Black Holes

Fabio Vito

We are pleased to welcome Fabio Vito as our guest blogger. Fabio and his colleagues led some of the latest work involving the Chandra Deep Field-South that were presented at the 229th meeting of the American Astronomical Society in January 2017. He obtained a Ph.D. degree in Astrophysics and Cosmology from the University of Bologna (Italy) in 2014. During his studies he collaborated with researchers from the Astronomical Observatory of Bologna and also spent a 6-months period at the University of Cambridge (UK). After one year in a postdoctoral position in Bologna, he moved to his current position as a postdoctoral researcher at the Pennsylvania State University. Fabio's work is mainly focused on the growth and evolution of supermassive black holes in the early Universe, exploiting some of the deepest X-ray data available.

Black holes are among the most fascinating objects in the Universe. Probably most people have at least heard about them, maybe reading about some pseudo-scientific speculations like wormholes, time travelling, etc. Or perhaps they have watched movies such as the famous 2014 movie "Interstellar", or even by listening to music, such as the "Supermassive Black Hole" song by the British band Muse.

However, despite their popularity, our knowledge of these monsters of the Universe is limited. We know that "normal" black holes (although nothing is normal about black holes), which have masses of a few to tens of times the Sun's mass, are formed when big stars die and explode as supernovas. However, there is more than just one type of black hole. At the centers of most galaxies, there is a "monster among the monsters." This is what astronomers call a supermassive black hole (SMBH), and they can weigh from millions to billions of solar masses. Despite the fact that almost all of the normal-sized galaxies in the Universe host a SMBH in their centers (even our Milky Way!), astronomers do not know when and how they formed.

Astronomers have used NASA's Chandra X-ray Observatory and ESA's XMM-Newton X-ray observatory to discover an extremely luminous, variable X-ray source located outside the center of its parent galaxy. This peculiar object could be a wandering black hole that came from a small galaxy falling into a larger one.

Astronomers think that supermassive black holes, with some 100,000 to 10 billion times the Sun's mass, are in the centers of most galaxies. There is also evidence for the existence of so-called intermediate mass black holes, which have lower masses ranging between about 100 and 100,000 times that of the Sun.

The 2016 Nobel Prize in physics will be announced in only 4 days, on Tuesday October 4th. Ronald Drever, Kip Thorne and Rainer Weiss, three founders of the detection of gravitational waves (2). They have already won multiple awards for this discovery including the Kavli Prize in Astrophysics, the Gruber Cosmology Prize, a Special Breakthrough Prize in Fundamental Physics and the Shaw Prize in Astronomy. (Kudos to those behind the Gruber Cosmology Prize and the Special Breakthrough Prize for explicitly naming the LIGO team in their awards, something the Nobel Prize award likely won’t do.)

Ronald Drever, Kip Thorne and Rainer Weiss (left to right). Credit: The Kavli Foundation.

We welcome back Jonathan Taylor as a guest blogger. Jonathan is a Senior Lecturer in Creative Writing at the University of Leicester, UK, along with an author and critic. He has written several poems for us in the past: “Black Hole in B-flat”, “History Lesson” and “!!**&@??”. He has also organized poetry competitions among his students, in blog posts here, here, here, here and here.

I was fascinated by Chandra’s press release of 27 June 2016, ‘Clandestine Black Hole May Represent New Population.’ The very title of the press release sounds ‘poetic,’ in the idea of ‘Clandestine’ – a concealed or secretive – Black Hole; and the findings described in the press release are even more so: having concluded that “a peculiar source of radio waves thought to be a distant galaxy is actually a nearby binary star system containing a low-mass star and a black hole,” astronomers have suggested that “there may be a vast number of black holes in our Galaxy that have gone unnoticed until now .... Because this study only covered a very small patch of sky, the implication is that there should be many of these quiet black holes around the Milky Way. The estimates are that tens of thousands to millions of these black holes could exist within our Galaxy, about three to thousands of times as many as previous studies have suggested.”

Gamma-ray bursts, or GRBs, are some of the most violent and energetic events in the Universe. Although these events are the most luminous explosions in the universe, a new study using NASA's Chandra X-ray Observatory, NASA's Swift satellite and other telescopes suggests that scientists may be missing a majority of these powerful cosmic detonations.

We are pleased to welcome Bailey Tetarenko as our guest blogger. She is the lead author on a paper featured in our latest press release about a possible new population of black holes in the Galaxy. Bailey received her undergraduate degree in Astrophysics at the University of Calgary and then a master’s in Physics at the University of Alberta in 2014. She is now two years into her Ph.D. in Physics at the University of Alberta, where she is studying the black hole population of the Milky Way.

From right to left Bailey Tetarenko, Dr. Arash Bahramian and Dr. Craig Heinke and Dr. Greg Sivakoff. Credit: John Ulan

For fans of black holes, we live in exciting times. Nearly all of our empirical knowledge about stellar mass black holes – that is, black holes weighing about 5 to 35 times the mass of the sun – comes from black hole X-ray binary systems. In these systems a black hole pulls in material from a nearby companion star, causing the system to become very bright in X-rays. But, recently gravitational waves have been detected from pairs of distant black holes that emit no electromagnetic radiation (a.k.a. all forms of light). And now, my team's work suggests that there are many black hole X-ray binaries in our own Milky Way that emit relatively little X-rays.

Fabio Pacucci

It is a pleasure to welcome Fabio Pacucci as a guest blogger. Fabio led the study that is the subject of our latest press release. He is going to defend his Ph.D. Thesis at the Scuola Normale Superiore in Pisa (Italy), under the supervision of Andrea Ferrara. During his Ph.D. he spent several months at the Institute d’Astrophysique de Paris (IAP) in France, Yale University and Harvard University in the USA. In September he is starting his first postdoctoral position at Yale University. Fabio has mainly been working on understanding the properties of the first black hole seeds, formed when the Universe was less than one billion years old.

It was a sunny and hot afternoon in Pisa when Andrea Ferrara, my Ph.D. supervisor, suggested that I study the first black holes formed in the Universe. This topic is among the most interesting in cosmology. We know that almost every galaxy hosts a supermassive black hole (SMBH) at its center. In the Milky Way there is a black hole about 4 million times more massive than the Sun, but objects up to 10 billion times the mass of the Sun have also been observed.

Astronomers have observed material being blown away from a black hole after it tore a star apart, as reported in our press release. This event, known as a "tidal disruption," is depicted in the artist's illustration.

Gabriele Ponti

Dr. Gabriele Ponti is the Marie Sklodowska-Curie EU Research Fellow at the Max Planck Institute for Extraterrestrial Physics in Germany. Prior to that, he was a post-doctoral fellow at the University of Southampton in the UK, after spending a year at Cambridge University’s Institute of Astronomy. Dr. Ponti earned his Ph.D. from Bologna University in Italy before moving on to the Laboratories Astro-Particule et Cosmologie in Paris. His doctoral thesis topic was studying relativistic effects in bright active galactic nuclei and he has been interested in this area since then.

As a boy, I read about the existence of black holes for the first time. I still remember the fascination of trying to grasp the physical concepts behind one of the weirdest manifestations of nature.

Black holes produce an enormous gravitational pull, as a consequence of being extremely compact: a significant amount of mass concentrated in a very small volume.

Three orbiting X-ray telescopes have been monitoring the supermassive black hole at the center of the Milky Way galaxy for the last decade and a half to observe its behavior. This long monitoring campaign has revealed some new changes in the patterns of this 4-million-solar-mass black hole known as Sagittarius A* (Sgr A*).