Exam 4
grand unified theories
(GUTs) physical theories that attempt to describe the four forces of nature as different manifestations of a single force
weakly interacting massive particles
(WIMPs) weakly interacting massive particles are one of the candidates for the composition of dark matter
central bulge
(or nuclear bulge) the central (round) part of the Milky Way or a similar galaxy
We receive a radio message from a civilization around a star about 40 lightyears from Earth? If we reply right away, how many years will it be between the time THEY sent the message and the time they receive our reply?
80
According to our textbook, roughly what percent of the mass and energy contents of the universe is made up of dark matter plus dark energy?
95%
The first satellite (spacecraft with instruments) to measure and confirm the cosmic microwave background was the:
COBE (COsmic Background Explorer)
If you wanted to write a complete "cosmic address" for yourself, including every location or structure you live in, which of the following would be that address?
Earth, the Solar System, the Milky Way Galaxy, the Local Group, the Virgo Supercluster
general theory of relativity
Einstein's theory relating gravity and the structure (geometry) of space and time
The astronomer who first solved the problem of the strange red-shifts seen in quasar spectra and thus helped us understand that the quasars must be distant objects was
Maarten Schmidt
Why is the use of Hubble's Law to measure distances to galaxies so important to astronomers?
Most galaxies are so far away, the only way to get distances to them is to use Hubble's Law
Galaxies that we see as they were 11 billion years ago or more, as compared to galaxies today, are generally
NOT is only an assumption, for which we don't have any real evidence yet
Astronomers can now report that active star formation was going on at a time when the universe was only 20% as old as it is today. When astronomers make such a statement, how can they know what was happening inside galaxies way back then?
NOT they look at a graph that shows the way galaxy redshifts change with time
What type of main-sequence star is most likely to become a black hole?
O
The two scientists who first discovered the cosmic microwave background radiation were:
Penzias and Wilson
The very strong source of radio waves at the center of our Galaxy is called
Sagittarius A
The standard bulbs (standard candles) that made it possible for astronomers to discover the acceleration in the expansion of the universe were
Type Ia supernovae
Astronomers today know a lot about the size and shape of the Milky Way Galaxy. Which of the following common objects most resembles the shape of our Galaxy?
a CD or DVD
event horizon
a boundary in spacetime such that events inside the boundary can have no effect on the world outside it—that is, the boundary of the region around a black hole where the curvature of spacetime no longer provides any way out
Objects orbiting around the center of the Milky Way obey Kepler's 3rd Law. This means that:
a cloud of gas or star that is further from the center will generally take more time to orbit
merger
a collision between galaxies (of roughly comparable size) that combine to form a single new structure
organic molecule
a combination of carbon and other atoms—primarily hydrogen, oxygen, nitrogen, phosphorus, and sulfur—some of which serve as the basis for our biochemistry
photosynthesis
a complex sequence of chemical reactions through which some living things can use sunlight to manufacture products that store energy (such as carbohydrates), releasing oxygen as one by-product
organic compound
a compound containing carbon, especially a complex carbon compound; not necessarily produced by life
Hubble constant
a constant of proportionality in the law relating the velocities of remote galaxies to their distances
gravitational wave
a disturbance in the curvature of spacetime caused by changes in how matter is distributed; gravitational waves propagate at (or near) the speed of light.
spiral galaxy
a flattened, rotating galaxy with pinwheel-like arms of interstellar material and young stars, winding out from its central bulge
deuterium
a form of hydrogen in which the nucleus of each atom consists of one proton and one neutron
Drake equation
a formula for estimating the number of intelligent, technological civilizations in our Galaxy, first suggested by Frank Drake
starburst
a galaxy or merger of multiple galaxies that turns gas into stars much faster than usual
elliptical galaxy
a galaxy whose shape is an ellipse and that contains no conspicuous interstellar material
irregular galaxy
a galaxy without any clear symmetry or pattern; neither a spiral nor an elliptical galaxy
According to the general theory of relativity, light and other radiation coming from a white dwarf or a neutron star should (and experiments show that it does) exhibit
a gravitational redshift
protein
a key biological molecule that provides the structure and function of the body's tissues and organs, and essentially carries out the chemical work of the cell
supercluster
a large region of space (more than 100 million light-years across) where groups and clusters of galaxies are more concentrated; a cluster of clusters of galaxies
How do astronomers know that there aren't significant amounts of dark matter within our solar system?
a lot of dark matter would affect the motions (orbits) of our spacecraft as the move through the solar system, and see no such effect
open universe
a model in which the density of the universe is not high enough to bring the expansion of the universe to a halt
closed universe
a model in which the universe expands from a Big Bang, stops, and then contracts to a big crunch
flat universe
a model of the universe that has a critical density and in which the geometry of the universe is flat, like a sheet of paper
RNA (ribonucleic acid)
a molecule that aids in the flow of genetic information from DNA to proteins
DNA (deoxyribonucleic acid)
a molecule that stores information about how to replicate a cell and its chemical and structural components
Which of the following types of objects (small or large) has NOT been ruled out as a potential source for dark matter in the Galaxy?
a new kind of subatomic particle
Which of the following is, to the best of our knowledge, in the habitable zone of its star:
a planet about 1.05 AU from a G-type main sequence star
galactic cannibalism
a process by which a larger galaxy strips material from or completely swallows a smaller one
What type of object shows the biggest redshift?
a quasar
void
a region between clusters and superclusters of galaxies that appears relatively empty of galaxies
black hole
a region in spacetime where gravity is so strong that nothing—not even light—can escape
Hubble's law
a rule that the radial velocities of remote galaxies are proportional to their distances from us
If you want to check on what conditions were like in the universe a few hundred thousand years after the Big Bang, what sort of instrument would it be best to use:
a satellite with infrared and microwave telescopes on board
Local Group
a small cluster of galaxies to which our Galaxy belongs
spiral arm
a spiral-shaped region, characterized by relatively dense interstellar material and young stars, that is observed in the disks of spiral galaxies
population I star
a star containing heavy elements; typically young and found in the disk
population II star
a star with very low abundance of heavy elements; found throughout the Galaxy
type Ia supernova
a supernova formed by the explosion of a white dwarf in a binary system and reach a luminosity of about 4.5 × 109 LSun; can be used to determine distances to galaxies on a large scale
inflationary universe
a theory of cosmology in which the universe is assumed to have undergone a phase of very rapid expansion when the universe was about 10-35 second old; after this period of rapid expansion, the standard Big Bang and inflationary models are identical
From which of the following will a wave of light show the greatest gravitational redshift:
a white dwarf
Factoring in everything we currently know about the history of the universe, our best estimate for the age of the universe is
about 13.8 billion years
Roughly how many galaxies make up our Local Group?
about 60 or so
dark energy
an energy that is causing the expansion of the universe to accelerate; the source of this energy is not yet understood
habitable environment
an environment capable of hosting life
gravitational redshift
an increase in wavelength of an electromagnetic wave (light) when propagating from or near a massive object
quasar
an object of very high redshift that looks like a star but is extragalactic and highly luminous; also called a quasi-stellar object, or QSO
extremophile
an organism (usually a microbe) that tolerates or even thrives under conditions that most of the life around us would consider hostile, such as very high or low temperature or acidity
thermophile
an organism that can tolerate high temperatures
In our modern view of the expansion of the universe, we understand that it is space that is stretching; individual galaxies don't speed away from each other as if they were rockets. In that case, why do galaxies show a red-shift?
as space stretches, the waves of radiation in space also stretch and their wavelength increases
Some astronomers searching for what the mysterious "dark matter" might be made of have pinned their hopes on MACHO's (MAssive Compact Halo Objects). What do they think these MACHO's are?
black holes, brown dwarfs, and white dwarfs in the regions outside the main disk of our Galaxy
How did Edwin Hubble establish that there are other galaxies, quite removed from the Milky Way Galaxy?
by observing a Cepheid variable in a nearby galaxy and using it to get the distance
When Einstein proposed his General Theory of Relativity, he suggested some pretty strange ideas about space, time, and gravity. How did scientists in 1919 show that Einstein's theory described the behavior of the real world and wasn't just a crazy hypothesis?
by observing starlight coming close to the Sun during an eclipse
According to the general theory of relativity, the presence of mass
causes a curvature (or warping) of spacetime
evolution (of galaxies)
changes in individual galaxies over cosmic time, inferred by observing snapshots of many different galaxies at different times in their lives
equivalence principle
concept that a gravitational force and a suitable acceleration are indistinguishable within a sufficiently local environment
Which of the following was not done by Edwin Hubble?
discovering the relationship between period and luminosity of a cepheid variable
Which type of galaxy is very difficult to see, but (astronomers recently realized) may be very common?
dwarf elliptical
Which type of galaxy is observed to contain mostly older stars?
elliptical
Where in space did the expansion of the universe begin?
everywhere at once
biomarker
evidence of the presence of life, especially a global indication of life on a planet that could be detected remotely (such as an unusual atmospheric composition)
Which of the following is a biomarker that could be used from an observatory around a nearby star, with the right equipment, to identify the Earth as a planet with life:
free oxygen in the Earth's atmosphere
When quasars "shine" (in visible light and other kinds of radiation) with a lot of energy, where (what location) does this huge amount of energy come from?
from an accretion disk around a supermassive black hole
active galactic nuclei (AGN)
galaxies that are almost as luminous as quasars and share many of their properties, although to a less spectacular degree; abnormal amounts of energy are produced in their centers
active galaxies
galaxies that house active galactic nuclei
What do the surveys of the three-dimensional distribution of groups of galaxies reveal about how groups and clusters of galaxies are organized?
galaxy groups are organized into huge filaments with great voids between them -- something like the structure one would see taking a cross-section of some soap bubbles
What objects did Harlow Shapley use as "signposts" to figure out the extent of the Milky Way Galaxy and the location of its center?
globular clusters
Scientists looking at an overview of physics today understand that there are four forces that govern all action in the universe. These four forces are the strong nuclear force, the weak nuclear force, electro-magnetism and
gravity
homogeneous
having a consistent and even distribution of matter that is the same everywhere
To map out how clusters of galaxies are distributed in the universe, astronomers needed to know where each cluster was in the sky AND
how far away from us each cluster was
In a distant galaxy, whose light is just arriving from 10 billion light years away, our spectroscope should reveal that the most common element is
hydrogen
anthropic principle
idea that physical laws must be the way they are because otherwise we could not be here to measure them
If we want to see what galaxies looked like at a time close to the beginning of the universe, where should we look?
in a direction away from the plane of the Milky Way, where we can see very faint galaxies that are more than 10 billion light years away
critical density
in cosmology, the density that is just sufficient to bring the expansion of the universe to a stop after infinite time
Where would you look for the youngest stars in the Milky Way Galaxy?
in the disk
How does a period of extremely fast inflation very early in the history of the universe explain the observation that the geometry of the universe looks flat (not curved) to us?
inflation increased the size of the universe so much that the resulting universe looks flat from any point of view
According to the Cosmological Principle, the universe
is isotropic and homogeneous
Which of the following is not true about the Local Group of galaxies (of which the Milky Way is a member)?
it has about a thousand member galaxies
If quasars are at the distances most astronomers believe they are, then (for the most luminous ones) their luminosities must be:
like the combined luminosity of a hundred trillion (1014) Suns
There is some irony in the fact that the Hubble Space Telescope has shown that Edwin Hubble's classification scheme for galaxy shapes only works in the later stages of the universe. What have really deep pictures (going way back in time) taken with the Hubble Telescope shown about galaxies long ago (in the first few billion years after the Big Bang)?
long ago, galaxy shapes were not (for the most part) regular and organized; galaxies looks chaotic and lumpy
hot dark matter
massive particles, not yet identified, that don't absorb, emit, or reflect light or other electromagnetic radiation; hot dark matter is faster-moving material than cold dark matter
Today, astronomers find compelling evidence that the energy source of the quasars and active galaxies is
matter falling toward a supermassive black hole at the center of a galaxy
In describing the universe using his equations of general relativity, Einstein assumed that it was isotropic (the same in all directions.) What recent observations have confirmed that the universe is isotropic on the large scale?
measurements of the 3-degree cosmic background radiation
cosmic microwave background (CMB)
microwave radiation coming from all directions that is the redshifted afterglow of the Big Bang
According to Hubble's Law, if two galaxies are not part of our Local Group, and galaxy B is three times farther away from us as Galaxy A, then Galaxy B will
move away from us three times faster than A
Astronomers have discovered a planet orbiting Proxima Centauri, the star closest to the Sun. This is a star of spectral type M, with 12% the mass of the Sun and 15% the size of the Sun. The habitable zone around this star would be
much closer to the star than the Sun's
In a globular cluster, astronomers (someday) discover a star with the same mass as our Sun, but consisting entirely of hydrogen and helium. Is this star a good place to point our SETI antennas and search for radio signals from an advanced civilization?
no, because such a star (and any planets around it) would not have the heavier elements (carbon, nitrogen, oxygen, etc.) that we believe are necessary to start life as we know it
dark matter
nonluminous mass, whose presence can be inferred only because of its gravitational influence on luminous matter; the composition of the dark matter is not known
Which of the following is not a way that astronomers can find how much dark matter there is in cluster of galaxies?
observe the radio waves coming from all dark matter; from the strength of the radio waves from each cluster, estimate the amount of dark matter needed to produce them
amino acids
organic compounds that are the molecular building blocks of proteins
Photosynthesis, once it was planet-wide, changed the atmosphere of the Earth by introducing a significant amount of
oxygen
Which band of the electromagnetic spectrum do astronomers suggest is likely to be the best (cheap, little competition from nature, penetrates atmospheres) for communication between civilizations around different stars?
radio waves
Today we know that what all quasars have in common is that they appear to be small sources of energy with
redshifts that indicate they are far away
Which of the following observations is a convincing argument for the idea that quasars are located inside galaxies?
relatively nearby quasars show "fuzz" around them with the same spectra and redshift as the quasar
Far away from a black hole (at the distance of another star), which of the following is a possible way to detect it?
search for flickering x-rays being given off from an accretion disk around the black hole, as it "eats" part of a neighbor star
cold dark matter
slow-moving massive particles, not yet identified, that don't absorb, emit, or reflect light or other electromagnetic radiation
Which of the following is a good summary of what most astronomers think about UFO reports in the popular media?
so far there is no scientific evidence that UFO's have anything to do with life outside the Earth
stromatolites
solid, layered rock formations that are thought to be the fossils of oxygen-producing photosynthetic bacteria in rocks that are 3.5 billion years old
Which of the following did NOT happen during the first few minutes after the Big Bang?
some very massive early stars formed
Our Milky Way Galaxy is what type of galaxy?
spiral
spacetime
system of one time and three space coordinates, with respect to which the time and place of an event can be specified
The new instrument that made it possible for Edwin Hubble to demonstrate the existence of other galaxies in the early 1920's was:
the 100-inch reflector on Mount Wilson
In which of the following domains of the universe have astronomers NOT found evidence for the presence of dark matter today?
the Solar System
How do astronomers currently think the amount of detectable (observable) matter in the universe compares to the amount of dark matter and dark energy?
the amount of detectable matter is far less than the amount of dark matter & energy
cosmological principle
the assumption that, on the large scale, the universe at any given time is the same everywhere—isotropic and homogeneous
Milky Way Galaxy
the band of light encircling the sky, which is due to the many stars and diffuse nebulae lying near the plane of the Milky Way Galaxy
gene
the basic functional unit that carries the genetic (hereditary) material contained in a cell
If a very distant galaxy looks blue overall to astronomers, from this they can conclude that:
the blue color indicates that they are still busy making stars. Young massive stars burn hotter and therefore bluer.
fusion
the building of heavier atomic nuclei from lighter ones
After the Big Bang, in order for the universe to become transparent to light and other electro-magnetic radiation, what had to happen?
the density of the universe had to decrease (to 1000 nuclei per cubic centimeter or less)
What observation in astronomy, made AFTER the discovery of quasars, was a big help to astronomers in figuring out what quasars really were?
the discovery that the Milky Way Galaxy has a black hole at the center with enough mass for 4 million Suns
accretion disk
the disk of gas and dust found orbiting newborn stars, as well as compact stellar remnants such as white dwarfs, neutron stars, and black holes when they are in binary systems and are sufficiently close to their binary companions to draw off material
A friend of yours who is a science fiction fan hears you talk about the fact that astronomers now believe that the mechanism for the large energy output of quasars involves a supermassive black hole. He challenges you, saying something like "Oh come on, every science fiction fan knows that nothing, not even light, can escape from a black hole! How can a black hole be an energy source?" How would you respond to his objection
the energy we see from quasars comes from regions where matter is falling in; these regions are still outside the event horizon
Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the
the faster it is moving away from us
Which of the following events in cosmic history is the most recent?
the formation of life on Earth
An astronomer is observing a distant galaxy which looks blue. Which of the following can she conclude from this observation?
the galaxy must have a lot of star formation going on at the time we are seeing it
differential galactic rotation
the idea that different parts of the Galaxy turn at different rates, since the parts of the Galaxy follow Kepler's third law: more distant objects take longer to complete one full orbit around the center of the Galaxy
The model of the universe that involves an enormous increase of scale during a very short time in the early universe is called:
the inflationary universe model
How do astronomers explain the energetic jets that come out of quasars and active galactic nuclei in opposite directions?
the jets are "spit out" from the chaotic accretion disks of supermassive black holes in directions that are perpendicular to the disk
dark matter halo
the mass in the Milky Way that extends well beyond the boundary of the luminous stars to a distance of at least 200,000 light-years from the center of the Galaxy; although we deduce its existence from its gravity, the composition of this matter remains a mystery
In the first direct detection of gravitational waves by LIGO in 2015, the waves came from
the merger of two black holes
astrobiology
the multidisciplinary study of life in the universe: its origin, evolution, distribution, and fate; similar terms are exobiology and bioastronomy
supermassive black hole
the object in the center of most large galaxies that is so massive and compact that light cannot escape from it; the Milky Way's supermassive black hole contains 4.6 millions of Suns' worth of mass
What leads astronomers to conclude that the proto-galactic cloud (the cloud from which our Galaxy formed) was roughly spherical?
the oldest stars in the Galaxy (Population II stars, globular clusters) form a spherical halo around the Galaxy; they outline the original shape of the cloud that gave the Galaxy birth
halo
the outermost extent of our Galaxy (or another galaxy), containing a sparse distribution of stars and globular clusters in a more or less spherical distribution
singularity
the point of zero volume and infinite density to which any object that becomes a black hole must collapse, according to the theory of general relativity
mass-to-light ratio
the ratio of the total mass of a galaxy to its total luminosity, usually expressed in units of solar mass and solar luminosity; the mass-to-light ratio gives a rough indication of the types of stars contained within a galaxy and whether or not substantial quantities of dark matter are present
habitable zone
the region around a star in which liquid water could exist on the surface of terrestrial-sized planets, hence the most probable place to look for life in a star's planetary system
isotropic
the same in all directions
SETI
the search for extraterrestrial intelligence; usually applied to searches for radio signals from other civilizations
According to Einstein's general theory of relativity, the stronger a star's gravity,
the slower time runs near it
multiverse
the speculative idea that our universe is just one of many universes, each with its own set of physical laws
The fastest speed at which we might communicate with another technological civilization among the stars (according to our present understanding of science) is
the speed of light
The first time that astronomers observed both gravitational waves and electro-magnetic waves from the same event, what they were observing was:
the spiraling toward each other of two neutron stars
What is the strongest known force in the universe?
the strong nuclear force
cosmology
the study of the organization and evolution of the universe
cosmological constant
the term in the equations of general relativity that represents a repulsive force in the universe
Big Bang
the theory of cosmology in which the expansion of the universe began with a primeval explosion (of space, time, matter, and energy)
lithium
the third element in the periodic table; lithium nuclei with three protons and four neutrons were manufactured during the first few minutes of the expansion of the universe
When astronomers say that the groups of galaxies are distributed isotropically, they mean that
the way galaxies are arranged in space looks the same in all directions
Edwin Hubble developed a classification scheme for galaxies. By what characteristic did he classify galaxies?
their shape
If quasars often resemble little blue stars, what was it about them that so surprised astronomers when they were discovered?
their spectral lines were at first hard to recognize and then turned out to have large redshifts
Recently, astronomers have observed stars and other objects that orbit the center of the Milky Way Galaxy farther out than our Sun, but move around faster than we do. How do astronomers think such an observation can be explained?
there must be a great deal of invisible dark matter outside the orbit of the Sun whose gravitational pull explains the faster motions we see out there
How do astronomers measure the mass that the Galaxy contains inside the orbit of the Sun?
they measure the distance to the center of the Galaxy and the period of the Sun's orbit and then use Kepler's Third Law
Astronomers have established that quasars and active galaxies have a lot of mass at their centers in a very small volume of space. Why can't this mass be in the form of a cluster of stars that are quite close to each other?
to fit as much matter into the cluster as we observe, the stars in the cluster must be so close to each other they would merge into a superstar and soon collapse into a black hole
Which of the following objects is considered useful to astronomers as a "standard bulb" or "standard candle" for determining distances?
type Ia supernovae
According to astronomers, which of the following places in the outer parts of our solar system might be a reasonable place for life to exist?
under the ice of Jupiter's moon Europa
After several decades of observation, astronomers have concluded that quasars are
very powerful and compact sources of energy at the centers of distant galaxies
What have we learned from the work of Harlow Shapley and others about the location of the Sun in the Milky Way Galaxy?
we are in the disk of the Galaxy, about 3/5 of the way from the center
Where is the approximate location of the Sun in the Milky Way Galaxy?
we are in the disk of the Galaxy, about 3/5 of the way from the center
Which of the following questions is NOT part of what astronomers call the "cosmic haystack problem" in receiving messages from other civilizations in space?
we don't know how to receive signals in the wavelength range that is the most likely for interstellar communications
redshift
when lines in the spectra are displaced toward longer wavelengths (toward the red end of the visible spectrum)
photon decoupling time
when radiation began to stream freely through the universe without interacting with matter
