Galaxies The Basic Element of Cosmology. Warm Up Please complete a K-W-L chart for the topic of...

GalaxiesGalaxies

The Basic The Basic Element of CosmologyElement of Cosmology

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Please complete a K-W-L chart for Please complete a K-W-L chart for the topic of galaxies.the topic of galaxies.

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1.1. What was the Hubble “Deep Field” What was the Hubble “Deep Field” project?project?

2.2. What did it discover?What did it discover?

3.3. What type of galaxy is our Milky What type of galaxy is our Milky Way galaxy?Way galaxy?

Edwin Hubble WebquestEdwin Hubble Webquest

http://www.nisk.k12.ny.us/faculty/http://www.nisk.k12.ny.us/faculty/hughes/Hubble3/hughes/Hubble3/edwin_hubble_web_quest.htmedwin_hubble_web_quest.htm

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1.1. What is a galaxy?What is a galaxy?2.2. What did Charles Messier do to link his name to What did Charles Messier do to link his name to

galaxies?galaxies?3.3. Who was Edwin Hubble and what did he do?Who was Edwin Hubble and what did he do?4.4. What are the three types of galaxies?What are the three types of galaxies?5.5. What is the difference between an E0 elliptical What is the difference between an E0 elliptical

galaxy and an E7?galaxy and an E7?6.6. What is the difference between an Sa spiral What is the difference between an Sa spiral

galaxy and an Sc?galaxy and an Sc?7.7. Draw and label the Hubble Galaxy Classification Draw and label the Hubble Galaxy Classification

scheme!scheme!

Deep Field The most important The most important picture ever taken?picture ever taken?

Hubble Ultra-deep FieldHubble Ultra-deep Field

Out beyond our galaxy…Out beyond our galaxy…

Out beyond our galaxy, the depths of Out beyond our galaxy, the depths of space is filled with other star space is filled with other star systems. Some are like our own.systems. Some are like our own.

GalaxiesGalaxiesWe call these star systems galaxies. We call these star systems galaxies. Galaxies come in many shapes and sizes. Galaxies come in many shapes and sizes. Some galaxies are egg-shaped with clouds Some galaxies are egg-shaped with clouds of stars evenly spread throughout.of stars evenly spread throughout.

GalaxiesGalaxiesSome galaxies are completely irregular in Some galaxies are completely irregular in shape.shape.

GalaxiesGalaxiesGalaxies not only differ in size and shape, but the Galaxies not only differ in size and shape, but the also differ in their content. Some galaxies are also differ in their content. Some galaxies are young and some are old.young and some are old.

What Is a Galaxy?What Is a Galaxy?

A A galaxygalaxy is an is an immense cloud of immense cloud of millions or billions of millions or billions of stars. Each star while stars. Each star while following its own orbit following its own orbit is locked in place by is locked in place by the gravitational the gravitational influence of all the influence of all the other stars in its other stars in its galaxy. Each galaxy is galaxy. Each galaxy is an independent and an independent and isolated star system.isolated star system.

Early ObservationEarly Observation

Because galaxies are Because galaxies are so distant, they are so distant, they are difficult to see with the difficult to see with the unaided eye. The unaided eye. The closest galaxy to our closest galaxy to our Milky Way is over Milky Way is over 150,000 light years 150,000 light years away. Al-Sufi, a away. Al-Sufi, a Persian astronomer, Persian astronomer, noted observing the noted observing the M31 (Andromeda) M31 (Andromeda) galaxy in the 10galaxy in the 10thth century. century.


1919thth century century Frenchman Charles Frenchman Charles Messier, studied Messier, studied comets. While looking comets. While looking for them he noticed a for them he noticed a number of faint, number of faint, diffuse patches of diffuse patches of light. To avoid light. To avoid confusing them with confusing them with comets in the future comets in the future he began to assign he began to assign them numbers. them numbers. Galaxies are still Galaxies are still referred to by their referred to by their “M” or Messier “M” or Messier number.number.


Other astronomers came Other astronomers came along, such as William along, such as William Herschel and John Dryer Herschel and John Dryer and created their own and created their own catalog. It became catalog. It became known as the New known as the New General Catalog or General Catalog or “NGC” for short. Some “NGC” for short. Some galaxies appear in both galaxies appear in both catalogs and therefore catalogs and therefore have two names. M82 is have two names. M82 is the same galaxy as NGC the same galaxy as NGC 30343034

Edwin HubbleEdwin Hubble

While today we know While today we know that galaxies are that galaxies are immense star immense star systems, the idea was systems, the idea was not widely accepted not widely accepted until the 1920’s. It until the 1920’s. It was a graduate was a graduate student at the student at the University of Chicago University of Chicago that would define the that would define the nature of galaxies. nature of galaxies. That man was Edwin That man was Edwin Hubble.Hubble.

Edwin HubbleEdwin HubbleEdwin Hubble noticed that when he looked at Edwin Hubble noticed that when he looked at galaxies that they looked quite different. galaxies that they looked quite different. However, many shared certain characteristics. However, many shared certain characteristics. Hubble used these similarities the categorize all Hubble used these similarities the categorize all galaxies.galaxies.

Types of GalaxiesTypes of Galaxies

Hubble defines three basic types of Hubble defines three basic types of galaxies: galaxies: the spiral galaxy,the spiral galaxy, the the elliptical galaxy and the irregular elliptical galaxy and the irregular galaxy. galaxy. These are often denoted by These are often denoted by the letters S, E and Irr, respectively.the letters S, E and Irr, respectively.

Subtypes of Galaxies/EllipticalSubtypes of Galaxies/Elliptical

Hubble subdivided the Hubble subdivided the elliptical elliptical galaxiesgalaxies (denoted as E). He ranked (denoted as E). He ranked them from E0 to E7. E0 galaxies had them from E0 to E7. E0 galaxies had zero eccentricity while E7 are highly zero eccentricity while E7 are highly elliptical.elliptical.

The Hubble Tuning ForkThe Hubble Tuning Fork

Galaxy E0 and E1Galaxy E0 and E1

Spiral GalaxiesSpiral Galaxies

Spiral galaxies (S) consist of central Spiral galaxies (S) consist of central bulges surrounded by sweeping bulges surrounded by sweeping spiral arms emanating from their spiral arms emanating from their centers. Hubble classified them from centers. Hubble classified them from Sa to Sd. Sa galaxies have large Sa to Sd. Sa galaxies have large central bulges and tightly wound central bulges and tightly wound arms while Sd galaxies have small arms while Sd galaxies have small central bulges with loosely wound central bulges with loosely wound spiral arms.spiral arms.

The Hubble Tuning ForkThe Hubble Tuning Fork

Subtypes of Galaxies/BarredSubtypes of Galaxies/Barred

Hubble recognized subgroups within the Hubble recognized subgroups within the major types as well. The first of these is major types as well. The first of these is the the barred spiral galaxy barred spiral galaxy (denoted SB). (denoted SB). Barred spiral galaxies have arms that Barred spiral galaxies have arms that emerge from an elongated central region. emerge from an elongated central region. Barred spirals are ranked from a to d, with Barred spirals are ranked from a to d, with SBa galaxies having large bulges and SBa galaxies having large bulges and tightly wound arms to SBd galaxies having tightly wound arms to SBd galaxies having very small bulges with very loosely wound very small bulges with very loosely wound arms.arms.

Barred Spiral Galaxies: SBaBarred Spiral Galaxies: SBa

Barred Spiral Galaxies: SBbBarred Spiral Galaxies: SBb

Barred Spiral Galaxies: SBcBarred Spiral Galaxies: SBc

Irregular GalaxiesIrregular Galaxies

S0 GalaxiesS0 Galaxies

S0 galaxies are those with nuclei surrounded by a S0 galaxies are those with nuclei surrounded by a disk-like structure without arms. The S0 galaxy disk-like structure without arms. The S0 galaxy shares properties of both spiral and elliptical shares properties of both spiral and elliptical galaxies and seems to bridge the gap between galaxies and seems to bridge the gap between the two major types of galaxies. the two major types of galaxies.

Hubble introduced the S0 class long after his Hubble introduced the S0 class long after his original classification scheme had been original classification scheme had been universally adopted largely because he noticed universally adopted largely because he noticed many highly flattened objects that otherwise had many highly flattened objects that otherwise had the properties of elliptical galaxies. the properties of elliptical galaxies.

S0 GalaxiesS0 Galaxies


Galaxies differ in ways other than Galaxies differ in ways other than shape, too. They differ in content as shape, too. They differ in content as well. Spiral galaxies have a pretty well. Spiral galaxies have a pretty even mixture of both old (population even mixture of both old (population II) and new (population I) stars. II) and new (population I) stars. Usually, spiral galaxies contain about Usually, spiral galaxies contain about 15% of their mass as gas and dust15% of their mass as gas and dust

Elliptical GalaxiesElliptical Galaxies

Elliptical galaxies contain mostly Elliptical galaxies contain mostly older, population II stars. However, older, population II stars. However, they generally retain about half their they generally retain about half their mass as dust and gas suggesting mass as dust and gas suggesting that they still have vast amounts of that they still have vast amounts of stars to create.stars to create.

Evolution?Evolution?

The Hubble “tuning fork” was not The Hubble “tuning fork” was not created to imply an evolutionary created to imply an evolutionary path for galaxies. However, path for galaxies. However, astronomers have seen evidence of astronomers have seen evidence of galaxies changing types. The galaxies changing types. The collision between spiral galaxies of collision between spiral galaxies of similar mass is believed to create similar mass is believed to create elliptical galaxies.elliptical galaxies.

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1.1. What is galactic cannibalism?What is galactic cannibalism?

2.2. When one galaxy absorbs another, what When one galaxy absorbs another, what evidence do you see?evidence do you see?

3.3. If two spiral galaxies combine, what is the If two spiral galaxies combine, what is the end product?end product?

4.4. What is the closest galaxy to our own?What is the closest galaxy to our own?

5.5. What is the period-luminosity relationship?What is the period-luminosity relationship?

6.6. How does the period-luminosity help to How does the period-luminosity help to determine how far another galaxy is away determine how far another galaxy is away from us?from us?

Creation of GalaxiesCreation of Galaxies

Merger seems to play an important role in Merger seems to play an important role in the formation of galaxies. Primarily the formation of galaxies. Primarily amount star clusters. This may be one way amount star clusters. This may be one way to explain the vast difference in the ages to explain the vast difference in the ages of stars contained in spiral galaxies. As a of stars contained in spiral galaxies. As a smaller galaxy is absorbed by another, its smaller galaxy is absorbed by another, its stars are attracted to the central portion of stars are attracted to the central portion of the larger bulge. Galactic collision. It’s the larger bulge. Galactic collision. It’s called called galactic cannibalismgalactic cannibalism, the big eating , the big eating the small.the small.

Galactic MergerGalactic Merger

The Causes of Galactic TypesThe Causes of Galactic Types

Astronomers are still uncertain as to Astronomers are still uncertain as to the exact causes of galaxy types. the exact causes of galaxy types. Spiral disks rotate rapidly when Spiral disks rotate rapidly when compared to elliptical halos. compared to elliptical halos. However, halos and bulges in spiral However, halos and bulges in spiral galaxies rotate much more slowly. galaxies rotate much more slowly. Thus astronomers believe that more Thus astronomers believe that more than a galaxy’s rotation determines than a galaxy’s rotation determines its type.its type.

Many astronomers believe that Many astronomers believe that galaxies form from merger of like galaxies form from merger of like galaxies followed my galactic galaxies followed my galactic cannibalism. Streams of stars can be cannibalism. Streams of stars can be seen trailing stretching from our seen trailing stretching from our galactic halo. Astronomers think galactic halo. Astronomers think theses stars are the remnants of theses stars are the remnants of smaller galaxies absorbed by our smaller galaxies absorbed by our Milky Way.Milky Way.

Galactic CannibalismGalactic Cannibalism

This beautiful, eerie silhouette of dark dust clouds against This beautiful, eerie silhouette of dark dust clouds against the glowing nucleus of the elliptical galaxy NGC 1316 may the glowing nucleus of the elliptical galaxy NGC 1316 may represent the aftermath of a 100-million-year-old cosmic represent the aftermath of a 100-million-year-old cosmic collision between the elliptical and a smaller companion collision between the elliptical and a smaller companion galaxy galaxy

Can Merger Explain the Differences Can Merger Explain the Differences between spiral and Elliptical Galaxies?between spiral and Elliptical Galaxies?

Many astronomers say yes. Both Many astronomers say yes. Both observation and computer modeling observation and computer modeling are compelling astronomers to are compelling astronomers to propose a new hypotheses for the propose a new hypotheses for the origin of spiral and elliptical galaxies. origin of spiral and elliptical galaxies. The theory should say that new The theory should say that new galaxies are born as disk-like galaxies are born as disk-like systems lacking a central bulge.systems lacking a central bulge.

Subsequent collisions and mergers Subsequent collisions and mergers with other star systems create with other star systems create elliptical galaxies. This theory has elliptical galaxies. This theory has added attractions as well. added attractions as well. Many astronomers once believed Many astronomers once believed that galaxies were formed from one that galaxies were formed from one creation event. But, looking at the creation event. But, looking at the bulge of our galaxy, you see stars of bulge of our galaxy, you see stars of various ages throughout.various ages throughout.

A massive black hole hidden at the center of A massive black hole hidden at the center of nearby galaxy, Centaursus A, feeds on a nearby galaxy, Centaursus A, feeds on a smaller galaxy in a spectacular collision.smaller galaxy in a spectacular collision.

Merger ModelMerger Model

With each merger, the left over gas With each merger, the left over gas from the cannibalized galaxy would from the cannibalized galaxy would gravitate to the center and begin to gravitate to the center and begin to form new stars. This accounts for form new stars. This accounts for the stars of various ages existing the stars of various ages existing there.there.

Merger ModelMerger Model

Another feature of the merger model Another feature of the merger model is that it also explains large spiral is that it also explains large spiral galaxies. When a large spiral galaxy galaxies. When a large spiral galaxy merges with an elliptical galaxy, the merges with an elliptical galaxy, the elliptical galaxy becomes the bulge elliptical galaxy becomes the bulge of the new spiral galaxy.of the new spiral galaxy.

Measuring the Properties of Measuring the Properties of GalaxiesGalaxies

Galaxies are Galaxies are separated by separated by enormous distances. enormous distances. The closest galaxy to The closest galaxy to our own is the Large our own is the Large Magellanic Cloud Magellanic Cloud about 150,000 light about 150,000 light years away. The years away. The distances are so great distances are so great that using parallax will that using parallax will not work to determine not work to determine distance.distance.

Candle PowerCandle Power

One of the techniques used to One of the techniques used to measure the size of the Milky Way measure the size of the Milky Way was “standard candles” of was “standard candles” of luminosity, discussed in Chapter 15 luminosity, discussed in Chapter 15 (The Milky Way). The most reliable (The Milky Way). The most reliable sources of known standard candles is sources of known standard candles is the “Cepheid variable” (Chapter 13). the “Cepheid variable” (Chapter 13).

Techniques for Measuring DistancesTechniques for Measuring Distances

CepheidsCepheidsCepheids are convenient to use for several Cepheids are convenient to use for several reasons. One, the are very bright, reasons. One, the are very bright, averaging about 1 million times the Sun’s averaging about 1 million times the Sun’s luminosity. They can be seen a very long luminosity. They can be seen a very long way away.way away.

CepheidsCepheids

Because Cepheids Because Cepheids are variable, are variable, astronomers can astronomers can use the period-use the period-luminosity luminosity relationship to relationship to determine exactly determine exactly how bright the how bright the variables are.variables are.

Red-shift and the Hubble ConstantRed-shift and the Hubble Constant

We know that when We know that when we look at other we look at other galaxies, the galaxies, the spectrum from spectrum from those galaxies is those galaxies is red-shifted. This is red-shifted. This is due primarily to the due primarily to the Universe Universe expanding. This expanding. This was first noticed by was first noticed by Vesto Slipher.Vesto Slipher.

Red-shift and the Hubble ConstantRed-shift and the Hubble ConstantOthers, like Hubble, also noticed that the dimmer Others, like Hubble, also noticed that the dimmer the star (i.e. the farther away the star), the larger the star (i.e. the farther away the star), the larger the red-shift. The speed that a galaxy moves the red-shift. The speed that a galaxy moves away from us (“V”), its away from us (“V”), its recessional velocityrecessional velocity, , increases with distance (“D”).increases with distance (“D”).

The Hubble lawThe Hubble law

Hubble defined the relationship with the Hubble Hubble defined the relationship with the Hubble law which says:law which says:

V=HD, whereV=HD, where

V = Recessional Velocity, in kilometers/secondV = Recessional Velocity, in kilometers/second

D = Distance, in parsecs (3.26 million light-years) D = Distance, in parsecs (3.26 million light-years) andand

H = Hubble Constant (70 km/sec/Mpc)H = Hubble Constant (70 km/sec/Mpc)

The Hubble ConstantThe Hubble Constant

The Hubble Constant The Hubble Constant created lots on created lots on controversy initially. controversy initially. To calibrate the To calibrate the formula, you have to formula, you have to know both the know both the distance and velocity distance and velocity of at least a few of at least a few galaxies. The solution galaxies. The solution was to simply assign was to simply assign the number 70 the number 70 km/sec/Mpc. km/sec/Mpc.

Measuring the Diameter of a Measuring the Diameter of a GalaxyGalaxy

To determine the diameter of a To determine the diameter of a galaxy, use the formula:galaxy, use the formula:

d = d = 22ADAD where:where:

360360d=diameterd=diameter

A=angular size A=angular size

D=distanceD=distance

Measuring the Mass of a GalaxyMeasuring the Mass of a Galaxy

We can use Kepler’s third law. The We can use Kepler’s third law. The orbital velocity tells you the mass. orbital velocity tells you the mass. There is one problem though. When There is one problem though. When you add up all the mass that we see, you add up all the mass that we see, it does not equal the mass indicated it does not equal the mass indicated by our galactic motion. by our galactic motion. It is always It is always less.less.

Why Less?Why Less?How is it that our galaxy is more How is it that our galaxy is more massive than the sum of all that we massive than the sum of all that we see? Easy, there is stuff out there see? Easy, there is stuff out there we can’t see. It’s called we can’t see. It’s called dark matterdark matter!!

Dark MatterDark Matter

Dark matter is what scientists Dark matter is what scientists believe accounts for the discrepancy believe accounts for the discrepancy between the mass we see and the between the mass we see and the mass needed to make our galaxy mass needed to make our galaxy move as it does. How much are we move as it does. How much are we talking here? Maybe 10 times more talking here? Maybe 10 times more massive. We are only seeing on massive. We are only seeing on average about 10% of a galaxies average about 10% of a galaxies mass. mass.

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