Topic 5: History and Structure of the Universe

Interesting Fact: When you look at the stars, you are actually looking back in time.

This is because light from stars and galaxies in far away distances take a long time, about thousands or even millions of years, before it can reach the Earth. The largest star is said to be 4,900 light years away from the earth. If you are looking at it now, you are actually seeing how it was 4,900 years ago! Cool!

Real picture taken in Hawaii

25 Crazy Facts About the Universe

The Universe – all the planets, stars and galaxies• The sun is the closest star to Earth • How do stars form?

1. All stars start out as a Nebula: huge cloud of hydrogen gas and dust

2. The gas begins to collide, collapse and heat up due to it’s own gravitational attraction.

3. When the core temperature becomes 10 000 000oC, nuclear fusion begins.

4. EMR and energy is produced, which prevents the star from collapsing

• All stars shine because of nuclear fusion

Eagle Nebula – Pillars of Creation.

Omega Nebula (M17)

Watch the lion king to see how stars are created

Nuclear Fusion• Nuclear fusion is a process in which 2

smaller nuclei join to form a larger nucleus releasing energy in the process– The ENERGY released is in the

form of different EMR such as gamma radiation as well as kinetic energy

• In the sun, 2 hydrogen nuclei collide to form helium, a neutron and gamma radiation:

• This produces EMR and makes stars shine • Nuclear fusion is also known as a proton-proton chain reaction (think

back to chemistry, what is a proton?)

Temperatures of stars• Stars appear to be different colours at night • The hottest stars have their peak in the

continuous spectrum within the ultraviolet region. Our eyes “see” these stars as bluish-white

• Our sun appears yellow – it is cooler than the hottest stars (5500°C)

• Even cooler stars (2900°C) appear to be red in the night sky

• This is similar to the energy of the colours in the visible spectrum

Hottest, most energy

Coolest, least energy

Evolution of Stars• All stars begin in regions that are rich in hydrogen and dust

but stars don’t shine forever• Hydrogen eventually runs out and nuclear fusion stop

– their life cycle depends on the original mass of the star• Stars are classified as Low-Mass (like our sun),

Intermediate-mass, or as a High-mass star• Reactions occur more rapidly in stars with large mass

The Evolution of our Sun – A Low Mass Star

• Low-mass stars spend their main-sequence lives fusing hydrogen into helium in their cores

• A low mass star is one that has a mass that is not more than1.4x the mass of the sun.

Nebula Low-mass star red giant expanding shell of gas white dwarf

Evolution of Intermediate Stars

Nebula Intermediate mass star supergiant star supernova neutron star

• Intermediate mass stars have a mass between 1.4 – 8x the mass of our sun

Evolution of High Mass Stars

• High mass stars have a mass greater than 8x the mass of our sun

Nebula high-mass star supergiant star collapsing star black hole

Black Holes – the last stage in the evolution of a high mass star

• An area in space with a gravitational field so strong that neither matter nor EMR can escape

• When a large star runs out of fuel it can no longer support its heavy weight. The pressure from the star's massive layers of hydrogen press down forcing the star to get smaller and smaller and smaller. Eventually the star will get even smaller than an atom.

• But the interesting part is if you make something smaller by squishing it, its gravity becomes much stronger. Imagine then, if you squish a star into the size of an atom how powerful its gravity would become.

• A black hole's gravity becomes so powerful that anything, including light that gets too close, gets pulled in.

• Found by watching the effect on matter outside the black hole.– The gas forms a disk around the black hole, heats up, & may give off X-rays

while accelerating into the hole

1, 3 and 2

Answer: A

Space Probes and Telescopes• Space probes and telescopes are used to study remote objects by

collecting different forms of EMR from space• Remember that visible light can only give us a finite amount of

information• Why would we want to collect EMR from space?

– EMR collected from space can help us determine the composition, temperature and speed of stars

Information from the sky!!• Telescopes such as the Hubble, satellites and space

probes all use and detect a range of EMR (such as infrared, UV, visible light, microwaves and radio waves)

• What are some benefits to using such expensive technology? – Allows us to determine the temperature, chemical

composition, geology and atmospheric gases of other planets and stars

– Allows us to locate supernovas, pulsars, neutron stars and black holes

– What planets are similar to Earth? Which are habitable?

– Allows us to understand the history of Earth better• What are some concerns regarding this technology?

– Cost – Materials used may be toxic, especially during

takeoff

TelescopesSimple Refracting Telescope

A telescope that magnifies an image by using lenses to bend light

• A larger opening = better resolution (less diffraction), but it is difficult to make

TelescopesReflecting TelescopeA telescope that magnifies an image by using concave mirrors

to reflect light • A reflecting telescope can have a larger opening and

collect more information

Large Reflecting Telescopes

CFHT: Canada-France-Hawaii Telescope is one of the largest reflecting telescopes with a mirror 3.6m in diameter• Its telescope is located on the summit ridge of

Maunakea, a 4200 meter, dormant volcano on the Island of Hawaii.

• Is used to observe infrared radiation emitted by objects in space

Observatories are usually at high altitudes to minimize the absorption and distortion caused by the Earth's atmosphere and can be controlled remotely from lower altitudes.

The CFHT observatory is involved in the study of the solar system, the birth and evolution of stars, the structure and content of galaxies, galaxy clusters, and other structures of the Universe.

Large Reflecting Telescopes

• The Hubble Space Telescope collects infrared, UV, visible light and any EMR emitted from planets, comets, asteroids and stars

What did the Hubble telescope see? Click if you are interested!

The Hubble telescope is 23 years old and going strong. It was predicted to last until at least 2015. Now, NASA officials say they are committed to keeping the iconic space observatory going as long as possible. In fact, Hubble supporters hope it will continue to run even after its successor, the James Webb Space Telescope (JWST), is launched — an event planned for 2018.

• Why are telescope launched above our stratosphere? • Telescopes are launched high into the sky so that Earth’s

atmosphere does not absorb any EMR

What penetrates the atmosphere?

High energy rays come from hottest stars

This is why telescopes are need to be above Earth’s atmosphere

Radio waves and visible light are the only EMR that can completely penetrate (pass through the stratosphere)

The Earth's atmosphere stops most types of electromagnetic radiation from space from reaching Earth's surface. This illustration shows how far into the atmosphere different parts of the EM spectrum can go into the atmosphere before being absorbed. Only portions of radio and visible light reach the surface.

TelescopesRadio TelescopeRadio telescopes detect and

record radio waves coming from stars and other celestial objects.

Why is such a large dish needed?

Radio waves have very long wavelengths

Analyzing Starlight: Emission & Absorption Spectra• After collecting EMR with telescopes,

astronomers analyze radiation by separation the radiation into its component wavelengths (colors)

• This can be done with a diffraction grating and spectrometer – A diffraction grating is a plastic sheet that

separates wavelengths– A spectrometer gives us the exact

measurements of each wavelength • Spectra’s can tell us about the composition

& temperature of stars

Different Types of Spectrums

Types of Spectrum1. Continuous all colors or wavelengths

present (observed on the surface of the sun)

2. Emission (bright line spectrum): a spectrum that has bright lines emitted from an excited gas under low pressure

3. Absorption (dark line spectrum): a spectrum with dark lines due to wavelengths of light being absorbed

Continuous Spectrum

Emission (bright line) spectrum

Absorption (dark line) spectrum

Make sure you know the type of spectrum produced based on temperature the EMR passes through

2, 4, 5, 3

B, since cool gases ABSORB energy of various wavelengths. Producing EMR would create an emission spectrum.

Unknown Star

• Besides temperature, you can find out information about the composition of stars by looking at the spectrum

• Each element has a unique absorption spectrum – like a fingerprint• We can look at the absorption spectrum from a star and compare it to reference

spectrums to tell us what elements make up the atmosphere of the star.

Spectral Analysis

Chromium Helium

Reference Spectrums

Barium

What elements does the unknown star contain?

How did the universe evolve?

There are 2 theories of how the universe evolved: 1. Steady State Theory: The universe is

expanding at a steady rate, galaxies are moving away from each other and the universe has no edge!

• The universe is infinite with no beginning and no end, in which matter is continuously created in the space between the galaxies.

2. Big Bang Theory: Universe began with a giant explosion and expands at different rates

• The universe was born 13.7 billion years ago, like a rapidly expanding balloon, it swelled from a size smaller than an electron to its current size within a tiny fraction of a second

Doppler Shift• The Doppler Effect affects sound, light and

other EMR• For example, when a police car

approaches you, the pitch of the siren changes. This is because the frequencies shift as a police car approaches and then quickly speeds away

• Frequencies of a star’s light also shifts as it moves toward or away from the earth

Sheldon and the Doppler Effect

Doppler Effect

The siren from a stationary police car will sound the same at A and B

(the frequency is equal at A and B)

The siren from a moving police car will sound louder at B than A

(sound waves are bunched at B= Higher frequency)

Doppler Effect Animation

Use the “Red Shift” app from the textbook to help explain the Doppler effect – it’s great!

The Doppler Effect for a moving sound source

Doppler EffectLong wavelengthLow frequency

Small wavelengthHigh frequency

Red Shift / Blue ShiftRecall (answer on your own): • Red light has low frequency and blue

light has high frequency • If an object is moving towards you the

frequency is higher, away from you the frequency is lower

• Galaxies are clusters of stars which typically rotate about some center of mass point.

• If the star is rotating in its cluster in a direction which is AWAY from the Earth EMR emitted would have a lower frequency than a stationary object• Lower frequency light is red, and thus

the stars spectrum would appear to be red shifted (a "red shift")

Red Shift / Blue ShiftRecall: • Red light has low frequency and

blue light has high frequency • If an object is moving towards you

the frequency is higher, away from you the frequency is lower

• If the star is rotating in its cluster in a direction which is TOWARDS the Earth, EMR emitted would have a higher frequency than a stationary object

• Higher frequency light is blue, and thus the stars spectrum would appear to be blue shifted (a “blue shift")

Red shift = low frequency, so the object is moving

away!

Blue shift = high frequency, so the object is moving

towards you!

Doppler Effect and StarsWhich spectrum represents a galaxy approaching and which spectrum represents a galaxy receding (moving away)?

• No matter what galaxy we obtained EMR from, all spectroscopes were red-shifted… meaning the universe is expanding at a constant rate!

• The amount of the shift shows us the velocity of the star• The greater the shift, the faster it is moving

To answer this question, figure out which side of the spectrum is red and blue using the wavelengths.

700nm is red and 400nm is blue

The spectrum has shifted towards the 400nm side, which is blue. Therefore the correct answer is C.