SPACE | BLACK HOLE
The Black Hole has remained an area of interest and mystery for astronomers, researchers, and scientists for centuries
The first direct visual evidence of a supermassive Black Hole and its shadow was unveiled, showcasing how the imagination and dedication of science around the world, willing to collaborate to achieve a huge goal, can be a model for large-scale success. Marking a revolution in space science, technical advancement, research, astronomy, science and human evolution itself, scientists have managed to obtain the strongest evidence to date about the existence of supermassive Black Holes. The first-ever image of a Black Hole taken through the Event Horizon Telescope (EHT) observations of the center of the galaxy M87 (Messier 87), have opened a new window to the study of Black Holes, their surroundings and gravity.
The captured image shows a bright ring formed, as light bends in the intense gravity around a Black Hole which is 6.5 billion times more massive than the Sun. At the heart of the M87 galaxy, 55 million light years from the Earth resides this Black Hole whose image has been captured displaying a halo gas tracing the gigantic outline of the Black Hole. The image allows us to have the first direct glimpse of a Black Hole’s accretion disk i.e. a ring of gas falling into the black hole. In the obtained picture, the crescent that the halo appears to be making is due to light on the side of the disk rotating towards the Earth which is bent toward the earth and hence appears brighter. The dark shadow in the middle shows the edge of the event horizon, also called the ‘point of no return’. Beyond this point, no matter (or even light) can travel fast enough to escape the relentless gravitational pull of the Black Hole.
The Black Hole has remained an area of interest and mystery for astronomers, researchers, and scientists for centuries. While there have been simulations and pictures thought to be of a certain way, there was never an actual image available of the Black Hole till date. Observations are also being made around the supermassive Black Hole called Sagittarius A, having a mass equal to about four million Suns, at the center of our galaxy, the Milky Way.
This daunting task could only be successful through the imagination and dedication of science around the world, willing to collaborate to achieve a huge goal
“Sagittarius A is also a very interesting target. We can see the event horizon and we should be able to resolve it. It is complex. M87 was in some sense the first source we imaged as it was easier to do so because the timescales don’t change much during the course of an evening. We are very excited to work on the Sagittarius star; we are doing that very shortly. We are not promising anything, but we hope to get that very soon,” said Shepherd Doeleman, the EHT Director of the Centre for Astrophysics, Harvard and Smithsonian during a press conference hosted by the National Science Foundation (NSF) which was one of the key funding agencies for the EHT project.
OBTAINING THE FIRST BLACK HOLE IMAGE
The image is an example that coming together is indeed a success. Capturing an image these days is a second’s work for us with the smartphones in our hands, but it was certainly not so in case of this cosmic giant. It took over 200 people, several institutes over 20 countries and regions, eight ground-based radio telescopes, an amalgamation of observations, theories, technology, and science and over a decade’s time to capture the image of this Black Hole.
The EHT gets its name from the Event Horizon of a Black Hole which is the gravitational boundary beyond which neither light nor matter can escape. To capture an image of the Black Hole what was needed was an Earth-sized telescope which was practically impossible, but what was made possible was a virtual telescope of the size of the Earth. EHT is a planetscale array of eight ground-based radio telescopes deployed at a variety of challenging high-altitude sites, forged through international collaboration, designed to capture images of a Black Hole. The EHT links telescopes around the globe to form an Earth-sized virtual telescope with unprecedented sensitivity and resolution. The locations included volcanoes in Hawai and Mexico, mountains in Arizona and the Spanish Sierra Nevada, the Chilean Atacama Desert and Antarctica.
The breakthrough was announced on April 10, 2019, in a series of six papers published in a special issue of The Astrophysical Journal Letters. Multiple calibrations and imaging methods have revealed a ring-like structure with a dark central region — the shadow of the Black Hole — that persisted over multiple independent EHT observations.
“We use a technique that has very long baseline interferometry. Radio waves from the Black Hole hit radio telescopes, where they are recorded with the position of atomic clocks, with only one second every 10 million years. When you register these radio waves so precisely, you can store them on hard drives or send them to a central facility where they can be combined precisely. It is exactly the same way that a mirror uses an optical telescope reflected by perfect synchronicity to a single focus. When we do this, we can synthesise a telescope that has the resolving power, as though we had one the size of the distance between these telescopes, truly turning the Earth into a virtual telescope. However, even this broad global network is not enough by itself to make an image. The key is that the Earth turns. In April 2017, all the dishes swiveled, turned and stared at M87, the galaxy 55 million light-years away,” Doeleman added.
This daunting task could only be successful through the imagination and dedication of science around the world, willing to collaborate to achieve a huge goal. “No single telescope on the Earth has the sharpness to create an un-blurred definitive image of the Black Hole. This team did what all good researchers do, they innovated. This was a huge task, one that involved overcoming numerous technical difficulties. It was an endeavor so remarkable that NSF has invested $28 million in more than a decade, joined by many other organisations in our support, as these researchers shaped their idea into reality. The event horizon project shows the power of collaboration, convergence and shared resources, allowing us to tackle the universe’s biggest mysteries,” said France Cordova, Director, and NSF, who believes the image, will demonstrate an imprint on people’s memories.
The challenges in the way were not just at technical and scientific levels, but also at the cosmic level which were pretty out of hand. “Also, there were some very interesting cosmic coincidences needed. Take for example the hot gas swirling around the Black Hole. Photon has to leave from the horizon, travel through the hot gas to the Black Hole and the light rays of a millimeter length, then that has to propagate 60,000 years through the galaxy and another 55 million years to intergalactic space. Then it winds up in the Earth’s atmosphere where there is its greatest enemy. The greatest danger is that it will be absorbed by water vapour in our own atmosphere. The telescope allows us to see what has traveled to us so far. It just takes light 55 million years to get here, so when we see M87 in this image you saw, that is what it looked like 55 million years ago,” said Doeleman. A light year is a measure of the total distance that a beam of light, moving in a straight line takes to travel in one year.
“Getting the site to work isn’t the end of the process, we also had to test them all because you really only get one shot. So, we spent years taking site by site, pairing them up and making sure that the observations would work. The last of these observations was in January 2017. By March 2017, we knew that it worked and we were ready to go. The image shown is from April 2017. But even with all of that in place, we still had to wait for the weather. We have to have good weather in Hawaii and Spain at the same time and Arizona in the South Pole. In 2017, we were very lucky. At the end of that, more than half a tonne of hard drives were recorded. It is equivalent to the entire selfie collection over a lifetime for 40,000 people. The image you saw isn’t that in size, it is a few hundred kilobytes, so our data analysis has to collapse this data into an image that is more than one billion times smaller,” said Dan Marrone, the Associate Professor of Astronomy at the University of Arizona. During the centennial year of the historic an experiment that first confirmed Einstein’s general relativity, this EHT’s accomplishment has allowed scientists a new way to study the most extreme objects in the Universe predicted by this theory.
“M87 was catching at a quiet point, which we can tell from historical multi-wavelength, I think we just got lucky, had it been flaring, we might have seen something that would have blocked the Hole as well.”
—Sera Markoff, Professor of Theoretical Astrophysics, University of Amsterdam
“There are a lot of clichés that get thrown around when talking about big scientific discoveries. Words like “breakthrough” or “game-changing” are often used. They grab people’s attention, but it’s fairly rare that they apply. Today’s announcement of the first image ever taken of a Black Hole, more precisely, of its shadow, truly rises up to that standard,”
—NASA’s ChandraXRay Observatory wrote about the Black Hole image capture
A century ago, astronomers proved that light bends around the Sun as Einstein predicted and around the same time this year, Einstein’s general theory of relativity has found evidence. “Einstein’s equation about his description of gravity, is fundamentally one of the most beautiful and serious theories we have even when history abounds around Black Holes,” Avery Broderick, Associate Faculty, Perimeter Institute & the University of Waterloo added. Known for its incredibly graceful, beautiful and accurate description of how the cosmos works, the general theory of relativity predicts that light coming from a strong gravitational field should have its wavelength shifted to larger values, what astronomers call a “red shift”.
“This is the strongest evidence that we have to date for the existence of Black Holes. It is also consistent with the precision of our measurements with Einstein’s predictions. This image forces a clear link between Supermassive Black Holes and the engines of bright galaxies. We now know clearly that Black Holes drive large structures in the universe from their home in the galaxy. We now have this highly new way of studying Black Holes that we have never had before. We have discovered and this is just the beginning.” Doeleman added.
“The Black Holes might be the most complex objects, but they have a lot of consequences of their own”, said Sera Markoff, Professor of Theoretical Astrophysics, and the University of Amsterdam. “The general relativity itself does not change when we look at different Black Hole masses, but it turns out that the impact of a Black Hole will actually change a lot. So we want to understand the role of Black Holes in the universe, then we need to have accurate determinations of the Black Hole masses,” she added.
While to us the image might appear fuzzy, it isn’t. Broderick explains,” We have spent considerable time trying to ascertain the particular details of the ring-like feature and the sharpness falls off less than ten percent of the radius. It is about the instrumental resolution that we practically have.” However, Doeleman said, “We think we can make the image perhaps sharper through algorithms, but we are embarking on a wonderful new series of putting new telescopes from places on the Earth, so if you add more telescopes, you build out that virtual mirror. Even adding two or three more stations in just the right places, will increase the fidelity of the image a lot.” Asymmetries around the ring, the brightness in the Southern part with a lot of future work on this to sharpen our focus on gravity, are some of the interesting things that the scientists hope to explore, having captured this image.
WHAT IS A BLACK HOLE?
Mysterious, extraordinary, ethereal, fascinating, formidable, bizarre sinkholes are some of the adjectives that have become synonymous with Black Holes over centuries as these enormous cosmic objects have continued to be a centre of amazement, curiosity and questions for scientists, astrophysicists, astronauts, students and people alike. Black Holes are known to have enormous mass, but the very compact size and their presence affects their environment in extreme manners, warping spacetime and super-heating any surrounding material.
“Black Holes are the most mysterious objects in the universe, they are cloaked by an event horizon that prevents even light from escaping and yet the matter that falls onto the event horizon is superheated so before it passes through, it shines very brightly. The gas that is superheated, lights up a ring where photons orbit the Black Hole and the interior of that is a dark patch that prevents light from escaping,” said Sheperd Doeleman. NASA defines Black Hole as a place in space where gravity pulls so much that even light cannot get out. The gravity is so strong because the matter has been squeezed into a tiny space.
SIZE OF A BLACK HOLE
Black Holes can be big or small. Scientists think the smallest black holes are as small as just one atom. These black holes are very tiny but have the mass (the amount of matter) of a large mountain. Another kind of black hole is called “stellar.” Its mass can be up to 20 times more than the mass of the Sun. There may be many stellar-mass Black Holes in Earth’s galaxy, called the Milky Way. The largest Black Holes are called “super massive” which have masses that are more than one million Suns together. Scientists have found proof that every large galaxy contains a super massive Black Hole at its centre.
FORMATION OF A BLACK HOLE
Scientists believe the smallest Black Holes were formed when the universe began, while the stellar ones are made when the centre of a very big star falls upon itself or collapse, causing a supernova which is an exploding star that blasts part of the star into space. The supermassive Black Holes were made at the same time as the galaxy they are in, think the scientists. An interesting fact about the Black Hole remains that it cannot be seen owing to the strong gravity that pulls all of the light into the middle of the Black Hole. However, scientists can see how strong gravity affects the stars and gas around the Black Hole. Scientists can study stars to find out if they are flying around, or orbiting a Black Hole.
When a Black Hole and a star are close together, high-energy light is made. This kind of light cannot be seen with the human eye, but satellites and telescopes are used in space to see the high-energy light. Black Holes continue to intrigue scientists to help them navigate better through the universe and understand the universe more closely.
COULD A BLACK HOLE DESTROY EARTH?
This has been a question of bewilderment for the masses for as long as one can remember and NASA has well addressed this question. ‘Black Holes do not go around in space devouring stars, moons, and planets. The Earth will not fall into a Black Hole because no one is close enough to the solar system for the Earth to do that. Even if a Black Hole with the same mass as the Sun and were to take the place of the Sun, the Earth would still not fall into it. The Black Hole would have the same gravity as the Sun.