astronomy creating of stars

emission nebula

hot stars illuminate a gas cloud. excited and/or ionized the gas(electrons kicked into higher energy states). electrons recombining , falling back to ground state, producing emission lines.

interstellar dust

probably formed i. the atmosphere of cold stars. observed through infrared emission

reflection nebulae

star illuminates a gas and dust cloud, star light is reflected by the same dust. appears blue, light is scattered by large angles than red light. same phenomenon makes sky blue

21-cm (radio) line (hydrogen i)

observingneutral hydrogen. electrons in ground state of neutral hydrogen have slightly different energies, depends on their spinning orientation.

opposite magnetic fields attract=lower energy

equal magnetic fields repel= higher energy

21 cm line of neutral hydrogen II

transition from the higher energy to the lower-energy spin state produces a characteristic 21 cm emission line.

neutral hydrogen can be traced by observing the 21cm radii emotion kk e

interstellar gas clouds

characteristics: gas hydrogen, 71% helium, 27% others

dust- microscopic particles of silicate, carbon, and iron.

temp- around 10k

initial collapse

low temp led to too low pressure to support the loud faint gravitational collapse

collapse may be triggered by collision with another cloud, a star explosion, or some other process.

non uniformity, clumpy nature of gas leads to formation of smaller, warmer, and denser clumps

protostar stage

characteristics: temp- about 1500k

Shine at infrared and radio wavelengths

low temp+ obscuring dust prevent visible detection

may be found in “ bok globules” dark blobs 0.2-2 lys across with mass up to 200 solar masses.

further collapse

gravity draws materials inward

protostar hearts up to 1 million k ion core hydrogen fusion comenses and a new star is born.

collapse of core ceases, but protostar continues to acquire material from disk for 10^6 years.

in falling materials: created violent changes in brightness and ultimately a strong outflow of gas

biopolar outflows

jets creat bi-polar outflows around protostar

easily seen at radio wavelegths

clears away most gas and dust around protostar

t-tauri star

yougn stars still partially immerse in interstellar matters

very erratically in brightness, perhaps due to magnetic activity

intense outward gas flows from the surface

occupy h-r diagram just about main-sequense

life of a star

gravity holds star together , pressure supports against gravities pull

star generated supporting pressure from energy produced in core by the conversion from hydrogen to helium

when out of fuel(hydrogen) star dies` quietly into a white dwarf or violently into a neutron star or black hole

violent explosions seed interstellar space making new generation of stars