Dr. Valeriu Tudose, researcher from the Institute of Space Science (ISS), observed the binary system V404 Cygni consisting of a star and a black hole, which at the end of June has come alive after 26 years of dormancy. The black hole began to violently devouring its companion star, causing one of the brightest objects in the sky. The radio observations were taken within the JACPOT collaboration.
Located 8 000 light years away from us, in our own Galaxy, the binary system V404 Cygni consists of a black hole and a star which are orbiting a common center of mass. In a gradual process, the black hole steals matter from the star, matter which flows from the star toward the black hole, forming an accretion disk around the latter, as can be seen in the artist’s impression below, released by the European Space Agency.
In late June, this process reached a critical threshold, at which point it became more violent and visible. The last time this happened was in 1989. Therefore astronomers from around the world are observing the rare process that has been observed only in two other occasions, in 1938 and 1956.
Among them is Dr. Valeriu Tudose, researcher at the Institute of Space Science (ISS), where he works in the Astroparticle Physics and Cosmology Laboratory. Tudose is also involved in the JACPOT (Jet Acceleration and Collimation Probe of Transient X-ray Binaries) collaboration.
“This collaboration brings together researchers from several countries with a common interest. We aim to observe transient binary systems, i.e. systems consisting of a compact object, a black hole or a neutron star and a normal star, which occasionally go into a very active state, when their luminosity increases by hundreds or thousands times. Our goal is to observe the jets which are formed in the process, matter ejected from the system at speeds which can reach tens of percent of the speed of light”, says Dr. Valeriu Tudose.
Following announcements made by various observatories starting 15 June regarding the increased activity of V404 Cygni , Tudose, together with his collaborators , turned to the EVN – the European VLBI Network (Very Long Baseline Interferometry) to make radio observations of the system. The EVN is a network of radio telescopes located mostly in Europe but also in South Africa and China, which together can act as a single telescope of continental dimensions.
The observations made by Tudose and his collaborators took place on 23-24 June and 5-6 July. Their goal is to better understand how jets interact with surrounding matter in a system such as V404 Cygni, where a black hole attracts matter from a star. It is still not known precisely how these jets form nor details on their connection with the accretion disc.
“These jets are essential to us as they provide important information on the process of accretion-ejection of matter near compact objects, with very strong gravitational fields. By understanding this process better in systems in our Galaxy, such as V404 Cygni, we can then generalise to other similar systems farther away and more difficult to study, such as super-massive black holes and the surrounding area in the center of active galactic nuclei”, says Tudose.
Along with radio observations made by the Institute of Space Science, in Romania optical observations were also conducted at the Astronomical Institute of the Romanian Academy. Together, these data correlated with observations of other researchers around the world, could help researchers to better understand what happens around black holes.
Preliminary results of the observations were reported in The Astronomer’s Telegram # 7730 and # 7742.
Valeriu Tudose began his academic training at the Department of Physics, University of Bucharest, which he graduated in 2001, and then continued his studies in astronomy/astrophysics at the Max Planck Institute for Radio Astronomy in Bonn, Germany. He obtained his doctorate at the Astronomical Institute ‘Anton Pannekoek’, University of Amsterdam, then did a post-doctoral internship at the Netherlands Institute for Radio Astronomy – ASTRON during 2009-2012.
Before joining the Institute of Space Science’ Cosmology and Astroparticle Physics Laboratory, Valeriu Tudose was research assistant (2002-2004), and then associate researcher (since 2004) at the Astronomical Institute of the Romanian Academy. Since 2012 he works as a researcher at the Institute of Space Science, while being also a member of Ad Astra, an online project pertaining to the Romanian scientific community (since 2009). His entire CV is available here.
Image captions:
Image A: Variations in the brightness of the binary system V404 Cygni observed in the radio band with the EVN network on 23-24 June, at 1.6 GHz. The animation includes 5 radio maps, each made with 2 hours of data. The binary system is extremely small and located at the centre of the images, but it cannot be seen on the maps because it is not visible at radio frequencies. What one can observe is the emission from the jets ejecting matter from the system. The radio maps are similar to topographic maps, with lines connecting regions of pixels that have the same brightness values. Colors also express brightness, increasing from blue to red (check the bar above the images). On the bottom left hand side of each map one can see the resolution of the observations. Its form and size are given by the number and the position on Earth of the radio telescopes observing the object at the same time. Throughout the 10 hours of observations the number of telescopes varied.
Credit: V. Tudose (ISS) et. al./JACPOT.
Image B (it can be downloaded form here): Variations in brightness of binary system V404 Cygni, observed during several hours in the optical spectrum using a Johnson V filter on the 0.5 metres telescope of the Astronomical Institute of the Romanian Academy.The binary system can be observed close to the centre of the image. Credit: A. Sonka et al./ The Astronomical Institute of the Romanian Academy.