Final answer:
A bright spot on the surface of a rapidly rotating compact object like a neutron star or black hole can appear when high-speed gas collides with the object's ring, heating the gas and causing it to emit radiation, such as X-rays. This process may also involve gravitational lensing and internal friction among atoms falling into a black hole.
Step-by-step explanation:
When massive stars collapse, they can form compact objects, such as neutron stars or black holes. The gravitational fields of these objects are extremely powerful, affecting nearby matter. Gas and dust that fall towards these objects are accelerated to high velocities, sometimes reaching relativistic speeds near the event horizon.
The intense gravitational field of a compact object can also cause it to act as a gravitational lens. This phenomenon can temporarily increase the brightness of a background star as the compact object passes between us and the star. However, the bright spots mentioned initially — associated with the surface of a rotating compact object — are the result of high-speed gas colliding with the object's ring, causing the gas to heat up and emit radiation, most notably X-rays due to the high temperatures achieved during the collision (more than 100 million K).
Bright spots can also appear as a result of internal friction among atoms as they fall into a black hole, creating flickering X-rays. Astronomers use space-based X-ray telescopes to observe these phenomena, as X-rays cannot penetrate Earth's atmosphere. If the compact object is both magnetic and spinning rapidly, it can eject material in narrow beams at speeds close to light, resulting in a visible bright spot.