Chapter 9

Interstellar gas is typically found in 2 forms:

- HI (H-one) clouds - HII Hot intercloud medium

What are the four main steps of star formation, in order from firs step to last step?

1- Interstellar gas collapses 2- protostars from 3- fusion begins 4- hydrostatic equilibrium is reached

Star formation: ISM collapses, has to overcome what 4 factors that want to push everything outward?

1- Thermal energy in the gas 2- Magnetic fields 3- Rotational motion of the ISM 4- Turbulence in the ISM

What information does 21 cm radiation provide about interstellar gas clouds?

1- their motion and distribution through space 2- their density 3- their temperature

Protostar

A contracting cloud of gas and dust with enough mass to form a star

Difference between proton-proton and CNO cycle

Carbon-12 starts and ends the cycle (it gets recycled - the carbon-12 at the beginning comes back at the end) Includes steps where the protons (hydrogen) combine withcarbon and nitrogen Why is this significant? C and N have a much higher mass than H, which means the energy needed in the process is a lot higher, KE = 12mv 2 . Higher energy = higher temperature. Temperatures greater than 16 million K are required for the CNO chain to take place(T at the center of the Sun is around 15.7 million K). Stars more massive than the Sun (8 times more massive) produce their energy through the CNO cycle/

What supports the helium-rich core of a low mass star?

Electron degeneracy pressure

Types of nebula

Emission, reflection, dark

What inevitable forces a star like the Sun to evolve away from being a main sequence star?

Helium builds up in the core, while the hydrogen burning shell expands

What is the interstellar medium?

Space is full of dust and gas. We call this the interstellar medium, or ISM. The densest clouds of the ISM are where stars are born.

_____________________ provides evidence of stellar evolution

Star clusters

Protostar in the H-R diagram

The birth line is the location on the H-R diagram where a protostar becomes detectable at visible wavelengths .

Why do low-mass stars last longer that high-mass stars?

The fuse more slowly than massive stars, which means they don't use up their source of fuel as fast as high-mass stars

What happens when stars run out of hydrogen in their core?

The outward radiation pressure is too small to overcome the inward pull of gravity, so they being to contract

During the hydrogen shell-burning phase

The star grows bigger and more luminous

Stars within what range of mass ca undergo the helium flash stage of stellar evolution?

Within 0.4 to 2 solar masses

Emission nebula

a glowing gaseous nebula whose light comes from fluorescence caused by a nearby star ionized hydrogen produces hydrogen's reddish-pink emission spectrum.

Dark nebula

a nonluminous nebula of dust and gas that is observable because it obscures light from other sources. visible where dense clouds of gas and dust show up dark against a brighter background (bright because the region is filled with stars or other, brighter nebula).

The HII regions is another name for

an emission nebula

In stars more massive than the Sun, hydrogen is fused into helium through the CNO cycle, a process which utilizes ______________ and occurs at __________________ temperatures than the proton-proton chain

carbon, nitrogen, oxygen; higher

HI

cold (T ∼ 100 K) clouds of neutral atomic or molecular hydrogen I moderate density; about 10 to a few hundred atoms per cubic cm

The overall dimming of starlight matter is called

extinction

Higher mass protostars enter the main sequence:

faster and at a higher luminosity and temperature.

The lifetime of a star depends on

fuel supply and rate of fuel consumption

The interstellar medium is made up of

gas and dust gas: hydrogen and helium dust: carbon and silicon

HII

hot (T ∼ a few 1000 K), ionized hydrogen (HII) I low density; about 0.1 atoms per cubic cm.

Interstellar gas in composed almost entirely of what two gases?

hydrogen and helium

Reflection nebula

interstellar dust that is visible due to reflected light from a nearby star. Such reflection nebulae are bluish in color due to the reflected light. produced when light is scattered by tiny dust particles mixed in with the gas. Characteristic of stars that aren't hot enough to ionize the hydrogen in the nebula.

A protostar becomes a star when

nucelar fusion begins

What type fo radiation is 21-centimeter radiation

radio waves

Interstellar reddening of starlight occurs because the interstellar dust preferentially ________ the blue light.

scatters

Why do reflection nebulae appear blue?

small dust particles scatter blue light at larger angles than they scatter longer wavelength light.

21-centimeter radiation results from the change of the __________ of the electron in a ____________ atom

spin; hydrogen

CNO cycle

the cycle of reactions by which intermediate and high mass stars fuse hydrogen into helium stars produce energy by nuclear fusion of hydrogen into helium. In stars, slightly more massive than the Sun, a more powerful energy generation mechanism takes pace: the CNO Cycle: Carbon, Nitrogen, Oxygen

Which of the following DOES NOT resist the contraction of a cloud of interstellar matter?

thermal motion ✅ rotational motion ✅ magnetic fields ✅ gravity ❌

Open clusters contain a few hundred _______________ stars that are loosely grouped together, while globular clusters are tightly clustered groups of hundreds to thousands of _______________ stars

young; old