Classification of stars

Question 1

how many arc seconds in an arc hour

Answer 1

its called a degree not an arc hour and 3600

Question 2

Name 3 methods of determining distance to stars

Answer 2

1: Stellar parallax, 100-1000pc
standard candles
2: type 1a super nova
3: Cepheid Variables, 1kpc to 50 Mpc

Question 3

define apparent and absolute magnitude

Answer 3

Apparent: The apparent magnitude (m) of a star is
the brightness when viewed from Earth
Absolute: The absolute magnitude (M) of a star is the
apparent magnitude it would have if measured
at a distance of 10 pc from the observer

Question 4

Define black-body radiation

Answer 4

A body that absorbs all wavelengths of
electromagnetic radiation and can emit all
wavelengths of electromagnetic radiation.

(also known as a perfect thermal source)

Question 5

Luminosity

Answer 5

the total energy given out per secon, so its power

depends on radius and surface temperature

(The total energy per unit time radiated
by a black body is proportional to the
fourth power of its absolute
temperature) 
stefans law:     L=σAT^4

Question 6

can you describe continuous, emission and absorption spectra

Answer 6

good job if you can if not ha ha

Question 7

emission and absorption spectra occur due to…..

Answer 7

excitation and de-excitation of electrons

Question 8

absorption and emission of visible light is part of the….

Answer 8

Balmer series
( to emit balmer lines the electron in a hydrogen atom must be in the n=2 state)

Question 9

hey neddy ayla

Answer 9

Oh Be A Fine Girl Kiss Me

Question 10

spectral classes

Answer 10

O: Blue 25,000 - 50,000 He+, He, H
B: Blue 11,000 - 25,000 He, H
A: Blue-White 7,500 - 11,000 H (strongest) ionised metals
F: White 6,000 - 7,500 Ionised metals
G: Yellow-White 5,000 - 6,000 Ionised & neutral metals
K: Orange 3,500 - 5,000 Neutral metals
M: Red <3,500 Neutral atoms, TiO

Question 11

can you describe a Hertzsprung-Russell diagram

Answer 11

well you better learn how to then

Notice that:-
the temperature scale is decreasing (50,000 K to
2,500 K).
the classes of star are placed alongside the
temperature scale;
the luminosity scale is logarithmic to compress
it;

Question 12

Red Giants

Answer 12

Objects that have a high luminosity and a low
surface temperature must have a large surface
area. (Stefan’s Law)
 These stars are called red
giants and are found in
the top right corner of
the HR diagram.

Question 13

White Draves

Answer 13

Torbjörn’s dad?

Objects that have a low luminosity and a high
surface temperature must have a low surface
area. (Stefan’s Law).
 These stars are called
white dwarfs and lie in
the bottom left hand
corner of the HR
diagram.
 White dwarfs are stars at
the end of their lives,
where all of their fusion
reactions have stopped
and are they are just

Question 14

stellar evolution in one slide

Answer 14

Stars are formed from great
clouds of gas and dust, most of
which is the remnants from
previous supernovae.
 When the clumps get dense enough, the cloud
fragments into regions called protostars that
continue to contract and heat up.
 Eventually the temperature at the centre of the
protostar reaches a few 106K and hydrogen
nuclei start to fuse together to form helium
The fusion of hydrogen
releases enough energy to
create enough radiation
pressure to stop the
gravitational collapse.
 The star has now reached the
main sequence and will
remain there while it fuses
hydrogen to helium
(continued on slide 2)

Question 15

stellar evolution the second half

Answer 15

Stars spend most of their lives
as main sequence stars.
As the star ages more and
more helium builds up in the
core.
Eventually all the hydrogen is
gone and you are left with a
core of only helium
When the hydrogen in its core runs
out, the outward radiation pressure
stops, gravity wins and the core
starts to contract.
 As the core contracts it heats up.
This raises the temperature of
hydrogen surrounding the core
enough for it to fuse.
When the helium runs out, the carbon-oxygen
core contracts again  shell helium “burning”.
For stars with mass similar to the of the Sun, the
carbon-oxygen core isn’t hot enough for fusion.
The core continues to contract until electrons
exert enough pressure to stop it collapsing
further

Question 16

ejecting your outer layer

Answer 16

The helium shell becomes more
and more unstable as the core
collapses.
 This causes the star to pulsate and
eject its outer layers into space
  planetary nebula.
 A hot dense solid core is left
behind
  white dwarf.

Question 17

a short but exiting life

Answer 17

is what stars of greater than 8 solar masses get

Question 18

how i want to die sadly im not a star :(

Answer 18

The radiation pressure rapidly decreases so gravity wins
and a rapid collapse occurs until the radius of the inner
core reaches about 30 km.
 Further collapse is stopped by strong force interactions
and the degeneracy pressure of neutrons
The in-falling matter, rebounds off the core producing
a shock wave that propagates outward 
SUPERNOVA

Question 19

how fat you are determines how your life will go

relative masses and the corresponding product at the end of the stars life

Answer 19

If the mass of the core is < 1.4 MΘ then a white dwarf
is formed.
If the mass of the core is > 1.4 MΘ then a neutron
star is formed.
If the mass of the core is > 3.0 MΘ then a black hole
is formed.
Important: Note that these values are for the mass of
the core left over – not the initial mass of the star.
Note: The 1.4 MΘ limit is known as the
Chandrasekhar limit

Question 20

Describe and name the coolest(not literally) star in the known universe

Answer 20

Neutron Stars
The core gets so dense that it overcomes the
electron degeneracy pressure.
Electrons are squashed onto the atomic nuclei
and combine with protons to form neutrons
A density is reached when the repulsive force of
the neutrons is sufficient to stop the collapse of
the stellar core  neutron degeneracy pressure.

can emit radio waves if oriented correctly they can be observed as pulsars because they pulse

Question 21

We are about to go where the sun doesn’t shine

Answer 21

Black Holes
There is no known force in nature that can stop
the collapse of cores greater than 3 solar masses.
The collapse continues until the core contracts
to an infinitely dense point known as a
singularity.
Even light cannot escape from the core within a
certain radius called the Schwarzschild Radius.

Question 22

event horrizon

Answer 22

Vesc=c

Question 23

The Schwarzschild Radius

Answer 23

radius of Vesc

Question 24

how do we know black holes are there

Answer 24

matter falling into them

objects orbiting around them

Question 25

calculating the density of a black hole

Answer 25

use The Schwarzschild Radius as its radius

Question 26

Type 1a super nova

Answer 26

The white dwarf reaches a larger mass,
approaching the Chandrasekhar limit
 But just before it would collapse into a
neutron star (within 1% of the limit), the
temperature and density inside the core
increase enough to allow the fusion of carbon
to take place.
Within a few seconds, a substantial fraction of the
matter in the white dwarf undergoes nuclear fusion,
releasing enough energy (1–2 × 1044 J) to produce a
supernova explosion.

Question 27

type 1a super nova the standard candle

Answer 27

It’s a standard candle, which means all
have the same peak
absolute magnitude, M
 That means the apparent magnitude can
be measured.
 Therefore, we can determine the distance
using distance modulus…...

Question 28

why is the luminocity curve of a type 1a super nova predictable

Answer 28

The light curve of a type Ia supernova is predictable as

it is due to the decay of Ni56 and Co56 isotopes

Question 29

O

Answer 29

25000-50000
Blue
He+, He, H

Question 30

B

Answer 30

11000-25000
Blue
He,H

Question 31

A

Answer 31

7500-11000
Blue-White
H(strongest) ionized metals

Question 32

F

Answer 32

6000-7500
White
Ionized metals

Question 33

G

Answer 33

5000-6000
Yellow-White
Ionized and Neutral metals

Question 34

K

Answer 34

3500-5000
Orange
Neutral metals

Question 35

M

Answer 35

2500-3500
Red
Neutral atoms, TiO