Perfecting Black Hole Imagery with space telescopes

Astronomers may have just captured the first image of a black hole, but work is already underway to perfect techniques to capture such objects — including launching radio telescopes into space.

With the first image of a black hole in the bag, the challenge now facing astronomers is how to take even sharper images in order to test Einstein’s Theory of General Relativity.

Radboud University astronomers — working with the European Space Agency (ESA) amongst others — have developed a plan to launch radio telescopes into space to tackle this problem.

The concept they have developed —named the Event Horizon Imager (EHI) — involves placing two or three satellites in a circular orbit around the Earth to observe black holes. In the study detailing the plans — published in the journal Astronomy & Astrophysics — the team present simulations of what images of the black hole Sagittarius A* would look if they were taken by satellites like these.

Space-based telescopes — More than five times as sharp

In space, the EHI has a resolution more than five times that of the EHT on earth, and images can be reconstructed with higher fidelity. Top left: Model of Sagittarius A* at an observation frequency of 230 GHz. Top left: Simulation of an image of this model with the EHT. Bottom left: Model of Sagittarius A* at an observation frequency of 690 GHz. Bottom right: Simulation of an image of this model with the EHI. ( F. Roelofs and M. Moscibrodzka, Radboud University)

Freek Roelofs, a PhD candidate at Radboud University and the lead author of the article, explains the advantages of space-based telescopes: “There are lots of advantages to using satellites instead of permanent radio telescopes on Earth, as with the Event Horizon Telescope (EHT).

“In space, you can make observations at higher radio frequencies, because the frequencies from Earth are filtered out by the atmosphere. The distances between the telescopes in space are also larger. This allows us to take a big step forward. We would be able to take images with a resolution more than five times what is possible with the EHT.”

The main advantage of sharper images of a black hole is detailed information that could be used to test Einstein’s Theory of General Relativity. Radio Astronomy Professor Heino Falcke says: “The fact that the satellites are moving around the Earth makes for considerable advantages.

“With them, you can take near perfect images to see the real details of black holes. If small deviations from Einstein’s theory occur, we should be able to see them.”

The EHI will also be able to image about five additional black holes that are smaller than the black holes that the EHT is currently focussing on — Sagittarius A* at the centre of our Milky Way and M87* at the centre of Messier 87, a massive galaxy in the Virgo Cluster.

The researchers have simulated what they would be able to see with different versions of the technology under different circumstances. To enable this, they made use of models of plasma behaviour around the black hole and the resulting radiation.

Roelofs says: “The simulations look promising from a scientific aspect, but there are difficulties to overcome at a technical level.”

Technological challenges and hybrid solutions

The astronomers collaborated with scientists from ESA/ESTEC to investigate the technical feasibility of the project. Volodymyr Kudriashov, a researcher at the Radboud Radio Lab who also works at ESA/ESTEC, explains: “The concept demands that you must be able to ascertain the position and speed of the satellites very accurately.

“But we really believe that the project is feasible.”

One of the main concerns relates to how the satellites exchange data. As Kudriashov points out: “With the EHT, hard drives with data are transported to the processing centre by aeroplane. That’s of course not possible in space.”

In this concept, the satellites will exchange data via a laser link, with the data being partially processed on board before being sent back to Earth for further analysis. As Kurdriashow points out, these links already exist.

Although the initial idea is for the satellites will initially function independently of the EHT telescopes, consideration is also being given to a hybrid system comprised of orbiting telescopes combined with the ones on Earth.

Falcke points out: “Using a hybrid like this could provide the possibility of creating moving images of a black hole, and you might be able to observe even more and also weaker sources.”

Original research: https://www.aanda.org/component/article?access=doi&doi=10.1051/0004-6361/201732423