True, Earth’s atmosphere at sea level is primarily composed of nitrogen and oxygen molecules., The interstellar medium (ISM) is not a perfect vacuum, as it contains gas and dust particles., Hydrogen is the most abundant element in the interstellar medium., A cubic centimeter of interstellar medium contains far fewer particles than a cubic centimeter of Earth’s air., Interstellar clouds make up only 10-20% of the total volume of the interstellar medium., Intercloud gas fills 80-90% of the ISM’s volume but holds only 20-30% of its total gas mass., Interstellar clouds have an extremely low temperature of 10-20 Kelvin., Intercloud gas is much hotter than interstellar clouds, with temperatures ranging from 1,000 to 10,000 Kelvin., The low temperature of interstellar clouds results in very low thermal pressure., Low thermal pressure in interstellar clouds allows gravity to pack particles tightly, creating high density., Interstellar clouds contain 70-80% of the total gas mass of the interstellar medium., Thermal pressure is an outward force created by the movement of gas particles in a cloud., Self-gravity of an interstellar cloud is an inward force that pulls particles toward the cloud’s center., A stable interstellar cloud is in equilibrium between self-gravity and thermal pressure., There is a negative feedback loop that stabilizes interstellar clouds against collapse and expansion., When an interstellar cloud starts to collapse, it compresses and heats up, increasing thermal pressure., Increased thermal pressure from cloud collapse stops further inward collapse in most cases., When an interstellar cloud expands, it cools down, causing its thermal pressure to decrease., Hot intercloud gas exerts external pressure that helps stop the expansion of interstellar clouds., Only very massive interstellar clouds can overcome the negative feedback loop and collapse to form new stars., False, The interstellar medium is mostly composed of nitrogen and oxygen, just like Earth’s atmosphere., A cubic centimeter of interstellar medium has more molecules than a cubic centimeter of Earth’s sea-level air., Interstellar clouds have a similar temperature to Earth’s average atmospheric temperature., Intercloud gas is colder and denser than interstellar clouds., Interstellar clouds fill most of the volume of the interstellar medium., Intercloud gas contains the majority of the ISM’s total gas mass., High thermal pressure in interstellar clouds allows them to become extremely dense., Self-gravity is an outward force that pushes interstellar cloud particles away from the center., Thermal pressure in interstellar clouds is stronger than the thermal pressure in intercloud gas., There is no balance between gravity and thermal pressure in stable interstellar clouds., When an interstellar cloud collapses, it cools down and loses thermal pressure entirely., Collapsing interstellar clouds never stop collapsing, even for low-mass clouds., Expanding interstellar clouds heat up and gain more thermal pressure as they grow., The negative feedback loop in interstellar clouds causes runaway collapse or expansion., All interstellar clouds will eventually collapse to form new stars and planets., Interstellar dust makes up 99% of the total mass of the interstellar medium., Hot intercloud gas feels hot to humans because of its high particle density., Interstellar clouds are dense because they have extremely high thermal pressure., Helium is the most abundant element in the interstellar medium., The particles in interstellar clouds move faster than the particles in intercloud gas..

Interstellar Medium

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