If the Rotational Speed of the Gas in the Disk

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Examlex · Accepted Answer

The Answer is The radius of the gas is:
r = 26,000 ly = 26,000 × 9.5 × 10¹⁵ m = 2.5 × 10²⁰ m
and the mass enclosed within this radius is equal to
M = v² r/G = (10⁵ m/s)² × 2.5 × 10¹⁰ m/(6.7 × 10⁻¹¹ m³/kg s²) = 3.7 × 10⁴⁰ kg × (1M_⨀/2 × 10³⁰ kg).
M = 1.9 × 10¹⁰ M_⨀.
The fraction of mass in dark matter is (M − M_luminous)/M = (19 − 5)/19 = 0.74,and thus 74 percent of the mass inside this radius is made of dark matter.

If the Rotational Speed of the Gas in the Disk

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