lecture 5 Flashcards
(17 cards)
What are supernovae?
Sudden very bright flare-ups of stars.
They can emit as much energy as the Sun in its whole 10 billion year lifetime.
How often do supernovae occur in our galaxy?
About every 30 years.
Only a few are bright enough to be visible to the naked eye.
What was the famous supernova observed by Chinese astronomers in 1054?
A supernova in the constellation Taurus, now the Crab Nebula.
It was so bright that it was visible in daylight.
What are the two types of supernovae?
Type I and Type II.
They are distinguished by their spectrum and light curves.
What characterizes Type I supernovae?
They suddenly become about 4 billion times as luminous as the Sun and decline rapidly in a few days.
They have weak hydrogen lines in their spectrum.
What causes a Type I supernova?
A white dwarf in a binary system accretes mass from a red giant and exceeds the Chandrasekhar limit.
This leads to collapse and explosion.
What is a standard candle in astronomy?
An object with a known brightness used to measure distances in the universe.
Type I supernovae are considered standard candles.
What is Hubble’s constant?
The velocity of recession divided by the distance (H = V/D).
It helps in measuring the expansion of the universe.
What characterizes Type II supernovae?
They are about 0.6 billion times the solar luminosity and contain hydrogen lines in their spectrum.
They result from the explosive end of very massive giant stars.
What happens when the core of a massive star becomes iron?
It collapses in about 1 millisecond to become a neutron star.
Most energy is emitted as neutrinos, not light.
What is observed after a supernova explosion?
A cloud of gas expanding away from the site of the explosion.
This can be visible for hundreds or thousands of years.
What is the significance of SN 1987A?
It was the first supernova in 400 years visible to the naked eye.
It was observed in the Large Magellanic Cloud.
What elements were observed in SN 1987A?
Radioactive elements heavier than iron, such as cobalt and nickel.
The mass of nickel produced was about 20,000 times the mass of the Earth.
What happens to the core of a Type II supernova after the explosion?
It is expected to become a neutron star.
This has not yet been observed for SN 1987A.
What is synchrotron radiation?
Radiation emitted by high-speed electrons spiraling around magnetic field lines.
It is observed in supernova remnants.
Fill in the blank: Type I supernovae do not leave __________.
remnant neutron stars.
They explode before a neutron star can form.
What is the Crab Nebula?
The expanding gas cloud resulting from the supernova observed in 1054.
It serves as an example of a supernova remnant.
