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astrophysics and cosmology Flashcards

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1
Q

What is a Planet

A

-An object that has a mass large enough for its own gravity to give it a round shape
-it is in orbit around a star
-it does not produce fusion reactions

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2
Q

What are Planetary Satellites? Give an example.

A

A body that is in orbit around a planet
eg the moon, manmade satellites

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3
Q

What is a comet?

A

A small irregular body made of ice, dusk and rock. The orbit stars in an elliptical orbit.

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4
Q

What is a Galaxy?

A

A collection of stars, interstellar dust/gas.

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5
Q

How are stars formed?

A
  1. dust and gas get closer together due to their gravitational pull on each other
  2. denser regions in the nebula form they become hotter as gravitational potential energy is converted into thermal energy
  3. a protostar is formed in a part of the cloud
  4. the protostar becomes a star when fusion occurs in its core. Hydrogen in the core has enough energy for fusion (due to the high thermal energy)
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6
Q

What are the stages of life for a low mass star?

A

main sequence, redgiant, white dwarf

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7
Q

What is the mainsequence?

A

When the gravitational force (compressing) and gas pressure/ radiation pressure caused by emitted photons during fusion (pushing outwards) are in equillibrium.

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8
Q

What happens in the core of a red giant?

A

The gravitational force greater than gas pressure and radiation as there is no
hydrogen in the core for fusion to occur.
-The core of the star begins to collapse.
-The core shrinks but pressure is high enough to start fusion in the shell around the core (hydrogen to helium).
-The star expands and layers move away from the core.

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9
Q

What are the properties of a White Dwarf? How are they Formed?

A

Formed when the layers from the red giant drift into space as planetary nebula and leave behind a hot core.

Very dense and small

No fusion occurs but energy is emited as photons that had previously been created leave.

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10
Q

What is electron degeneracy pressure? How does this occur in White Dwarfs?

A

The White dwarf collapses under the force of gravity and electrons squeeze together.
This creates a pressure that prevents the core from further collapse.

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11
Q

What is Chandrasekhars limit?

A

The electron degeneracy pressure is only sufficient enough to prevent the collapse of cores with a mass less than 1.44 M

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12
Q

What are the stages of life for a more massive star?

A

main sequence, red supergiant, super nova, neutron star or blackhole.

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13
Q

What occurs in the core of a red supergiant?

A

Temperatures are high enough for fusion to occur with heavier elements. Shells are created inside the star. The fusion of heavier elements occur futher towards the centre of the star.

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14
Q

How does a type 2 super nova occur? What is a type 2 supernova?

A

In the core of red super giants the process of fusion of heavier elements continues until the star has an iron core. The star can no longer produce energy so the star dies.

The type 2 super nova is an implosion that causes the layers of elements to bounce off of the solid core.

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15
Q

How does a supernova occur?

A

At a certain point the fusion taking place in the core of the red supergiant in unable to widthstand the gravitational force. This causes the star to collapse on itself.

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16
Q

What conditions are needed for a Neutron star to be formed?

A

The mass of the core is greater than the chandrasekhars limit of 1.44 M

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17
Q

What is a neutron star

A

a star mostly made of neutrons and has a similar density to a nucleus

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18
Q

What conditions are needed for a black hole to be formed?

A

The mass of core is greater than 3M

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19
Q

What are the properties of a black hole?

A

Very strong gravitational field.
Any object would have to have an escape velocity larger than the speed of light in order to escape it. Even light cannot escape a black hole.

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20
Q

What is an Astronomical unit?

A

1 Au is equal to the average distance between the Sun and the Earth. 1.5*10^15 m

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21
Q

What is a light year?

A

The distane travelled by light in a vacuum in one year. 9.46*10^15

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22
Q

What is a parsec (pc)

A

the distance at which one Au subtends an angle of 1 arcsecond

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23
Q

What is 1 arcminute in degrees?

A

1/60 degrees

24
Q

What is an arc second in degrees?

A

1/3600 degrees

25
Q

What is Stellar Parallax?

A

A technique used to determine the distance of stars from the Earth under 100pc away from Earth.

26
Q

Why is stellar parallax only limited to stars under 100pc away from Earth?

A

the larger the distance from Earth the smaller the parallax angle. The angle would be too small to measure accurately.

27
Q

What is the Cosmological Principle?

A

the universe is isotropic, homogeneous and the laws of physics are universal

28
Q

What is the equation for stellar parallax?

A

p=1/d p is the parallax in arcseconds and d is the distance from the Earth

29
Q

What is the Doppler Effect?

A

When the wavesource moves relative to an observer, the frequency and the wavelength recieved by the observer changes compared to what is observed without relative motion.

30
Q

What happens when a wavesource moves towards the observer?

A

The waves recieved by the observer are ‘compressed’ this means the wavelength appears shorter and the frequency appears to higher.

31
Q

What happens when a wavesource moves away from the observer?

A

The waves recieved by the observer are ‘stretched’ this means the wavelength appears longer and the frequency appears lower.

32
Q

What is blue shift?

A

The galaxy/star observed is moving towards the Earth. The absorption line spectrum shits towards the blue end of the spectrum.

33
Q

What is red shift?

A

The galaxy/ star observed is moving away from Earth the emission line spectrum shifts to the red end of the spectrum.

34
Q

What is the doppler equation?

A

(change in wavelength/frequency)/frequency = v/c
v is the velocity between the wavesource and the observer

35
Q

What is hubbles law?

A

v= Hod where v is the recession velocity and Ho is hubbles constant = 2.2*10^18 s^-10

36
Q

What are the 2 pieces of evidence that supports the theory that the universe is expanding?

A

Hubbles law
Microwave background radiation

37
Q

How does hubbles law support the big bang theory?

A

-hubbles law shows us that the universe is expanding in all different directions.
if we go back in time the universe gets smaller, denser and hotter until all mass is at a single point (a singularity) as described in the big bang

38
Q

How does microwave background radiation support the theory of the big bang? 2 ways

A
  1. In the beginning stage of the universe space was saturated with high energy photons. The universe expanded- space stetched over time. This stretched the wavelength of the high energy photons into microwaves detected in present day.
  2. The universe was incredibley hot and dense but the expansion of the universe reduced the temperature of space to 2.7k . The universe is treated as a black body radiator that has a corresponding 1mm max wavelength that is similar to the wavelength of s microwave
39
Q

What is the estimation of the age of the universe?

A

1/Ho

40
Q

What happened in the big bang?

A

time and space is created the universe is a singularity it is infinitely dense and hot.

41
Q

What happened 10^-35 seconds after the big bang?

A

repid expansion and a incredible stage of acceleration called inflation.
Theres is no matter and only high energy photons the temperature is 10^28 K

42
Q

What happened 10^-6 sceonds after the big bang?

A

first fundamental particles created (quarks and leptons)

43
Q

What happened 10^-3 seconds after the big bang?

A

first hadrons are formed (protons and neutrons). Mass was created mostly through pair production. (high energy photons transforming into partical antipartical pairs)

44
Q

what happened 1 second after the big bang?

A

the creation of matter stops and the temperature has dropped to 10^9K

45
Q

What happened 100s seconds after the big bang?

A

protons and neutrons fuse together and form deuterium and helium nucleii
no heavier elements are created due ot the rapid expansion of the universe.

46
Q

What happend 380,000 years after the big bang?

A

first atoms are formed because the universe is cool enough.

47
Q

what happened 30 million years after the big bang?

A

first stars are formed. heavier elements are formed through nuclear fusion.

48
Q

What happened 200 million years after the big bang?

A

The milky way is formed.

49
Q

What happend 9 billion years after the big bang?

A

The solar system was formed.

50
Q

What is dark matter?

A

matter that does not absorb or emit any light. matter we cant see.

51
Q

What is dark energy?

A

A form of energy we havent detected yeat that is the cause from the accelleration of the expansion of the universe.

52
Q

What is a continous spectrum?

A

it shows all visible frequencies/ wavelengths

53
Q

What is an emission line spectrum?

A

each element creates a unique spectrum showing the frequency/ wavelength of photons they emit due to their specific energy levels.

54
Q

What is an absorption line spectrum?

A

They are created when light from a continous spectrum passes through a cool gas. a continous spectrum with black lines that indicate the wavelenghts that are absorbed by the gas.

55
Q

What is weins displacement law?

A

maximum wavelength is proportional to 1/temperature (K)

56
Q

What is stefans law?

A

luminosity of a star (L)= 4pir^2*(constant)T^4

physics (5 decks)

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