How Black Holes Affect Dark Matter

Black holes do not destroy dark matter in the traditional sense, but their interactions with dark matter can lead to interesting effects. To understand these interactions, we first need to delve into the nature of dark matter and explore its interactions with black holes.

Nature of Dark Matter

Dark matter is a mysterious form of matter that does not emit, absorb, or reflect light. It remains invisible and is detectable only through its gravitational effects. Astronomers estimate that dark matter makes up about 27% of the universe's mass-energy content, a significant portion of which is distributed throughout the cosmos.

Interaction with Black Holes

When dark matter comes close to a black hole, the black hole's gravitational field can affect dark matter particles. In some cases, dark matter particles can be captured by the black hole, much like regular matter. However, the interaction between dark matter and black holes is not as violent as the interaction between ordinary matter and black holes.

Gravitational Effects

As dark matter is drawn into a black hole, it contributes to the black hole's mass. But due to the unique properties of dark matter—such as its minimal interaction with other forms of matter—the presence of dark matter within a black hole does not result in the same types of energy releases as ordinary matter. Instead, dark matter simply adds to the black hole's mass, contributing to its growth over time.

Cosmological Implications

The accumulation of dark matter around black holes has significant implications for the formation and growth of black holes in the universe. This is an area under active research, where scientists are increasingly interested in understanding how the distribution of dark matter influences the evolution of black holes.

Black Hole Information and No-Hair Theorem

The no-hair theorem posits that two black holes with the same mass, angular momentum, and electric charge are indistinguishable. This theorem states that dark matter falling into a black hole increases its mass, but the black hole's overall macroscopic state remains unchanged.

However, astrophysicists note that the information about what dark matter or other matter falls into a black hole is presumably stored in the quantum state of the black hole, but in a very scrambled form. The black hole is not expected to be different in any way that could be practically tested. While the fraction of dark matter ingested by a typical black hole is not very high, the study of this phenomenon is ongoing.

Consequences for Ordinary Matter and Dark Matter

When ordinary matter approaches a black hole, it can be slowed down by the already orbiting matter. Much of this matter forms an accretion disk and is gradually consumed by the black hole. In contrast, dark matter approaching a black hole follows a ballistic path due to its minimal interactions with other matter, primarily through gravitation.

From the cosmic microwave background, it is understood that dark matter interacts minimally with other dark matter particles. If we were to ignore general relativity, the path of dark matter approaching a black hole would resemble a hyperbola, where, unless it collides with the event horizon, it would pass through and escape. However, the actual path of dark matter is more complex due to the effects of general relativity, particularly inside the photon sphere.

In conclusion, while black holes can capture dark matter, they do not destroy it in the conventional sense. Instead, dark matter contributes to the mass of the black hole, with implications for the growth and evolution of black holes in the universe.