Nebulas & Formation
What is a nebula?
A nebula is a big cloud of gas and dust and the birthplace of stars.
What does a star’s temperature tell us about its color?
A star’s temperature is linked to its color.
After the main sequence, what stage do low‑mass stars often become?
Red giant.
High‑mass main sequence stars are usually what colors?
Blue or white
What two things does the H‑R Diagram plot?
The H‑R Diagram plots magnitude (luminosity/brightness) against temperature (color).
What two main kinds of material are nebulae made of?
Gas (mostly hydrogen) and dust (mostly carbon and silicon).
Cooler stars look what color and hotter stars look what color?
Cooler stars are red; hotter stars are blue.
What happens to the outer layers and the core of a star as it becomes a red giant?
The outer gas layers expand and the core shrinks.
What can happen to a very massive star at the end of its life?
A supernova (a giant explosion) can occur.
In what units is temperature measured for stars?
Temperature is measured in Kelvin (K).
What happens inside a nebula that leads to a protostar forming?
Gravity pulls gas and dust together into regions of greater density, forming a protostar.
What does luminosity mean?
Luminosity is the amount of energy (light) a star emits — how bright a star is.
What is a planetary nebula?
A planetary nebula is when the outer layers are expelled and appear as brightly colored clouds; the leftover core becomes a white dwarf.
What is a neutron star?
A neutron star is the very dense core left after a supernova; material is pressed so tightly that protons and electrons combine to make neutrons.
Luminosity in simple terms?
Luminosity: the amount of energy (light) a star emits; how bright a star is.
Why is a protostar described as unstable?
A protostar is unstable due to many reactions occurring within it.
What two things determine a star’s luminosity?
Luminosity is determined by the size and temperature of the star.
What is a white dwarf?
A white dwarf: forms when a low‑mass star runs out of fuel; it is the hot, dense core of a planetary nebula and is very dense (notes say gravity about 350,000 times Earth's).
Black hole: what is one key idea about its gravity?
Its gravity is so strong that nothing can escape, not even light
What does magnitude measure? (hint: what are its synonyms?)
Magnitude measures a star’s brightness or luminosity.
What starts in a protostar when the core reaches about 15 million degrees Celsius?
Nuclear fusion begins (hydrogen fuses into helium), releasing light and heat when the core reaches around 15 million degrees Celsius.
How is apparent magnitude different from absolute magnitude?
Apparent magnitude is how bright an object appears from Earth (or where you're observing). Absolute magnitude is the measure of a star's brightness as if it were at a standard distance of exactly 10 parsecs.
What is the final stage after a white dwarf?
Black dwarf.
Describe the sequence from a high‑mass main sequence star to a neutron star
High‑mass main sequence star → red supergiant or blue giant (outer layers expand; core shrinks) → supernova → neutron star (or black hole depending on mass).
Explain the difference between apparent magnitude and absolute magnitude (mention the standard distance for absolute magnitude for extra points).
Apparent magnitude (m) is how bright an object appears from Earth; absolute magnitude (M) is the brightness the star would have at a standard distance of exactly 10 parasecs