Astronomers show first image of black hole

Astronomers from the Event Horizon Telescope, a global partnership with a network of radio telescopes, showed the first image of a black hole at a European Commission press conference. It is Messier 87*, or M87*, in the Virgo cluster.

Heino Falcke, professor of astroparticle physics and radio astronomy at Radboud University Nijmegen, has presented the first image of the black hole and its shadow. The black hole is ‘named’ M87*, has a diameter of 100 billion kilometers and is located at the center of the galaxy Messier 87, a massive, huge, elliptical galaxy in the Virgo cluster. The black hole is 55 million light-years from Earth with a mass 6.5 billion times that of our sun. The mass of the black hole was determined based on the size of the shadow. Carlos Moedas, EU Commissioner for Research, Science and Innovation, calls it ‘a major breakthrough for humanity’. The European Union has invested a total of 44 million euros in the international project.

Falcke explains that it has been established that it really is a black hole, because the image material has been compared with simulations and theoretical expectations. “If the black hole is in a bright region, such as a disk of glowing gas, we expect it to create a dark region, similar to a shadow. We also compared the image with supercomputer simulations of various models of black holes. simulations match the observations surprisingly well and make it possible to determine the properties of the black hole.”

On the left the various telescopes whose data has been merged and next to it an image of the Event Horizon Telescope of Messier 87

The black hole’s shadow is caused by the curvature of space and by the absorption of light in the black hole’s event horizon, or event horizon. As a result, the light is deflected. The event horizon is the name for the edge of the black hole where gravity is so strong that even light cannot escape it. According to Falcke, the shape and size of the shadow fit perfectly with what the researchers expected based on Einstein’s general theory of relativity and the existence of an event horizon.

After seeing the first results, all attention is focused on M87* and not on Sagittarius A*, the black hole at the center of the Milky Way Galaxy. According to Falcke, the problem with Sagittarius A* is that it is about a thousand times smaller than M87*. Although this black hole is at the center of the Milky Way, it is about a thousand times closer and therefore has a similar shadow size, but it also moves a thousand times faster. The professor described making an image of this as making a still image of a toddler who moves for eight hours. M87* is comparatively larger and moves much less, making it a much more suitable candidate for a first shot. Incidentally, this was not known beforehand; the format of M87* was previously unknown. Falcke did say the team is spending extra time working on Sagittarius A*, though it’s unclear whether that will produce such an image in the long run.

The Event Horizon Telescope is a worldwide network of eight radio telescopes, supplemented by three other telescopes. The data was combined with data from multiple very-long-baseline interferometry stations scattered around the Earth, taking advantage of the fact that the Earth rotates on its axis. In fact, this creates a virtual telescope the size of the Earth. The VLBI technique allows observation in the 1.3mm wavelength region. Each telescope has measured the radiation emanating from the copious amounts of gas, or actually plasma, and dust, which have always been suspected to surround black holes. These gas clouds become extremely hot, causing a lot of radiation, which can be observed from Earth.

All that data from the different telescopes has been merged by supercomputers, creating the images as if looking through a single, gigantic telescope. The enormous computing power was not an unnecessary luxury; never before has so much data been collected by telescopes for a project. To merge the data from the different telescopes, the data was put on hard drives that were brought by plane to centers where supercomputers could merge it. That cannot be sent via fiber optic lines, partly because the telescopes are spread all over the world and are therefore not connected to each other. For example, a telescope was also used in Antarctica, where take-off had to be delayed, because it is almost always dark there during half of the year.

The researchers want to make even sharper images in the future. To achieve this, the sensitivity of the virtual telescope must be increased. In that context, there is the plan to build a millimeter telescope in Africa. According to Falcke, the first parties and companies have already registered to make this possible.

Six papers have been devoted to the discovery, which have been published in the scientific journal The Astrophysical Journal Letters.

The image of M87*