exam 4 homework stars and cosmology.
When we observe a distant galaxy whose photons have traveled for 10 billion years before reaching Earth, we are seeing that galaxy as it was when the universe was -0 billion years old. -7 billion years old. -4 billion years old.
4 billion years old.
Shortest peak wavelength to highest.
500,000 years after the Big Bang, 1 million years after the Big Bang, 100 million years after the Big Bang, 1.5 billion years after the Big Bang, Today
Shortest wavelength to highest.
500,000 years after the Big Bang, 1 million years after the Big Bang, 100 million years after the Big Bang, 1.5 billion years after the Big Bang, Today
High angular momentum leads to faster rotation. Why does faster rotation tend to lead to a spiral galaxy, rather than an elliptical galaxy? -Spiral arms rotate like giant pinwheels, and therefore they need to rotate very fast. -Stars in spiral galaxies orbit the galactic center faster than stars in elliptical galaxies. -Individual stars in spiral galaxies rotate faster than those in elliptical galaxies. -Faster rotation leads to collisions among gas particles that cause the gas to settle into a spinning disk, rather than a more spread out cloud.
-Faster rotation leads to collisions among gas particles that cause the gas to settle into a spinning disk, rather than a more spread out cloud.
What is the typical hydrogen content (by mass) of stars that are forming right now in the vicinity of the Sun? -75% hydrogen -70% hydrogen -100% hydrogen
70% hydrogen
Central black holes can be very efficient for converting the mass-energy of infalling matter to thermal energy in the accretion disk. Roughly what percentage of the mass-energy can be converted to other forms of energy as matter falls into a black hole? -0.7% -1%-4% -100% -10-40%
10-40%
Spiral galaxies have:
A flattened disk of stars. Contain abundant clouds of cool gas and dust. Contain many bright, hot stars. Are rare in central regions of galaxy clusters. Have significant, ongoing star formation.
Suppose a collision strips gas out of a spiral galaxy. Why would this tend to change the spiral galaxy into an elliptical galaxy? -The loss of gas will cause the galaxy to start rotating faster. -The collision will disrupt the orbits of stars in the galaxy's halo. -The collision will cause stars that were on circular orbits to change to elliptical orbits. -A galaxy cannot have a disk if it does not have gas.
A galaxy cannot have a disk if it does not have gas.
What is the disk?
A portion of a spiral galaxy looks like a disk and contains an interstellar medium with cool gas and dust; stars of many ages are found in the disk component.
Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply? -The jets seen in many active galactic nuclei must cause them to move far away from us. -Active galactic nuclei exist tend to become less active as they age. -Active galactic nuclei can form only at large distances from the Milky Way. -Supermassive black holes existed only when the universe was young, and no longer exist today.
Active galactic nuclei exist tend to become less active as they age.
The Big Bang theory is closely linked to Hubble's discovery that the universe is expanding, which seems to imply that there was a time in the past when the expansion first began. Nevertheless, the Big Bang theory did not gain widespread acceptance among scientists until the 1960s. Why wasn't expansion alone enough to convince scientists that the Big Bang really happened? -Although expansion seems to imply a Big Bang, no other specific predictions of the Big Bang theory were tested and confirmed until the 1960s. -The idea of a Big Bang seemed so strange to scientists that they resisted it, despite the observational evidence of an expanding universe. -Expansion alone is enough to prove that there was a Big Bang, but most scientists didn't believe the observational evidence for expansion until the 1960s. -Expansion implies a Big Bang only if the rate of expansion is quite high, and the rate wasn't measured until the 1960s.
Although expansion seems to imply a Big Bang, no other specific predictions of the Big Bang theory were tested and confirmed until the 1960s.
Elliptical galaxies:
Are more reddish in color and contain primarily old, low-mass stars.
Today, most scientists accept the Big Bang theory because its predictions agree so well with observations. But a scientific theory can always be revised or discarded if future observations do not agree with its predictions. Consider the following hypothetical future observations. Which one(s) would be inconsistent with the Big Bang theory? -Careful studies of quasar spectra show that, 12 billion years ago, the temperature of the cosmic microwave background was slightly lower than it is today. -Over the next 10 years, the temperature of the cosmic microwave background falls to 1 K. -Astronomers discover a nearby galaxy that has a helium abundance of 27%. -Astronomers discover distant protogalactic clouds with a helium abundance below 20%. -Astronomers find an error in previous measurements that means the temperature of the cosmic microwave background is actually 2.71 K rather than 2.73 K.
Careful studies of quasar spectra show that, 12 billion years ago, the temperature of the cosmic microwave background was slightly lower than it is today. Over the next 10 years, the temperature of the cosmic microwave background falls to 1 K. Astronomers discover distant protogalactic clouds with a helium abundance below 20%.
Which statement best describes the fundamental difference between spiral and elliptical galaxies? -Spiral galaxies are more massive than elliptical galaxies. -The oldest stars in spiral galaxies are younger than the oldest stars in elliptical galaxies. -Elliptical galaxies lack a disk.
Elliptical galaxies lack a disk.
Why should galaxy collisions have been more common in the past than they are today? -Galaxies were more active in the past and therefore would have collided with each other more frequently. -Galaxies were much bigger in the past since they had not contracted completely. -Galaxies were closer together in the past because the universe was smaller. -Galaxies attracted each other more strongly in the past because they were more massive; they had not yet turned most of their mass into stars.
Galaxies were closer together in the past because the universe was smaller.
The observed relationship between the masses of central black holes and the bulge masses of galaxies implies that: -Quasars were more common 10 billion years ago than they are today. -The black hole will eventually suck in the rest of the galaxy. -The biggest galaxies have the most luminous quasars. -Galaxy formation and supermassive black hole formation must be related somehow.
Galaxy formation and supermassive black hole formation must be related somehow.
Which of the following statements is not an assumption used in models of galaxy formation? -The universe started out filled almost uniformly with hydrogen and helium. -Gas contracted to form the disks of galaxies before any stars were born. -The universe is expanding. -Some regions in the universe were slightly more dense than others.
Gas contracted to form the disks of galaxies before any stars were born.
Spectra of very distant galaxies show very large redshifts, and we say that the wavelengths of the photons from these galaxies are longer because of cosmological redshift. According to our modern perspective on the universe, what is the cause of cosmological redshift? -The galaxies from which these photons come are plowing through the pre-existing structure of space at very high speed. -The light from distant galaxies is reddened by interactions with intergalactic dust grains. -Individual photons stretch to longer wavelength as the universe expands.
Individual photons stretch to longer wavelength as the universe expands.
Suppose you have a compressed gas, like that in a piston in a car engine. As the piston moves so that the gas expands, what happens to the gas temperature? -It cools as it expands. -It heats up as it expands. -Its temperature stays the same as it expands.
It cools as it expands.
Classify each statement below as an OBSERVATION or as an inference based on the current Big Bang model.
Large-scale structure looks about the same in all directions. The temperature of the cosmic microwave background varies slightly with direction. The cosmic microwave background temperature is 2.73 K. The helium abundance is at least 25% in every galaxy studied so far.
What additional data would be most valuable in helping scientists evaluate whether the accelerating model really is the best of the four models? -Observations of white dwarf supernovae that can be plotted to the right of the "now" line -Observations of supernovae from massive stars (rather than white dwarfs) -More observations of nearby white dwarf supernovae -More observations of very distant white dwarf supernovae
More observations of very distant white dwarf supernovae
During the history of the universe, what important event occurred about 0.001 seconds after the Big Bang? -Space-time rapidly expanded during a brief period of inflation. -The first massive supernova explosions occurred. -Light began to travel freely through the universe. -Most matter was annihilated by antimatter.
Most matter was annihilated by antimatter.
If the Andromeda Galaxy collided with the Milky Way, what would most likely happen to Earth? -The Sun would not be disturbed, but the solar system would be ripped apart. -The Sun and all its planets would be crushed by collisions with stars and planets from the Andromeda Galaxy. -Nothing -The Sun will turn into a red giant and explode.
Nothing
Why do virtually all the galaxies in the universe appear to be moving away from our own? -Because we are located near where the Big Bang happened. -Because we are located near the center of the universe. -Observers in all galaxies observe a similar phenomenon because of the universe's expansion.
Observers in all galaxies observe a similar phenomenon because of the universe's expansion.
All of the following observations are real. Which one does not support the model in which active galactic nuclei are powered by accretion disks around massive black holes? -The total luminosity of an active galactic nucleus can be as high as about 10 billion times that of the Sun. -Spectra of active galactic nuclei show that clouds of gas are orbiting a central object at very high speed. -The most luminous active galactic nuclei have huge redshifts. -X-ray emission from active galactic nuclei can vary significantly in times as short as a few days.
The most luminous active galactic nuclei have huge redshifts.
Which of these items is a key assumption in our most successful models for galaxy formation? -The distribution of matter was perfectly uniform early in time. -Some regions of the universe were slightly denser than others. -Galaxies formed around supermassive black holes.
Some regions of the universe were slightly denser than others.
Which characteristic is not generally true of a starburst galaxy? -The observed features of the starburst are thought to be caused by the presence of a supermassive black hole in the galaxy's center. -The observed features that cause us to classify it as a "starburst" must be only temporary phenomena in the galaxy's history. -Its rate of star formation is many times higher than the rate of star formation in the Milky Way. -Supernovae occur so frequently that their effects combine to drive a galactic wind that blows material into intergalactic space.
The observed features of the starburst are thought to be caused by the presence of a supermassive black hole in the galaxy's center.
What is the halo?
The spherical region surrounding the disk of a spiral galaxy is the halo.
Which of the following important events occurred earliest in the history of the universe? -Space-time expansion increased the average distance between galaxies. -Space-time rapidly expanded during a brief period of inflation. -The first massive supernova explosions occurred. -Light began to travel freely through the universe.
Space-time rapidly expanded during a brief period of inflation.
What are globular clusters?
Spherical clusters of a million or more stars, globular clusters are found primarily in the halos of galaxies and contain only very old stars.
What are spiral arms?
Spiral arms are bright, prominent arms, usually in a spiral pattern, found in most spiral galaxies.
Which statement below best describes the most fundamental difference between spiral and elliptical galaxies? -Spiral galaxies have a disk of gas and elliptical galaxies do not. -Elliptical galaxies form from protogalactic clouds and spiral galaxies do not. -Spiral galaxies have more stars than elliptical galaxies.
Spiral galaxies have a disk of gas and elliptical galaxies do not.
Which statement below best describes the most fundamental difference between spiral and elliptical galaxies? -Spiral galaxies have more stars than elliptical galaxies. -Spiral galaxies have a disk of gas and elliptical galaxies do not. -Elliptical galaxies form from protogalactic clouds and spiral galaxies do not.
Spiral galaxies have a disk of gas and elliptical galaxies do not.
What are spiral galaxies?
Spiral galaxies look like flat, white disks with yellowish bulges at their centers. The disks are filled with cool gas and dust, interspersed with hotter ionized gas, and usually display beautiful spiral arms.
These distinctions between the disk and halo are fundamental to understanding the structure and evolution of galaxies, including the Milky Way.
Stars in the disk all orbit in the same direction and nearly the same plane, while halo stars have more randomly oriented orbits. Gas and dust are abundant in the disk but not in the halo. Clusters of young stars are found only in the disk. Disk stars come in a broad range of masses and colors, while halo stars are mostly of low mass and red.
Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude? -The X-ray source contains a black hole with an accretion disk. -The X-ray source is a quasar. -The X-ray source is no more than a few light-days in diameter. -The X-ray source must have a strong, rapidly varying magnetic field.
The X-ray source is no more than a few light-days in diameter.
What is the bulge?
The central portion of a spiral galaxy is roughly spherical (or football shaped) and bulges above and below the plane of the galactic disk to form the bulge.
Interactions among galaxies also are thought to influence a galaxy's type in at least some cases. Which of the following does not support the idea that interactions can shape galaxies? -The presence of features such as "tails" extending out of galaxies, bridges between galaxies, and rings of stars around galaxies. -Computer modeling of collisions between galaxies. -The fact that more distant galaxies have larger redshifts. -The fact that galaxies with distorted appearances are more common at great distances than nearby.
The fact that more distant galaxies have larger redshifts.
Which of the following phenomena are not thought to be results of collisions or other interactions between galaxies? -The presence of very large, central dominant galaxies in clusters of galaxies. -The fact that elliptical galaxies are more common in clusters of galaxies than outside clusters. -The fact that spiral galaxies have both disk and halo components. -Starbursts.
The fact that spiral galaxies have both disk and halo components.
We can study how galaxies evolve because ______. -Galaxies are transparent to visible light. -We can watch as they interact in real time. -We are really smart astronomers. -The farther away we look, the further back in time we see.
The farther away we look, the further back in time we see.
Supermassive black holes found at the centers of galaxies are related to the properties of those galaxies in which of the following ways? -The mass of the black hole is related to the mass of the galaxy's bulge. -The luminosity of the active nucleus is related to the mass of the galaxy's disk. -The luminosity of the active nucleus is related to the luminosity of the galaxy's bulge.
The mass of the black hole is related to the mass of the galaxy's bulge.
Which of the following best explains why the night sky is dark? -The distribution of matter in the universe is not uniform on very large scales. -The universe has not always looked the way it looks today. -The universe is not infinite in space.
The universe is not infinite in space.
Coolest temp to hottest temp.
Today, 1.5 billion years after the Big Bang, 100 million years after the Big Bang, 1 million years after the Big Bang, 500,000 years after the Big Bang
__________ are defined as subatomic particles that have more mass than neutrinos but do not interact with light.
WIMPs
Quasar spectra often show many absorption lines that all appear to be due to the same electron transition (such as level 1 to level 2 in hydrogen) but that fall at different wavelengths in the spectrum. Why do we think this is the case? -No one knows - it remains perhaps the greatest mystery about quasars. -Quasars are rotating rapidly, and this rotation produces spectral lines with a wide variety of Doppler shifts. -The lines fall at different wavelengths because they are produced by different chemical elements. -We are seeing absorption lines from clouds of gas that lie between us and the quasar, and therefore each cloud has a different redshift.
We are seeing absorption lines from clouds of gas that lie between us and the quasar, and therefore each cloud has a different redshift.
Although we can divide the history of the universe into many distinct "eras," sometimes it's useful just to have a broad perspective on what events occurred in the very early universe and what events occurred later. Listed following are events that occurred either before or after the first five minutes in the history of the universe. Match these events to the appropriate time period.
Within the first five minutes anti electrons (positrons) as common as electrons, temperature fell to 10^15 K, strong force and electroweak force first became distinct,inflation occurred Sometime after the first five minutes galaxies formed, photons of cosmic microwave background released, carbon nuclei formed by fusion, stars formed
What is the current temperature of the universe? -absolute zero -a few K -a few thousand K
a few K
About how many galaxies are there in a typical cluster of galaxies? -about 10 -a few dozen -a few hundred
a few dozen
What is the earliest time from which we observe light in the universe? -a few hundred million years after the Big Bang -a few minutes after the Big Bang -a few hundred thousand years after the Big Bang
a few hundred thousand years after the Big Bang
The halo of the galaxy is __________. -a large, spherical region that is bright with densely packed stars -a large, spherical region that contains few bright stars -a ring-shaped region of stars that surrounds the galactic center
a large, spherical region that contains few bright stars
A hydrogen nucleus consists of __________. -a single proton -one proton and one electron -two protons and two neutrons
a single proton
One possible explanation for a galaxy's type invokes the angular momentum of the protogalactic cloud from which it formed. Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed due to other interactions, we'd expect this galaxy to be ______. -an irregular galaxy -a torn and incoherent galaxy -an elliptical galaxy -a spiral galaxy
a spiral galaxy
Which kind of object is the best standard candle for measuring distances to extremely distant galaxies? -parallax -a Cepheid variable star -a white dwarf supernova
a white dwarf supernova
Which model is most strongly supported by the data on the graph?
accelerating
Which model predicts the largest average distance between galaxies 6 billion years ago? -accelerating -coasting -critical -recollapsing
accelerating
Which of the models predict that galaxies should be getting farther apart now? (Keep in mind that now is located at time=0years on the graph.) -accelerating -coasting -critical -recollapsing -none of the models
accelerating coasting critical recollapsing
Essentially all the hydrogen nuclei that will ever exist in our universe were created __________. View Available Hint(s) -at the time that the first stars and galaxies began to form -by the time the universe was about 3 minutes old -at the end of the era of nuclei, when light began to -travel freely through the universe -shortly after the era of galaxies ended
by the time the universe was about 3 minutes old
Listed following are three possible models for the long-term expansion (and possible contraction) of the universe in the absence of dark energy. Rank each model from left to right based on the ratio of its actual mass density to the critical density, from smallest ratio (mass density much smaller than critical density) to largest ratio (mass density much greater than critical density).
coasting universe, critical universe, recollapsing universe
When a proton and an antiproton collide, they -repel each other. -fuse together. -convert into two photons.
convert into two photons.
Matter consisting of particles that differ from those found in atoms is generally referred to as ______________ matter.
exotic (or nonbaryonic)
The disk of the galaxy __________ than the bulge. -extends to much greater distances from the galactic center -is much smaller and closer to the galactic center
extends to much greater distances from the galactic center
Compared to when the cosmic microwave background was first released, the radiation of the cosmic microwave background today is __________. View Available Hint(s) -brighter and has most of its photons at longer wavelengths -fainter and has most of its photons at shorter wavelengths -fainter and has most of its photons at longer wavelengths -brighter and has most of its photons at shorter wavelengths
fainter and has most of its photons at longer wavelengths
Each data point represents a single white dwarf supernova that has been observed. The data points that appear farthest to the left on the graph represent the white dwarf supernovae that are the __________. -farthest away from us -most luminous -brightest in our sky -most recent in the history of the universe
farthest away from us'
Young stars can only be found in areas where there is ongoing star formation, and star formation requires the presence of __________. -gas and dust -globular clusters -spiral arms
gas and dust
A massive object can distort the light of more distant objects behind it through the phenomenon that we call _________________.
gravitational lensing
The primary source of a quasar's energy is -chemical energy. -nuclear energy. -gravitational potential energy.
gravitational potential energy.
Most globular clusters are located in the _____ of the galaxy. -bulge -disk -halo
halo
Where would you expect to find stars with the highest proportions of elements heavier than hydrogen and helium? -in the bulge -in the disk -in the halo
in the disk
Which of these forms of radiation passes most easily through the disk of the Milky Way? -red light -blue light -infrared light
infrared light
Models show that the _____________ of the universe is better-explained when we include the effects of dark matter along with the effects of luminous matter.
large-scale structure
The charge of an antiproton is -negative -neutral -positive
negative
Which of the following does not provide strong evidence for the Big Bang theory? -observations of the cosmic microwave background -observations of the amount of hydrogen in the universe -observations of the ratio of helium to hydrogen in the universe
observations of the amount of hydrogen in the universe
Old stars are generally __________. -of low mass and red -of high mass and blue -of any mass and any color
of low mass and red
Halo stars (green) are?
oldest stars, globular clusters, stars with the smallest abundance of heavy elements, stars whose orbits can be inclined at any angle
Clouds of gas and dust that are currently giving birth to stars are found in _____. -only the disk -only the halo -both the disk and halo
only the disk
Matter made from atoms, with nuclei consisting of protons and neutrons, represents what we call ____________________ matter.
ordinary (or baryonic)
Spiral galaxy:
protogalactic cloud has high angular momentum, most protogalactic gas settles into a disk
Which model is most clearly ruled out by the data on the graph? -accelerating -coasting -critical -recollapsing
recollapsing
Which of the models predict that galaxies will eventually get closer together in the future? -accelerating -coasting -critical -recollapsing -none of them
recollapsing
Listed following are four models for the long-term expansion (and possible contraction) of the universe. Rank the models from left to right based on their predictions for the average distance between galaxies five billion years from now, from smallest to largest. youngest to oldest
recollapsing universe, critical universe, coasting universe, accelerating universe
Two ways in which the starting conditions in a protogalactic cloud might cause it to become an elliptical (rather than spiral) galaxy are if the cloud begins with either: -relatively little angular momentum or relatively high density -relatively low mass and a -relatively high abundance of heavy elements -relatively high angular momentum or relatively low density. -relatively high mass and a relatively low abundance of heavy elements
relatively little angular momentum or relatively high density
The _________________ of spiral galaxies provide strong evidence for the existence of dark matter.
rotation curves
Observations indicated that over billions of years, galaxies in general tend to change from _________. -smaller and bluer to larger and redder -larger and bluer to smaller and redder -smaller and redder to larger and bluer -larger and redder to smaller and bluer
smaller and bluer to larger and redder
Elliptical galaxy:
stars form rapidly as the protogalactic cloud shrinks, protogalactic cloud rotates very slowly, a galaxy collision strips away gas, protogalactic cloud has high density
Which of these pieces of evidence supports the idea that inflation really happened? -the enormous size of the observable universe -the apparently "flat" geometry of the universe -the large amount of dark matter in the universe
the apparently "flat" geometry of the universe
As gravity shrunk the protogalactic cloud that gave birth to our galaxy, the first region to take shape was _____. -the disk -the halo
the disk
The basic difference between the disk and halo in shape is __________. -the disk is flat and the halo is spherical -the halo is flat and the disk is spherical -the disk rotates in one direction and the halo rotates precisely opposite the disk
the disk is flat and the halo is spherical
Which of the following structures exhibits clear, organized rotation patterns? -the disk of a spiral galaxy -the halo of a spiral galaxy -an elliptical galaxy -all of the above
the disk of a spiral galaxy
A quasar's spectrum is hugely redshifted. What does this large redshift tells us about the quasar? -the composition of the quasar -the type of host galaxy in which the quasar resides -the size of the quasar's central, supermassive black hole -the distance to the quasar
the distance to the quasar
We measure the mass of the black hole at the galactic center from: -the orbits of stars in the galactic center. -the orbits of gas clouds in the galactic center. -the amount of radiation coming from the galactic center.
the orbits of stars in the galactic center.
Which of the following does inflation help to explain? -the origin of hydrogen -the origin of galaxies -the origin of atomic nuclei
the origin of galaxies
The luminosity of a quasar is generated in a region the size of -the Milky Way. -a star cluster. -the solar system.
the solar system.
Consider Object 1 with temperature 10 K and Object 2 with temperature 20 K. According to the laws of thermal radiation __________. -the spectrum of Object 1 has a shorter peak wavelength than the spectrum of Object 2 -the spectrum of Object 2 has a shorter peak wavelength than the spectrum of Object 1 -both objects have spectra with the same peak wavelength
the spectrum of Object 2 has a shorter peak wavelength than the spectrum of Object 1
Which of the following does inflation help to explain? -the uniformity of the cosmic microwave background -the amount of helium in the universe -the temperature of the cosmic microwave background
the uniformity of the cosmic microwave background
Consider this statement from Part A: "Photons of the cosmic microwave background have traveled through space for almost 14 billion years." This statement follows from our model of the Big Bang, because the Big Bang model is based on the idea that __________. -photons of the cosmic microwave background were produced by the first stars that existed in the early universe -microwave photons could have been produced only by the heat of the Big Bang -the universe began very hot and dense and has been cooling as it expands -the universe has always had the 2.73 K temperature that we seen in the cosmic microwave background today
the universe began very hot and dense and has been cooling as it expands
One of the inferred statements from Part A is that "Large-scale structure grew around density variations present in the early universe." Observational evidence that such density variations really existed comes from the fact that the cosmic microwave background exhibits __________. -a perfect thermal radiation spectrum -patterns that are a precise match to the patterns of ---large-scale structure that we observe in the universe today -tiny temperature variations in different directions -a temperature of 2.73 K
tiny temperature variations in different directions
When the ultraviolet light from hot stars in very distant galaxies finally reaches us, it arrives at Earth in the form of -X rays. -slightly more energetic ultraviolet light. -visible light.
visible light.
Disk stars (yellow) are?
youngest stars, the Sun, stars that all orbit in nearly the same plane, high-mass stars
High density tends to lead to more rapid star formation in a protogalactic cloud. Why does this rapid star formation tend to lead to an elliptical galaxy, rather than a spiral galaxy? -Stars that form early in a galaxy's history tend to have orbits with more random inclinations. -Rapid star formation means that there may not be enough gas left to make a disk. -Elliptical galaxies are characterized by higher rates of ongoing star formation than spiral galaxies.
Rapid star formation means that there may not be enough gas left to make a disk.
During the history of the universe, what important event occurred about 380,000 years after the Big Bang? -Space-time rapidly expanded during a brief period of inflation. -Light began to travel freely through the universe. -Most matter in the early universe was annihilated by antimatter. -The first massive supernova explosions occurred.
Light began to travel freely through the universe.
Classify each statement below as an observation or as an INFERENCE based on the current Big Bang model.
Photons of the cosmic microwave background have traveled through space for almost 14 billion years. The cosmic microwave background is radiation left over from the Big Bang. Fusion during the universe's first five minutes produced 75% hydrogen and 25% helium (by mass). Large-scale structure grew around density variations present in the early universe.
