This morning, an international team of scientists released the first ever image of a black hole's event horizon, a stunning achievement that marks an incredible milestone for radio astronomy and physics.
Capturing Images of the Black Hole at the Heart of Messier 87
Scientists working with the Event Horizon Telescope (EHT) released the first ever images of a black hole's event horizon today, marking one of the greatest achievements for radio astronomy and physics and finally confirming the existence of a structure first theorized by Albert Einstein a century ago.
The supermassive black hole (SMBH) lies at the heart of the distant elliptical galaxy Messier 87 (M87), 5 billion billion kilometers away from us, has a mass equal to 6.5 billion times that of our sun, with an event horizon, the threshold beyond which no light can escape, stretching 38 billion kilometers across. The more challenging of the two targets of the EHT, the image of M87 SMBH's event horizon was as hard to capture as a mustard seed in Washington, DC be as seen from Brussels.
Why We Haven’t Seen a Black Hole Until Now
If you take a moment to think about it, it isn’t hard to see why capturing an image of a black hole hasn’t been done until now. Black holes are the most exotic structures in physics, objects so massive and so dense that their gravity captures every form of radiation that crosses their event horizon. Without radiation, including visible light, a black hole literally cannot be seen against the backdrop of space and their incredible density and compact dimensions make it all but statistically impossible to identify a black hole by it’s eclipsing of some background source of radiation.
They have proven to be so elusive that until today, there were some who argued that black holes didn’t even exist.
We’ve long been certain of their existence, however, by the effects its gravity has on its surroundings. The existence of black holes have long been taken for granted because of the severe affect its gravity has on the orbits of stars in the galactic core. In the above time-lapse video from the European Southern Observatory taken over 20 years, the elliptical orbit of the star closest to Sagittarius A*, the SMBH that sits in the center of our galaxy, shows the star accelerating to a significant fraction of the speed of light at the perigee of its orbit, that is its closest position relative to the object it orbits, which could only be produced by an object of immense mass that could only be a SMBH.
While incredibly strong evidence of the existence of black holes, this still isn’t directly observing the thing itself.
In order to capture an image of any significant detail, scientists needed to capture the radiation from M87 SMBH at a wavelength of 1 mm. Our most high resolution radio telescopes are capable of capturing 1 cm wavelengths, so anything below that was necessarily bound to be blurry and distorted, especially when considering all of the gases, temperature anomalies, and other conditions that could distort the radio waves coming from just before the event horizon of a SMBH.
That is what makes the achievement of the EHT so incredible.
How the Event Horizon Telescope Pulled It Off
In order to capture the wavelength required to capture a detailed image of a SMBH, a radio telescope thousands of miles wide would be required. Given the impossibility of building one physically, the EHT decided to build one virtually.
Using a technique known as Very Long Baseline Interferometry (VLBI), astronomers constructed a network of radio telescopes around the world and coordinated their efforts to produce a series of images from different vantage points. Collecting one million gigabytes of data over several days, a computer algorithm has spent the past two years stitching together the different data to effectively create a gigantic virtual radio telescope as wide as the Earth itself, allowing it to achieve the resolution necessary to capture the detailed image shown off today.
This story is developing.