The Event Horizon Telescope: Are We Close to Imaging a Black Hole?

A modelled black hole shadow (left) and two simulated observations using a 7-telescope and 13-telescope array (Fish & Doeleman)
A modelled black hole shadow (left) and two simulated observations using a 7-telescope and 13-telescope array (Fish & Doeleman)

All the evidence suggests there is a supermassive black hole lurking in the centre of our galaxy. We’ve known as much for quite some time, but it wasn’t until recently that we’ve been able to confirm it. As it turns out, most galactic nuclei are predicted to contain supermassive black holes in their cores.

The Milky Way’s supermassive black hole is called Sagittarius A*, a well-known compact radio source used by radio astronomers as an instrumental calibration target. The black hole driving this emission has been calculated to weigh in at a whopping 4×106 solar masses.

So, we’re certain Sgr A* is a supermassive black hole, how can we use it?

Using our Sun as an example, stellar physicists use the Sun as an up-close laboratory so they can better understand stars located many light years away. It is an up-close star that we can study in great detail, gleaning all kinds of information, helping us learn more about how stars work in general.

What if Sgr A* could be used in a similar way, not in the study of stellar physics, but in the pursuit to understand the dynamics of black holes throughout the Universe?

This is exactly the question Vincent Fish and Sheperd Doeleman from the MIT Haystack Observatory ponder in a recent publication. The researchers make an important point early in their paper:

Due to its proximity at ~ 8 kpc [26,000 ly], Sgr A* has the largest apparent event horizon of any known black hole candidate.

The centre of our galaxy as imaged by Spitzer (NASA)
The centre of our galaxy as imaged by Spitzer (NASA)

In other words, the supermassive black hole in the centre of the galaxy is the largest observable black hole in the sky. As Sgr A* is so massive, its event horizon is therefore bigger, providing a sizeable target for Earth-based observatories to resolve.

Although the black hole is quite a distance from us, the size of its event horizon more than makes up for its location, it even trumps closer, less massive stellar black holes. Sgr A* could therefore be our own personal black hole laboratory that we can study from Earth.

But there’s a catch: How do you directly observe a black hole that’s 26,000 light years away? Firstly, you need an array of telescopes, and the array of telescopes need to have very large baselines (i.e. the ‘scopes need to be spread apart as wide as possible). This means you would need an international array of collaborating observatories to make this happen.

The authors model some possible results using many observatories as part of a long baseline interferometry (VLBI) campaign. As Sgr A*’s emissions peak in the millimetre wavelengths, a VLBI system observing in millimetre wavelengths could spot a resolved black hole shadow in the heart of Sg. A*. They also say that existing millimetre observations of Sgr A* show emission emanating from a compact region offset from the centre of the black hole, indicating there is some kind of structure surrounding the black hole.

The results of their models are striking. As can be seen in the three images at the top of this post, a definite black hole shadow could be observed with just 7 observatories working together. With 13 observatories, the resolution improves vastly.

Could we be on the verge of tracking real-time flaring events occurring near the black hole? Perhaps we’ll soon be able to observe the rotation of the supermassive black hole as well as accretion disk dynamics. If this is the case, we may be able to also witness the extreme relativistic effects predicted to be acting on the volume of space surrounding Sgr A*.

The best news is that technological advancements are already in progress, possibly heralding the start of the construction of the world’s first “Event Horizon Telescope.”

Source: Observing a Black Hole Event Horizon: (Sub)Millimeter VLBI of Sgr A*, Vincent L. Fish, Sheperd S. Doeleman, 2009. arXiv:0906.4040v1 [astro-ph.GA]

15 thoughts on “The Event Horizon Telescope: Are We Close to Imaging a Black Hole?”

    1. Black holes don't have enough pull to swallow up an entire galaxy. Instead, the energy of the galaxy around them is going to fade away and the black hole will just be floating through space until it (possibly) evaporates away.

      1. Nope black holes self combust. They die out like everything else and when they do, all the energy they swallowed creates a star:D

  1. There are supermassive black holes in the center of every galaxy, at least the ones we've checked. It is how the galaxies were formed, and they know the mass of the black holes because of the relative speed of the stars that orbit it.( All of them all the way to the edge of that galaxy. Our black hole is dormant right now, Its pushed everything back with its jet to far back and cannot feed anymore. Black holes only create stars while they're feeding. when the gasses falling in create huge amounts of friction starting a Nuclear reaction. No one is for sure what happends to them, but everything has a cycle a positive and neg force. it is quite feasible that indeed everything that falls into a black hole it in fact the complete reverse in a parallel universe.

  2. If nothing escapes a black hole, how come we are getting all thatradio emission from it? Either it isn't a black hole, or we are wrongabout black holes!

    1. As gas and dust falls towards the event horizon of a black hole, it is accelerated to high speeds, generating enormous friction, heat, and radiation. That's how we can detect them. A black hole all by its lonesome in an empty part of space would be beyond our ability to detect, since we can only really detect them by their impact on other objects.

  3. Could we be on the verge of tracking real-time flaring events occurring near the black hole? Sure, if you accept a delay between event and observation of tens of thousands of years.

    1. The difference between the mass of the galaxy and the mass of the supermassive black hole is about 1000 times.Recently, scientist have calculated that the mass of the supermassive black holes in the center of every galaxy is directly proportional with the mass of the galaxy and the rotation speed of the stars around it (even the ones at the remote edge of the galaxy).That evidence supports the theory that the central black holes in each galaxy are resposable for the creation of the galaxies in their current form.A galaxy is initially a huge cloud of hydrogen. It is theorized that a black hole is formed in the center. As it starts to feed, faster that it can 'chew', it becomes a Quasar. Incandescent gas is pulverised away, and by condense with the rest of the gas, stars are formed. At some point, the supermassive black hole pushes everything away and becomes dorment, and the galaxy cools off and becomes inactive, like the milky way is right now.

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