Astronomy Final

Define or describe: Red Dwarf and Brown Dwarf

"substars" too small to sustain fusion. Bigger than planets, 75:25 H/He ration. Classes L, T, Y. Cool in temp. - extremely low mass, no fusion in cores, not actually stars.

Define or describe: Galactic or "Open" Cluster

A cluster of up to several thousand stars; open clusters are found only in the disks of galaxies and often contain young stars.

Define or describe: Protostar

A contracting cloud of gas and dust with enough mass to form a star.

Define or describe: Supernova Remnant

A glowing, expanding cloud of debris from a supernova explosion

Define or describe: Galaxy

A huge group of single stars, star systems, star clusters, dust, and gas bound together by gravity.

Define or describe: Schwarzschild Radius

A measure of the size of the event horizon of a black hole

Define or describe: Accretion Disk

A rapidly rotating disk of material that gradually falls inward as it orbits a starlike object (e.g. white dwarf, neutron star, or black hole)

What are the requirements for life to form?

A source of nutrients (atoms and molecules) from which to build living cells, energy to fuel the activities of life weather from sunlight chemical reactions or the heat of Earth itself, and liquid wate

Define or describe: Globular Cluster

A spherically shaped cluster of up to a million or more stars; globular clusters are found primarily in the halos of galaxies and contain only very old stars.

Define or describe: Gamma Ray Burst

A sudden burst of gamma ray's from deep space; such bursts apparently come from distant galaxies, but their precise mechanism is unknown.

Define or describe: Spectral Type

A way of classifying a star by the lines that appear in its spectrum; it is related to surface temperature. The basic spectral types are designated by a letter (OBAFGKM, with O for the hottest stars and M for the coolest) and are subdivided with numbers from 0 through 9.

How is the HR Diagram used to determine the age of a star cluster?

An H-R diagram plots stars according to their surface temperatures (or spectral types) and luminosities. Stars spend most of their lives fusing hydrogen into helium in their cores, and stars in this stage of life are found in the H-R diagram in a narrow band known as the main sequence. Giants and supergiants are to the upper right of the main sequence and the white dwarfs are to the lower left.

Define or describe: Black Hole

An object whose gravity is so strong that nothing can escape

Define or describe: Apparent vs. Absolute Magnitude

Apparent: A measure of the apparent brightness of an object in the sky, based on the ancient system developed by Hipparchus. Absolute: A measure of an object's luminosity; defined to be the apparent magnitude the object would have if it were located exactly 10 parsecs away.

Define or describe: Standard Candle

Bright stars (giants, supergiants, novae) can be used as distance indicators Large globular clusters and supernovae are of consistent brightness so they, too, can be used to determine distances to more distant galaxies

Define or describe: Molecular Cloud

Cool, dense interstellar clouds in which the low temperatures allow hydrogen atoms to pair up into hydrogen molecules (H2)

Define or describe: Theory of Relativity

Einstein's theories that describe the nature of space, time, and gravity

Is the universe expanding or contracting? Is it speeding-up or slowing-down?

Expanding. Speeding up.

Approximately how long has life existed on Earth?

Fossil evidence suggests 3.5 billion years ago. Carbon isotope evidence pushes this date to more than 3.85 billion years ago.

Groups, Clusters, and Superclusters.

Group: a few to a few dozen galaxies bound together by gravity Cluster: a few dozen or more galaxies bound together by gravity, bigger than a group Supercluster: the largest known structures in the universe, consisting of many clusters of galaxies, groups of galaxies, and individual galaxies.

Hubble's Law, the Hubble Constant, and how they are used

Hubble's Law: expresses a relationship between galaxy speeds and distances, which allows us to determine a galaxy's distance from its speed. Hubble Constant: the gradient of a graph of galaxy speed vs. distance

What determines whether a spiral or elliptical galaxy forms?

If the gas cloud was slowly rotating, then the collapsing gas cloud formed most of its stars before the cloud could flatten into a disk. The result was an elliptical galaxy. If the gas cloud was rotating faster, then the collapsing gas cloud formed a disk before most of the stars were made. The result was a spiral galaxy. The rate of star formation may be the determining factor in what type of galaxy will form.

What makes interstellar travel difficult?

Interstellar travel remains well beyond our technological capabilities, because of the technological requirements for engines, the enormous energy needed to accelerate spacecraft to speeds near the speed of light, and the difficulties of shielding the crew from radiation.

Beyond Earth, where is the next most likely place to find life?

Mars

Define or describe: The relationship between Luminosity, Mass, and Lifetime

Mass-luminosity relation: More massive stars are much brighter Mass-lifetime relation: As mass increases, the main sequence lifetime decreases

Why might the velocities of some galaxies not "obey" Hubble's Law?

Nearly all galaxies experience gravitational tugs from other galaxies, and these tugs alter their speeds from the values predicted by Hubble's Law.

Have we yet discovered life beyond the Earth?

No

Where are we in the Milky Way?

Our sun, the Earth, and all the other planets in our solar system reside within this Orion Arm.

In what constellation do we look to view toward the Galactic center? What kind of object do we believe exists in the Galactic center?

Sagittarius. Black hole.

SETI

Search for Extra Terrestrial Intelligence. Effort to detect signals- such as radio or laser communication- coming from civilizations o other worlds.

Define or describe: E = mc2. What does it mean? What are some beneficial applications and dangerous applications in the real world?

Shows that the increased relativistic mass (m) of a body comes from the energy of motion of the body- that is, its kinetic energy (E)—divided by the speed of light squared (c squared) This equation expresses the fact that mass and energy are the same physical entity and can be changed into each other.

Define or describe: OBAFGKM

Spectral type in order from hottest to coolest stars based on surface temperature. "Oh Be A Fine Guy, Kiss Me!"

Compare Spiral, Elliptical, and Irregular galaxies.

Spiral: The disks are filled with cool gas and dust, interspersed with hotter ionized gas, and usually display spiral arms. Looks like a flat white disk with yellowish buldges at the center. Elliptical: Redder, rounder, and often elongated like a football.Contain very little cool gas and dust, but often contain very hot ionized gas. Irregular: A galaxy with an undefined shape; neither disklike or rounded.

Define or describe: Mass Loss

Stellar mass loss is a phenomenon observed in some massive stars. It occurs when a triggering event causes the ejection of a large portion of the star's mass. Stellar mass loss can also occur when a star gradually loses material to a binary companion or into interstellar space.

Approximately, what masses of stars form the following kinds of objects: Supergiants, White Dwarfs, Neutron Stars, Black Holes, Red Dwarfs, Brown Dwarfs.

Supergiant- at least 10 solar masses White Dwarf- comparable to the sun Neutron Stars

Define or describe: Luminosity

The amount of energy radiated by a star per unit time, i.e. the power radiated by the star. Luminosity depends on the surface temp T and surface area A of the star. Given by L = σAT⁴. The constant σ is the Stefan-Boltzmann constant.

Compare and contrast the "Dots on a Balloon" and "Raisins in a Cake" models of the expansion of the universe.

The ballon's spherical surface has no center and no edges, just as no city is the center of the Earth's surface and no edges exist where you could walk or sail off Earth. We can represent galaxies with plastic dots attached to the ballon, and we can make out model universe expand by inflating the balloon. A cake has a center and edges that grow into empty space as it bakes.

Where did elements heavier than H and He come from?

The big bang created hyrdogen, helium, and trace amounts of lithium. The other elements have been created inside of stars through the process called fusion. Our sun will fuse elements through carbon and oxygen, but it will stop there. It's not big enough to fuse carbon and oxygen together to form iron. A really big star, a supergiant, will create iron in its core. Eventually, the iron builds up and the internal pressure causes an explosion called a supernova. At the moment of that explosion, many other elements are created (also through fusion) and all of them are scattered out into space to form new stars and planets.

Define or describe: Event Horizon

The boundary that marks the "point of no return" between a black hole and the outside universe.; events that occur within the event horizon can have no influence on our observable universe.

What happens if galaxies collide?

The collisions are so tame that they are usually just referred to as 'mergers'. Because of the huge amount of stuff in a galaxy they have a strong gravitational influence. This can cause them to interact with each other as they get close together. In mergers we see galaxies pull and twist each other, stretching out huge bulks of material. This can change the structure of galaxies, destroying things like spiral arms, resulting in more globular types.

Define or describe: Nova

The dramatic brightening of a star that lasts for a few weeks and then subsides; it occurs when a burst of hydrogen fusion ignites in a shell on the surface of an accreting white dwarf in a binary system

What kind of galaxy is the Milky Way and how do we know?

The name of our galaxy, a spiral galaxy that contains about 400 billion stars

Define or describe: Singularity

The place at the center of a black hole where, in principle, gravity crushes all matter to an infinitely tiny and dense point

Define or describe: Main Sequence Turnoff

The point on a cluster's H-R diagram where its stars turn off from the main sequence; the age of the cluster is equal to the main-sequence lifetime of the stars at the main-sequence turnoff point

Define or describe: Main sequence

The prominent line of points (representing main-sequence stars) running from the upper left to the lower right on an H-R diagram.

Liquid water and the "Habitable Zone".

The region around a star in which it is possible for a plaent to have "just right" conditions for surface liquid water.

Describe the Mass-Luminosity Relationship. L depends on M to what power?

The relation between the luminosity and the mass of a main sequence star, L ∝ Mⁿ, where 3 < n < 4. It can be used to explain why massive stars spend little time on the main sequence.

Define or describe: Neutron Star

The small dense remains of a high mass star after a super nova.

What will be the ultimate fate of our Universe?

The universe is doomed to expand forever, its galaxies receding even more quickly into an icy, empty future.

Define or describe: What is the difference between a planet and a brown dwarf?

Ultimately, the International Astronomical Union considers any object high enough to fuse deuterium a brown dwarf, while objects with less than that 13-Jupiter mass are considered planets.

Compare the age of the Universe, galaxies, Milky Way, Sun, and Earth.

Univserse: 13.82 billion years Milky Way: 13.21 billion years Sun: 4.6 billion years Earth: 4.5 billion years

Drake Equation

What is reasonable number of civilizations in our Galaxy that we could communicate with; The great number of stars in our Galaxy is the largest indication of the possibility of extraterrestrial life in our Galaxy N = R ✕ fp ✕ nh ✕ fl ✕ fi ✕ fc ✕ L

Define or describe: Helium burning

When the temperature in the core of a star reaches about 100 million degrees, three colliding helium nuclei can fuse to form a carbon nucleus. This set of reactions is also called the triple alpha process. Helium burning occurs after the star has evolved off the Main Sequence, when it is a red giant.

Define or describe: White Dwarf

White dwarfs are exposed cores of stars that have already died, meaning they have no further means of generating energy through fusion. The hot, compact corpses of low-mass stars, typically with a mass similar to that of the Sun compressed to a volume the size of Earth.

Define or describe: Interstellar Dust Cloud

a cloud of gas and dust between the stars

Define or describe: Gaseous Nebula

a cluster of stars within an intricate cloud of gas and dust

Define or describe: Tidal Force

a force that occurs when the gravity pulling on one side of an object is larger than that on the other side, causing the object to stretch

Define or describe: Quasar

a massive and extremely remote celestial object, emitting exceptionally large amounts of energy, and typically having a starlike image in a telescope. It has been suggested that quasars contain massive black holes and may represent a stage in the evolution of some galaxies.

Primordial Soup

a solution rich in organic compounds in the primitive oceans of the earth, from which life is hypothesized to have originated.

Define or describe: Cepheid Variable

a star whose luminosity changes periodically due to contractions and expansions of its surface. Has a period of variation of the luminosity and the peak luminosity. Thus, knowledge of the period gives the peak luminosity L which, together with the known peak apparent brightness b, gives the distance d through b = L / 4πd².

Define or describe: Inflation

a sudden and dramatic expansion of the universe thought to have occurred at the end of the GUT era.

Define or describe: Binary Star System

a system that contains two stars

Define or describe: Conservation of Angular Momentum

an objects angular momentum cannot change unless it transfers angular momentum to or from another object

How do brown dwarfs fit into the grand scheme of planets and stars?

astronomical object that is intermediate between a planet and a star. The difference between brown dwarfs and stars is that, unlike stars, brown dwarfs do not reach stable luminosities by thermonuclear fusion of normal hydrogen. Both stars and brown dwarfs produce energy by fusion of deuterium (a rare isotope of hydrogen) in their first few million years. The cores of stars then continue to contract and get hotter until they fuse hydrogen. However, brown dwarfs prevent further contraction because their cores are dense enough to hold themselves up with electron degeneracy pressure.

Is the Universe Open or Closed Universe? How does this relate to its mass density?

but if the universe is flat and the density of matter is low -- including visible matter, invisible matter, and ordinary energy (which is equivalent to matter) -- something must provide the missing density. That something is the cosmological constant, or some other form of dark energy.

How does "carbon chemistry" relate to life in the universe?

carbon is the only element capable of supporting life chemistry

Define or describe: Large Scale Structure

generally refers to the structure of the universe on size scales larger than that of clusters of galaxies

Define or describe: Supergiant

giants and supergiants are stars that have exhausted their core supplies of hydrogen for fusion and are undergoing other forms of fusion at a more rapid rate as they near the ends of their lives.

Why do you and I, and atoms not fly apart as the universe expands?

gravity

Define or describe: Dark Matter

matter that is too cold to radiate, and so cannot be detected. It has been invoked to solve the puzzle of the missing mass of the universe. As much as 90% of the mass of the universe may be in the form of dark matter.

Define or describe: Dark Energy

name sometimes given to energy that could be causing the expansion of the universe to accelerate

How were the elements made in the early universe?

nucleosynthesis

Why is the night sky (looking out into the universe) "dark"?

olbers paradox

Define or describe: Pulsar

rotating neutrons stars emitting radio waves

Why is there a "Main Sequence"?

stars on the main sequence are fusing hydrogen into helium in their cores. A stars position along the main sequence depends on its mass: High-mass stars are at the upper left and masses become progressively smaller as we move toward the lower right. Lifetimes vary in the opposite way, because higher-mass stars live shorter lives.

How large is the Milky Way, and how far is it between galaxies?

the Milky Way is about 1,000,000,000,000,000,000 km (about 100,000 light years) across. Depending upon which galaxies that are in consideration, the distance between two galaxies can be almost zero to 13 billion light years

Define or describe: Parallax

the apparent shifting of an object against the background, due to viewing it from different positions

Define or describe: Nucleosynthesis

the cosmic formation of atoms more complex than the hydrogen atom.

Define or describe: CNO Cycle

the cycle of reactions by which intermediate- and high-mass stars fuse hydrogen into helium

Define or describe: Planetary Nebula

the ejection of mass from an exploding red giant star

Define or describe: Supernova

the explosion of a star

Define or describe: Gravitational Lens

the magnification or distortion (into arcs, rings, or multiple images) of an image caused by light bending through a gravitational field, as predicted by Einstein's theory of relativity

Define or describe: Nuclear Fusion

the process in which two (or more) smaller nuclei slam together and make one larger nucleus

Define or describe: Cosmic Microwave Background

the remnant radiation from the Big Bang, which we detect using radio telescopes sensitive to microwaves (which are short-wavelength radio waves)

Describe how the Rotation Curve relates to how mass is distributed.

the rotation curve of a galaxy is the variation in the orbital circular velocity of stars or gas clouds at different distances from the center. The manner in which the velocities vary with radius reflects the distribution of mass in the galaxy

Define or describe: Interstellar Dust

tiny solid flecks of carbon and silicon minerals found in cool interstellar clouds; they resemble particles of smoke and form in the winds of red giant stars

What was the Miller Experiment and why is it important?

The Urey-Miller experiment took place in 1953 permformed by Stanly Miller. The experiment was so important because it showed that an organic compound can be created in a laboratory with two inorganic compounds at the proper conditions.