1.Rank the labelled stars in terms of their temperature, from hottest to coldest

Question

1.Rank the labelled stars in terms of their temperature, from hottest to coldest:

Select one:

B, C, A

C, A, B

C, B, A

A, C, B

B, A, C

A, B, C

2.Assume for a moment that the three stars are all burning hydrogen in their cores. Which of the stars would you expect to have the longest lifetime?   

Select one:

A

C

B

3.We have begun to find Earth-like planets around other stars. In the near future we will start to search these planets for signs of life.

Let us assume that the full lifetime of our Sun, from its birth to its death, is 11.2 billion years.

If we assume that it would take life 870 million years to become sufficiently well-established on a given planet that we could detect it from the Earth, what is the mass of the most massive star that could host a detectably habitable planet?

?times the mass of the Sun.

Note:

One million = 1 000 000 = 1 x 10^6

One billion = 1 000 000 000 = 1 000 million = 1 x 10^9

Explanation / Answer

1) B, A, C

2) C; Stars that are cooler and less luminous live for longer times

3) More massive star has the shorter life span.

Sun has a life span of about 11.2 billion years

Using the equation life time= 1/(star's mass)p-1 × 1010 years (for massive stars that is Mass of star > 30Msun, p = 3 and for low-mass stars,that is Mass of star < 10 Msun, p = 4) we can determine life time of stars.

A 1.5 Solar mass star has a life span of about 3 billion years.

And 3 Solar mass star has only a life span of about 370 million years.

It would take life, around 870 million years to become sufficiently well-established on a given planet.

So a 1.5 Solar mass star with a life span of about 3 billion years is the most massive star that could host a detectably habitable planet.

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