Sec. 3 Lives of Stars

lifetimes of stars

• how long a star lives depends on its mass

• greater the mass- shorter the lifetime

star’s life cycle

• nebula= large cloud of gas & dust

• birthplace of stars

Image by NASA/STSCI/Nolan Walborn/Hubble Heritage Team

nebula

1. protostar

• Earliest stage in star’s life

• Contracting cloud of gas & dust w/ enough mass to make star

sun

2. main sequence star (developed star)

3. red giant or supergiant

start to run out of fuel- outer layers expand

When star runs out of fuel, becomes :

• white dwarf or

• neutron star or

• black hole

depends on star ’s mass

small & medium stars become

4.white dwarf-

cooled blue-white core left behind

about size of Earth

same mass as Sun

This Hubble Space Telescope image shows Sirius A, the brightest star in our nighttime sky, along with its faint, tiny stellar companion, Sirius B.

Astronomers overexposed the image of Sirius A [at center] so that the dim Sirius B [tiny dot at lower left] could be seen.

• 5. black dwarf-

when white dwarf stops glowing

•giant & supergiant stars

4. supernova- explosion of a dying giant or supergiant star

• one of the most dazzling events in the universe

supernova

• 5. neutron star- small, dense star

- 3 X mass of Sun

pulsar

• Spinning neutron star

• Emits pulses of radio waves

• 5. black hole- most massive stars

• form from stars that have 40 times the mass of sun

• gravity is so strong that nothing can escape- not even light

• x-rays detect them

The remains of the most massive stars collapse into black holes. This artist’s impression shows a black hole pulling matter from a companion star.

Not even light can escape from a black

hole.

(unsequenced human life cycle page)

nebula

protostar

developed star

supergiant

supernova

black hole

nebula

protostar

protostar

protostar

Life Cycle Life Cycle of a Starof a Star

nebula= huge cloud of gas & dust

protostar= beginning of star

red giant or supergiant= star expands, outer layers cool

supernova= enormous explosion of a giant star

white dwarf= dim star that forms from a red giant

black dwarf= runs out of fuel dead star

black hole= core collapses to a tiny point with a very strong gravitational pull

neutron star=

dense remains of a massive star’s core

low mass star

high mass starvery high mass

massive star

developed star (main sequence star)