The European Research Council has published a video about the BlackHoleCam project featuring the three Principal Investigators: Heino Falcke, Michael Kramer and Luciano Rezzolla.

In case of any questions, please contact Katharina Königstein, Radboud University.

Ciriaco Goddi, BlackHoleCam Project Scientist from ALMA

Ciriaco Goddi, BlackHoleCam Project Scientist from ALMA

Geplaatst door ALMA Observatory op donderdag 19 april 2018
ALMA Observatory Facebook Live – Apr 19, 2018

Dr. Ciriaco Goddi, BlackHoleCam Project Scientist from Radboud University, is at the ALMA observatory  for the 2018 observing campaign of the Event Horizon Telescope.
In this video, he explains what VLBI is, the interferometric technique to make very high-angular resolution images of radio cosmic sources, and which are the challenges of these observations, which will eventually lead to the first image of a super-massive black hole.

Click on the ALMA Observatory Facebook Page for more videos.

One of the most fundamental predictions of Einstein’s theory of relativity is the existence of black holes. In spite of the recent detection of gravitational waves from binary black holes by LIGO, direct evidence using electromagnetic waves remains elusive and astronomers are searching for it with radio telescopes. Astrophysicists at Goethe University Frankfurt, and collaborators in the ERC-funded project BlackHoleCam in Bonn and Nijmegen have created and compared self-consistent and realistic images of the shadow of an accreting supermassive black hole – such as the black-hole candidate Sagittarius A* (Sgr A*) in the heart of our galaxy – both in general relativity and in a different theory of gravity. The goal was to test if Einsteinian black holes can be distinguished from those in alternative theories of gravity.

Not all of the light rays (or photons) produced by matter falling into a black hole are trapped by the event horizon, a region of spacetime from which nothing can escape. Some of these photons will reach distant observers, so that when a black hole is observed directly a “shadow” is expected against the background sky. The size and shape of this shadow will depend on the black-hole’s properties but also on the theory of gravity. Because the largest deviations from Einstein’s theory of relativity are expected very close to the event horizon and since alternative theories of gravity make different predictions on the properties of the shadow, direct observations of Sgr A* represent a very promising approach for testing gravity in the strongest regime. Making such images of the black-hole shadow is the primary goal of the international Event Horizon Telescope Collaboration (EHTC), which combines radio data from telescopes around the world.

Scientists from the BlackHoleCam team in Europe, who are part of the EHTC, have now gone a step further and investigated whether it is possible to distinguish between a “Kerr” black hole from Einstein’s gravity and a “dilaton” black hole, which is a possible solution of an alternative theory of gravity.

The researchers studied the evolution of matter falling into the two very different types of black holes and calculated the radiation emitted to construct the images. Furthermore, real-life physical conditions in the telescopes and interstellar medium were used to create physically realistic images. “To capture the effects of different black holes we used realistic simulations of accretion disks with near-identical initial setups. These expensive numerical simulations used state-of-the- art codes and took several months on the Institute’s supercomputer LOEWE,” says Dr. Yosuke Mizuno, lead author of the study.

Astrophysicists at Goethe University Frankfurt answer this question by computing images of feeding non-Einsteinian black holes: At present it is hard to tell them apart from standard black holes. Moreover, expected radio images obviously have a limited resolution and image fidelity. When using realistic image resolutions, the scientists found, to their surprise, that even highly non- Einsteinian black holes could disguise themselves as normal black holes.

“Our results show that there are theories of gravity in which black holes can masquerade as Einsteinian, so new techniques of analyzing EHT data may be needed to tell them apart,”remarks Luciano Rezzolla, professor at Goethe University and leader of the Frankfurt team.“While we believe general relativity is correct, as scientists we need to be open-minded. Luckily, future observations and more advanced techniques will eventually settle these doubts,”concludes Rezzolla. “Indeed, independent information from an orbiting pulsar, which we are actively searching for, will help eliminate these ambiguities,” says Michael Kramer, director at the MPI for Radio Astronomy in Bonn. Heino Falcke (professor at Radboud University), who 20 years ago proposed using radio telescopes to image the shadow of black holes, is optimistic.“There is little doubt that the EHT will eventually obtain strong evidence of a black-hole shadow. These results encourage us to refine our techniques beyond the current state of the art and thus make even sharper images in the future.”

The results of this research have been published as Letter of Nature Astronomy and on the preprint archive (arXiv:180405812).

The Royal Netherlands Academy of Arts and Sciences (KNAW) has selected twelve new PhD students to be the national Faces of Science. One of them is Jordy Davelaar – an aspiring postgraduate within the BlackHoleCam project at the Radboud University Nijmegen. During the time of his PhD, Jordy will share what it is like to do research on black holes amongst other things on the website.

Jordy Davelaar

Being nominated was already a great recognition for the PhD student, but being selected is like a dream come true. “I feel honored that I am selected by KNAW to be a part of this project and I am looking forward to share the wonders of black holes with the general public and help students in making a decision towards their career path.”, says Jordy humbled. With his theoretical research, Jordy wants to understand how radiation is produced around black holes and he visualizes these models in virtual reality, an example can be watched on YouTube. Especially the latter is a great tool for Jordy to reach people outside of science and bring them closer to the topic.

Marijke Haverkorn and Heino Falcke nominated Jordy for Faces of Science. Marijke’s motivation was: “Jordy is an ideal candidate for Faces of Science. He is an excellent researcher working on black holes, a subject that quickly catches the interest of many people. He is active in various forms of science communication, such as giving lectures, organizing star gazing events, and enthusiastically disseminates astronomy on social media.”

Already at a very early stage, Jordy had the ambition to work in Astrophysics, so it was very natural for him to do his Bachelor and Master studies in Astrophysics. Jordy successfully graduated in 2016 with his Master and is now doing his PhD studies under the supervision of Monika Mościbrodzka in the group of professor Heino Falcke. Together with Monika, Jordy is researching the environments of black holes to get a better understanding of their observational appearance. Monika is very pleased about the cooperation with Jordy: “It is a true pleasure to be the supervisor of Jordy Davelaar. He was a brilliant student right from the beginning. In his first year, Jordy already published two scientific publications. He is also a very active science popularizer and great mentor for junior students. One could set him as an example of a perfect PhD student that everyone would like to work with”.

Congratulations to Jordy on behalf of the BlackHoleCam collaboration!

The press release of KNAW is published here. (Dutch only)

In case of any questions, please reach out to Jordy Davelaar via email or twitter.