Dr. Gustavo R. R. Soares, PhD in Astrophysics

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 SĂŁo 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 SĂŁo Paulo.

Gustavo presenting his thesis work

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.

Massive presence of the group at the Brazilian Astronomical Society Meeting

The Black Hole Group had a massive presence at the 43th meeting of the Brazilian Astronomical Society—Sociedade Astronômica Brasileira, SAB.

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? 🙂

Gustavo Soares’s talk at the 43th SAB meeting.

Group taught course at ICTP-SAIFR high-energy astrophysics school

From August 8 to 13, our group taught two courses at the high-energy astrophysics school at ICTP-SAIFR. The first was taught by myself and gave a broad overview of the active galactic nuclei phenomenon, including blazars. The second course was about Fermi LAT observations and taught by Fabio Cafardo, a PhD student in the group who is working of gamma-ray astronomy.

Fabios’s lecture also included a fun hands-on tutorial, teaching the students to analyze gamma-ray observations of the blazar TXS 0506+056. This is the famous blazar which was observed to emit gamma-rays flares and produce a high-energy neutrino at the same time: the second source ever observed in multimessenger astronomy. The first was the neutron star collision observed in gravitational waves with LIGO/Virgo and electromagnetic radiation.

Here is the official abstract for the AGNs and blazars course:

I will give a broad overview of the phenomenology and theory behind the active galactic nuclei (AGN) phenomenon. I will give a particular emphasis on systems which produce relativistic jets such as blazars, given their importance in multimessenger astronomy. I will cover the basic physics of gas accretion and jet production from Kerr black holes. I will also give an overview of the electromagnetic signature from AGNs and blazars, focusing on their gamma-ray emission commonly observed with the Fermi, HESS, MAGIC telescopes, and in the future CTA.

And here is the official description of the Fermi LAT tutorial:

The Fermi Gamma-ray Observatory has revolutionized our understanding of the high-energy universe. Over the last 10 years, the Fermi Large Area Telescope has been observing the entire sky from space every three hours in the 100 MeV to 500 GeV energy range. In this lab activity, We will give a short presentation highlighting the main results and importance of the Fermi Telescope—particularly for blazar and dark matter indirect searches. The talk will be followed by a hands-on tutorial where the students will get familiar with the analysis of space-based gamma-ray observations. 

Here is the material that we covered:

  1. Active galactic nuclei and blazars (Nemmen). Two lectures, 3 hours. Lecture 1, lecture 2
  2. Fermi LAT (Cafardo). Lecture, 1 hour
  3. Fermi LAT hands-on session (Cafardo). 1.5 hours

If you want to run tutorial #3 at home, you can download all the material from the third lecture and perform the analysis without needing to install a lot of additional software. We prepared the tutorial such that you only need to install one software and run an install script.

I suggested some reading for the students interested in diving deeper into AGN physics:

  1. Physical processes in active galactic nuclei, Blandford (cf. from p171 onwards in the PDF). Even though this is a quite dated treatment—from 20 years ago!—and a lot has changed since then, this paper does a great job in summarising the basic physics of the AGN phenomenon. 
  2. Relativistic jets in active galactic nuclei, arXiv:1812.06025. Up-to-date review about AGN jets
  3. Foundations of black hole accretion disk theory. Focuses on black hole accretion, with a general relativistic treatment

Here are some pictures from the event.

Rodrigo Nemmen and Pasquale Blasi tackling questions from the audience. Credit: Ivan Almeida.
Fabio Cafardo teaching the Fermi LAT hands-on tutorial. Credit: Rodrigo.
Another shot of Fabio during his course. Credit: Ivan.
Some of the diverse audience at the school. Credit: Fabio.

Thanks Fabio Iocco for the invitation. This was fun!

Course on General Relativistic Magnetohydrodynamics by Yosuke Mizuno

Yosuke Mizuno (Goethe University, Frankfurt) taught an advanced course on general relativistic magnetohydrodynamics on August 13-17 at our institute. General relativistic magnetohydrodynamics—or GRMHD—is an essential tool to model high-energy astrophysical phenomena such as accreting black holes and relativistic jets—precisely the type of phenomena that our group loves and cherishes. This course was very useful for everybody in the group. 

The slides are available on this website.

Yosuke Mizuno lecturing about GRMHD at IAG USP. Credit: Rodrigo Nemmen.

His visit was supported by FAPESP grant 2013/10559-5.

Group will teach analysis of Fermi LAT data in dark matter school

On the final week of July, members of our research group (Fabio, Raniere & Rodrigo) will be teaching a lesson on the analysis of Fermi LAT gamma-ray observations in the School and Workshop on Dark Matter and Neutrino Detection at ICTP-SAIFR. In this hands-on activity, we will teach how to analyze gamma-ray data for a dwarf galaxy, do a simple estimate of the dark matter cross section and reproduce the analysis described in Ackermann et al. (2015).

It will be fun!

Multi-messenger astronomy: detection of gravitational waves and electromagnetic counterparts in neutron star merger

The most recent news in astronomy consists of the report that scientists have managed to record a collision of neutron stars in both gravitational waves and electromagnetic waves. This is a remarkable feat for many reasons. First of all, this is the first time that astronomers detected the gravitational waves that are produced when these neutron stars orbit each other in a deadly inspiral. Equally impressive was the fact that this event was also “seen”: it has been detected and monitored all across the electromagnetic spectrum. There were observations in gamma rays, X-rays, ultraviolet, visible light, infrared and radio. Moreover, the short gamma-ray burst detected shortly after the gravitational waves provided sound evidence that these bursts are associated with the collision of neutron stars. Finally, this merger has given us very sound evidence that such destructive events are responsible for the creation of heavy chemical elements in the periodic table, such as gold and platinum.

The gravitational waves, which are ripples in spacetime that occur when these massive objects orbit each other, were picked up by the LIGO twin detectors in the United States, as well as by Virgo, a gravitational wave detector in Italy. These are the same detectors that have been picking up gravitational waves from the mergers of black holes – the first detection gave 3 LIGO scientists the 2017 Nobel prize in Physics. However, this was the first time that scientists were able to detect gravitational waves from a merger of neutron stars, rather than black holes.

Just like black holes, neutron stars are one of the possible outcomes for a star when it runs out of fuel and collapses due to its own gravity. In order to become a neutron star, a star has to be very massive – much more than the Sun – but not extremely massive, otherwise it will collapse into a black hole. Mergers of black holes are thought to produce very little – if any – light, so they are difficult to “see” with traditional (electromagnetic) astronomy, although we are now able to “hear” them due to the gravitational waves produced in these collisions. Mergers of neutron stars, however, are a different story.

Less than two seconds after the gravitational waves were detected by LIGO and Virgo, the space telescope Fermi detected gamma rays coming from the same region where the gravitational waves came from. Alarms were sounded and telescopes all over the world, as well as in space, started to sweep the sky in order to pinpoint the location of this event. The Swope telescope, in Chile, was the first to report the location as the galaxy NGC 4993, in the constellation of Hydra, about 130 million light-years distant from the Earth.


Above, we see the detections of gravitational waves as well as observations across the entire electromagnetic spectrum. Source: LIGO.

The gamma rays detected by Fermi are what we call a short gamma-ray burst (sGRB). Before this detection, there were strong suggestions that these sGRB were produced when two neutron stars collide, but this was the first conclusive evidence that this is indeed what happens.

Once the telescopes were pointed to the sky, astronomers noticed a blob at the very place where this collision occurred. This blob is what we call a kilonova: a violent explosion that occurs when two neutron stars merge. Upon measuring the electromagnetic spectrum of this kilonova, astronomers detected the presence of heavy chemical elements, such as gold and platinum. This confirmed theoretical predictions that stated that these heavy elements are produced in such collisions, which are so strong that neutrons are literally forced into the nuclei of atoms, making them heavier and therefore creating heavier elements. This implies that the idea that we are all made of stardust also applies to our jewelry.

This detection of gravitational waves and the subsequent observation of this collision across all types of electromagnetic radiation marks the beginning of multi-messenger astronomy: we are now able to study the same event occurring in the universe using two very different types of information. It was a massive effort done by thousands of scientists scattered across the globe and is a small sample of the true power of scientific collaborations.

XLI SAB 2017

During the week of September 4th to 8th, 2017, the XLI SAB (Brazilian Astronomical Society) meeting took place in São Paulo. It was a week  when astronomers from all corners of Brazil got together to discuss about astronomy and astrophysics.

The SAB was created in 1974 and every year the association promotes this meeting. The main objective of the reunion is to integrate Brazilian researchers and to plan the future of the astronomy in Brazil.

The XLI SAB was a great event, it was close to 300 participants presenting their current work. It is a very prolific environment for any astronomer or astrophysicist to discuss and learn with other researchers.

The members of the IAG Black Hole Group were present and exhibited their interesting works about black holes and high energy astrophysics. Gustavo Soares, Phd student, presented about “Spectral simulations of accreting black holes”, Raniere Menezes, Phd student, presented other poster with the title “Optical observations of blazar candidates and unknown gamma-ray sources” and Ivan Almeida, MSc student, presented his work about “The multiwavelength spectrum of NGC 3115: Hot accretion flow properties“.

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