3D rendering of a supermassive black hole, in the foreground against a galaxy and starry sky

How are black holes detected?

August 1, 2019

One of the most discussed concepts amongst the astrophysics community is black holes. A black hole is a volume of space where the presence of gravity is so extreme that fast moving particles or light cannot escape. 

As black holes do not emit visible light, astronomers have been unable to observe a clear picture of a black hole, hence the detection of black holes has long been impossible – but with advancements in vacuum technology, this is no longer the case. 

Black hole discovery with gravitational wave detectors 

On April 10th, 2019, astronomers were able to obtain the first image of a black hole using the Event Horizon Telescope (EHT). Enabled by international collaboration, EHT is a planet-scale arrangement of eight radio telescopes which record electromagnetic radiation and combine the multiple sources of radio data results using very-long-baseline interferometry (VLBI).

Thanks to the EHT, the first visual evidence of a supermassive black hole, as well as its shadow, was illustrated. This black hole was found on the galaxy Messier 87 and resides 55 million light-years from Earth.

The discovery resulted in a major confirmation to Einstein’s Theory of General Relativity. This marked the birth of the concept of black holes, which were described as “extreme concentrations of mass with a gravitational effect that engulfs matter and even traps light”. 

Gravitational wave detectors also play a significant role in how black holes are detected. In December 2018, The Laser Interferometer Gravitational-Wave Observatory (LIGO) and The Virgo interferometer announced four new black hole mergers and gravitational waves created from 10 stellar-mass binary black hole mergers and a merger of neutron stars. 

Black holes and vacuum fluctuations 

A significant effect of the recent black hole discovery is the new insight into Hawking Radiation Theory. This predicted that black holes could create and emit sub-atomic particles until they exhaust their energy and eventually evaporate.

From a quantum perspective, the existence of black holes suggests that the vacuum of space is not completely empty. A quantum fluctuation (also known as a vacuum state fluctuation) is the temporary appearance of energetic particles from an empty space. This allows the creation of particle-antiparticle pairs of virtual particles. The Black Hole’s strong gravitational field separates these fluctuations into the outgoing particles that make up Hawking Radiation.

Black hole scientific debates

Black holes have created an array of discussion and debate in the scientific community.  One of the main debates is regarding vacuum decay. This is based on a static black hole centered by a bubble that ‘nucleates’, either replacing the black hole with a true vacuum or nucleating a static bubble. The result of this is a residue black hole surrounded by true vacuum.  It is widely believed that this ‘bubble’ will eventually take over the universe. However, this does not take gravitational fields into account which may increase the instability of the vacuum due to small black holes acting as nucleation seeds.

Black holes are centered by a gravitational singularity. This is a one-dimensional point consisting of a substantially small space where gravity and density become infinite and space-time curves. Many argue that as objects fall into a black hole and reach the singularity, they are altered by various gravitational attractions. This challenges the theory of General Relativity which emphasizes the quantum effects in the existence of black holes.

Although telescopes play a fundamental role in how black holes are detected, with vacuum technology advancing at an accelerated pace, it has been suggested that applications in vacuum science such as CERN's Large Hadron Collider (LHC) can result in the creation of black holes. This is due to the particles produced when pairs of protons collide. Such a formation would confirm theories that the universe is not four dimensional, but instead hosts other dimensions.

Black holes retain a certain enigmatic status in the world of physics. But with the recent observation, as well as progression of vacuum technology seen in telescopes and gravitational wave detectors, the observation of black holes will enable researchers to make new predictions and discoveries about the universe and its origins. 

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