Quiz 2: The formation of stars and protoplanetary disks & orbital dynamics

What happens when the Jeans mass is reached?

A molecular cloud contracts into a protostar

What keeps a star from collapsing under its own gravitational force?

The heat of nuclear fusion in its core

What happens when the Jeans mass is reached?

A molecular cloud contracts into a protostar

What keeps a star from collapsing under its own gravitational force?

The heat of nuclear fusion in its core

What keeps a molecular cloud from collapsing under its own gravitational force?

Gas pressure

Could our solar system have formed with the Universe's first generation of stars? Explain.

No. The first generation of stars (called Population III stars) contained only H and He, and no heavier elements and metals needed to form the rocky planets as well as the gas giants in our solar system.

What is meant by the metallicity of a star?

It is the percentage of that star which is not made up of hydrogen and helium

Briefly describe how a binary star system forms. Is this more or less common than forming a single star?

After the Jeans mass is reached and the gas cloud collapses into a core, if the core is spinning fast enough it may break up into two or more sub-clouds which orbit each other. A binary system is more common than a single star system.

What is the solar wind, and how is it driven as it propagates out into the Solar System?

The solar wind is composed of protons and electrons and ions, which propagate at a speed of 350-700 km/s driven by the magnetic field of the Sun (charged particles in a magnetic field will start to move due to the Lorentz force).

What will happen to our Sun in the next few billion years as it moves up along the main sequence?

It will gradually get hotter

What happens when a star enters the Red Giant phase?

All the above: Helium fusion starts, as there is no more hydrogen, The outer

layers swell and cool, turning it red, The core shrinks

What is a planetary nebula?

It is the outer layers released from a dying star

Where were the first molecules form in our solar system?

in the pre-solar nebula

Which telescope do we use to observe protoplanetary discs?

ALMA

What determines the structure of a protoplanetary disc?

Angular momentum and heat

Give an example of one distinct region of a protoplanetary disc and which wavelength you would use to observe that region.

An example of such a region is the Dust inner rim which can be observed with the IR wavelengths

What does the chemical composition of the Sun tell us about the protoplanetary disc?

It tells us about the original elemental composition of the protoplanetary disc

What happens when you cross the frost line, on your way away from a star?

Volatile compounds condense into solid grains

Tycho Brahe was a notorious party animal. What did he suffer from?

his own mental rigidity

How did observing Jupiter's moons help Galileo in confirming Kepler's theory of how planets orbit the Sun?

He showed that Jupiter's moons orbit Jupiter in accordance with Kepler's laws. This confirmed that Kepler's laws were universal for orbiting bodies in the solar system, applying to moons orbiting planets and planets orbiting stars alike.

A note about Kepler's laws and Galileo

The important thing to note about Galileo's contribution to Kepler's theories was that his observations of Jupiter confirmed the universality of Kepler's laws. It may seem obvious to you now that the laws which govern how planets orbit stars and how moons orbit planets are the same. But you have to realize that all of this drama was unfolding before Newton's universal law of gravitation. For all they knew, these could be totally unrelated phenomena governed by completely different rules.

Our progress in physics deals largely with attempting to make our theories more universal, so that we can explain all of the phenomena around us with the same set of rules. Further down the line of scientific progress we are sure to find universal underlying principles to phenomena that we now assume to be unrelated to each other.

At which point in its orbit is the orbital velocity of Earth fastest?

Perihelion, when it’s closest to the Sun

If you wanted to throw an average apple (0.1 kg) into space, so that it would leave Earth's orbit, you would have to pitch it at 11.2 km/s. How fast would you have to throw a 5 kg bowling ball to achieve this?

11.2 km/s