The First-ever Image of a Black Hole

- The First Direct Images of a Black Hole at the Heart of Messier 87

"An international team of over 200 astronomers, including scientists from MIT’s Haystack Observatory, has captured the first direct images of a black hole. They accomplished this remarkable feat by coordinating the power of eight major radio observatories on four continents, to work together as a virtual, Earth-sized telescope. 

In a series of papers published today (April, 10, 2019) in a special issue of Astrophysical Journal Letters, the team has revealed four images of the supermassive black hole at the heart of Messier 87, or M87, a galaxy within the Virgo galaxy cluster, 55 million light years from Earth. 

All four images show a central dark region surrounded by a ring of light that appears lopsided — brighter on one side than the other. 

Albert Einstein, in his theory of general relativity, predicted the existence of black holes, in the form of infinitely dense, compact regions in space, where gravity is so extreme that nothing, not even light, can escape from within. By definition, black holes are invisible. But if a black hole is surrounded by light-emitting material such as plasma, Einstein’s equations predict that some of this material should create a “shadow,” or an outline of the black hole and its boundary, also known as its event horizon. 

Based on the new images of M87, the scientists believe they are seeing a black hole’s shadow for the first time, in the form of the dark region at the center of each image. 

Relativity predicts that the immense gravitational field will cause light to bend around the black hole, forming a bright ring around its silhouette, and will also cause the surrounding material to orbit around the object at close to light speed. The bright, lopsided ring in the new images offers visual confirmation of these effects: The material headed toward our vantage point as it rotates around appears brighter than the other side. 

From these images, theorists and modelers on the team have determined that the black hole is about 6.5 billion times as massive as our sun. Slight differences between each of the four images suggest that material is zipping around the black hole at lightning speed..........] -- [MIT News]

(Katie Bouman - This is the MIT computer scientist whose algorithm led to the first real image of a black hole.)

As stunning and ground-breaking as it is, the EHT project is not just about taking on a challenge. It's an unprecedented test of whether Einstein's ideas about the very nature of space and time hold up in extreme circumstances, and looks closer than ever before at the role of black holes in the universe. To cut a long story short: Einstein was right. 

A black hole is a region of space whose mass is so large and dense that not even light can escape its gravitational attraction. Against the black backdrop of the inky beyond, capturing one is a near impossible task. But thanks to Stephen Hawking's groundbreaking work, we know that the colossal masses are not just black abysses. Not only are they able to emit huge jets of plasma, but their immense gravity pulls in streams of matter into its core.  

When matter approaches a black hole's event horizon - the point at which not even light can escape - it forms an orbiting disk. Matter in this disk will convert some of its energy to friction as it rubs against other particles of matter. This warms up the disk, just as we warm our hands on a cold day by rubbing them together. The closer the matter, the greater the friction. Matter closer to the event horizon glows brilliantly bright with the heat of hundreds of Suns. It is this light that the EHT detected, along with the "silhouette" of the black hole.  

To give a sense of how hard this task is, while the Milky Way's black hole has a mass of 4.1 million Suns and a diameter of 60 million kilometres, it is 250,614,750,218,665,392 kilometres away from Earth – thats the equivalent of travelling from London to New York 45 trillion times. As noted by the EHT team, it is like being in New York and trying to count the dimples on a golf ball in Los Angeles, or imaging an orange on the moon.  

To photograph something so impossibly far away, the team needed a telescope as big as the Earth itself. In the absence of such a gargantuan machine, the EHT team connected together telescopes from around the planet, and combined their data. To capture an accurate image at such a distance, the telescopes needed to be stable, and their readings completely synchronised. 

To accomplish this challenging feat, the team used atomic clocks so accurate that they lose just one second per hundred million years. The 5,000 terabytes of data collected was so large that it had to be stored on hundreds of hard drives and physically delivered to a supercomputer, which corrected the time differences in the data and produced the image above.

- Scientists Observe Light From Behind a Black Hole

An astrophysicist from Stanford University made the first direct observation of light from behind a black hole. In doing so, they confirmed a prediction made in Einstein's theory of general relativity. The observation is unusual due to the fact that black holes are known for sucking in all surrounding matter and light, meaning we should not be able to see light from behind one of the massive celestial objects. 

While analyzing X-rays emitted by a supermassive black hole 800 million light-years from Earth, Stanford University astrophysicist Dan Wilkins noticed a series of bright flares of X-rays, which were unusual but not unprecedented. Following that observation, however, he saw more flashes of X-rays in a different "color" — these smaller flashes were consistent with theories regarding X-rays reflected from behind a black hole, a scenario that had only been theorized and had never been observed before. 

The theories state that smaller flashes, occurring shortly after larger ones are the same X-ray flares as the larger flashes, just reflected from the far side of the black hole. "Any light that goes into that black hole doesn’t come out, so we shouldn’t be able to see anything that's behind the black hole," said Wilkins. "The reason we can see that is because that black hole is warping space, bending light and twisting magnetic fields around itself," he continued. The impressive discovery, outlined in a paper in Nature (July, 2019), was made during an investigation into the black hole corona, a swirling ring of high-energy particles that surrounds the celestial object's central event horizon.