Exceeding Theoretical Limits: Ultra-Bright X-Ray Sources

Ultra-bright X-ray sources known as ultra-luminous X-ray sources (ULXs) have been found to exceed the Eddington limit, which restricts the maximum brightness of an object based on its mass. This is due to the incredibly high gravitational force, which is about one hundred trillion times stronger than on Earth. Scientists at the Jet Propulsion Laboratory (JPL) of NASA have recently published details of a unique measurement of a ULX that was carried out with the Nuclear Spectroscopic Telescope Array (NuSTAR). The results confirm that these light emitters are indeed as bright as they appear and that they exceed the Eddington limit.

One hypothesis suggests that this excessive brightness is due to the strong magnetic fields of the ULXs. However, this idea can only be verified through observations. ULX magnetic fields, which are billions of times stronger than the strongest magnets ever produced on Earth, cannot be replicated in the laboratory. The recent study focused on the same ULX that was at the center of the 2014 discovery and found that M82 X-2, like a cosmic parasite, steals about nine billion trillion tons of material from a neighboring star annually. This corresponds to about 1.5 times the mass of the Earth.

By knowing the amount of material that hits the surface of the neutron star, scientists can estimate how bright the ULX should be. Their calculations match independent measurements of brightness. The work confirmed that M82 X-2 exceeds the Eddington limit. If scientists can confirm the brightness of other ULXs, they could refute a remaining hypothesis that explains the apparent brightness of these objects without ULXs exceeding the Eddington limit.

These observations allow us to see the effects of these incredibly strong magnetic fields, which we could never reproduce with current technology on Earth. This is the beauty of astronomy. By observing the sky, we expand our ability to explore the workings of the universe. On the other hand, we cannot really conduct experiments to get quick answers; we have to wait for the universe to reveal its secrets to us.