What is a protostar?

A fully formed star in its first million years A young stellar object that is contracting under gravity but has not yet begun hydrogen fusion A failed star that never gets hot enough to glow A very old star near the end of its life

What source of energy makes a protostar glow?

Nuclear fusion of hydrogen in the core Radioactive decay of heavy elements in the core The conversion of gravitational potential energy into heat as the cloud collapses inward Chemical burning of hydrogen and oxygen

What forms around a protostar as it contracts?

A thick atmosphere like the one on Jupiter A rotating disk of gas and dust called a protoplanetary disk A second protostar that always orbits the first A shell of dense dark matter that traps heat

What is the T Tauri phase?

The final stage of a star before it becomes a supernova A stage of stellar development after the protostar stops accreting most material but before it reaches the main sequence The stage when a star first runs out of hydrogen in its core An old star that has expanded into a red giant

What critical temperature must the core of a protostar reach for hydrogen fusion to begin?

About 1,000 Kelvin — similar to the temperature of a campfire About 100,000 Kelvin — the temperature of a white dwarf surface About 10 million Kelvin About 1 billion Kelvin — the temperature needed for helium fusion

How does the time it takes to form a star compare between massive stars and Sun-like stars?

Both types take about the same time — around 10 million years Sun-like stars form faster because they are smaller and more common Massive stars form in as little as 100,000 years; a Sun-like star takes about 50 million years Massive stars take billions of years to form because they need more material

What are the bipolar jets seen coming from some protostars?

Rings of material orbiting the protostar at its equator Nuclear explosions on the surface of the protostar Narrow streams of gas blasted outward from the poles of the protostar along the rotation axis Streams of dark matter flowing into the protostar from space

What happens when a protostar finally ignites hydrogen fusion in its core?

It explodes as a supernova immediately It cools down and stops glowing It expands into a red giant right away It becomes a true main sequence star, stabilized by the balance between gravity and fusion energy pressure

Why are newly born massive stars already surrounded by glowing gas even before their planets finish forming?

Massive stars have larger protoplanetary disks that glow more brightly Massive stars are born so hot that their intense radiation immediately ionizes the surrounding gas, creating an emission nebula The surrounding gas heats up because massive stars are closer to the galactic center Massive stars trigger nearby supernovae that light up the surrounding cloud

What is the significance of the protoplanetary disk that forms around a protostar?

It is leftover material that eventually falls into the star It produces the jets that are seen shooting from young stars It is the material from which planets, moons, asteroids, and comets form around the new star It becomes the star's atmosphere once the star fully forms