We know plenty about blackholes but never got a glimpse at any photo. And because of the powerful gravity that they have, no science and no instrument so far had been able to capture the image of a blackhole in more than 100 years of it existence in theory. But today, we have the first ever picture of the blackhole, all thanks to the scientific community that worked on it.
The Event Horizon Telescope
The Event Horizon Telescope (EHT) is an assembly of a number of telescopes brought in together making an array with the aim to capture the first ever picture of a blackhole. The array of these telescopes essentially makes one big telescope the size of the earth, making it a very powerful telescope and an instrument that we have no other way to build. This EHT is the reason why we now don’t have to rely on black hole illustrations anymore, which we have had ever since physicists had first conceived a blackhole.
The EHT making one big earth-sized telescope consists of 8 telescopes from around the world, each of which had generated about 350 terabytes of data per day and was synced with atomic clocks, accurate to within one second every 100 million years.
Many institutes and 8 telescopes are a part of this project and two of India’s telescopes also are a part of it. India’s Giant Metrewave Radio Telescope (GMRT) of the National Center for Radio Astrophysics, Pune and the Ooty radio telescope are the two Indian telescopes.
In order to understand the detection mechanism of a black hole, it is important to understand what an event horizon is. An event horizon is a boundary at which all the matter begins to suck into a blackhole. At the centre of this black hole is the singularity a point with infinite density called singularity and this is where the physics that we know till today becomes questionable.
It the point where nothing, not even light can escape.
The Mechanism Behind
This particular method of imaging an astronomical object with the help of an array of telescope is called Very Long Baseline Interferometry (VLBI). It correlates time-stamped data from distant telescopes, to boost the signals and quiet the noise. Each pair of telescopes contributes to the final image obtainable.
SCIENTISTS: “We’ve produced the first-ever image of a supermassive Black Hole, 55-million light years away” RESPONSE: “Oooh!”
SCIENTISTS: “We’ve concluded that humans are catastrophically warming Earth” RESPONSE: “That conflicts with what I want to be true, so it must be false”
It is difficult to directly image a blackhole because of a number of reasons:
1. Small size: Although blackholes are huge in mass, they are also compact. They are very tiny objects and with the instruments that we have today it is difficult to measure them. The blackhole at the centre of our galaxy Sagittarius A* has a mass of 4 billion suns, fitting inside the orbit of Mercury. It has an event horizon smaller across than the distance between the sun and Earth. And it’s roughly 26,000 light-years away, so it takes up a minuscule amount of sky, which is just a few billionths the width of the full moon. That shows how compact they are. The larger the telescope, the more resolving power it has, and the smaller the details it can make. To detect something this compact with the telescope resolutions that we have is impossible.
2. Distance: Apart from the blackholes being compact objects, they are also very far away. It gives the same hurdle of the telescope. Our star Sun lies at 8 kiloparsec from the center of our galaxy, on what is known as the Orion Arm of the Milky Way. With the resolution that we have today, it is impossible to capture an object which is tiny and that far away.
3. Frequency: In order to detect a blackhole image from the earth, there has to be some amount of light that has to travel from the edge of the blackhole and reach the telescopes without getting absorbed or disturbed by any obstacle on the way. It also has to make it through the earth’s atmosphere. A lot of frequencies of light do not make it through the Earth’s atmosphere, making it difficult to achieve.
Another challenge was the weather. They had to have clear weather at all these pla es of telescopes in the world at the same time so that the image is captured the ssame eay from all telescopes.
About The Image
The first blackhole image released on 10th April is of the center of the galaxy called M87 and is 54 million light years away, which means that the image is very old. It is named Pōwehi, meaning “embellished dark source of unending creation” in Hawaiian.
The image has a central dark region surrounding a dark region around it. The bright part is the matter and light swirling around the central blackhole, with the brighter side moving toward us. The dark part is the blackhole’s shadow, which includes the event horizon, plus the region where light could escape but does not. The size and the shape of the shadow that is seen is a confirmation from the general theory of relativity. This is in excellent correlation with Einstein’s prediction of relativity, passing one of his theories another crucial test.
Contribution From A Grad Student
The black hole picture also has a major contribution from a grad student from MIT, Katie Bouman, who helped develop a computer program while still in school in 2016. It helped create the image of the black hole. She also led testing to verify the images.
The algorithm was named CHIRP (Continuous High-resolution Image Reconstruction using Patch priors) and it needed to combine data from the eight radio telescopes around the world working under Event Horizon Telescope. Astronomical signals reach the radio telescopes at slightly different rates, the researchers had to figure out how to account for that so calculations would be accurate and visual information could be extracted.
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