Quiz 5 Flashcards
Astronomers estimate that new stars form in our galaxy at the rate of about
2-3 a year
By mass the interstellar medium in our region of the Milky Way consists of
70% hydrogen, 28% helium, and 2% heavier elements
The typical density and temp of molecular clouds are
300 molecules per cubic centimeter 10-30 kelvin
The most abundant molecule in a molecular cloud is
H2
The typical size of an interstellar dust grain is
1 micrometer
If you wanted to observe a molecular cloud, in what wavelength would you most likely observe
Infrared
What happens to the visible radiation produced by new stars within a molecular cloud
It is absorbed by dust grains and hears up the cloud
What prevents the pressure from increasing as a cloud contracts due to gravity
Thermal energy is conveyed to radiative energy via molecular collisions and released as photons
Calculations show that gravity begins to overcome thermal pressure in clouds that are
More massive than a hundred times the sun
What is the likely reason that we cannot find any examples of the first generation stars
The first generation stars were all very massive and exploded as supernova
Why do we think the first generation of stars would be different from stars born today
Without heavy elements the clouds Could not reach as low a temperature as today and had to be more massive to collapse
What happens when the rotation of a molecular cloud as it collapses to form a Star
The rotation increases and results in a disk of material around a protostar
When does a protostar become a true star
When nuclear fusion begins in the core
When does a star become a main sequence star
When the rate of hydrogen fusion within that stars core is high enough to maintain gravitational equilibrium
What happens to the surface temp and luminosity when gravity first assembled a protostar from a collapsing cloud
It’s surface temp and luminosity increase
What happens to the surface temp and luminosity when a protostar undergoes convective contraction
It’s surface temp remains the same and it’s luminosity decreases
What happens to the surface temp and luminosity when a protostar radiatively contracts
It’s surface temp and luminosity increase
What is the smallest mass a newborn star can have
80 times the mass of Jupiter
What is the greatest mass a newborn star can have
150 solar masses
No stars have been found with masses greater than 200 times our sun because..?
They would generate so much power that they would blow themselves apart
Which of the following discoveries if they existed, would necessitate a re-evaluation if our ideas of stellar formation
A 0.01 solar mass Star
What is the eventual fate of a brown dwarf
It gradually cools down and becomes even dimmer
Where would a brown dwarf be located on an HR diagram
Below and to the right of the lowest part of the main sequence
