Module 9 Flashcards

Question

What role does turbulence play in star formation within molecular clouds?

Answer 1

It can prevent gravity from overcoming pressure, requiring more mass for star formation ## Footnote Internal motions in clouds can tear them apart if not for gravity.

Answer 2

They prevent charged particles from moving freely, inhibiting gas movement ## Footnote Magnetic fields can slow or halt gravitational collapse depending on their strength.

Answer 3

It splits into numerous individual cloud fragments, each potentially forming stars ## Footnote These fragments are referred to as molecular cloud cores.

Answer 4

dense ## Footnote Such clouds can have just a few solar masses of material.

Answer 5

Only hydrogen and helium ## Footnote They formed in clouds without heavy elements, as these elements had not yet been produced.

Answer 6

Above 100 K ## Footnote This temperature is necessary to excite hydrogen molecules.

Answer 7

It becomes trapped, raising the interior temperature ## Footnote This leads to the formation of a protostar as thermal pressure begins to resist gravitational collapse.

Answer 8

A dense center of a cloud fragment that is not yet hot enough for nuclear fusion ## Footnote It has surface temperatures and luminosities similar to those of true stars.

Answer 9

Gas from outer regions of the cloud fragment rains down onto the protostar ## Footnote This occurs as the outer gas has little pressure support after the inner regions have contracted.

Answer 10

It contracts in an inside-out fashion due to gravity. ## Footnote Gravity is strongest near the protostar, where the gas density is greatest.

Answer 11

It initially remains behind as the protostar forms due to weaker gravitational pull. ## Footnote The outer regions are left with little pressure support from below.

Answer 12

Gas from the outer regions rains down onto the protostar, gradually increasing its mass.

Answer 13

The star's radiation and stellar wind can blow the gas away. ## Footnote This process is similar to how the Sun's radiation and solar wind cleared out excess gas during our solar system's formation.

Answer 14

It can lead to violent births and the formation of jets of gas. ## Footnote This is a consequence of the law of conservation of angular momentum.

Answer 15

A structure formed around a protostar where gas settles due to rotation. ## Footnote It helps transfer angular momentum away from the infalling gas.

Answer 16

Gas particles gradually spiral inward toward the protostar, increasing its mass.

Answer 17

Accretion.

Answer 18

It slows the protostar's rotation by transferring angular momentum to outlying material.

Answer 19

High-speed streams of gas fired into interstellar space by young protostars.

Answer 20

They link the angular momentum of the protostar's disk to the outflowing gas in the jet.

Answer 21

A pair of stars that orbit closely around each other, typically with separations of less than 0.1 AU.

Answer 22

A mass that allows central temperatures to exceed 10 million K.

Answer 23

A pressure that halts gravitational contraction in low-mass clouds without allowing fusion to begin.

Answer 24

It initially rises but stabilizes around 3000 K during most of the contraction process.

Answer 25

Convection, until the temperature allows for radiative diffusion.

Answer 26

The ignition of hydrogen fusion in the core.

Answer 27

* Formation of a Protostar * Convective Contraction * Radiative Contraction * Self-Sustaining Fusion.

Answer 28

The fusion rate balances with the rate at which energy escapes, stabilizing the star.

Answer 29

It shows the luminosity and surface temperature relation during a star's life track.

Answer 30

Degeneracy pressure is the pressure that pushes outward against gravity and depends only on density, not temperature. ## Footnote It prevents objects with masses below about 0.08 solar masses from becoming true stars.

Answer 31

Degeneracy pressure depends only on density, while thermal pressure depends on temperature. ## Footnote This distinction is crucial for understanding the behavior of protostars.

Answer 32

They become brown dwarfs, which are failed stars that slowly radiate away their internal thermal energy. ## Footnote These objects do not reach the conditions necessary for nuclear fusion.

Answer 33

A brown dwarf is an object that occupies a fuzzy gap between planets and stars, failing to sustain nuclear fusion due to insufficient mass. ## Footnote They are primarily detected in infrared and appear deep red or magenta.

Answer 34

They are far dimmer than normal stars, making them extremely difficult to detect even when nearby. ## Footnote Their existence was predicted for decades before the first one was identified in 1995.

Answer 35

Astronomers classify brown dwarfs as L, T, and Y spectral types. ## Footnote These classifications are based on surface temperatures: L (2200 K to 1400 K), T (1400 K to 500 K), Y (below 500 K).

Answer 36

The maximum mass is not well defined, but it is suggested to be at least 150 solar masses. ## Footnote Observations of eclipsing binary systems indicate the potential for even higher masses.

Answer 37

Radiation pressure is the pressure exerted by light, caused by photons striking matter. ## Footnote It becomes significant in massive stars, countering gravity and affecting their stability.

Answer 38

They lose mass as radiation pressure drives their outer layers into space. ## Footnote This process leads to a rapid loss of mass and prevents them from lasting long.

Answer 39

Low-mass stars greatly outnumber high-mass stars in newly formed star clusters. ## Footnote For every star above 1 solar mass, there are typically 10 stars between 0.5 and 1 solar mass.

Answer 40

Gravity must be strong enough to overcome thermal pressure for a star to form in a molecular cloud. ## Footnote This process leads to the fragmentation of clouds into clusters of stars.

Answer 41

The core starts trapping thermal energy from gravitational contraction, pushing back against the contraction. ## Footnote This marks the transition to a protostar.

Answer 42

Conservation of angular momentum causes a protostar to spin rapidly, forming a protostellar disk. ## Footnote Planets may form in this disk, and jets may be driven outward along the rotation axis.

Answer 43

Nuclear fusion becomes self-sustaining when the core temperature rises above 10 million K. ## Footnote This process is critical for a star to achieve stable fusion.