The Dynamics of Visible Objects in the Universe

How do we measure distance of these objects ?

Distance Measure a) Laser beam + mirrors

Earth-Moon distance was determined

Stellar Parallax

Caused by the heliocentric orbit of Earth

Parallax phenomenon + trigonometry stellar distances

This equation can be summarized as: or

Distance Measure b) Parallax

(a) The geometry of stellar parallax. For observations made 6 months apart, the baseline is twice the Earth—Sun distance, or 2 A.U. (b) The parallactic angle is usually measured photographically (the shift is greatly exaggerated in this drawing) .

http://lifeng.lamost.org/courses/astrotoday/CHAISSON/AT317/HTML/AT31701.HTM

Stellar Parallax

.7”

Text

Distance to star = 4.4 ly

D

d(istance)

D/d = angle (in radians)

Distance Measure b) Parallax

biased for “near-by” objects

Nearest NeighborsA plot of the 30 closest

stars to the Sun, projected so as to reveal their three-

dimensional relationships. Notice

that many are members of multiple-star systems. All lie

within 4 pc (about 13 light years) of Earth.

http://lifeng.lamost.org/courses/astrotoday/CHAISSON/AT317/HTML/AT31701.HTM

How do we know the dynamics of these objects ?

Phenomenon exhibited by a moving source of light:

Doppler effect

Which direction is the wave source moving?

Blue shift

Red shift

Doppler Shift Method:

Limitation: wavelength shifts

are tiny

Doppler Shift Method:

example: star wobbles in response to

planet orbiting it

observer

Emitted Star Light(intrinsic)

Observed Star Light(detected)

Doppler Shift of lightwavelength stretched object moving away the observer

wavelength compacted object is moving towards the observer

800 nm400 nm

Red ShiftReceding

“- v”: TOWARD the observed

“+v”: AWAY from the observed

“Galaxy Crash” can be loaded from the following website:

http://burro.cwru.edu/JavaLab/GalCrashWeb/main.html

select option “applet” and then you can specify some parameters of the 2 galaxies whose interactions you would like to model

The Dynamics of Visible Objects in the Universe

Key Concepts for Week-4, Class-1:

(what You need to know, as You will be tested on this material): 

Term “Proxy” Proxy for distance (mirrors & laser light, parallax)

Proxy for velocity (Doppler Shift Method) Doppler Shift Phenomenon / Method

Blue shift (moving towards) & Red shift (moving away) Atomic line spectrum (atomic fingerprint) as an aid

for applying Doppler Shift Method Value of Models in Astronomy

Lesson 8

The Birth of the Universe

Edwin Hubble’s tests reveal “Steady State Theory” of the Universe is Invalid

Proxy for velocity Doppler shift

Distance Measurement Parallax or other more sophisticated methods

Proxy for velocity Doppler shift

Distance Measurement Parallax or other more sophisticated methods

Hubble’s Law states galaxies are moving away from us.

SADLY, HUBBLE DIDN’T REALIZE THE IMPLICATION OF HIS DISCOVERY…

Fall 2007

The Ramifications of Hubble’s Law

Monseigneur Georges Lemaître

The Cosmic Microwave Background Radiation (CMB) is Additional Evidence for the Big Bang & Expanding Universe

background temperature of the Universe

So, there are 3 lines of evidence for the “Big Bang” Theory

Galaxies are moving away from usCosmic Microwave Background Radiation

Observed abundance of Helium matches the expectations of Helium based on the Big

Bang theory

We Can Visualize this with a Model

What are Models?

help us visualize aspects of nature that seem fairly abstract & build intuition

Models provide a conceptual framework for interpreting the data we collect.

They help us understand what is happening in the otherwise (to us) invisible world.

Exploring Hubble’s Law

Balloon Activity

Tips before you start:

• Don’t place marks too close to the neck or far end of the balloon - it doesn’t stretch uniformly in these areas

• Blow the balloon up as much as reasonably possible!

• Measure the distance between points along the shortest path

• When done, add your data points to the plot on the board. Each group use a different type of symbol/color so we can distinguish the data sets.

Modeling the Big Bang and the Expansion of the Universe with a Balloon

Modeling the Big Bang and the Expansion of the Universe with a Balloon

How is it a good model?How is it a bad model?Are there better models?

Modeling the Big Bang and the Expansion of the Universe with a Balloon

How is it a good model?

- it produces an expansion law qualitatively similar to Hubble's Law, in that the velocity of expansion (with respect to the origin) is proportional to distance (from the origin)

- it shows that no matter where you draw the origin (i.e., no matter your location), you will always observe that all points are moving away from YOU

Modeling the Big Bang and the Expansion of the Universe with a Balloon

How is it a bad model?

The balloon is finite

The surface of the balloon is only 2-dimensional + curved

The marks drawn on the balloon also expand (they shouldn’t, as galaxies are held by gravity)

The balloon may not expand uniformly (especially if not inflated fully)

Modeling the Big Bang and the Expansion of the Universe with a Balloon

rising loaf of breadbetter, since the raisins (“galaxies”) don’t expand as loaf expands

Another model

This plot can be thought of as a calibrating relationship for using velocity as a proxy to measure distance

Velocity is proportional to distance

What does it mean that distance and velocity are proportional?

Can we trace the expansion back to the point where it began?

If the Universe is expanding, does that also mean that the Galaxy and the Solar system are expanding?

balloon is stretched (multiplicatively) by some factor -we need to think of the Universe the same way

that “point” is now the whole balloon/whole Universe... so no.

What does it mean that distance and velocity are proportional?

Can we trace the expansion back to the point where it began?

If the Universe is expanding, does that also mean that the Galaxy and the Solar system are expanding?

no, they are bound by gravity - they represent parts of the Universe that have been gravitationally extracted (for now) from the initial expansion

What is the importance of Hubble’s law?

• Universe expands, changes over time• Universe had a beginning in time: observable Universe is

finite – we can measure its age!• once relationship is established, it can be used as an easy

way to measure distances to galaxies

Think to the sinusoidal wave drawn on the balloon…

wavelengths get stretched

longer wavelength radiation becomes more red

Galaxy voids and Galaxy Clusters

Expansion competes with gravity:

• galaxies = places where gravity “wins”

• voids = places where expansion “wins”

The Birth of the UniverseKey Concepts for Week-4, Class-2:

(what You need to know, as You will be tested on this material): 

Hubble’s Diagram & Hubble’s Law The significance of Hubble’s constant (inverse time)

Implications behind Hubble’s Law Big Bang Theory

Evidence for Big Bang Theory Recall modeling the expansion of the Universe with Balloons

(recall good & bad aspects of this model).