Astronomy Final Review

Flashcards about the Interstellar Medium, Nebulae, Star Birth, and Planet Formation

What is the Interstellar Medium (IM)

The name for all material between the stars, made of gas and dust.

What is the composition of the Interstellar Medium (IM)

75% Hydrogen, 24% Helium, 1% Dark Dust

What is the temperature and Density of the Interstellar Medium

Very cold (10-100* K) and extremely low density

What does the composition of the Interstellar Medium (IM) prove?

That the sun was made from the IM.

What is a Nebula?

Any blob of gas and dust in space.

Where atoms stay together to become molecules

In dark nebulae (colder clouds of gas and dust)

Who first proposed the idea of the birth of stars?

Immanuel Kant

Which stars are born most quickly?

Heavier stars

What are the early steps in the growth of a star

• As the original cloud collapses, the cloud’s temperature gets hotter;

• 99% of the cloud material gets to the center and begins to resemble a protostar (center is about 1,000,000* K)

What happens to the spin of a cloud after it collapses?

The cloud spins faster.

What happens as a result of increased cloud spin during the birth of a star?

The cloud flattens into a disk shape, called a proplanetary disk.

What are the later steps in the growth of a star

• Nuclear fusion begins in its core once it reaches the appropriate, hot, temperature;

• Fusion causes energy to flow out, providing outward pressure as it flows;

• The star is no longer being shrunk by gravity, making it a “real star”

Why are Brown Dwarfs considered “failed stars”?

Their masses are too light, making the temperature inside too cold to perform nuclear reactions.

How do protoplanets start to form?

• Grains/clumps of dust cling to each other by the electromagnetic force, creating clumps of dust called planetesimals;

• Once the planetesimals gain mass, their gravity increases, causing mass to be added on at a faster rate (accretion);

• Gravity makes the planetesimals rounder, forming protoplanets

Why did planets nearest to the sun not grow large?

• There was less material for them to scoop up in their shorter paths;

• The temperature was too hot meaning that material was not solid, preventing growth (planets need solid materials to grow large)

How did outer planets, like Jupiter & Saturn, grow to be so huge?

• There was more material in their longer paths;

• Many gases out there froze, creating solids which then fuel growth.

What caused the era of bombardment?

Outer layers of young planets turned solid, as well as planetesimals. These bodies collided a lot, leading to shattering and meteors flying everywhere, constantly striking planets and moons.

How was Mercury affected during the era of bombardment?

Some of its thin, outer layers were removed.

How was Mars affected during the era of bombardment?

Its northern parts were knocked off, and some of that debris made Mars’s 2 moons.

How was the Moon affected during the era of bombardment?

Material was ripped off of Earth, loose material clung back together to create the Moon.

What affected planets’s orbits, causing planetary migration after being born?

Planets pulled on each other;

Jupiter invaded the Asteroid Belt;

Uranus & Neptune invaded the Kuiper Belt

How did liquid water end up being on Earth?

Melted ice that came from comets and asteroids which were tossed around due to the gravity of invading planets.

What will happen when the Sun dies?

A Planetary Nebula will appear; A White Dwarf (remaining dead core of a star) will be seen

What are Exoplanets?

Planets that orbit other stars (not the Sun)

How many exoplanets have we found so far?

Thousands

Why do we search for Exoplanets?

To answer the following questions:

• How are planets born?

• Are Earth-like planets common or rare?

• Can we find life on other worlds?

What is the Astrometric Method for finding Exoplanets?

A technique that measures the position of a star shifting side-to-side to detect the gravitational pull of an orbiting planet.

What kind of stars are commonly found using the Astrometric Method?

Dim companion stars

What is the Radial Velocity, or Wobble Method for finding Exoplanets?

A technique that measures a star’s speed using the Doppler Effect. We use it when a star looks like it is wobbling toward and away from us.

How do we know if a star is wobbling due to an Exoplanet’s gravitational pull?

If the star’s light shifts closer to blue as it’s moving towards us.

What are the 3 reasons why some exoplanets cause a greater wobble than others do?`

• The exoplanet’s mass could be very massive, giving it more gravity to make the star wobble more

• The mass of the star could be light, making it easier to budge

• The orbit of the exoplanet may be close to the star, so the exoplanet’s gravity makes the star wobble stronger

What is the time for one full wobble of a star?

The Period

What does it mean if one planet has a shorter period compared to the period of another planet in the same system?

The size of the first planet’s orbit is smaller.

What was the first success of the Wobble Method?

Planet DImidium, a Hot Jupiter

Why are Hot Jupiters so easy to find when using the Wobble Method?

• They are very massive, like Jupiter, causing a stronger, more obvious wobble

• They are closer to their host stars, causing an even stronger wobble

• Their orbits are small, causing less time to be needed to make the discovery

What is considered the habitable zone of a star system?

The range of distances away from a star where liquid water can exist at the surface of a planet.

Which stars have more distant habitable zones?

Hotter stars

What is the Transit Method for finding exoplanets?

A technique that observes the dimming of a star's light when an exoplanet passes in front of it, causing a temporary and periodic decrease in brightness.

How can we learn the diameter of a planet using the Transit Method?

How much a star’s light dims during a transit; the greater the dimming, the larger the planet's diameter.

What does a light curve show when plotted?

How a star’s brightness changes when a planet transits.

What are some disadvantages in using the Transit Method?

• Orbits of many stars are at bad viewing angles so then there will be no transits

• We cannot learn masses of most planets until further study

• We cannot be sure we really have found most planets until we rule out fakes

Which method can we use to confirm transiting planets?

The Wobble Method

What is the Direct Imaging Technique for finding Exoplanets?

A method that captures images of planets directly by blocking the light from their parent stars, allowing for detailed observations. Instead of looking at reflected light that our eyes can see, we look for their body heat, which is infrared light.

For which kinds of planets does the Direct Imaging Technique work best?

• Planets that are in long, large orbits (It is easier to see the planet apart from the star)

• Planets that are near to us (The planet will not be lost in the glare & the brightness of nearby planets will look greater than farther planets)

• Young planets (Temperatures are hotter, so they glow brighter)