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ASTRONOMY Stars

OBJECTIVES By the end of this presentation, students will be able to Trace the formation and life cycle of a star based on its initial gas cloud mass; illustrate the life span of the sun; describe the formation and structure of a black hole.

Recall the 6 stages of stellar formation: 1.Protostar Stage 2.Pre-Main Sequence Stage 3.Main Sequence Stage 4.Giant Stage 5.Variable Stage 6.Terminal Stage

Stellar Formation and Life Cycle What happens to a star during each of these phases is directly related to the mass of the initial gas cloud.

Stellar Formation and Life Cycle Cloud mass; solar masses: Forms an infrared source in the pre-main sequence stage (stage 1); Never settles on the main sequence; Never becomes a giant or variable star; Fizzles out as a brown dwarf with a mass of to 0.08 solar masses (stage 6).

Stellar Formation and Life Cycle Cloud mass; solar masses: Forms an infrared source in the pre-main sequence stage (stage 1), becoming a T-Tauri type star (stage 2); Settles to a red dwarf on the main sequence (stage 3); Explodes to form a white dwarf until it fizzles out with a mass of 0.08 to 0.4 solar masses (stage 6).

Stellar Formation and Life Cycle Cloud mass; solar masses: Forms an infrared cocoon star in the pre-main sequence stage (stage 1), becoming a T-Tauri type star (stage 2); Settles to a yellow to orange main sequence star (stage 3);

Stellar Formation and Life Cycle Cloud mass; solar masses: Fluctuates, forming a long-period variable star (stage 5); Explodes to form a white dwarf until it fizzles out with a mass of 0.4 to 0.7 solar masses (stage 6).

Stellar Formation and Life Cycle Cloud mass; solar masses: Forms an infrared cocoon star (stage 1), becoming a T-Tauri type star (stage 2); Settles to a white to yellow main sequence star (stage 3); Expands to form a red giant (stage 4);

Stellar Formation and Life Cycle Cloud mass; solar masses: Fluctuates, forming a semi-regular variable star (stage 5); Explodes to form a white dwarf until it fizzles out; mass of 0.7 to 1.4 solar masses (stage 6).

Stellar Formation and Life Cycle Cloud mass; 3-5 solar masses: Forms an infrared cocoon star (stage 1), becoming a T-Tauri type star (stage 2); Settles to a blue to white main sequence star (stage 3); Expands to form a giant (stage 4);

Stellar Formation and Life Cycle Cloud mass; 3-5 solar masses: Fluctuates, forming a Cepheid variable star (stage 5); Explodes, leaving behind a neutron star core; mass of 1.4 to 2.3 solar masses (stage 6).

Stellar Formation and Life Cycle Cloud mass; 5-10 solar masses: Forms an infrared cocoon star (stage 1), becoming a T-Tauri type star (stage 2); Settles to a blue giant to blue main sequence star (stage 3); Expands to form a red supergiant (stage 4);

Stellar Formation and Life Cycle Cloud mass; 5-10 solar masses: Fluctuates, forming a Cepheid variable star then supernovas (stage 5); The explosion leaves behind a neutron star core; mass of 2.3 to 3.6 solar masses (stage 6).

Stellar Formation and Life Cycle Cloud mass; solar masses: Forms an infrared cocoon star (stage 1); Settles to a blue giant main sequence star (stage 3); Expands to form a supergiant (stage 4); Supernovas (stage 6); Leaves behind a neutron star core; mass of 3.6 to 5 solar masses.

Stellar Formation and Life Cycle Cloud mass; solar masses: Forms an infrared cocoon star (stage 1); Settles to a blue giant main sequence star; Expands to form a hypergiant (stage 4); Fluctuates to a Wolf-Rayet star (stage 5); Fluctuates to supernova (stage 6); Leaves behind a neutron star core; mass of 5 to 8.3 solar masses; possibly a black hole.

Stellar Formation and Life Cycle Cloud mass; solar masses: Forms an infrared cocoon star (stage 1); Fragments into smaller proto-stars or complete disruption of the process (stage 6) or… Supernovas (stage 6); Leaves behind a neutron star core; mass of 8.3 to 20 solar masses; possibly a black hole.

Protostar – the cloud of interstellar gas that is dense enough and cool enough to begin contracting into a star. Cocoon Nebula – gaseous remnants of the original cloud obscuring the original star. T-Tauri Star – named after the young stars in Taurus that have variable light output and out-flowing gas. Stellar Formation and Life Cycle

Variable Star – one that varies in brightness. (some 28 varieties) Cepheid Variable – very luminous giants with periods from 1 to 50 days. Long Period Variable – pulsating red giants with periods from 75 days to 2 years. Stellar Formation and Life Cycle

Semi-Regular Variables – giants with poorly defined periods, subject to unpredictable variations. Irregular Variable – giants of various colors with no definite periods. Nova – hot sub-dwarf stars that brighten explosively in a few days and fade back to normal in a few years. Stellar Formation and Life Cycle

Nova – hot sub-dwarf stars that brighten explosively in a few days and fade back to normal in a few years. ■ explosions equal the energy output of 10,000 stars. ■ novas occur in our galaxy each year. Stellar Formation and Life Cycle

Supernova – the spontaneous explosion of a star that is so massive, its variable stage is too violent to be a smooth transition. ■ the explosion blows much of the star’s convective zone into space, leaving behind the dense core. ■ explosion equals the energy output of 10,000,000,000 stars. Stellar Formation and Life Cycle

Supernova Stellar Formation and Life Cycle

Supernova Stellar Formation and Life Cycle

Supernova Stellar Formation and Life Cycle

Supernova Stellar Formation and Life Cycle

Neutron star – a planet-sized star, more massive than the white dwarf, in which the repulsion forces between protons in the atom has been overcome, forming Neutron Material. ■ one cm 3 could weigh 1x10 14 tons. ■ the core often spins rapidly. Stellar Formation and Life Cycle

Pulsar star – pulsing low-energy radiation sources. ■ Spinning neutron stars create strong magnetic fields. Viewing these from the right direction, flashes of the radiation would be seen. The flashes occur at 0.25 to 13 second intervals. Stellar Formation and Life Cycle

Black Holes – supernova remnants so dense, their gravitational fields are so strong light is prevented from escaping. ■ core is 1.25 to 2 miles in diameter. ■ mass is greater than 5 Suns. ■ edges of black hole is 12.5 to 20 miles in diameter. Stellar Formation and Life Cycle

Excretion stream Accretion disk Event Horizon Core

Cygnus X-1 Black Hole (not visible)

M-87 Galactic Core

Excretion Stream ?

ASTRONOMY Stars