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The Aging of High Mass Stars is Completely Different. Whereas low mass stars ultimately become white dwarfs, higher mass stars ultimately blow themselves to high heaven . The same stages happen, but no helium flash or horizontal branch… just straight to the super giant phase !

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slide1

The Aging of High Mass Stars is Completely Different

Whereas low mass stars ultimately become white dwarfs, higher mass stars ultimately blow themselves to high heaven.

The same stages happen, but no helium flash or horizontal branch… just straight to the super giant phase!

The nuclear burning shells also build up, but now there is high enough temperature and pressure to burn carbon into neon, into oxygen, into silicon, and finally into iron.

The iron core never burns.

slide2

Massive stars undergo multi-layered shell burning.

The time duration that each shell burns becomes shorter and shorter as the star becomes desperate to battle against the merciless crushing force of its own gravity.

Hydrogen .…… 7 million yrs Oxygen ………. 1/2 yr

Helium …….… 500 thousand yrs Silicon ……….. 1 day

Carbon …….… 600 yrs Iron collapse … 0.1 second

slide3

The core collapses and becomes a big neutron ball (called a neutron star). Sometimes it becomes a black hole.

This results in many neutrinos being emitted into space.

Then the envelope bounces off of it!

BOOM- Supernova

Before and After photos of SN 1987A.

In an instant… more energy than all the stars in all galaxies in the universe.

slide4

Supernovae Remnants in Our Galaxy

Young

Old

Supernova in a distant galaxy.

slide5

HR Diagram Changes as a cluster Ages: 106 – 107 yrs

106 yrs: The massive stars have already formed and some have aged into super giant stars. The majority of stars, the low mass stars, have not fully formed yet and are making their way down to the main sequence line.

O B A F G K M

107 yrs: The O stars have already vanished as supernovae! The B stars are beginning to become super giant stars. The low mass stars are still being born. Recall they take 100 million years to birth.

O B A F G K M

slide6

HR Diagram Changes as a cluster Ages: 108 – 109 yrs

108 yrs: The O and B stars have all vanished as supernovae! The A stars are becoming red giant stars. The low mass stars are not on the main sequence.

108 yrs = 100 million yrs

Red Giants

O B A F G K M

109 yrs: The A stars have all become red giant stars. The F stars are forming the red giant branch (on their way to becoming red giant stars), and the G stars are just beginning to move off the main sequence.

Red Giants

Red Giant

Branch

O B A F G K M

slide7

HR Diagram Changes as a cluster Ages: 1010 yrs

HGB = Horizontal Giant Branch

1010 yrs: The O, B, and stars are all gone. The A and F stars are on the horizontal giant branch. The G stars are on the red giant branch, and the K and M stars are firmly on the main sequence.

Red Giants

HGB

Main sequence

Turn off

Red Giant

Branch

O B A F G K M

This all means that we can use the HR diagram of a cluster to tell the clusters age!

We just look at the placement of all the stars and see where the main sequence ends.

This location is called the main sequence turn-off. We also look to see if there is a horizontal giant branch, which forms at 10 billion yrs.