The First Picture Of A Black Hole Revealed
In case you missed it, scientists of the Event Horizon Telescope (EHT) program, an international collaboration of observatories scattered around the world, unveiled probably one of the most important achievements in astronomy of the beginning of the 21st century. 235 years after the idea of body so massive that even light could not escape was first theorized by English clergyman John Michell, scientists successfully took the first picture of a supermassive black hole.
This monster has a mass equivalent of 6.5 billion suns. It is located in the heart of the supergiant galaxy Messier 87, or M87, devouring anything that comes within its grasp: stars, planets, gas, dust, and even light. Some theories argue that a body this massive could bend space and time.
A Telescope The Size Of Earth
More than 200 scientists participated in the global collaboration to manipulate the array of observatories scattered around the world in six locations: Arizona and Hawaii in the United States, Mexico, Spain, Chile, and the South Pole. This combined array is equivalent to a telescope the size of the Earth. In April 2017, this giant telescope stared at M87’s black hole and collected more than a petabyte of data (i.e. one million gigabytes). Two full years were necessary to analyze the data and assemble the final picture.
The result may not seem impressive at first sight, but it is the very first direct visualization of a black hole. Before now, the evidence that black holes even existed was captured through indirect methods, like identifying specific radiation, looking for stars orbiting around bizarre objects, or by observing extremely energetic jets of particles. For an non-expert, it might be hard to understand why it is so difficult to see an object so big that you would need 2.98 million Earths lined up in a row just to span the 23.6 billion miles of just the black void (i.e. not counting the giant rings of trapped light orbiting it).
To really grasp this scientific exploit, picture these facts. First, taking the picture of this black hole was like taking the picture of an orange on the moon. Second, the amount of data collected was so massive that it was faster and more efficient to physically ship the hard drives themselves between laboratories than to transfer it digitally via the internet.
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The Six Main Features Of A Black Hole
The picture confirms the theoretical model of a massive black hole developed conjointly by astrophysicists and computer scientists. They based their simulations on relativistic physics pioneered by Albert Einstein in the early 1900s which relies on the equally famous e=mc2. A monster black hole like the one at the heart of galaxy M87 is characterized by six main features:
Gravitational Singularity: the one-dimensional point in the heart of a black hole which contains a huge mass in an infinitely small space. These points are formed by collapsing stars where density and gravity become infinite, curving space-time.
Event horizon: sometime referred to as the “point of no return”. The gravitational forces of a black hole are so strong that its escape velocity exceeds the speed of light which is then trapped in its grasp.
Accretion disk: the accumulation of extremely hot materials, such as gas and dust from dead stars, planets, and other stellar objects that got too close to a black hole but didn’t quite fall into it. These disks next to the event horizon create a “shadow” that was seen by astronomers of the EHT project.
Innermost stable circular orbit (ISCO): the smallest circular orbit where matter can stably evolve around a massive object without falling into it.
Relativistic jet: as black holes “eat”, they shoot out powerful beams of ionized matter accelerated close to the speed of light from their rotation poles.
Photon sphere: or photon circle is the region where the photon of the light emitted by jets and in-falling matter are forced to travel in orbits due to the massive gravitational forces.
The Next Challenge Of The EHT Project
The original target of the EHT project was not M87 but a black hole called Sagittarius A*. It is about two thousand times smaller than M87, only four million suns, but it is also about two thousand times closer to the Earth, drawing the same angular size on the sky. The ETH scientists are currently re-targeting Sag A* as their next picture challenge.
Further in the future, the EHT team would like to add several space telescopes to its array which would avoid interference from Earth’s atmosphere.