
a. True b. False
All active galaxies are far away. a. True b. False
All quasars are far away. a. True b. False
Many nearby normal galaxies may once have been quasars. a. True b. False
Quasars emit about as much energy as normal galaxies. a. True b. False
The quasar stage of a galaxy ends because the central black hole uses up all the matter around itself. a. True b. False
When galaxies collide, what happens in general to the stars contained within them?

a. They are captured in large numbers within the supermassive black holes at the centers of each galaxy.
b. They collide head-on with stars in the other galaxy, forming larger stars.
c. They merge into one galaxy, leaving the other one relatively underpopulated.
d. They mostly pass by the stars in the other galaxy without colliding.
e. They get dimmer due to obscuration by gas and dust in the other galaxy.
d. They mostly pass by the stars in the other galaxy without colliding.
What can we conclude from the pattern of redshifts and blueshifts evident among the galaxies that we observe?

a. The universe itself is expanding in all directions.
b. Almost all galaxies are moving toward each other and will one day collide.
c. All galaxies are rotating at approximately equal rates.
d. Cosmic rays seem to originate only from the redshifted galaxies.
e. Approximately as many galaxies are moving toward us as are moving away from us.
a. The universe itself is expanding in all directions.
What is the best description of the distribution of the galaxies that lie within about 200 Mpc of the Earth?

a. The galaxies show up at random positions throughout the universe.
b. The galaxies appear to be clustered into small spherical regions.
c. The galaxies appear to be arranged in a network of filaments or strings surrounding large, empty regions of space known as voids.
d. The galaxies seem to be arranged on the points of a grid.
e. The galaxies are arranged in clusters that are randomly scattered throughout the universe.
c. The galaxies appear to be arranged in a network of filaments or strings surrounding large, empty regions of space known as voids.
Homogeneous means "the same _______."
Isotropic means "the same in all _______."
Together, the assumptions of cosmic homogeneity and isotropy are known as the _______.
cosmological principle
If the universe had an edge, this would violate the assumption of _______.
If the universe had a center, this would violate the assumption of _______.
Luminous matter makes up at most _______ percent of the critical density.
The surface of a sphere is a two-dimensional example of a _______ universe.
The present average temperature of the universe, as measured by the cosmic microwave background, is _______ K.
Comparing the mass density of radiation and matter, we find that, at the present time, _______ dominates.
When the universe was a few minutes old, nuclear fusion produced _______ and _______.

What is the cosmological principle?
homogenity vs. isotropy
What is Olbers’s paradox? How is it resolved?
Why isn’t it correct to say that the expansion of the universe involves galaxies flying outward into empty space?
universe evenly filled with matter
Why are recent observations of distant supernovae so important to cosmology?
candle to measure great distances
Where and when did the Big Bang occur?
15 million years ago
What is the cosmic microwave background, and why is it so significant?
old x-ray/gamma rays are very old
Why do all stars, regardless of their abundance of heavy elements, contain at least 25 percent helium by mass?
25% is the base created at the universe's beginning
When did the universe become transparent to radiation?
when universe colled to temperature to combine electrons with nuclei
What is the connection between dark matter and the formation of large-scale structure in the universe?
no dark matter can produce large scale structures
What did dark-matter models predict that was later found by the COBE satellite?
all dark matter is consistent with degree of isotropy and background radiation
All points in space appear to be at the center of the expanding universe. a. T b. F
As it travels through space, a photons wavelength expands at the same rate as the universe expands. a. True b. False
Cosmic homogeneity can be tested observationally, but cosmic isotropy has no observational test. a. True b. False
Observations of supernovae imply that the expansion of universe is slowing down faster than can be accounted for by gravity alone. a. True b. False
Olbers paradox asks, "Why is the night sky dark?" a. True b. False
The Big Bang is an expansion only of matter, not of space. a. True b. False
The cosmic microwave background is the highly redshifted radiation of the early Big Bang. a. True b. False
Where did the Big Bang occur?
a. at a single point in the center of the then-existing universe
b. at all points simultaneously on the surface of an expanding balloon
c. everywhere in the universe at once, because the entire universe (including space itself) was a point
d. First the fabric of space came into existence; then the Big Bang appeared at some arbitrary point within it.
e. All of these statements are equally correct.
c. everywhere in the universe at once, because the entire universe (including space itself) was a point
About what density of material, on average, is needed in order for the universe that we live in to be just barely bound, or "closed"?
a. about 6 atoms per cubic meter of space.
b. roughly 5000 atoms per cubic meter of space
c. roughly 800 atoms per cubic kilometer of space
d. about 75,000 atoms per cubic centimeter of space
e. The universe will expand forever, regardless of the amount of material contained within it.
a. about 6 atoms per cubic meter of space.
Why do most cosmologists believe that the first large-scale structures to appear did so as clumps in the dark matter that comprises most of the universe?
a. Normal matter did not exist until later in the formation of the universe.
b. The background radiation in the early universe was so intense that it prevented normal matter from forming clumps, just as the radiation pressure in stars prevents them from collapsing. Dark matter is relatively unaffected by radiation.
c. Dark matter forms clumps more easily than normal matter because it interacts very strongly with other dark matter. Normal matter does not interact so strongly with other normal matter.
d. When we look at dark matter today, we find that it is very lumpy.
e. There is so much more dark matter than normal matter that it overwhelms the interactions of normal matter
b. The background radiation in the early universe was so intense that it prevented normal matter from forming clumps, just as the radiation pressure in stars prevents them from collapsing. Dark matter is relatively unaffected by radiation.
Which of the following is not a possible scenario for the past and future development of the universe, according to the available astrophysical evidence?
a. If the universe has sufficient overall density, it will eventually cease expanding and re-collapse in a "Big Crunch."
b. The universe could have existed in an infinitely large state for all eternity, with galaxies forming and dissipating continuously in a uniform manner.
c. The universe could continue to expand forever at a rate that slows continuously, eventually slowing to a halt at infinite time.
d. The universe could continue to expand forever at a rate that slows continuously, but never slows to a halt, even at infinite time.
e. The universe could continue to expand forever at a rate that actually increases with time, requiring rethinking of our views of the early history of space and time.
b. The universe could have existed in an infinitely large state for all eternity, with galaxies forming and dissipating continuously in a uniform manner.
What is interstellar medium?
the matter between the stars
what is the dust grain?
interstellar dust particle
what is reddening?
when distant stars are robbed of their higher frequency components due to the decreasing wavelenth
what is an emission nebulae?
glowing clouds of hor interstellar gas
what is a nebula?
refers to any fuzzy patch on the sky
what are dust lanes?
they are woven through the nebular gas and obscure nebular lights
what is a dark dust cloud?
cooler clouds then the surroudnings that are often called dense interstellar clouds b scientists
what is a 21 centimeter line?
the spectral emission line that results from a hydrogen flip process
what are molecular clouds?
regions within the cold neutral gas of interstellar regions
what are molecular cloud complexes?
this contains not only interstellar dust byt also interstellar gas. these two cannot seperate from each other and this is what it represents
what is a protostar?
an embryonic object perched at the dawn of star birth
what is evolutionary track?
motion of a point around the diagram as the star evolves
what is a T-Tauri phase?
the fourth phase of protostellar evolution in which the star is very violent and active. named after the T-Tauri, the first star to be observed doing these thigns
what is the zero age main sequence?
the main sequence band predicted by theory is usaly called this.
what is a star cluster?
a group of stars alll formed from the same parent cloud lying in the same region of space.
what is brown dwarf?
cold fragments of unburned matter
what is an open cluster?
a type of loose irregular cluster found mainly in the plane o the milky way
what are associations?
less massive, but more extended clusters
what is a core-hydrogen burning?
when a star slowly fuses hydrogen into helium in its core.
what is the hydrogen shell burning stage?
the shrinkage of helium core releases gravitational energy, driving up the central temperature and overlying laters, causing the hydrogen there to fuse even more rapidly than before.
what is a subgiant branch?
the star's rougly horizontal track from its main-sequence location to stage eight
what is a red giant branch?
the nearly vertical path followed by the star between stages 8 and 9
what is a helium flash?
once the burning stars, the core cannot respod quickly enough to the runaway explosion
what is a horizontal branch?
a well defined region of the H-R diagram
what is planetary nebula?
it becomes so hot that its ultraspectacular violet radiation ioizes the innter parts of the surrounding cloud and produce the planetary nebula
what is a black dwarf?
a cold dense burned out ember in space
what is a nova?
when a white dwarf becomes explosively active
what is an accreation disk?
the area around a white dwarf that holds the stuff in the main sequence companion
what is a red supergiant
when a star stays roughly constant as its radius increase and its surface temperature drops
what is a core collapse supernova?
a spectacular explosion of a high mass star
what is a type I supernovae?
this contains very little hydrogen, according to their spectra, and have light curves somewhat similar in shape to those of typical novae
what is a Type II supernovae?
hydrogen rich and usually have a charcateristic "plateau" in the light crve a few months after the maximum
what is a carbon detonation supernova?
an event comparable in violence to the core collapse supernova associated with the death of a hihg mass star
what are supernova remnants?
the glowing remains of supernovas
what is a nuetron star?
after the violence of a supernova has subsided, this ultracompressed ball of nuetrons is all that is left
what is a pulsar?
a pulsating object that emits radion radiation in the form of pulses
what is the lighthouse model?
when the hot spots radiate more or less steadil, and the resulting beams sweep through space like a revolving lighthouse beacon.
what is X-ray bursters?
places in space that emits much of their energy in violent eruptions, each thousands of times more lumnious than our Sun but only lasting a few seconds
what are millisecond pulsars?
a class of rapidly roatating objjects that spin hunderds of times per second
what are gamma ray bursts?
bursts that consist of bright, irregular flashes of gamma rays that typicall last only a few seconds
what is a black hole?
the bizarre end point of stellar evoliton in whihc the core of a very high mass star collapses on itself and vanishes forever
what is the general theory of relativity?
what is the schwarzschild radius?
after Karl Schwarschild, the german scientist who first studied properties the radius of any bject is proportional to its mass
what is gravitational redshift?
result of the blackhole's gravitational field, clearly predicted by Einstein's genneral theory of relativity
what is a spiral galaxy?
a galaxy that is in the shape of a spiral
what is a galatic disk?
the disk of a spiral galaxy
what is a galatic bulge?
the center of the spiral galaxy
what is the galatic halo?
ththe roughly spherical ball of old stars around the spiral galaxy
what are variable stars?
an important by product of the laborious effort to catalog stars around teh turn of the twentieth century
what are pulsating varable stars?
vary cyclically in characterisitc ways according to RR Lyraw variable and Cepheid variable
RR Lyrae and Cephid variable stars are recongnizable by the characteristic shape of their ________.
light curve
what is the galatic center?
the hubof all the collection of matter within the galaxy
what are spiral arms
the pinwheel like structures originaing close to the galatic bulge and extending outward thoroughout much of the galatic disk
what are spiral density waves?
coiled waves of gas compression that move through the galatic disk, squeezing clouds of interstellar gas and triggering the process of star formation as they go
what is self propagating star formation?
can only produce only pieces of sprials, as are seen in some galaxies
what is a rotation curve?
plots the roation speed of the galatic disk against the distance of the galatic center
what is a dark halo?
dwarfs the inner halo of stars and globular clusters and extends well beyong the 15-kpc radois oonce thought to represent the limit of our galaxy
what is dark matter?
what most of the galaxy is made up of, yet something that cannot be determined yet by its precise nature
what is the gravitational lensing?
when a star apears to be brighter due to an interfering object
what is the hubble classification scheme?
the scheme in which galaxies are classifid into four basic types: spirals, barred spirals, ellipicals, and irregulars
what is a barred spiral galaxy?
Barred spirals differ from the ordinary spirals mainly by the presence of an elongated "bar" of stellar and interstellar matter passing through
what is an elliptical galaxy?
in most cases, they often exhibit little internal stucture of any kind
what are SBO galaxies?
when a bar is present
what is an SO galaxy?
when no bar is present
what are irregular galaxies?
nmaed because their apperance does not allow us to place them into any of the other categories discussed.
what are magellanic clouds?
a famous pair of Irr I galaxies that orbit the Milky Way Galaxy
what are standard candles?
easily recognizable astronimcal objects whose luminsities are confidently known
what is the Tully-Fisher relation?
as it is knnown, allows us to obtain a remarkably accurate estime of a sprial galaxy's luminosity simply by observing how fast it rotates
what is the local group?
a new level of strcture in the universe above the scale of our galaxy
what is a galaxy cluster?
a group of galaxies held togther by their mutral gravitational attraction
what is cosmological redshift?
redshift resulting from the hubble flow
what are active galaxies?
20-25% of all galaxies that have luminosities sometimes thousands of times brighter than the milky way
what is active galatuic nuclei?
a system where the abnormal activity is related to violent events occuring in or near the galatic nucleus
what are Seyfert galaxies?
a class of astronomical objects whose properties lie between those of normal galaxies and those of the most energetic active galaxies known
what is a galactic nucleus?
the center of the overexposed white patc of a galaxy
what are radio galaxies?
active galaxies that emit large amounts of energy in the radio portion of the electromagnetic spectrum
what are radio lobes?
roundish clouds of gas spanning about half a megaparsec, lying well beyond the visible galaxy
what is a blazar?
the radiation recieved is both intense and doppler shifted toward short wavelength
what is a quasar?
quasi stellar radio sources

although faint, these are brightest stars in the universe
what is a starburst galaxy?
a galaxy where stars are formed by a sudden, intense burst
what are superclusters?
the clusters of galaxies
what is critical density?
the density corresponding to a universe in whihc gravity acting alone would be just sufficent to hald the present expansion
what is a closed universe?
a universe that is curved so much that it bends back and clses in on itself
what is an open universe
a low density saddle curved universe in extent
what is the cosmological constant?
a "vaccum pressure" associated with epty space and effective only on very large scales
what is the cosmic microwave background?
the background hiss that Penzias and Wilson discoever that was nothing less than the fiery creation of the universe itself
what is a matter dominated universe?
a universe in whihc the matter in a universe exceeds the radiation
what is radiation dominated?
when radiation dominates the galaxy
what is a primordial nucleosynthesis
the production of nuclear fusion sortly afte the big bang
what is decoupling?
the period during whihc the nuclei and electrons combined to form atoms
what is the flatness problem?
the idea that the universe is close to being flat, but there is no good reason that the universe should have formed with a density curve very close to critical
what is the Grand Unified Theories?
the describe this superforce is that the three forces are unified and inistinguishable from on another only at enormoulsy high levels
what is inflation?
the period of unchecked cosmic expanison
How many supernova have been observed in our galaxy over rougly the past one thousand years?
In the Black Hole video Kip Thorne and Roger Penrose stated that the concept to use wormholes to travel in faraway galaxies...
won't work
stars amount to 0.5 % of
ordinary matter