The black hole group has a new master: Artur Vemado defended his MsC dissertation, entitled “radiative cooling and state transitions in stellar mass black holes”. The defense was very successful.
Here, Artur reported his numerical simulations of black hole accretion flows where he incorporated radiative cooling (with some approximations otherwise the problem is essentially intractable!). We observe the self-consistent emergence of a hot corona enveloping a cold thin accretion disk. Artur quantified the inner radius of the thin disk, the size of the corona, and how these properties respond to varying the mass accretion rate onto the black hole. The resulting simulated black holes are similar to observations of stellar mass black holes in binary systems.
We are looking forward to reporting these exciting results on the emergence of the corona (not the covid-19!) and truncated disk in an upcoming publication.
Many thanks to FAPESP funding through grant 2017/25710-1.
Congratulations to the now Dr. Gustavo R. R. Soares, for a successful PhD thesis defense! 🎉🍾
The thesis is entitled “Accretion discs, jets, and black hole spins: a study of blazars” and was done under my supervision. The whole defense was entirely online, following the social distancing recommendations of the World Health Organization and the São Paulo State government, in order to ensure the safety of all involved with respect to COVID-19.
The defense lasted for almost five hours (!!), with the thesis committee members in two countries—Brasil and US—and in three states in Brasil: Pernambuco, Rio de Janeiro and São Paulo.
Thanks to Dr. Soares’s work, we now we know a bit more about the role of black holes in the universe, and how the supermassive ones power relativistic jets.
Gustavo will begin a postdoc at Oregon State University in the Fall. We are all wishing Gustavo a huge success for his future career!
Our thanks to the Brazilian science funding agencies CAPES, CNPq and FAPESP. Without them, this work would not have been possible.
After Marta Volonteri’s review talk on the cosmic evolution of massive black holes, Fabio gave a presentation about the current status of his analysis of Fermi LAT observations of the Galactic Center—we are finishing the first paper of the series which should be submitted very soon.
After Fabio’s talk, we’ve had Ivan’s talk on his numerical hydrodynamical simulations of radiatively inefficient accretion flows and their winds.
Roberta Pereira presented her poster on applying deep learning to predict the future of accreting black holes, which are an extreme example of spatiotemporally chaotic systems.
Finally, Gustavo won one of the best poster prizes at the meeting, and was awarded a talk at the meeting. Wait, is that an award? 🙂
In this work we studied how accreting supermassive black holes generate winds that can potentially interact with the host galaxy. Our target was an active galactic nuclei (AGN) with very low accretion rates, like the famous M87*. Can these underfed systems generate powerful winds that will change the fate of the whole galaxy?
We performed diverse simulations of accretion disc flows around Schwarzschild black holes under an hydrodynamic treatment. Our simulations were some of the longest ones of our knowledge. The results show that some systems can create powerful thermally driven black hole winds that can be related to what we call “AGN feedback”. AGN feedback can be understood as the interaction between the ejected material/energy from the accretion flow and the host galaxy, this effect is crucial to understand galaxy evolution and currently it is a very active topic of research in astronomy. With this work we explored the possibility of thermally driven winds as a mechanism to explain this effect.
In the video below we show one of the simulations. On the top we have the gas density and each horizontal panel is the same disc but with different zoom levels, the scale is in Schwarzschild radius. On the bottom of the video we plot the wind efficiency. In practical terms, higher values here indicate stronger material ejection and production of more powerful winds.
Fabio e Rodrigo começamos o dia fazendo uma apresentação no IAG sobre a ciência do Event Horizon Telescope, e depois transmitimos a coletiva de imprensa da NSF. Nota: não fazemos parte da colaboração Event Horizon Telescope.
A partir daquele momento, houve uma gigantesca procura da imprensa pelo nosso grupo de pesquisa de buracos negros, para comentar sobre a incrível primeira fotografia de um buraco negro.
Nas mídias de vídeo, fomos procurados pela Band News e Globo News (Rodrigo) e Gustavo apareceu no AstroTubers.
Link para matéria na Band News (8 minutos em horário nobre!).
Link para matérias na Globo News (Rodrigo aparece nos 5:00 do vídeo) e aqui.
Ficamos contente que o nosso grupo de pesquisa esteja realizando um papel importante de disseminação e clarificação da ciência para o público—afinal de contas, nossos recursos de pesquisa são custeados pelos impostos pagos pela população.
Ontem foi um dia muito especial para o nosso grupo de pesquisa, com a divulgação da primeira imagem do horizonte de eventos de um buraco negro da história, pela colaboração Event Horizon Telescope (EHT) (press releases da NSF e ESO).
Este resultado científico é um grande divisor de águas na astronomia. A partir de agora, na astrofísica de buracos negros, vamos nos referir à era “antes do EHT” e “depois do EHT”. Buracos negros, que eram antes entidades abstratas—comumente ilustradas em filmes e desenhos animados, mas das quais tínhamos somente observações indiretas—agora tem uma imagem concreta.
A ilustração publicada no site xkcd revela bem as gigantescas escalas do astro. O horizonte de eventos em M87 tem 38 bilhões de km de diâmetro, que é um pouco maior que o nosso Sistema Solar! Apesar disso, lá dentro há uma quantidade de matéria seis bilhões de vezes maior que a massa do Sistema Solar. São números quase inimagináveis para quem não é da área.
É interessante mencionar que, ao olharmos para a mancha escura no centro da imagem acima, estamos nos defrontando com um imenso vazio cósmico. A massa de seis bilhões de Sóis que existe dentro do buraco negro de M87 está totalmente concentrada num ponto central chamado de singularidade. E entre a singularidade e o horizonte de eventos—nome que damos para superfície absolutamente negra do buraco negro—não há nada. É literalmente um coração das trevas, como o título do romance de Joseph Conrad.
A auréola dourada mostra a radiação eletromagnética com comprimento de onda de 1.3 mm, emitida pelo gás nas partes internas do turbilhão espiralando na direção do horizonte de eventos—chamado de disco de acreção—pouco antes de cair dentro do buraco negro e se perder para sempre do nosso universo.
We studied the Akira galaxy, which was named after the Akira manga by Edmond Cheung. Its companion galaxy is called Tetsuo. Akira is an interesting galaxy because it hosts a supermassive black hole fed at quite low rates—we call it a low-luminosity active galactic nucleus.
The black hole seems to be ejecting gas quite vigorously. In fact so vigorously that the BH outflow is capable of quenching star formation in the galaxy. Cheung et al. called this galaxy a “red geyser”.
We observed the nucleus of the galaxy (where the black hole is located) with Gemini integral field spectroscopy (IFU) in order to characterise the black hole outflow. This is a powerful technique because it gives us high-spatial resolution information on several emission and absorption lines.
Below is the money plot of the paper. It tells us that the outflow coming from the black hole is changing its orientation as it propagates away from the galactic nucleus! How to interpret this?
First of all, we do not think we are seeing a jet because this galaxy does not show any extended radio structures. We think this is a subrelativistic, uncollimated wind as shown in the illustration below. We interpreted this as a precessing wind, with the likely cause of the precession being a misalignment between the accretion disk and the BH spin aka Lense-Thirring precession.
Let’s congratulate Ivan on his brilliant masters dissertation defense. His dissertation’s title is “Winds and feedback from supermassive black holes accreting at low rates”. In this work, Ivan performed a suite of hydrodynamical simulations of hot accretion flows with a large dynamical range and long durations (comparable to the viscous timescale), aiming at better understanding black hole wind production and feedback in low-luminosity AGNs hosted by quiescent galaxies.
We have a paper coming out soon, where we will report the results of this work. Stay tuned!
The evaluation committee was composed of Thaisa Storchi Bergmann, Roderik Overzier and Diego Falceta Gonçalvez.
This work was funded by a FAPESP scholarship, grant number 2016/24857-6. It has made use of the following computing facilities:
Laboratory of Astroinformatics (IAG/USP, NAT/Unicsul; FAPESP grant 2009/54006-4)
Aguia cluster, HPC resources of Universidade de São Paulo
Raniere will be visiting the University of Torino over the next year, working with Prof. Francesco Massaro, in order to continue our group’s research to understand the unidentified gamma-ray sources observed with Fermi Large Area Telescope. In particular, he will use a suite of optical observations to try to pinpoint the nature of such sources.
Raniere’s visit will be funded by a FAPESP BEPE scholarship, grant number 2018/24801-6.
Hi! I’m Roberta Duarte Pereira and I’m a physicist graduated at IFSC-USP. I just started my master’s degree in the Black Hole Group at IAG-USP under the supervision of Prof. Rodrigo Nemmen. Since my childhood, one of my main passions in life is Astronomy, mainly Black Holes because they are so interesting and they always fascinated me. During my time in undergrad course, Computational Physics also called my attention. So I decided to connect both of my passions. Recently, I started a project – under the supervision of Professor Rodrigo—in astrophysical simulations with deep learning. It’s a project that may bring some new insights about how we see numerical simulations nowadays and we could gain so much in this area! I’m very happy and greatly motivated with this project and also for being in the Black Hole Group.
Roberta will work on applying machine learning and deep learning to numerical simulations of black holes, in collaboration with João Paulo Navarro from NVIDIA.
Welcome aboard, Roberta! We are glad you chose to come work in our group, and excited for the discoveries in the computational universe that will come from your project.