Chapter 5 : The formation of stars and planets

Question 1

star

Answer 1

a dense cloud of gas that produces energy in its core by fusing light atoms into heavier ones

Question 2

Kelvin temperature scale

Answer 2

use this to measure temperature of stars and other objects

Question 3

interstellar cloud

Answer 3

cloud of cool dust and gas in the space between stars, it has self-gravity

Question 4

self-gravity

Answer 4

a gravitational attraction among all parts of the same object

Question 5

hydrostatic equilibrium of a cloud

Answer 5

when the forces on a cloud are balanced

Question 6

molecular clouds

Answer 6

• the densest, coolest, interstellar clouds

- composed of hydrogen, dust and other gases

Question 7

Once a molecular-cloud core begins to collapse, what happens?

Answer 7

the innermost core becomes a star, the outer parts form planets

Question 8

protostar

Answer 8

innermost part of a collapsing molecular-cloud core

Question 9

Formation of a protostar

Answer 9

• Molecular cores continue to collapse under their own gravity
• As cloud collapses, force of gravity increases and the collapse accelerates
• Center shrinks fastest; outer layers later
• Produces a dense protostar

Question 10

Star Formation: Growing Protostar at the Center

Answer 10

-Protostar heats up due to the conversion of gravitational energy into thermal energy: Particles collide as they are pulled towards the center, Raises the temperature of the core, Pressures and temperatures are not yet high enough for fusion to occur

Question 11

Wien’s Law

Answer 11

Relationship between temperature of an object and peak wavelength the object emits

Question 12

Flux

Answer 12

Energy emitted by one square meter of the object every second

Question 13

Luminosity

Answer 13

Total energy emitted every second

Depends on temperature and size of the star

Question 14

nebula

Answer 14

interstellar cloud of gas and dust

Question 15

Protostars emit mainly what type of light? (due to their cool temperatures)

Answer 15

infrared

Question 16

When a protostar is in balance, what is happening?

Answer 16

the force from hot gas pushes outward and the force of gravity pulls inward

Question 17

A protostar becomes a star when?

Answer 17

• Core’s temperature and density increase until nuclear fusion is possible
• Hydrogen begins turning into helium in the core
• It becomes a star

Question 18

brown dwarf

Answer 18

• Critical temperature for fusion of hydrogen to helium: 10 million Kelvin
• Protostars less than 0.08 solar masses never start that reaction
• “failed stars”

Question 19

Collapse is slowed ____ to the rotation axis. (perpendicular or parallel?)

Answer 19

Collapse is slowed perpendicular to the rotation axis (toward or away from the axis) but not parallel to it (up or down the axis).

Question 20

accretion disk

Answer 20

a disk that forms from the accretion of material around a massive object

Question 21

The accretion disk will have an overall rotation (clockwise or counterclockwise), due to conservation of ____ _____.

Answer 21

angular momentum

Question 22

angular momentum

Answer 22

conserved quantity of a revolving or rotating system with a value that depends on both the velocity and distribution of the mass

Question 23

Amount of angular momentum depends on 3 things:

Answer 23

1) How fast the object is rotating. (faster = more angular momentum)
2) Mass of object (more mass = more angular momentum)
3) Distribution of mass of object (more spread out = more angular momentum)

Question 24

conservation of angular momentum

Answer 24

angular momentum must remain the same in the absence of an external force

Question 25

refractory material

Answer 25

Does not melt at high temperatures (metals and rock)

Question 26

Volatile material

Answer 26

Melts at low temperatures (methane and other hydrocarbons)

Question 27

Inner disk has only _____ materials. Outer disk has _____ and _____ materials.

Answer 27

Inner disk has only refractory materials

Outer disk has refractory and volatile materials

Question 28

primary atmosphere

Answer 28

the gas (mostly hydrogen and helium) captured by a planet at the time of its formation

Question 29

secondary atmosphere

Answer 29

forms later in the life of a planet

Question 30

Four inner planets (terrestrial):

Answer 30

Mercury, Venus, Earth Mars

Question 31

Four outer planets (jovian):

Answer 31

Jupiter, Saturn, Uranus, Neptune

Question 32

Extrasolar planets

Answer 32

planets that orbit stars other than our Sun

Question 33

The Doppler effect

Answer 33

Motion of a light source toward or away from us changes the wavelength of the waves reaching us.
Redshift = Motion away
Blueshift = Motion toward

Question 34

Transit method

Answer 34

a planet passing in front of a star causes the total brightness of the star to decrease