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Question 1

What causes a nova in a white dwarf system?

Answer 1

Surface-burning of material accreted from a companion star, which is unstable compared to core-burning.

Question 2

How does material transfer lead to nova in a white dwarf?

Answer 2

Material from a companion star falls onto the white dwarf. Once enough accumulates, fusion reignites suddenly, burning off the new material.

Question 3

What is a nova and how does it behave in terms of brightness?

Answer 3

A nova flares up suddenly and then returns to former luminosity. Its brightness can increase by 10,000 times for a few months.

Question 4

What do the images of Nova Persei and Nova Cygni show?

Answer 4

They show expanding ejected material from the star after a nova explosion.

Question 5

What is a carbon-detonation supernova?

Answer 5

Occurs when a white dwarf exceeds the Chandrasekhar limit of 1.4 solar masses, triggering carbon fusion and an explosion.

Question 6

What differentiates Type I and Type II supernovae?

Answer 6

Type I is from a binary system with a white dwarf; Type II results from iron core collapse of a massive star.

Question 7

What happens in a binary system that leads to Type-I SN?

Answer 7

One star dies leaving a white dwarf which may later accrete enough mass from its companion to trigger a supernova.

Question 8

Why is Sirius B potentially dangerous?

Answer 8

If it becomes a supernova, being only 9 light years from Earth, it could cause mass extinction.

Question 9

What conditions must be met for Pegasi-A to transfer mass to Pegasi-B?

Answer 9

Pegasi-A must expand to a radius of 24.4 R☉; then nova or Type-I SN can occur depending on mass accumulation.

Question 10

Describe the mechanisms behind Type-I and Type-II supernovae.

Answer 10

Type-I: WD accretes >1.4 M☉, fusion ignites throughout, leading to explosion. Type-II: High-mass star core collapses after iron fusion ends.

Question 11

What is the fate of low-mass vs high-mass isolated stars?

Answer 11

Low-mass stars eject outer envelopes and become white dwarfs. High-mass stars end in Type-II SN after iron core collapse.

Question 12

What happens to a white dwarf in a binary when mass >1.4 M☉?

Answer 12

It undergoes carbon fusion throughout and explodes as a Type-I SN.

Question 13

What occurs in a semidetached binary system during mass transfer?

Answer 13

Gentle mass transfer alters star evolution but doesn’t cause supernova immediately.

Question 14

How does mass transfer affect binary star evolution?

Answer 14

As a red giant transfers mass, the smaller star may become more massive and evolve into a blue giant.

Question 15

What is a contact binary?

Answer 15

A binary system where mass is shared extensively, often beginning as a detached binary and evolving over time.

Question 16

What causes X-ray bursts in neutron-star binaries?

Answer 16

Explosive nuclear burning on the surface of an accreting neutron star.

Question 17

What are the possible outcomes of mass transfer in binary systems?

Answer 17

Nova, Type-I SN, X-ray burst, gamma-ray burst depending on the components (e.g., star+WD, star+NS, star+BH).

Question 18

How bright is a supernova compared to a nova?

Answer 18

Supernova is over a million times brighter than a nova, reaching luminosities of a billion suns.

Question 19

Why are Type-I supernovae considered cosmic yardsticks?

Answer 19

Because all Type-I SN reach the same peak luminosity, 9×10^34 W, due to uniform explosion conditions.

Question 20

What is a standard candle and how is Type-I SN used as one?

Answer 20

An object with known absolute brightness used to measure distance by comparing to apparent brightness.

Question 21

What is the energy source for the Sun?

Answer 21

Nuclear fusion.

Question 22

What is the relation between mass and energy?

Answer 22

E = mc², where energy equals mass times the speed of light squared.

Question 23

What is an electron volt (eV)?

Answer 23

It is the energy gained by an electron when pushed by a potential difference of 1 volt. 1 eV = 1.602 x 10^-19 J.

Question 24

What is the Q value in nuclear reactions?

Answer 24

It is the change in total mass energy of a system, positive when energy is released.

Question 25

What is the PP-chain reaction?

Answer 25

A 3-step fusion process in stars, converting hydrogen to helium and releasing energy in the form of gamma rays and neutrinos.

Question 26

Why is iron the limit for fusion in stars?

Answer 26

Fusion of iron does not release energy; instead, it consumes it, triggering core collapse.

Question 27

What are the remnants of a high-mass star explosion?

Answer 27

They can be neutron stars (if core <3 solar masses) or black holes (if >3 solar masses).

Question 28

What is the HR diagram used for?

Answer 28

It plots luminosity against temperature and helps classify stars and understand stellar evolution.

Question 29

What causes Doppler shifts in exoplanet studies?

Answer 29

The motion of stars due to gravitational tug from orbiting planets.

Question 30

What determines a star's color?

Answer 30

Its surface temperature: cooler stars are redder, hotter stars are bluer.

Question 31

What is a pulsar?

Answer 31

A rotating neutron star emitting beams of radiation observed as pulses.

Question 32

What is a protostar?

Answer 32

A collapsing cloud of gas and dust that heats up but hasn’t started fusion yet.

Question 33

What happens when a low-mass star dies?

Answer 33

It ejects outer layers as a planetary nebula, leaving a white dwarf.

Question 34

What is the magnitude scale in astronomy?

Answer 34

A logarithmic scale measuring apparent brightness, where a lower magnitude means a brighter object.

Question 35

How does spectroscopic parallax measure distance?

Answer 35

By comparing a star’s spectral class and apparent magnitude to determine luminosity and distance.

Question 36

What is electromagnetic radiation?

Answer 36

Transmission of energy through space via varying electric and magnetic fields.

Question 37

What does the equation E = hf represent?

Answer 37

The energy of a photon, where h is Planck’s constant and f is frequency.

Question 38

What generates Earth's magnetic field?

Answer 38

The rotating molten core of Earth.

Question 39

How did the Moon form?

Answer 39

Likely from a giant impact between Earth and a Mars-sized object.

Question 40

What is the nebular theory?

Answer 40

A model explaining the formation of the solar system from a collapsing cloud of gas and dust.

Question 41

What is the frost line in planet formation?

Answer 41

The distance from the Sun where it was cold enough for ices to form.

Question 42

What is the Doppler Effect?

Answer 42

The change in frequency or wavelength of a wave in relation to an observer moving relative to the source.

Question 43

What does a red shift indicate?

Answer 43

An object is moving away from the observer.

Question 44

What do spectral lines tell us?

Answer 44

They identify the elements in a star or gas.

Question 45

What is an absorption line?

Answer 45

A dark line where light at a specific wavelength has been absorbed by a substance.

Question 46

What are meteoroids, meteors, and meteorites?

Answer 46

Meteoroids are space rocks; meteors are streaks seen in the sky; meteorites reach Earth's surface.

Question 47

Where do most comets originate?

Answer 47

Kuiper Belt or Oort Cloud.

Question 48

What is the habitable zone?

Answer 48

The distance from a star where conditions may allow liquid water.

Question 49

What percentage of solar system mass is in the Sun?

Answer 49

0.9990000000000001

Question 50

What causes tidal forces?

Answer 50

Differences in gravitational pull on different parts of a body.

Question 51

What is tidal locking?

Answer 51

When an object's orbital and rotational periods match, showing the same face.

Question 52

What is linear momentum?

Answer 52

The product of an object's mass and velocity.

Question 53

What is angular momentum?

Answer 53

The rotational equivalent of linear momentum, defined as L = Iω.

Question 54

What is mechanical work in physics?

Answer 54

Work done when a force causes displacement. W = F·d·cos(θ)

Question 55

What is the Work-Kinetic Energy Theorem?

Answer 55

The net work done on an object equals its change in kinetic energy: Wnet = ΔK.

Question 56

What is gravitational potential energy near Earth's surface?

Answer 56

Ug = mgh, an approximation valid only near Earth's surface.

Question 57

What is the escape speed from Earth?

Answer 57

About 11.2 km/s.

Question 58

What is total mechanical energy in orbit?

Answer 58

E = K + U = -GMm/2a for elliptical orbit, constant for bound motion.

Question 59

What is non-conservative work?

Answer 59

Work done by forces like friction, altering mechanical energy: ΔE = Wnc.

Question 60

What is the expression for gravitational potential energy at large distances?

Answer 60

Ug = -GMm/r.

Question 61

Why do astronauts appear weightless on the ISS?

Answer 61

Because both they and the station are in free fall; gravity is present but there's no normal force.

Question 62

What is the equivalence principle?

Answer 62

It's impossible to distinguish between gravitational acceleration and acceleration from motion.

Question 63

What defines the Schwarzschild radius?

Answer 63

The radius where escape speed equals the speed of light: Rs = 2GM/c².

Question 64

What is the event horizon?

Answer 64

The boundary of a black hole beyond which nothing, not even light, can escape.

Question 65

What is gravitational lensing?

Answer 65

The bending of light around massive objects due to curved spacetime.

Question 66

What causes gravitational time dilation?

Answer 66

Clocks run slower in stronger gravitational fields.

Question 67

What is a wormhole?

Answer 67

A theoretical bridge through spacetime connecting distant points.