Help
Options
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't Know
Remaining cards (0)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
LAST PHYS TEST
| Question | Answer |
|---|---|
| Edwin Hubble was able to show that the Andromeda Nebula is a galaxy independent of our Milky Way. How was he able to do this? Be sure to describe the special type of star that played a key role in his analysis. | Edwin Hubble was able to show that the Andromeda Nebula is a galaxy independent of the Milky Way by using observations of Cepheid variable stars to estimate the distance to Andromeda. |
| Harlow Shapley used RR Lyrae stars in globular clusters to map out the spatial extent of the Milky Way. How was he able to do this? | He found that the clusters have a roughly spherical distribution in space, but the center of the sphere lies far from the Sun. The globular clusters are now known to map out the true extent of the luminous portion of the Milky Way Galaxy. |
| What evidence is there for the presence of dark matter in the Milky Way? | The flat rotation curve of the Milky Way indicates that our galaxy is imbedded within a giant halo of matter that does not emit or reflect light. |
| Describe some possible candidates for dark matter. | black holes, sub-atomic particles, white dwarfs, brown dwarfs. |
| What is the Hubble "tuning fork" diagram? | The Hubble tuning fork diagram is an illustration of the different classes of galaxies |
| were thought to be possible collections of distant stars that were comparable to the Milky Way | spiral nebulae |
| argued that these spiral nebulae were in our Galaxy | Harlow Shapley |
| argued that these spiral nebulae were very distant | Heber Curtis |
| Thankfully, a new method of measuring distances had recently been discovered. This involved .... stars | Cepheid |
| their periods of variation range from 1 to 50 days | Cepheid stars |
| n 1908, astronomer Henrietta Leavitt measured the period and luminosity of a large number of Cepheid stars – to measure luminosity (or absolute magnitude), she also had to estimate the ....... to these stars | distance |
| She discovered a relationship (or correlation) between the period of a Cepheid and its average luminosity | Henrietta Leavitt |
| the most luminous Cepheids have the longest periods | the period-luminosity relationship |
| Knowing the period-luminosity relationship, it is possible to use Cepheids to measure ...... in astronomy | distances |
| Cepheids can be identified by their ..... of variation | periods |
| the period-luminosity relationship gives an estimate of the luminosity (or .................) of each star | absolute magnitude M |
| The average ................... of each Cepheid can also be measured | apparent magnitude (m) |
| The equation m-M=5 log(d/10) then gives the ........... | distance |
| An American astronomer named ................. took on the challenge of resolving the debate, by trying to measure the distance to the Andromeda nebula. | Edwin Hubble |
| Hubble photographed the Andromeda Nebula and detected several Cepheid stars within it • Careful measurements yielded a distance estimate of about ................... This demonstrated conclusively that Curtis was correct | 1 million light years! |
| We now know that the Universe contains many ..... of galaxies, of which the Milky Way is but one. | billions |
| Each galaxy contains millions or billions of ...... | stars |
| Galaxies also contain ........... and ............ | interstellar matter and dark matter |
| A galaxy is held together by the mutual ............ attraction of its stars and other matter | gravitational |
| Galaxies are usually separated from each other by vast regions of mostly empty space – hence, galaxies are often called ...... | island universes |
| In the year 1785, English astronomer William Herschel constructed the first 3-D map of the Milky Way. • To do this, he needed to find the ........ of the stars | distances |
| Herschel found that the Milky Way has a flattened, disk-like shape. In addition, he concluded that the Sun lies at or near the ...... The latter is now known to be wrong | center |
| Herschel’s method had several shortcomings • The most important was that, at the time, astronomers did not realize how important ......... is | extinction |
| In order to make a more realistic map of the Milky Way, an improved technique for estimating distances was needed. ...... stars were well suited to this task | RR Lyrae |
| All RR Lyraes have approximately the same average ...... brightness | intrinsic |
| have approximately the same average intrinsic brightness – they are about 100 times more luminous than the Sun | RR Lyraes |
| RR Lyraes are often found in ....... | globular clusters |
| In 1917, Harlow Shapley identified RR Lyraes in 93 globular clusters – this allowed him to measure distances to these clusters • He found that these clusters were distributed in a roughly ......... throughout the Milky Way | spherical manner |
| he estimated that the Milky Way was about 100,000 light years in diameter • He found that the Sun was not at the center! – instead, he estimated that the Sun was about 25,000 light years from the center of the Milky Way | Harlow Shapley |
| We now know that our Galaxy has three distinct components: | The Galactic disk, The Galactic bulge, The Galactic halo |
| most of the Milky Way’s young stars, star-forming regions, and interstellar matter are found here | The Galactic disk |
| this dense region contains many types of stars and interstellar matter | The Galactic bulge |
| the halo is made up of relatively old stars and clusters – the halo contains very little interstellar matter | The Galactic halo |
| ..... and ...... stars orbit the center of the Galaxy – however, they orbit in random directions – these stars often pass through the disk | Halo; bulge |
| ..... stars also orbit the center of the Galaxy – however, their orbits are more orderly – they generally revolve in the same plane | Disk |
| The central region of the Milky Way’s bulge is called the ...... | nucleus |
| this region contains a very high density of stars, and looks very unusual at different wavelengths | nucleus |
| The nucleus is difficult to see in ..... light, since it is heavily obscured by dust | optical |
| ........ light is less susceptible to extinction – observations of stars close to the center of the nucleus indicate that they are orbiting at very high speeds | Infrared |
| ........ observations indicate the presence of a bright radio source, known as Sagittarius A* • These observations indicate that the nucleus harbors a supermassive black hole with a mass of about 4 million M | Radio |
| How much mass is contained within the Milky Way? One method of estimating the mass is to use the Sun’s .... | orbit |
| How much mass is contained within the Milky Way? | equivalent to about 100 billion Suns |
| an unseen component of matter – this is now known as ....... | dark matter |
| Current measurements indicate that about .....of the Milky Way’s matter is dark matter! | 90% |
| Edwin Hubble was the first to establish the existence of ...... beyond the Milky Way. In fact, he pioneered a whole new branch of astronomy – the study of galaxies. | galaxies |
| Hubble divided galaxies into three main categories: | Spiral galaxies (S) – Elliptical galaxies (E) – Irregular galaxies (Irr) |
| The Milky Way and Andromeda are both examples of spiral galaxies. • All spiral galaxies contain a flattened .... | disk |
| Spiral galaxies also contain a .....and a ...... | bulge; halo |
| The appearance of a spiral galaxy depends on its ........ (or inclination) with respect to us | orientation |
| if a spiral galaxy’s disk is aligned towards us, it is called an ....... spiral | edge-on |
| if its disk is at right angles to us, it is called a ......spiral | face-on |
| Hubble specified three different types of spiral galaxies | a type, b type, c type |
| (Sa galaxies) have the largest bulges and the mostly tightly wound spiral patterns | a type spirals |
| (Sb galaxies) have average sized bulges and moderately wound spiral arms | b type spirals |
| (Sc galaxies) have the smallest bulges and the most loosely wound spirals | c type spirals |
| Some spiral galaxies have a feature called a .... | bar |
| A bar is made up of ...... | stars and interstellar matter |
| Spiral galaxies with bars are denoted SB rather than S this gives three new sub-classes: | SBa, SBb, and SBc |
| .......... galaxies are the second major Hubble type. | Elliptical |
| These galaxies have no spiral structure, and very little in the way of interstellar matter | Elliptical |
| Stars in elliptical galaxies orbit in ....... directions | random |
| Elliptical galaxies have a range of possible ...... | elongations |
| circular elliptical galaxies are called ... galaxies | E0 |
| – the most elongated ellipticals are called E7 galaxies | E7 |
| The third major class of galaxies contains a wide variety of galaxies, none of which fall into the spiral or elliptical categories. These are known as | irregular (Irr) galaxies. |
| These galaxies lie midway between elongated ellipticals (E7) and bulge-dominated spirals (Sa and SBa) | S0 (or lenticular) galaxies. |
| the ...... galaxies tend to be ellipticals | largest/luminous |
| Hubble’s tuning fork diagram shows Hubble’s overall classification scheme. What it doesn’t show is that, for a given type, galaxies have a large range in .... and .... | size; mass. |
| Small galaxies are referred to as ........ | dwarf galaxies |
| most galaxies in the Universe are either ....... or ........ | dwarf irregulars or dwarf ellipticals |
| Like most giant galaxies, the Milky Way has ...... | satellites |
| The closest galaxy is the ...... dwarf irregular | Canis Major |
| The Milky Way’s largest satellites are called the ...... | Large and Small Magellanic Clouds. |
| The Milky Way’s largest satellites are called the Large and Small Magellanic Clouds. • Both of these galaxies are | dwarf irregulars |
| The Milky Way and its satellite galaxies form part of a small galaxy group called the | Local Group |
| The Local Group is dominated by two giant galaxies | the Milky Way – Andromeda |
| The Local Group is dominated by two giant galaxies – the Milky Way – Andromeda • These 2 galaxies are separated by about 2.5 million LY • Each has a number of smaller ...... | dwarf companions |
| Overall, the Local Group contains more than .... galaxies | 40 |
| As we look beyond the Local Group, we find that galaxies are not strewn at random throughout the Universe, nor are they isolated. In fact, most galaxies are found in ..... | groups |
| Most groups contain at least two giant galaxies, and some may contain several dozen giant galaxies • These giant galaxies are usually accompanied by a larger number of dwarf galaxies • The galaxies within a group are . to one another | gravitationally bound |
| Some galaxies are found in larger groups, called ..... | clusters |
| is a cluster of galaxy groups and clusters | supercluster |
| The Local Group is a member of the ...... | Local Supercluster |
| If two galaxies of similar size undergo a strong interaction, they will eventually merge to form a single galaxy. • This type of event is referred to as a | major merger |
| A major merger may take about a billion years to occur • During a merger, stars rarely collide with one another • However, clouds of interstellar matter will collide – this may trigger an intense burst of ..... | star formation |
| The Milky Way and Andromeda may merge in about ....... | 5 billion years |
| A rare but more spectacular event is a ...... | multiple merger |
| A rare but more spectacular event is a multiple merger. • This occurs when 3 or more galaxies merge together at roughly the same time • This phenomenon may be responsible for the equally rare ...... | ultra-luminous infrared galaxies |
| Soon after Hubble developed his system for classifying galaxies, astronomers discovered that a small fraction of these galaxies were quite distinct and unusual. • These particular galaxies are called ....... | active galaxies |
| active galaxies have ..... (central regions) which are much brighter than the nuclei of normal galaxies | nuclei |
| three main types of active galaxies (AGN): | Seyfert galaxies – Radio galaxies – Quasars |
| In 1943, an American radio astronomer named Carl Seyfert discovered a new class of galaxies. They are now known as ...... | Seyfert galaxies |
| Outside the nucleus, most of the light from a Seyfert galaxy is produced by .... | stars |
| Outside the nucleus, most of the light from a Seyfert galaxy is produced by stars – most of this light is in the optical part of the spectrum • Within the nucleus, most of the optical light is produced by .. close to the center galaxy | hot gas |
| Within the nucleus, most of the optical light is produced by hot gas that is very close to the center of the galaxy • This hot gas originally gives off most of its radiation in the form of ..... | X-rays |
| The spectra of Seyfert galaxies contain strong ...... due to ionized heavy elements (especially iron) | emission lines |
| The spectra of Seyfert galaxies contain strong emission lines due to ionized heavy elements (especially iron) – these emission lines are not seen in the spectra of normal spiral galaxies – these lines are due to emission from the .... | hot gas |
| By monitoring the ......... of Seyfert galaxies over time, astronomers discovered something very surprising! • The brightness of the nucleus can vary by large amounts – in some cases, the nucleus may double in brightness | brightness |
| Seyfert galaxy has a very bright nucleus, which is surrounded by hot, rapidly rotating gas. This gas is confined to a very small region. • This information indicates that there must be a very object at the center of a Seyfert galaxy. | massive but small |
| Elliptical galaxies can be active too. Active ellipticals have bright nuclei like Seyfert galaxies, but also emit lots of radio waves. Hence, they are called ..... | radio galaxies. |
| Normal stars very weak radio sources • By examining their spectra, Maarten Schmidt showed that they were way beyond the Milky Way itself (large redshift) implied were extremely luminous objects known as ..... | quasars |
| It appears that all active galaxies and quasars are fueled by the accretion of gas onto a ................. | supermassive black hole |
| the study of the origin and nature of the Universe itself. | Cosmology |
| In 1912, an American astronomer named Vesto Slipher obtained the spectra of many nearby spiral galaxies He noticed that their spectra were...... in wavelength | shifted |
| Vesto Slipher noticed that their spectra were shifted in wavelength • This was attributed to the relative motion between the spiral nebulae and us, which results in the ....... | Doppler effect |
| In the 1920’s, Edwin Hubble used Cepheids to measure the ....... to many spiral galaxies. He found a connection between a galaxy’s distance and the size of its ..... | distances; redshift |
| ........ galaxies have relatively small spectral redshifts | Nearby |
| ......... galaxies have relatively large redshifts | Distant |
| In fact, on average, redshift (and therefore recession velocity) is directly proportional to distance In fact, on average, redshift (and therefore recession velocity) is directly proportional to distance • this empirical relationship is known as | Hubble’s Law |
| Hubble’s Law has some very profound implications… • The most straightforward interpretation is that the space between galaxies is ........ in a uniform manner | expanding |
| In 1927, suggested that the Universe is expanding (“hypothesis of the primeval atom”). Early version of the Big Bang Theory. | Father Georges Lemaître |
| Hubble’s Law tells us that the Universe is expanding smoothly. With careful measurement, it is also possible to determine ..... it is expanding. | how fast |
| Ho is the ...... | Hubble Constant |
| Measuring the Hubble Constant: can be measured to very high precession, particularly for distant galaxies | Recession velocities |
| Measuring the Hubble Constant: ...... measurements are much more uncertain | Distance |
| The fact that the Universe is expanding implies that things were closer together in the past. In fact, we can use the Hubble constant to estimate the ...... of the Universe itself. | age |
| Measurements of the Hubble constant tell us ..... the Universe is expanding at present | how fast |
| rough estimate of the age of the Universe | about 14 billion years |
| The Universe is thought to have begun with a huge explosion known as the ...... | Big Bang |
| The redshift seen in spectra of distant galaxies is due to the expansion of the Universe, rather than the movement of galaxies through space. • This referred to as a ...... | cosmological redshift |
| If the rate of deceleration is large enough, the Universe might eventually stop expanding and begin to collapse – this scenario is referred to as a ..... | bound Universe |
| If the rate of deceleration is large enough, the Universe might eventually stop expanding and begin to collapse – this scenario is referred to as a bound Universe – this Universe would presumably end in a | Big Crunch |
| If the rate of deceleration is small enough, the Universe will expand forever – this is called an ........ | unbound Universe |
| Measuring Changes in the Expansion Rate: Modern day astronomers have been working hard to establish which scenario is correct. This can be done by ....... in the expansion rate of the Universe | measuring changes |
| Modern day astronomers have been working hard to establish which scenario is correct. This can be done by measuring changes in the expansion rate of the Universe. • The first such measurement came from astronomers studying distant ..... | carbon detonation supernovae |
| There must be an additional repulsive force at work • This mysterious force is sometimes referred to as .... | dark energy |
| The presence of dark energy is also relevant for answering another fundamental question: ...... | is the Universe infinite? |
| is the Universe infinite? | To answer this question, we need an accurate census of all the stuff in the Universe that can curve space • The measurement of this material is expressed using the cosmological density parameter, Omega (Ω) |
| If Ω > 1, the Universe has positive curvature and is | finite |
| If Ω = 1, the Universe is spatially flat and | infinite |
| If Ω < 1, the Universe is negatively curved and is | infinite |
| Everything you can see (i.e. ordinary matter) is only ~5% of the Universe! | 95% of the Universe is unknown!!! |
| Will The Universe Expand Forever? | Universe will expand forever at an increasing rate due to dark energy |
| 1. How would you determine the distance to a distant galaxy? | Hubble's Law, Red shift |
| 2. What is the Local Group? | the galaxy group that includes the Milky Way. |
| 3. What are the differences between the disk, halo, and bulge of the Galaxy? | The disk stars have nearly circular orbits The halo and bulge orbits are less organized: they vary from round to very elliptical, and don't lie on a plane |
| 4. What is the position of the Milky Way relative to the Local Supercluster? | in a small group of galaxies towards edge of relatively small super cluster on the outskirts |
| 5. How do astronomers determine the masses of galaxies? | By studying stellar motions in elliptical galaxies |
| 6. What evidence is there for dark matter on the scales of galaxies and clusters of galaxies? | Flat rotation curve in clusters and gravitational arc |
| 7. What are some of the candidates for dark matter? | Subatomic particles |
| 8. What were RR Lyrae and Cepheid stars used for? | to measure distance |
| 9. What are the four major types of galaxies? What differences/similarities exist between them? | Elliptical, spiral, barred spiral, and irregular. These types of galaxies are further divided into subcategories while at the same time other types of galaxies exist based on their size and other unique features |
| 10. What is the “tuning fork” diagram? | Classification of different galaxies |
| 11. What type of galaxies are the most luminous in the Universe? | Those that contain quasars are their centers. Partially elliptical galaxies |
| 12. What will most-likely happen to the Milky Way and the Andromeda Galaxy? | They will merge |
| 13. What is the Hubble Law? | The further away the greater the sectional velocity |
| 14. What is the cosmological redshift? | Expansion of space |
| 15. What is the cosmic microwave background? | Leftover heat from the Big Bang |
| 16. Why is the cosmic microwave background significant? | Represents one of the pillars of the Big Bang |
| 17. What is the observed evidence for the Big Bang? | Four pillars: hydrogens, leftover heat, expansion & evolves |
| 18. How can we determine when the Big Bang occurred? | Hubble's content |
| 19. What important discovery was made in 1998 that revolutionized our thinking regarding the expansion of the Universe? | Dark energy |
| 20. What is the source of energy that powers Active Galactic Nuclei? | supermassive black hole |
| 21. What evidence do we have that the energy source that powers quasars is small in size? | small space because of the variations of the light being short, so it makes it small in size for the time scale |
| 22. What lies at the heart of our Galaxy and how do we know? | Black hole; The power of the black hole is greater than anything else that has been found so far |
| 23. What is the critical density of the Universe? | The state of the universe if its total mass and energy density is greater than a specific value |
| 24. What are the three possible geometries of the Universe? | Positive, flat, and negative |
| 25. What is our present best estimate of the geometry of the Universe? | Flat, no curve |
Created by:
Edens