I'm having a little bit of a problem with this one. Here's the question:(adsbygoogle = window.adsbygoogle || []).push({});

X-ray pulses from Cygnus X-1, a celestial x-ray source, have been recorded during high-altitude rocket flights. The signals can be interpreted as originating when a blob of ionized matter orbits a black hole with a period of 4.7 ms. If the blob were in a circular orbit about a black hole whose mass is 18 * MSun, what is the orbit radius?

Here's my train of thought. I used one of Kepler's laws:

[tex]

\begin{equation*}

\begin{split}

T^2 = \frac{4\pi^2r^3}{GM_{blackhole}}\\

r = (\frac{T^2GM_{blackhole}}{4\pi^2})^(\frac{1}{3})\\

\end{split}

\end{equation*}

[/tex]

I changed the milliseconds to seconds, and I got a answer of 110196.285 meters. I'm letting the mass of the sun be 1.991 x 10^{30}kg.

I enter this into webassign, but I doesn't like it. What am I doing wrong?

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# Homework Help: Universal Gravitation and X-ray pulses

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