The world is eagerly awaiting the release of the first-ever highly-detailed picture of a black hole, expected on April 10. Astronomers have been studying black holes for a century now, through physics, computer simulations, and we have even taken a few low-resolution photographs of these enigmatic bodies. So, what can we expect from this new image coming from the world’s largest collection of radio telescopes, and how could it help us answer the greatest question in physics?
The Event Horizon Telescope (EHT) is a worldwide network of eight radio telescope observatories, working together, providing astronomers with an instrument having the resolution of a single telescope nearly as large as the Earth. Astronomers utilizing this observatory have been studying two massive black holes — Sagittarius A* (SgrA*), at the center of the Milky Way Galaxy, and a much-larger supermassive black hole in the galaxy M87, 54 million light years from Earth. Images of both of these bodies are likely to be released, at various times, by astronomers using the EHT.
Despite all the research put into understanding black holes, we still do not know exactly what the structure of matter looks like around these bodies. Within the critical region known as the event horizon, nothing — not even light — can escape, giving us the term black hole. However, just outside this horizon, matter glows as it spirals into to the black hole, or is shot out (at tremendous velocities) into space. The widespread collision of matter within this accretion disk can cause the “hungriest” black holes to glow brighter than the entire galaxies in which they reside.
Even prior to its release, this new image is being hailed as one of the most important photographs in the history of astronomy. Here, we cover just a few reasons this new image is so important.
It’s Always Nice to Have a Photo
One of the greatest things we can learn from seeing a detailed pictures of a black hole for the first time may be the most obvious — we will finally get to see what the region around a black hole looks like! Computer simulations predict the accretion disk will look much like a whirlpool, and jets of charged particles could form along magnetic lines caused by the body.
It is likely that the image we see will appear lopsided, or asymmetrical, as gravity will bend light coming from near the black hole to a greater degree than light coming from material further from its center.
Oddly enough, we might even see objects behind the black hole, through a principle known as gravitational lensing. Extreme concentrations of gravity can act like a lens, bending light around objects such as quasars or distant clusters of galaxies. A black hole may act in the same manner, bringing distant objects into focus, like a gigantic, natural telescope.
(Sing with Me) Ohhh… Wooo… JET!
Supermassive black holes, like people, can have vastly different appetites. While SgrA* at the core of our own galaxy only takes in a small amount of material from its surrounding space, the object sitting at the center of M87 is a voracious eater, having a mass between 3.5 and 7.2 billion times greater than our sun.
This means this black hole has between two and five times the mass of the entire Milky Way Galaxy. The supermassive black hole at the center of M87 has developed a glowing jet of energized material, reaching 5,000 light years from end to end. So far, no one knows what could power the creation of such massive structures. Observations of the M87 black hole could help piece together the mystery of how these jets form, including how they are powered.
Are There Pulsars in the Center of Our Galaxy?
By photographing the supermassive black hole at the center of our galaxy, we may learn for the first time if SgrA* is surrounded by pulsars — energetic bodies that emit vast amounts of radiation as they rapidly rotate around their centers. Optical telescopes are unable to see any, due to vast quantities of dust near the center of our galaxy. Radio of infrared telescopes are needed to see through this haze, and the EHT has the greatest resolution of any such instrument yet built.
As light heads out from regions of extreme gravity, the frequency of the light becomes stretched out, appearing redder than we would otherwise expect to see. This effect has already been spotted from signals coming from near SgrA* in a 2018 study.
This gravitational redshift would be even easier for astronomers to see, if it were coming from a pulsar. This is due to the fact that a massive gravitational field would appear to change the precise timing of beams of energy coming from a pulsar spinning near a massive black hole. So far, no pulsar has been found close enough to SgrA* for this effect to be measured. But, radio observations conducted by astronomers utilizing the EHT could change that fact. If such an effect on light from a pulsar near SgrA* is found, it could provide one of the greatest tests of relativity ever observed.
An Origin Story Worthy of a Blockbuster Movie
A question which may seem to be the simplest of all inquires about supermassive black holes has also, so far, escaped having an answer — How do these bodies form? Do they start small and grow over time, as dust and gas falls within their event horizon, or are they the result of a number of smaller black holes joining together? The answer may even be a little of both. By examining the accretion disk around SMBH’s, we may find the answer to that mystery, as well as other mysteries in astrophysics.
We May Answer The Greatest Question in Physics
The two great pillars in modern physics are relativity and quantum mechanics. Relativity explains effects on objects traveling at tremendous speeds, and in high gravitational fields (or experiencing acceleration), while quantum mechanics governs the bizarre world of the very small. Both theories appear to be true in the own realms. We are dependent on relativity when we use the Global Positioning System (GPS), while transistors would not function without the odd behavior of sub-atomic particles determined by quantum mechanics.
The trouble is, these two arms of modern physics appear to be incompatible with each other. One of the main problems is that three of the four fundamental forces of nature — electromagnetism (which includes light and radio waves), the weak force (which governs some forms of radiation) and the strong force (which keeps protons within atoms from flying apart), have all been explained through the exchange of quanta (or discrete packets) of energy. So far, no one has found a quantum theory of gravity, which appears to propagate through a continuous curvature of spacetime.
“Space and time in Einstein’s universe are no longer flat (as implicitly assumed by Newton) but can pushed and pulled, stretched and warped by matter. Gravity feels strongest where spacetime is most curved, and it vanishes where spacetime is flat. This is the core of Einstein’s theory of general relativity, which is often summed up in words as follows: ‘matter tells spacetime how to curve, and curved spacetime tells matter how to move’,” Stanford University researchers explain.
The shape of the ring seen in the upcoming image could provide the answer to this great conundrum in physics. If quantum mechanics, as it is currently understood, is true, then the ring will take one shape. If relativity holds true, the ring will take another form. By studying this shape, we may find the answer to the great conflict between relativity and quantum physics.
The EHT is a groundbreaking instrument, and releasing the first-ever detailed image of the region surrounding a black hole could answer questions which have puzzled physicists for generations. It is also likely to generate a new slew of mysteries, waiting to be answered by the next generation of telescopes and scientists.