1. Other Stars

2. How Bright is That Star?
Luminosity: A measure of the total amount of _____________ it radiates per second.
power is in joules per second (J/s)
Some stars are ____________ times less luminous than the sun.
Some stars are _____________ times more luminous than the sun.
Absolute Magnitude: How bright a star would be at a distance of 32.6 light-years from _____________.
Absolute magnitude of the sun is about 4.7 (rather faint).

3. The Colour and Temperature of Stars
Through a powerful _________________, you would see that some stars are bluish, bluish-white, yellow, orangish, or reddish.
Astronomers use the colour of a star to determine the star’s surface ___________________.
Reddish: 3300°C
Yellowish: 6000°C
Bluish: Between 21, 000°C
and 35,000°C.

4. The Composition of Stars
Spectroscope: an _________________ instrument that produces a pattern of colours and lines, called a _________________, from a narrow beam of light.
Spectral lines: certain specific wavelengths within a spectrum characterized by lines; identify specific chemical _______________.
Every element is uniquely identified by its spectrum.
Spectral lines indicate which visible wavelengths are being absorbed by a material.

5. The Mass of Stars
Most of the stars seen from Earth are __________________ stars.
Binary Stars: two stars that orbit each other.
By knowing the size of the _______________ of a binary pair and the ______________ the two take to complete one orbit, astronomers were then able to calculate the _______ of each star.
Solar Mass: The sun is ___ solar mass. Other stars range from 0.08 solar masses to over 100 solar masses.

6. The Hertzsprung-Russell Diagram
In 1920s, astronomers Hertzsprung (Netherlands) and Russell (U.S.A) were working independently of each other.
Each star type has certain properties
Data compiled into a graph.

7. The Main Sequence
The Main Sequence: narrow band of stars on the H-R diagram that runs from ______________to _________________. Includes about 90% of stars, including the ________________.
Example of exception: Antares: 3500°C but 15 brightest star in the night sky.
Not yet known why these exceptions exist.

8. How Stars Evolve Stars eventually run out of fuel.
In final stages of life, can become a white dwarf, a neutron star, or a black hole.
What it becomes depends on initial mass on the main sequence: Low mass, Intermediate-mass, High-mass

9. 1) Low-Mass Stars (Red Dwarfs)  White Dwarfs  Black Dwarfs
Less mass than the _________.
Consume hydrogen slowly over a period of over ____________________years, losing significant mass, leaving only a very faint white dwarf.
White Dwarf: a small, dim, hot star.
No longer producing energy of their own
Still very hot due to residual heat
Takes 10s of billions of years to cool down
Astronomers theorize that they will become dark embers called black dwarfs.
Do any black dwarfs exist right now? ____

10. 2) Intermediate-Mass Stars  Red Giant  White Dwarf  Black Dwarf
Example: Sun
Consume hydrogen faster than low mass stars, over a period of about ______ billion years.
When hydrogen used up, core collapse, temperature increases, outer layers expand, cool, and appear red.
Red Giant: very large star of high ________________ and low surface _____________________. Thought to be in late stage of evolution.
The Sun will be eventually be so large that its diameter will extend out to the current orbit of Mars. Eventually, layers will dissipate, and Sun will become white dwarf.

11. 3) High-Mass Stars  Supergiant  Supernova
12+ solar masses
Consume fuel faster than intermediate-mass stars.
Die quickly and violently.
Core heats up to much higher temperatures, heavier elements form by fusion, and the star expands to a supergiant.
Supergiant: Largest stars in the universe. Can be thousands of times bigger than our Sun.
Iron forms in the core, core collapses violently, and shock wave travels through the star. Outer portion of the star explodes, producing a supernova.
Supernova: a massive explosion in which the entire outer portion of a star is blown off.
Heavier elements are ejected into the Universe to become parts of new stars, planets, and other celestial bodies.
Remaining star will either become a neutron star or a black hole.

12. Your body contains many atoms that were fused in the cores of old stars!
We can conclude that 93% of the mass in our body is stardust.
- American Physical Society, 2017

13. 3a) Neutron Star
If star begins with a mass of 12 – 15 solar masses, core shrinks to approximately 20km in diameter.
Pressure is so great, electrons & protons squeezed into neutrons.
Neutron Star: a star so dense that only neutrons can exist in the core

14. 3b) Black Holes Initial masses are 25+ solar masses
After supernova, nothing can compete with the crushing force of gravity.
Black Hole: tiny patch of space that has no volume, but does have mass.
Gravitational force is so great that nothing can escape a black hole, even light.
A black hole cannot be seen – only the evidence
Swallow up matter, compress it to enormous temperatures before it disappears.
Astonomers look for gas, dust, and stars being “devoured” using radio, X-ray, and gamma ray telescopes.

15. Seatwork/Homework 1:
Create a concept map that outlines the evolution of stars based on their initial masses.
Include information such as solar masses, chemical/physical/nuclear processes occurring, etc. 2:
Page 342 #1, 4
Page 347 #5-8
Page 349 #1, 3, 4, 6
3: (Chapter Review)
Page 356 #4-7, 9, 13-17