Light source and projector

A light source comprising:

• an arc tube having a light-emitting portion having a discharge space in the interior thereof and first and second sealing portions provided on both sides of the light-emitting portion along an optical axis;
• a reflector arranged so that a center where the optical axis passes is located on the side of the first sealing portion with respect to the light-emitting portion, and having a main reflecting surface configured to reflect a luminous flux emitted from the light-emitting portion;
• and
• a sub-mirror arranged on the side of the second sealing portion so as to oppose the reflector, the sub-mirror includes,
• a main body portion provided with a sub-reflecting surface configured to reflect part of a luminous flux emitted from the arc tube toward the discharge space,
• a mounting portion configured to be fixed to the second sealing portion and supporting the main body portion, and
• a cooling air ventilating portion penetrating through the mounting portion in the direction of the optical axis at least on the opposite side from the direction of gravitational force.