Exam 17: Evolution of High-Mass Stars

Suppose you observe three star clusters. Cluster 1 has a main-sequence turnoff point at spectral type G, Cluster 2 has a turnoff point at spectral type A, and Cluster 3 has a turnoff point at spectral type B. Which cluster is youngest and which is oldest? Explain why. What is the approximate age of the oldest cluster?

You observed three different star clusters and found that the main-sequence turnoff stars in Cluster 1 had spectral type F, the main-sequence turnoff stars in Cluster 2 had spectral type A, and the main-sequence turnoff stars in Cluster 3 had spectral type G. Which star cluster is the youngest and which one is the oldest?

A main-sequence star of 25 solar masses has about 12.5 times the luminosity of a 10 solar mass star. This is because:

Massive stars explode when they:

The Type II supernova that created the Crab Nebula was seen by Chinese and Arab astronomers in the year 1054 CE. Because the star is 6,500 light-years away from us, we know the star exploded in the year:

Why does the CNO cycle happen only in high-mass stars?

Of all the main-sequence stars ever formed with a mass equal to 25 percent of the Sun's mass, how many are still on the main sequence today?

Why do massive stars explode once they generate an iron core?

Why does the luminosity of a high-mass star remain nearly constant as the star burns heavy elements in its core, even though it is producing millions of times more energy per second than it did on the main sequence?

About 2% of the mass of the Sun is in elements heavier than helium. Where did these elements come from?

Why do free neutrons released in supernova reactions so easily create new heavy elements?

Which has a smaller radius, a 2M _$\odot$ neutron star or a 3M _$\odot$ neutron star? What supports each of these stars from collapsing to form a black hole?

What mechanism provides the internal pressure inside a neutron star?

The collapse of the core of a high-mass star at the end of its life lasts approximately:

Most of the uranium (atomic mass= 238) found on the Earth was formed in Type II supernova explosions.

Explain why the pulsars we see might only be a fraction of the neutron stars in the Milky Way.

During the main-sequence evolution of a massive star, increasingly heavier elements are fused in the core, giving the core support for:

One reason why we think neutron stars were formed in supernova explosions is that:

Explain why a blue star cluster is likely younger than a red star cluster.

Massive stars explode soon after fusion to iron begins because: