9 - hubble laowocki/phys133/9 - hubble law.pdf · 2018-09-28 · phys133 lab 9 the hubble law udel...

UDel Physics 1 of 8 Fall 2018

PHYS133 – Lab 9 The Hubble Law

Goals:

Find the relationship between the

redshift in spectra of distant

galaxies and the rate of the

expansion of the universe.

Use observations of the redshifts

of galaxies, along with their

coordinates in the sky, to produce

a three‐dimensional map of a

nearby region of the sky.

Understand how matter is

distributed on the largest scales in

the universe and appreciate some

of the difficulties involved in

making and interpreting large‐

scale maps of the universe.

What You Turn In:

Data section at the end of this

manual.

All printouts from the software.

Answers to the questions in this manual.

BackgroundReading:Background reading for this lab can be found in your text book (specifically, Chapters 16.2 and 18.3) and the

notes for the course.

Equipmentprovidedbythelab: Computer with Internet Connection • Project CLEA program “VIREO”

Equipmentprovidedbythestudent: Pen

Calculator

PHYS133 Lab 9 The Hubble Law


Background:

TheHubbleRedshiftDistanceRelation The late biologist J.B.S. Haldane once wrote: “The universe is not only [weirder] than we suppose, but [weirder] than we can suppose.” One of the weirdest things about the universe is that virtually all the galaxies in it (with the exception of a few nearby ones) are moving away from the Milky Way. This curious fact was first discovered in the early 20th century by astronomer Vesto Slipher, who noted that absorption lines in the spectra of most spiral galaxies had longer wavelengths (were “redder”) than those observed from stationary objects. Assuming that the redshift was caused by the Doppler shift, Slipher concluded that the red‐shifted galaxies were all moving away from us. In the 1920’s, Edwin Hubble measured the distances of the galaxies for the first time, and when he plotted these distances against the velocities for each galaxy he noted something even weirder: The further a galaxy was from the Milky Way, the faster it was moving away. Was there something special about our place in the universe that made us a center of cosmic repulsion? Astrophysicists readily interpreted Hubble’s relation as evidence of a universal expansion. The distance between all galaxies in the universe was getting bigger with time, like the distance between raisins in a rising loaf of bread. An observer on ANY galaxy, not just our own, would see all the other galaxies traveling away, with the furthest galaxies traveling the fastest. This was a remarkable discovery. The expansion is believed today to be a result of a “Big Bang” which occurred between 10 and 20 billion years ago, a date which we can calculate by making measurements like those of Hubble. The rate of expansion of the universe tells us how long it has been expanding. We determine the rate by plotting

the velocities of galaxies against their distances, and determining the slope of the graph, a number called the Hubble Parameter, H0, which tells us how fast a galaxy at a given distance is receding from us. So, Hubble’s discovery of the correlation between velocity and distance is fundamental in reckoning the history of the universe. Using modern techniques of digital astronomy, we will repeat Hubble’s experiment.

The technique we will use is fundamental to cosmological research these days. Even though Hubble’s first measurements were made three‐quarters of a century ago, we have still only measured the velocities and distances of a small fraction of the galaxies we can see, and so we have only a small amount of data on whether the rate of expansion is the same in all places and in all directions in the universe. The redshift distance relation thus continues to help us map the universe in space and time.

Figure 1: Hubble’s Constant



Procedure

PARTI:TheHubbleRedshiftDistanceRelation UsingtheHubbleRedshiftProgram Open the CLEA lab titled “VIREO” by double clicking on the Icon labeled VIREO.

1. Click on File ‐> Login. Enter the names of each group member and click OK and then YES.

2. Click on File ‐> Run “The Hubble Redshift‐Distance Relation”.

3. Click on Telescopes ‐> Optical and access the 4.0 m telescope.

4. Open the Dome and Turn the Telescope Control Panel On.

5. The telescope control panel will open (see below)

a. You must turn Tracking “On” in order to have the telescope stay pointed at the same place in the sky (i.e. compensate for the Earth’s rotation).

b. You can move the telescope by pressing the N, W, S, or E buttons.



c. By default, you’re are looking through the finder scope, you can change this by switching the View (right hand side). The central red box in the Finder view shows the field of view of your telescope. The small circle in Telescope view shows what data will be taken.

d. There are various instruments for taking data. We will use the Spectrometer.

6. Move the telescope to its first target by selecting Slew ‐> Observation Hot List ‐> Select from List. The galaxies will be listed.

a. Right Click on target and choose Slew to Selection.

b. Click OK in the Sky Coordinates box and confirm the slew.

This moves the telescope to the target galaxy.

7. Switch from Finder to telescope view. The galaxy should be centered in the Spectrometer (between the red lines).

8. Access the Spectrometer.

a. Click “Go”.

Depending on the object’s brightness (visual magnitude), it may take some time to build up a spectrum.

b. Once the Signal to Noise Ratio reaches 50 (or greater) you can stop recording.

c. Record the object name and its visual magnitude in your table.

d. Choose File ‐> Save Spectrum. You can keep the default file name.

9. Slew to the next target on the list and repeat step 8. Continue until you have data for all galaxies

10. Close the Spectrometer window.



11. On the main screen, go to Tools ‐> Spectrum Measuring. The Spectrum Measuring Engine will open.

a. Click File ‐> Data ‐ > Load Saved Spectrum, and load the first of your saved spectra.

b. Choose Comparison Spectrum ‐> Select… and pick the “Absorption lines in normal galaxies (H, K & G band)”

c. Use the slider, reset and controls to alight the red lines with the absorption bands.

d. Click File ‐> Data ‐> Record Measurements and click OK”

e. Complete this for all the spectra.

f. When all of the spectra are analyzed, File ‐> Exit Spectrum Measuring.

This will conclude the data taking part of the lab.

Analysis1. Open the Excel File “Excel Data Sheet for Hubble Law”. DO NOT EDIT OR CHANGE ANY CELLS WITH A BLUE

BACKGROUND (i.e., the Distance and Velocity columns).

2. You need to fill in the table with the Apparent Magnitudes and Redshifts for each galaxy you have measured. You can view this data in VIREO under Results Editors ‐> Observational Results ‐> Display/Print/Save Text

3. The excel file is setup such that it will calculate the Distances in Mega‐parsecs and Velocities in km/s. It will then use that to plot the data and the slope of the line of best fit will be the Hubble Constant.

4. You also need to set the absolute magnitude of the galaxies (the default is ‐20)

5. You should manually calculate the distance and velocity for the first galaxy (or one selected by your TA) in the space provided. You must submit your calculations.

5 /5 6

5

10 1M pc 10 pc

c 3.00 10 km/ s

m Md

zc

v

6. Print out this file when completed and submit with your lab report.



7. Use the Tools ‐> Isochrones tool to determine the age of your cluster by when the main sequence turnoff occurs.

a. Use all three parameters – Log(age/yr), Adjust B‐V and Metallicity to find the best fit for the cluster’s age.

b. Record this value (given in Gyr) in the upper right box.

8. Looking at your HR diagram, there are clearly some stars off in the Red giant/supergiant range. Identify them by using the B‐V color and V magnitudes.

Print out your data tables, diagrams and analysis and attach to your Write – up!



Names: _________________ Section: ______________ _________________ Date: ________________

Manually calculate the recession velocity and distance of one galaxy below: Determining the Age of the Universe

The Hubble Law, 0H Dv , can be used to determine the age of the universe. Using your average value of H,

calculate the recessional velocity of a galaxy which is 800 Mpc away.

Velocity of a galaxy 800 Mpc away: _______________________________km/sec Verify your velocity by looking it up on your Hubble diagram. You now have two important pieces of information:

1. How far away is the galaxy. 2. How fast it is moving away from us.

You can visualize the process if you think about a trip in your car. If you tell a friend that you are 120 miles away from your starting point and that you traveled 60 miles per hour, your friend would know you had been traveling TWO hours. That is your trip started two hours ago. You know this from the relationship:

Distance equals Rate ( or velocity ) * Time



which we can write as D t v or D

t v

Thus, 120 mi

2 hr60 mi / hr

Now let’s determine when the universe “started its trip”. The distance is 800 Mpc, but first convert Mpc into km because the rate, or velocity, is in km/sec.

800 Mpc = _____________________km Determine how many seconds ago the universe started:

_____________________secs There are about 3.15 x 107

seconds in one year. Convert your answer into years:

_____________________years The age of the universe is ____________________ years. SHOW MATH IN AN ORGANIZED FASHION.

MAKE SURE YOU ATTACH ALL DATA SHEETS AND GRAPHS

9 - hubble laowocki/phys133/9 - hubble law.pdf · 2018-09-28 · phys133 lab 9 the hubble law udel...

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