New paper: Winds and feedback from supermassive black holes fed at low rates

We have a new paper out now on arXiv and submitted to the MNRAS: Winds and feedback from supermassive black holes accreting at low rates: Hydrodynamical treatment. This paper is the outcome of my MSc dissertation.

winds-arxiv

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.

For more details, please read our paper.

This work was supported in part by FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) under grant 2017/01461-2 and grant 2016/24857-6.fapesp_logo-lowres

Imagem do buraco negro: repercussão na imprensa brasileira

Esta Quarta-feira, 10 de Abril de 2019, foi um dia que ficará para a história, como o dia em que conseguimos o impossível: a humanidade conseguiu fazer a primeira fotografia de um buraco negro.

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!).

Gustavo no AstroTubers
Rodrigo na Globo News 1/2 (ao vivo, 19:45)

Link para matérias na Globo News (Rodrigo aparece nos 5:00 do vídeo) e aqui.

Link para vídeo no Jornal da Band

E tem mais: fomos procurados também pela Veja, Isto É, Revista Pesquisa FAPESP, Estadão, Jornal da USP e Fantástico.

Matéria de capa no Estadão com entrevista de Rodrigo.

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.

A primeira fotografia de um buraco negro

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).

A primeira imagem de um buraco negro: o buraco negro supermassivo na galáxia M87. Crédito: Event Horizon Telescope Collaboration.

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.

Crédito: xkcd.

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.

A partir de agora, nosso grupo vai se debruçar sobre os seis artigos científicos publicados pela colaboração EHT, e disseca-los nas nossas reuniões semanais de Journal Club. Será muito divertido!

New paper: precessing winds from a low-luminosity AGN

We have a new paper out in collaboration with Rogemar Riffel and others accepted in MNRAS: Precessing winds from the nucleus of the prototype Red Geyser.

Riffel, Nemmen, et al., MNRAS, in press

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.

Equivalent widths of hydrogen alpha in Akira, measured with Gemini. The outflow is marked in orange. Notice that the EWs are telling us that this outflow is consistent with being produced from a black hole (AGN), not from stars.

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.

Cartoon for the precessing wind launched by the supermassive black hole in the Akira galaxy. The only difference is that Akira is not a radio galaxy, so we do not see extended relativistic jets as shown in the cartoon. Credit: ESA/AOES Medialab.

For more information, please read the paper.

This work was supported in part by FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) under grant 2017/01461-2.

Ivan defends his MsC dissertation

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!

From left to right: Diego Falceta Gonçalvez, Rodrigo Nemmen, Ivan de Almeida, Thaisa Storchi Bergmann and Roderik Overzier.

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 visiting Torino to continue exploration of the unknown gamma-ray sky

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.

Roberta joins the group

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.

Roberta Duarte Pereira and Rodrigo Nemmen

Group funded by FAPESP

We are very happy to announce that our research group is receiving a large, competitive grant from FAPESP (Jovem Pesquisador, R$415k, grant 2017/01461-2). Besides including funding to support the group’s computational needs, this grant includes 1 PhD, 1 MsC and 2 undergraduate scholarships.

415k reais may not look like much when converted to dollars, but this amount of funding is quite hard to get lately in Brasil, especially for junior faculty.

Fermi Symposium + Collaboration meeting + NASA GSFC visit

The PhD students of the group working on gamma-ray observations—Fabio and Raniere—spent the last two weeks in Washington DC and surroundings. They went to the Fermi LAT Collaboration meeting at George Washington University, where they interacted with gamma-ray astronomers in the Fermi Collaboration. Raniere presented his ongoing analysis of the gamma-ray emission of a population of nearby AGNs.

IMG-20181011-WA0014
Raniere de Menezes presenting his work on low-luminosity AGNs at the Fermi LAT Collaboration Meeting, Washington DC.

Following the Collaboration meeting, the students presented their research at the Fermi Symposium in Baltimore. Raniere presented a poster about his work on the pulsar populations in Milky Way globular clusters—which is about to be submitted for publication—while Fabio gave a talk describing his analysis of the gamma-ray emission from the Galactic Center on constraints on Sgr A* physics.

20181018_121850
Fabio Cafardo presenting his work on the gamma-ray emission of Sgr A* at the Fermi Symposium, Baltimore.

After the symposium, Fabio and Raniere spent a couple of days visiting NASA Goddard Space Flight Center to discuss their research with GSFC scientists.

Their visit was possible thanks to NASA funds, grant xxxxxx.