WHY THIS MATTERS IN BRIEF
Taking a photo of a Black Hole was always thought to be impossible, until now and it’s going to be awesome.
Scientists believe they are on the verge of obtaining the first ever picture of a black hole, and in order to accomplish the once thought impossible feat, they’ve built an Earth sized “virtual” telescope by linking together a large array of radio receivers around the world – from the South Pole, to Hawaii, to the Americas and Europe.
There’s optimism in the scientific community that the observations, which will take place between the 5th and 14th of April could finally produce one of the most anticipated photos of all time, because black holes, like children, are camera shy, but unlike children who just run from the nearest camera, the gravitation within black holes is so great they suck the light right into them. Hence the name.
The so called “Event Horizon Telescope,” or EHT for short, will be trying to photograph the monster black hole at the centre of our own galaxy, and although it’s never been seen directly, this object, called simply “Sagittarius A*,” has been determined to exist because of the way it influences the orbits of nearby stars which race around a point in space at thousands of km per second, suggesting it has a likely mass of about four million times that of our Sun.
As colossal as that sounds though scientists believe that the “edge” of the black hole could be more than 20 million kilometres wide, and at a distance of 26,000 light years from Earth, this makes Sagittarius A* nothing more than a tiny dot in the sky.
The EHT team is nonetheless bullish.
“There’s great excitement,” said project leader Sheperd Doeleman from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, “we’ve been building and tuning the EHT for almost two decades now, and in April we’re going to make the observations that we think have the first real chance of bringing a black hole’s event horizon into focus.”
The EHT will take the photo using a technique called Very Long Baseline Array Interferometry (VLBAI) that uses a network of widely spaced radio antennas to mimic a telescope aperture that can produce the resolution necessary to perceive a dot in the sky.
Initially the team want the EHT to get down to 50 microarcseconds – a level of sharpness that’s the equivalent of seeing something the size of a grapefruit on the surface of the Moon, and the team have a clear expectation of what they ought to see.
Simulations, that are rooted in Einstein’s equations, predict a bright ring of light fringing a dark feature. The light would be the electromagnetic emission coming from the gas and dust that are accelerated to high speed and torn apart just before disappearing into the hole, and the dark feature would be the shadow the hole casts on this maelstrom.
“Now, it could be that we will see something different,” Doeleman said, “as I’ve said before, it’s never a good idea to bet against Einstein, but if we did see something that was very different from what we expect we would have to reassess the theory of gravity. I don’t expect that is going to happen, but anything could happen and that’s the beauty of it.”
Over the years, more and more radio astronomy facilities have joined the project. A key recent addition is the Atacama Large Millimeter Submillimeter Array (ALMA) in Chile whose extraordinary state-of-the-art technology has at a stroke increased the EHT’s sensitivity by a factor of 10. Hence, the optimism ahead of April.
Even so, scientists have had to install special equipment at all the radio facilities involved in the observation, including big hard drives to store the colossal volumes of data, and atomic clocks to precisely timestamp it all. Once the observations begin the data will be collected and flown back to the MIT Haystack Observatory in Westford, just outside Boston, Massachusetts.
“Our hard drive modules hold the capacity of about 100 standard laptops,” said Haystack’s Vincent Fish, “we have multiple modules at each telescope and we have numerous telescopes in the array. So, ultimately, we’re talking about 10,000 laptops of data.”
It’s in Haystack’s correlator computer that the synthesis will begin and some very smart imaging algorithms have had to be developed to make sense of the EHT’s observations, but processing all the data will take time and it could be the end of the year, or the start of 2018 when the team finally release a picture to the public.
Looking into the future, the scientists are already thinking about how to improve and extend their techniques. For example, the matter closest to the event horizon and about to disappear into Sagittarius A* should take about 30 minutes to complete an orbit, and Katie Bouman, from MIT’s Computer Science and Artificial Intelligence Laboratory, thinks it might be possible to capture its movement.
“We want to push boundaries and to try to make movies from the data,” she said, “maybe we can actually see some of the gas flowing around the black hole. That’s really the next stage of what we’re trying to accomplish with these imaging algorithms and the EHT.”
Before the observations can get underway though the team’s going to need good weather at the participating observing stations, and they’ll try to view the black hole’s galactic centre at a wavelength of 1.3mm (230GHz). This has the best chance of piercing any obscuring gas and dust in the vicinity of the black hole – but if there is too much water vapour above the array’s receivers, the EHT will struggle even to see through Earth’s atmosphere.
Just getting a resolved view of Sagittarius A* would be a remarkable triumph in itself, but the real objective will be to use the EHT’s imaging capability to test some of the laws of general relativity.
If there are flaws to be found in Einstein’s ideas, and scientists suspects there are more complete explanations of gravity out there waiting to be discovered, then they’ll be found in the extreme environments of black holes.
Meanwhile though, here back on Earth, scientists are still trying to unravel the mysteries of how to take photos of children… maybe one day, but for now bring on 2018.