AST201H1 Lecture Notes - Star Formation
DepartmentAstronomy & Astrophysics
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February 15, 2010
How long stars live
x Most stars form in clusters. We can use the H-R diagram of a cluster to figure out how
old the cluster is.
o Look at a cluster, young stars: lots of gas and dust. Older no gas and dust from
when it was formed
o Measure luminosity and spectral classes/surface temps. Then you plot them all up.
o Pleiades, you can see with your naked eye.
o Peeling away from 100 million years, that tells you that every star in that cluster is
lifetime of less than 100 million years you know they have already died.
o All of the young stars are dead in the 7Gyr, only the old stars are left
x The one that turns away form the main sequence closer to the bottom is the oldest cluster.
x Stars are born and the die.
x Spectroscopy, hydrogen emits or absorbs a HUGE amount of red light.
x Dark region is a region of presence of a lot of gas and dust which blocks out gas and light
x Between the spirals balls of hydrogen balls and dust are related
x Red Nebulae Æ hydrogen gas. Aslo, dust and blue stars
x Lots of blue starsÆ lots of young stars
Most distant stars we can see are blue because although these stars are rare, they are extrememly
x Blue stars are rare and exotic.
x Elliptical galaxy, functionally dead. Usually enormous with trillions of stars.
x Sentoras A, lots of gas, eating up another galaxy.
x Taking pictures in multiple parts of the electromagnetic spectrum is essential to
understand star formation.
x Infrared light shows cold dust.
x Where there is a lot of dust there are a lot of red nebulae and blue stars.
x Orion, 2 blue stars. Orion Nebula, full of young stars embedded in the gas.
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