Making It Real — First-Ever Picture Of A Black Hole!

The Event Horizon Telescope (EHT) — a planet-scale array of eight ground-based radio telescopes — captured this image of the supermassive black hole in the galaxy M87 in Virgo, the first-ever of a black hole. We see the shadow of the black hole framed by bright gases that are spinning around it. The black hole’s boundary, called the event horizon, is around 2.5 times smaller than the shadow it casts and measures just under 25 billion miles (40 billion km) across. While this may sound huge, it’s equivalent to measuring the length of a credit card on the surface of the moon. ESO Collaboration

 

After Einstein predicted black holes more than a century ago, we finally got a look at one today. When the first photo was revealed at today’s press conference in Brussels, I was surprised at how familiar it looked. Exactly as the models had predicted, here was a dark nothing surrounded by a thick disk of hot, glowing gases whirling around the hole’s event horizon. Is science wonderful or what? Einstein predicted, astronomers painstakingly gathered evidence, and in the end, astronomers got it right. Simply amazing.

Screen grab from this morning’s press conference.

The black hole, informally called M87* (M87 star), hides out in the core of the gigantic elliptical galaxy M87 55 million light years away in the constellation Virgo. While the object is enormous — 25 billion miles across — it’s so remote that getting a picture of it is the equivalent to photographing a credit card on the moon. By measuring how the hole pulls on surrounding material falling into it, astronomers pegged its mass at 6.5 billion times that of the sun. For comparison, if M87’s black hole were put in place of the sun, it would reach far beyond Pluto deep into the Kuiper Belt.


Zoom into the heart of the galaxy M87 in Virgo to see its supermassive black hole

The image shows the hole in “radio light.” Although we can’t see radio waves, there’s as much a form of light as that streaming through your window. Radio waves penetrate dust that blocks visible light, allowing astronomers to peer inside the cores of distant galaxies.

To get a picture of the remote black hole, scientists had to link nine different radio telescopes around the globe, in effect creating a telescope the size of the Earth.  The technique is called VLBI or Very Long Baseline InterferometryNOAO / EHT

It took a lot of telescope power to crack the case. Eight different radio telescopes across the globe — dubbed the EHT or Event Horizon Telescope — synchronized the data they gathered on M87’s black hole using atomic clocks to precisely time their observations. Each telescope of the EHT produced enormous amounts of data – roughly 350 terabytes per day – which was stored on high-performance, helium-filled hard drives. All the data were flown back to special supercomputers called correlators and combined then converted into an image.

“This shadow, caused by the gravitational bending and capture of light by the event horizon, reveals a lot about the nature of these fascinating objects and has allowed us to measure the enormous mass of M87’s black hole,” said EHT science council Heino Falcke.

From my understanding, the shadow is an image of the event horizon — the black, lightless outline of the hole — warped by the black hole’s strong gravitational field and superimposed over the bright, glowing gases.

M87 in Virgo is about 120,000 light years across. The “tail” you see is a powerful jet of matter shot out by the supermassive black hole in the galaxy’s center. It’s thousands of light years long. All those little dots that look like stars are globular clusters orbiting the core of the galaxy M87 in Virgo. NASA/ESA

It was sweet that all this happened during the centenary year of the historic 1919 eclipse observation that first confirmed Einstein’s prediction that gravity bends light. Black holes are one of the most compelling topics in astronomy whether you’re a scientist or a man or woman on the street. Everyone is captivated by them.

In a nutshell, a black hole is a region of space where matter is wadded up so tightly that its gravity is powerful enough to hold back anything, even light, from escaping. Without light, holes appear as empty spots but are often surrounded by disks of bright material that’s heated to millions of degrees as it swirls past the hole’s “edge,” called the event horizon. It all heads for a microscopically small point of infinite density known as the singularity. Here, the predictive power of science reaches an end … for now.

Model of a black hole. NASA/Chandra

Black holes usually form when a massive star explodes as a supernova, leaving behind a superdense core that contracts to only a few miles across, small enough to arrest light.  The astronomers checked and re-checked using different imaging methods over multiple observations to confirm that the black hole they imaged was the real deal.

“The confrontation of theory with observations is always a dramatic moment for a theorist. It was a relief and a source of pride to realize that the observations matched our predictions so well,” said EHT Board member Luciano Rezzolla.

M87 is a bright galaxy in the spring sky in the constellation Virgo below the tail of Leo. It’s faintly visible as a blurry glow in 50mm binoculars from a dark sky. Stellarium

The Milky Way also has a supermassive black hole with the equivalent of 4 million suns. Even though much smaller than the one in M87, it’s much closer so appears about the same size. Good news. It’s on the EHT’s to-do list but wasn’t picked for the first image because it jiggles around too much to get a clear picture. A scientist at the press conference described it as a busy “toddler” compared to the “big bear” in M87 which moves around much less.

Look at the picture again, and you’ll see that some of the gas around the hole is much brighter. That’s probably due to rotation: either the hole or the gas around it is spinning. Besides being a spectacular achievement and an example of how cooperation has led to one of most significant discoveries of our age, scientists can now begin to study and experiment on a real, physical object. Black holes aren’t just a concept anymore. They’re real!

6 Responses

  1. caralex

    Bob, can you explain what the ‘shadow’ of a black hole actually is? How does an invisible object cast a shadow? I’m having trouble understanding exactly what we’re looking at in the centre.

    1. astrobob

      Great question and I’m still trying to understand it myself. The shadow is apparently an image of the event horizon, lensed by the black hole’s strong gravitational field around and superimposed over the background light from the glowing gas.

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