White holes, unlike black holes, are hypothetical objects that do not allow anything to enter them but instead expel matter and energy. If white holes were real, the observational differences compared to black holes would be significant:
Radiation and Emission: While black holes famously trap everything, including light, beyond their event horizons, white holes, by contrast, would expel particles and radiation. Observationally, this might manifest as a source that emits vast amounts of energy without any apparent accretion of matter. Telescopes would detect radiation being expelled outward rather than absorbed inward.
Gravitational Effects: Black holes exert a tremendous gravitational pull that draws objects in, creating an observable gravitational lensing effect or accretion disks that spiral inward. In contrast, a white hole would theoretically repel objects due to its ‘opposite’ nature. Instead of accretion disks, one might expect a region of space that seems to push matter away or scatter light differently than the gravitational lensing seen around black holes.
Temporal Characteristics: A key feature of black holes is Hawking radiation, which might eventually lead to their evaporation over astronomical timescales. White holes, as theorized, could exhibit different time dynamics, possibly appearing more transient, as they might ‘spontaneously’ emit all their matter and energy in explosive outbursts.
Absence in Galactic Centers: Most galaxies are known to house supermassive black holes at their centers. If white holes were present, they would not fit this pattern. We would not expect to find regions of high mass concentration surrounded by inflows of matter typical of black holes.
Event Horizon Signature: The detection of event horizons in black holes through observations of stars and gas clouds rapidly accelerating and disappearing provides indirect black hole evidence. With white holes, their event horizons would act completely differently, possibly detectable as sharp boundaries from which matter is continuously expelled.
Thus, if white holes were real, their observational signatures in the universe would stand in stark contrast to the familiar features of black holes, offering an intriguing, albeit elusive, new cosmic phenomenon for astronomers to seek out.