Stars and cosmology

Question 1

Describe the Hertzsprung Russel diagram

Answer 1

made up of the main sequence (which flattens slightly in the middle), red giants and red supergiant’s and then white dwarfs

Question 2

What is the Y Axis of the Hertzsprung Russel diagram and what is its range?

Answer 2

Absolute magnitude (15 at the bottom to -10 at the top)

Question 3

What is the X Axis of the Hertzsprung Russel diagram and what is its domain?

Answer 3

Decreasing temperature (non linear scale) from 50,000K to 2500K or just the spectral class (OBAFGKM)

Question 4

How does the formation of a protostar occur?

Answer 4

Cloud of dust and gas slowly undergoes gravity till its dense enough to make a protostar, this continues to contract and heat up till a few million degrees and hydrogen nuclei start to fuse to form helium. This creates enough radiation pressure to stop gravitational collapse and form main sequence star.

Question 5

What is the sequence of star similar size to the sun?

Answer 5

Star turns to a Red Giant then to a White Dwarf and planetary nebula

Question 6

What is the sequence of a star larger than the sun?

Answer 6

Star turns into Red Supergiant then supernova occurs making it into either a black hole or a neutron star

Question 7

What is a parsec?

Answer 7

The distance at which one AU subtends an angle of 1/3600th of a degree

Question 8

Describe the process of sunlike star in terms of the HR diagram?

Answer 8

Starts off in main sequence until core runs out of hydrogen, it then leaves main sequence to become red giant getting brighter, then it leaves from top right to bottom left where it becomes a white dwarf (stars spend most of life in main sequence)

Question 9

What is a supernova and what are its characteristics?

Answer 9

Occurs with stars bigger than the sun after red supergiant explodes, brief and rapid increase in absolute magnitude occurs

Question 10

What happens after Red super giant collapses?

Answer 10

Supernova and burst of gamma rays can be emitted

Question 11

What is a standard candle?

Answer 11

An object where absolute magnitude is known/ the absolute magnitude can be calculated…

Question 12

What are the characteristics of a type 1a supernovae?

Answer 12

They have a rapid massive increase in absolute magnitude shown by graph at day 0 as it decreases to day 40. can also be used as a standard candle since they all have same mas when they explode.

Question 13

What is the energy output of a supernova compared to the energy output of the sun?

Answer 13

Around 10 to the power of 44 Joules (roughly the same as the sun over its entire lifetime)

Question 14

How is a neutron star formed?

Answer 14

As the core of a massive star contracts, the electrons in the core of the material get squashed onto the atomic nuclei and combine with protons to form neutrons and neutrinos

Question 15

How is a black hole formed?

Answer 15

If core of a star is more than 3 times the mass of the sun then core contracts to form neutrons but gravity collapses into infinity

Question 16

Define a black hole

Answer 16

An object with an escape velocity greater than the speed of light

Question 17

What is the density and size of a neutron star?

Answer 17

4 times 10^17 kilograms per metre cubed and typically 20km across

Question 18

What is the belief around black holes?

Answer 18

Astronomers believe that there is a supermassive black hole at the centre of each galaxy

Question 19

What is the doppler effect?

Answer 19

The change in frequency and wavelength as an object moves

Question 20

What is Red shift?

Answer 20

Example of doppler effect, if object is moving away then the wavelength facing earth is increased (HENCE RED AS IT IS LARGES WAVELEGTH OF COLOUR) the faster the object the more red it appears.

Question 21

What is Hubbles law?

Answer 21

V=Hd, he basically found out that velocity of galaxies is proportional to the distance away….

Question 22

How can you is ethe hubbles constant to work out the age of the universe?

Answer 22

H is speed per distance so 1/T hence 1/H=T

Question 23

What is the big bang theory?

Answer 23

The universe started off very hot and very dense and has been expanding ever since (the universe is expanding and cooling down)

Question 24

Evidence for the big bang?

Answer 24

1) Relative abundance of H and He
2) Cosmic Background Radiation

Question 25

How is CMBR evidence for the big bang theory?

Answer 25

CMBR is radiation coming from all parts of the universe. Big bang model predicts radiaition was produced very early in universe, This was released as gamma rays but have been stretched to microwaves (doppler effect) and this accounts for 2.7K of temperature.

Question 26

How does the abundance of H and He support the big bang theory?

Answer 26

When the univers was very young hydrogen fused to create helium. Fusion stopped as the universe expanded and cooled. This resulted in ratio of hydrogen to helium of 3/1 (universe cooled too rapidly for creation of larger nuclei)

Question 27

What do you need to know about dark energy?

Answer 27

It is a possible explanation for an expanding universe but is a controversial theory. (would explain why the expansion is accelerating as something ,ust be pushing it out counteracting gravity of universe)

Question 28

What are spectroscopic binary stars?

Answer 28

Stars sometimes orbit each other in pairs, when stars complete one full orbit there will between times in which each planets move parallel to observer with one being red shifted the other blue shifted, max and min on the absorption spectrum

Question 29

What are Quasars?

Answer 29

Bright radio sources and the most distant objects we can measure (formed from supermassive black holes)

Question 30

How do astrophysicists know that quasars are so far away?

Answer 30

Quasars show large optical red shifts, indicating they are very far away

Question 31

How can you work out the distance and power output of quasars?

Answer 31

Using power is directly proportional to intensity times by distance squared

Question 32

What is an exoplanet?

Answer 32

Any planet not in our solar system

Question 33

Why are exoplanets hard to detect?

Answer 33

1) They orbit bright stars and are small so hard to see 2) Too small to distinguish from nearby stars

Question 34

What are the two methods used to detect exoplanets?

Answer 34

1)Doppler shift (Radial velocity) 2) Transit (Change in apparent magnitude)

Question 35

How can doppler shift be used to detect exoplanets?

Answer 35

Star and exoplanet orbit the same centre of mass hence periodic shift in spectra of star (red shift and blue shifted emissions) allowing mass of exoplanet to be solved (observer must be aligned with movement) OR periodic Doppler shift in light received

Question 36

How can transit/apparent magnitude be used to detect an exoplanet?

Answer 36

exoplanet blocks star as they orbit same mass which dims the brightness of the star but alignment must be correct for planets to eclipse

Question 37

What is black body radiation?

Answer 37

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

Question 38

What did the discovery of supernovae 1a lead to?

Answer 38

Went against predictions oh Hubble law so universe must be expanding at an increasing rate (accelerating) this isn’t known why but could be dark energy.

Question 39

What are the links between galaxies,black holes and quasars?

Answer 39

Quasars are produced by supermassive black holes and these black holes are at the centre of active galaxies