This Is How We Will Successfully Image A Black Hole’s Event Horizon
“Normally, the resolution of your telescope is determined by two factors: the diameter of your telescope and the wavelength of light you’re using to view it. The number of wavelengths of light that fit across your dish determines the optimal angular diameter you can resolve. Yet if this were truly our limits, we’d never see a black hole at all. You’d need a telescope the diameter of the Earth to view even the closest ones in the radio, where black holes emit the strongest and most reliably.
But the trick of very-long baseline interferometry is to view extremely bright sources, simultaneously, from identical telescopes separated by large distances. While they only have the light-gathering power of the surface area of the individual dishes, they can, if a source is bright enough, resolve objects with the resolution of the entire baseline. For the Event Horizon Telescope, that baseline is the diameter of the Earth.”
The Event Horizon Telescope is one of the best examples of international collaboration, and its necessity, in answering questions that are too big for any one nation to do alone. Part of the reason for that is geography: if you want to get the highest-resolution information possible about the Universe, you need the longest-baseline of simultaneous observations that it’s possible to make. That means, if you want to go as hi-res as possible, using the full diameter of the Earth. From the Americas to Eurasia to Africa, Australia and even Antarctica, radio astronomers are all working together to create the first image of a black hole’s event horizon.
What does it look like? Is General Relativity correct? As soon as the Event Horizon Telescope team releases their first images, we’ll know. Come watch a live-blog of a talk from their team today, and get the answers as soon as we know them!
This Is Why The Event Horizon Telescope Still Doesn’t Have An Image Of A Black Hole
“Of all the black holes visible from Earth, the largest is at the galactic center: 37 μas.
With a theoretical resolution of 15 μas, the EHT should resolve it.
Despite the incredible news that they’ve detected the black hole’s structure at the galactic center, however, there’s still no direct image.”
Last year, data from the South Pole Telescope, a 10-meter radio telescope located at the South Pole, was added to the Event Horizon Telescope team’s overall set of information. Here we are, though, half a year later, and we still don’t have a direct image of the event horizon for the galactic center’s black hole. There aren’t any problems; the issue is that we have to successfully calibrate and error-correct the data, and that takes time and care to get it right. Science isn’t about getting the answer in the time you have to get it; it’s about getting the right answer in the time it takes to get things right. From that point of view, there’s every reason this is worth waiting for.
The Event Horizon Telescope team is on the right track; here’s where we are right now in our quest to create the first image of a black hole’s event horizon!
2018 Will Be The Year Humanity Directly ‘Sees’ Our First Black Hole
“No longer will we need to rely on simulations or artist’s conceptions; we’ll have our very first actual, data-based picture to work with. If it’s successful, it paves the way for even longer baseline studies; with an array of radio telescopes in space, we could extend our reach from a single black hole to many hundreds of them. If 2016 was the year of the gravitational wave and 2017 was the year of the neutron star merger, then 2018 is set up to be the year of the event horizon. For any fan of astrophysics, black holes, and General Relativity, we’re living in the golden age.”
Black holes have been dreamed up by theorists for centuries. Even in the aftermath of Newtonian gravity, a spectacular realization came about that if you gathered enough mass together into a small enough volume, the gravitational effects would be so pronounced that nothing, not even light, could escape. These black holes show up with very specific properties in General Relativity, and today in modern astrophysics, we know of three independent ways to make them. But despite observing their effects in many different wavelengths of light, such as the radio and X-ray, we’ve never imaged an event horizon directly. Although a telescope the size of Earth would be able to, that technology is out of reach. Owing to collaboration and human ingenuity, however, we’ve developed an array known as the Event Horizon Telescope that should reveal its first image next year!
Will we see the event horizon of a black hole for the first time? My bet is on yes. Come get the science as to why!
Ask Ethan: Could Matter Escape The Event Horizon During A Black Hole Merger?
If two black holes merge, is it possible for matter that was within the event horizon of one black hole to escape? Could it escape and migrate to the other (more massive black hole)? What about escape to outside of both horizons?
Imagine that you’ve got two black holes about to merge in space. They’re radiating energy away, spacetime itself is at its most distorted, and perhaps you have particles just crossing over the event horizon for the first time. Is there any way you could configure it to have them escape, or to have a particle jump from one event horizon to another? The situation is incredible, and involves some of the strongest gravitational fields ever considered in the Universe. But numerical relativists are up to the challenge of simulating these spacetimes, and we can see what happens! Believe it or not, even as energy is radiated away and the total mass drops, the event horizons themselves never decrease in size, and the total volume encapsulating the “no-escape zone” only increases as time goes on!
Come learn the reason why matter can’t escape the event horizon, even during a black hole merger, on this week’s Ask Ethan!
Universe’s Largest Black Hole May Have An Explanation At Last
“The brightest, most luminous objects in the entire Universe are neither stars nor galaxies, but quasars, like S5 0014+81. The sixth brightest quasar known so far, its mass was determined in a 2009 study: 40 billion Suns. Its physical size would have a radius that’s 800 times the Earth-Sun distance, or over 100 billion kilometers. This makes it the most massive black hole known in the entire Universe, as massive as the Triangulum galaxy, our local group’s third largest member.”
The largest black hole in the Universe was a shocker when it was first discovered. At 40 billion solar masses, it certainly is impressively large. Like other quasars and active galaxies, it has a luminous accretion disk that can be seen from a great distance. Like only a few, one of its two incredibly energetic, polar jets is pointed directly at Earth, creating a blazar, the brightest of all active galaxies. But what makes this object, known as S5 0014+81, so special is that it got so big and massive so quickly. Its light comes to us from a time when the Universe was only 1.6 billion years old: just 12% of its current age. If this brilliant, massive object were located a mere 280 light years away, or ‘only’ 18 million times the Earth-Sun distance, it would shine as brightly as our life-giving star.
Come learn about the largest ultramassive black hole known in the Universe, what explains its existence, and how there might be an even more massive one out there for Mostly Mute Monday!
Is it possible to pull something out of a black hole?
“Once something falls into a black hole, it can never get out. No matter how much energy you have, you can never move faster than the speed of light, and yet you’d need to in order to exit of the event horizon once you’ve crossed inside. But what if you tried to cheat that little rule by tethering a tiny object that just dipped inside the event horizon to a much larger, more massive one that was destined to escape? Could you pull something out of a black hole that way, or any other way? The laws of physics are restrictive, but they should tell us whether it’s possible or not. Let’s find out!”
So you’re passing by a black hole in a massive, fast-moving spaceship, and you want to do an experiment: you tether a small mass outside of the ship and let it fall into the black hole, just allowing it the tiniest bit inside, while your ship takes off to try and escape. If you can keep the tether from breaking and your ship from getting stretched apart, what’s going to happen? Will you manage to make off with your object, despite dipping it into the abyss, perhaps even obtaining information about the inside of the black hole in the process? Or will the gravitation of the black hole inevitably suck you in, forcing you to either cut the tether or wind up at the core singularity, where you’ll be unable to avoid being torn apart?
Physics holds the answer, and one thing is clear: don’t bet against the laws of Einstein!
Nothing Escapes From A Black Hole, And Now Astronomers Have Proof
“Our work implies that some, and perhaps all, black holes have event horizons and that material really does disappear from the observable universe when pulled into these exotic objects, as we’ve expected for decades. General Relativity has passed another critical test.”
Are event horizons real? With data taken from around a dozen observatories earlier this year, simultaneously, the Event Horizon Telescope is poised to put together the first-ever direct image of the black hole at the center of our galaxy Sagittarius A*. If event horizons are real, this data should be able to create the first-ever image of it, proving that nothing escapes from inside a black hole once you’ve been swallowed. But why wait? Through a very clever technique, a team of astronomers used data from the Pan-STARRS telescope to test the alternative: that there’d be a hard surface exterior to where the event horizon is supposed to be. If that were the case, stars that collided with these hard surfaces would create a transient signal in the visible and infrared, which is exactly what Pan-STARRS is sensitive to.
The lack of such signals, even though a significant number would be expected, shows that the alternative to event horizons cannot stand. Event horizons are real, and now we have indirect proof!
Ask Ethan: What Should A Black Hole’s Event Horizon Look Like?
“Shouldn’t the event horizon completely surround the black hole like an egg shell? All the artist renderings of a black hole are like slicing a hard boiled egg in half and showing that image. How is it that the event horizon does not completely surround the black hole?”
Black holes were one of the first consequences of general relativity that were predicted to exist, and the more we’ve studied the Universe, the more interesting they’ve become. We’ve calculated their physical sizes, their effects on the curvature of spacetime, their apparent angular sizes, and the properties of matter that gets caught in an accretion disk around them. But we’re about to take another giant leap forward: we’ve about to directly observe one for the first time. Sure, it will be in radio frequencies rather than visible light, but we should be able to directly image the event horizon, and contrast those observations with our best predictions. What should that event horizon look like, though, and why – if it’s completely black – should we be able to see it at all? The answers are both fascinating and informative, and when the results are released later this year, you’ll want to know.
Come learn all about it on this week’s Ask Ethan!