Chapter 21

What sustains such a wave of star formation in a giant molecular cloud?

When massive stars form, their ultraviolet radiation and later their final explosions compress the gas in the cloud and cause a new group of stars to form

The Orion Nebula is

A large cloud of gas and dust illuminated by the light of newly formed stars within it

A graduate student is given the assignment to find stars with dusty disks around them. What kind of telescope would it be best for her to use for this purpose?

A large telescope that detects infrared radiation

Which of these stars will take the longest time to go from the earliest protostar stage to the main sequence?

A star 1/10th the mass of our Sun

Which of the following possibilities is most likely to result in a detection by Kepler in a few year's time? Assume all systems to be in circular orbits viewed edge-on.

An Jupiter-like planet in a 1 AU radius orbit

Planets in the habitable zone of their stars:

Are at a temperature where water can exist as a liquid

Cores

Are the embryos of stars. The conditions in these cores are low temperature and high density, which is required to make stars.

When astronomers carefully examine the planets found by Kepler and draw conclusions from the Kepler sample, what do they conclude about planets the size of Earth?

Earth-sized planets are common, but so are planets somewhat bigger than Earth

The existence of exoplanets is typically known through

Effects on a parent star

As our part of the early nebula evolved to form our solar system, it

Expanded, rotated more rapidly, and heated up

Massive stars on the main sequence have

High temperatures and high luminosities.

Stars of masses much higher than the Sun's reach the main sequence

In a few thousand to a million years.

How long it takes a star to form depends on

Its mass.

Low-mass stars have

Low temperatures and low luminosities

Tens of millions of years are required for stars of__________to evolve to the lower main sequence.

Lower mass

In figuring out the evolutionary tracks on the H-R diagram, astronomers

Make model stars on a computer and then follow how their characteristics will change with time

Positive Radial Velocity

Moving away from Earth

Negative Radial Velocity

Moving towards Earth

The Kepler Space Telescope is searching for exoplanets by the transit method. It is necessary for Kepler to monitor a large number of stars because

Only a small percentage of systems have the correct orbital tilt for transits to be observed Planets will be transiting the star for only a small percentage of the orbit

The histogram shows the number of new planets discovered each year up to 2015. The planets in the circle were predominantly discovered by

Radial velocity method

The first planetary system was found in 1999 using

The Doppler method

When the star's central temperature becomes high enough (about 12 million K) to fuse hydrogen into helium

The star has reached the main sequence

Our current theory of planet formation states that planets form as a natural byproduct of star formation. This implies that

There should be very many planets orbiting other stars

Giant Molecular Clouds

These clouds have cold interiors with characteristic temperatures of only 10-20 K; most of their gas atoms are bound into molecules. The Birthplaces of most stars

How did astronomers determine that the planet orbiting the star HD 209458 is a gas giant like Jupiter and not made mostly of rocks or metals?

They knew that any planet as close to its star as this one was could not be made of rock or metal They measured the mass of the planet, which immediately told them whether it was gas or rock