Use the Luminosity Distance Formula to find the distance to a star with a luminosity of [tex]L = 5.2 \times 10^{24} \text{ watts}[/tex] and an apparent brightness at Earth of [tex]2.0 \times 10^{-10} \text{ watt/m}^2[/tex].

Formula: Apparent Brightness (AB) = Luminosity / [tex]4 \pi r^2[/tex]

A. [tex]4.549 \times 10^{16} \text{ m}[/tex]
B. [tex]4.549 \times 10^{-16} \text{ m}[/tex]
C. [tex]3.654 \times 10^{16} \text{ m}[/tex]
D. [tex]3.654 \times 10^{-16} \text{ m}[/tex]



Answer :

To find the distance to a star given its luminosity and apparent brightness, we need to use the Luminosity Distance Formula:

[tex]\[ AB = \frac{L}{4 \pi r^2} \][/tex]

where:
- [tex]\( AB \)[/tex] is the apparent brightness,
- [tex]\( L \)[/tex] is the luminosity,
- [tex]\( r \)[/tex] is the distance to the star.

We are given:
- [tex]\( L = 5.2 \times 10^{24} \)[/tex] watts,
- [tex]\( AB = 2.0 \times 10^{-10} \)[/tex] watt/m².

We need to find the distance [tex]\( r \)[/tex]. Let's rearrange the formula to solve for [tex]\( r \)[/tex]:

[tex]\[ r^2 = \frac{L}{4 \pi AB} \][/tex]

By taking the square root of both sides, we get:

[tex]\[ r = \sqrt{\frac{L}{4 \pi AB}} \][/tex]

Now, we can plug in the values given:

[tex]\[ r = \sqrt{\frac{5.2 \times 10^{24}}{4 \pi \times 2.0 \times 10^{-10}}} \][/tex]

Evidently, the calculation of this expression will yield a numerical distance. Performing the calculation yields the result:

[tex]\[ r \approx 4.5486418414672296 \times 10^{16} \, \text{meters} \][/tex]

Therefore, the correct answer from the choices provided is:

[tex]\[ 4.549 \times 10^{16} \, \text{meters} \][/tex]

This matches precisely with the first option listed:

[tex]\[ 4.549 \times 10^{16} \, \text{m} \][/tex]