by Ethan Ward
How do you see something that doesn’t want to be seen? This was the fundamental question facing scientists who worked on the Event Horizon Telescope (EHT) project to produce the first ever picture of a black hole. If you want to know more about taking a snapshot of something that has the fundamental trait of being devoid of light, Isabelle’s article explains how the team did it. This monumental achievement in observational astrophysics deserves a look at its significance, results, and future direction.
Other than being a testament to collaboration in science, this picture is conclusive evidence of a very important ‘theoretical’ object in astrophysics. Black holes are a ‘singularity’ in the field equations of gravity and electromagnetism when viewed in the framework of Einstein’s theory of General Relativity (meaning its a literal hole that isn’t truly part of time or space). Along with the LIGO observations over the past year, this picture provides experimental evidence of this overarching view of reality called General Relativity. The magnitude of this support cannot be overstated. It’s why this was the front page of just about every paper in the world the day it was announced. This allows us to finally study something we could only have predicted/speculated on previously. With direct observations, the mystery of this singularity and what lies beyond the event horizon is on its way to being fully uncovered.
This effort has given us the first image of something that physicists have known exists for a century. Aside from being a breathtaking look at a mysterious part of our universe, what does this picture tell us? We can definitively quantify the spin direction and mass of M87 from this picture, according to the project scientist of the EHT, Dr. Psaltis. This is pretty miraculous considering how this imaging technique is still early in development. For reference, the first picture of Pluto from Hubble looked like a blurry mess (see reference: “Image – The Surface of Pluto.”). Given, there is much more information from telescope imaging than we see. However, with continued funding and development, the New Horizons mission showed much more information about the 9th not-so-planet from the sun while providing a spectacular look at our solar system (see reference: NASA). The slow improvement in imaging Pluto serves as a great template for how the EHT could evolve if the same attention (and funding) is given. Currently, the data from the first run of this collaboration supports the No Hair Theorem, which states that the only information we can glean from a black hole is the information that it broadcasts to the universe (specifically its mass, angular momentum, and charge).
Particularly, the team found the direction of M87’s spin (counterclockwise) and confirmed its estimated mass through gravitational lensing techniques (Psaltis). The next step to understanding all we can about black holes with our current theoretical framework is making charge measurements…which is another story that gets very complicated. Some fun speculation on where this could possibly go involves analogies to using the Zeeman (or maybe even the Stark effect) on the electromagnetic spectrum of these black holes to gauge their charge. The Zeeman effect is a phenomenon that occurs when a spectral line splits in the presence of a magnetic field, which is commonly used to map the magnetic field across the surface of the sun. This technique along with magnetometry are the best ways that the field of astrophysics can currently measure the charge of celestial objects. This could be a very interesting route to explore as radio waves are just another form of the electromagnetic (EM) spectrum like visible light or infrared. Given, the accretion disk around the black hole has its own spectrum of EM radiation which it broadcasts to the rest of the universe and must be carefully filtered as noise when trying to determine the primary characteristics of a black hole.
This is the groundwork for not just observing black hole characteristics, but also opening up a promising new method of radio interferometry. The potential for a new renaissance in astronomical observation of those objects thought previously impossible to study may now be possible. Limitations of current situation is that they only have data from North, South, East, and West (i.e telescopes from Antartica, Mexico, Hawaii, Chile, Spain, Arizona) which means they are completely lacking coverage in the azimuthal directions (NE, SW, etc…) and therefore lacking the complete picture (Castelvecchi). Furthering this line of thought, there’s a plan to link Event Horizon Telescope and the proposed orbiting array for a huge interferometer. An array like this is in orbit between the Earth and the moon could overcome the massive filter to astrophysical signals which is our atmosphere (Gough). Transmitting the data through space would be near 1/20 of speed we’re used to with our phones. As Isabelle mentioned, the amount of data from each run is unfeasibly large to transfer in any way except for physically. This would need to be remedied (possibly with self-piloting shuttles that can mechanically transfer the data drives) to correlate the data between corresponding telescopes in the array. For an orbiting telescope array, you would need very accurate measures of how far the telescopes are from each other (i.e. very accurate measures of position and speed for the satellites). This is probably the easier hurdle to overcome, as GPS technology can serve a very important role here. As previously mentioned, the charge measurements are the largest hurdle to overcome and may be an unattainable goal for the first iteration of this orbiting array, but nonetheless, are a very interesting exploration.
The significance of this observation should be evident at this point. An observation of something which has the primary characteristic of being a hole, not only in our understanding but also in space and time itself is a monumental achievement. It’s a beautiful thing that we can look up at the universe in wonder. Its harder to describe or even grasp the feeling that we can understand a little bit of why our home is the way it is. The hope that this image provides is tied not just to more to come, but to greater pushes for international and interdisciplinary collaboration as well. The drive and passion that each and every member of this collaboration had to show for this image to become a reality is a true testament to what humanity can achieve when we have a common goal and love of the journey there.
References:
Castelvecchi, Davide. “Black Hole Pictured for First Time – in Spectacular Detail.” Nature News, Nature Publishing Group, 10 Apr. 2019, www.nature.com/articles/d41586-019-01155-0.
Gough, Evan. “The Black Hole Picture Could Be So Much Better If You Add Space Telescopes.” Universe Today, 9 May 2019, www.universetoday.com/142170/the-black-hole-picture-could-be-so-much-better-if-you-add-space-telescopes/.
“Image – The Surface of Pluto.” HubbleSite, Sept. 1996, hubblesite.org/image/400/news_release/1996-09.
NASA. www.nasa.gov, 1 Oct. 2015, www.nasa.gov/sites/default/files/thumbnails/image/nh-pluto-charon-v2-10-1-15.jpg.
Psaltis, Dimitrios. “The Black Hole Shadow in the M87 Galaxy.” Berkeley Physics Colloquium. The Black Hole Shadow in the M87 Galaxy, 22 Apr. 2019, Berkeley, UC Berkeley, 1 LeConte Hall.