A different perspective on the M87: A Supermassive Blackhole
On 10th April 2019, the Event Horizon Telescope group released the first-ever image of a black hole. 2 years later, on 24th March 2021, we received an updated image of the same black hole with beautifully defined lines in its accretion disk. Let’s find out what’s new to this image and how did scientists come around doing this.
Back in 2006, the scientists from the EHT (Event Horizon Telescope) had a crazy idea. It seemed impossible, but in 2017 the EHT took an image of a supermassive black hole in the middle of a massive galaxy called Messier-87. 2 years later when they were done with the computation, they released an image that almost looks like a fuzzy coffee mug stain.
Don’t be fooled by its simplicity. This image rocked the scientific community, telling us whether the predictions made by the General Theory of Relativity were right. This image is one of the most important images of the 21st century.
The galaxy gets its name from the French Astronomer, Charles Messier. He was obsessed with comets. He loved them so much that he cataloged everything that wasn’t a comet and everything that would prevent you from seeing one to find more of them. He ended up publishing a catalog consisting of 110 nebulae and faint star clusters, which came to be known as the Messier objects. Our object of interest is the 87th object in this very catalog. To a layman, it definitely looks like a comet. It is essentially the most massive nearby galaxy within the span of 100 million light-years. It is present 55 million light-years away from us. And it goes without saying that this massive galaxy harbors a supermassive Blackhole.
This image shows that this black hole is producing this huge astrophysical jet colored in blue. This jet itself extends up to 5000 light-years. Surprised? You won’t be when I tell you that the mass of the Blackhole is 65 billion times the mass of the sun. This jet is almost pointing towards us, which means we took the image of the black hole almost perpendicularly.
So, how did we go about photographing this Black Hole?
Despite the overwhelming size of the black hole, it was the size of only 40 (μ arc seconds) relative to how far it was. To get a clear picture of an object that small we would need a telescope as big as the whole Earth, and that is impossible. So, scientists collaborated with 8 different telescope sites over the globe to create a virtual telescope that is as big as the Earth. Here we use radio waves of medium frequency, not too short, not too long. This portion of the spectrum is employed to create the image because it can reveal structures near the event horizon and can travel through the accretion disc and interstellar dust to reach the telescope. After taking the image, petabytes of data from each telescope site are collected and computed by complex algorithms and supercomputers. And Voila, here we have the first image of a black hole. Trust me, it’s easier said than done.
Moving on to a clearer image
Here’s the thing about scientists, they are never satisfied. They always want the next big thing. 2 years later scientists did a study which made this image more interesting, well at least for themselves. They upgraded the previous image to this:
Except for the stripes, it’s practically identical. They depict polarised light. In essence, polarised light is light that has some polarity. Sunlight is unpolarized light, which means its polarisation is random. When this light reaches an item, it has a propensity to reflect more polarised light than others. Certain phenomena, such as magnetism, can polarise light. So, for example, if a certain sector of the sun emits more polarised light than others, the only explanation is that the magnetic or electromagnetic field in that location has increased. Therefore, different types of polarisations and the extent of polarisation are an indication of the presence or absence of magnetic fields.
Scientists were able to observe the polarisation of light relatively close to the black hole in the M87 galaxy. They were then able to create the image shown above. They also analyzed the polarisation of light at distances of 0.25 light-years and 1300 light-years from the black hole, as illustrated in the image below. The earlier image of the black hole with spurting blue jet rays was now portrayed as the magnificent polarisation image, which illustrates how the magnetic fields vary throughout the jet as it travels out from the black hole, and this is the most crucial component of the finding. It indicates that black holes have extremely powerful magnetic fields caused by the interaction of the accretion disc that orbits the black hole. We also saw that these very powerful magnetic fields were present near the black hole’s edge and further out from the black hole as the astrophysical jet emanated from the core.
These photos give crucial information for understanding how these astrophysical jets emerge. Though it is not completely understood, scientists believe it is formed by the interplay of magnetic fields and the breaking of magnetic lines, which actually propel matter in a manner similar to how matter is propelled from our sun. Coronal mass ejection happens for the same reason. However, only in a black hole are the magnetic fields much stronger than in our sun, and the material expelled is generally expelled at a velocity approaching the speed of light. That explains why we witness such massive astrophysical jets bursting from the centre.
This also implies that the black hole’s magnetic field lines govern and, most likely, aid or prevent the black holes from consuming excessively. They fundamentally control how matter distributes around a black hole and appear to be capable of directly boosting the mass of a black hole or preventing it from developing. The magnetic fields near the black hole are powerful enough to readily drive away some of the additional material that would otherwise fall too swiftly into the black hole. But, once again, we are not certain.
Future operations on M87 will want to know why black holes get so large. What causes astrophysical jets to form? Also, what happens in and around the black hole in general? We may never find out, but I am certain that we will not give up.
