Black Holes

Guang Yang

We welcome Guang Yang, a 4th-year Astronomy graduate student at Penn State, as a guest blogger. Guang led one of the two studies reported in our new press release about the evolution of supermassive black holes and galaxies. Before studying at Penn State, he obtained his astronomy B.S. degree at the University of Science and Technology of China.

Supermassive black holes, with masses over million times that of our sun, sit in the centers of galaxies. The evolution of these black holes and their host galaxies in the past billions of years of cosmic history is still an unsolved mystery. A prevailing idea is that black hole growth is synchronized with host-galaxy growth, i.e., the ratio between black hole and galaxy growth is constant. "What a beautiful theory," I told my advisor Prof. Niel Brandt, and colleagues Dr. Chien-Ting Chen and Dr. Fabio Vito. "But is it true?” I asked. “Has someone proved it?"

We searched large amounts of literature but did not find dedicated works proving the idea, although it is widely quoted in published papers. "Then why not prove it with observations?" said my advisor. "It can be a great thesis topic for you." I was so happy that my thesis topic was settled and I even dreamed about how our data might nicely support the theory.

We painstakingly analyzed a large amount of data in the Chandra Deep Field-South & North and COSMOS surveys. We successfully tracked the black hole and galaxy growth in the distant universe with NASA's Chandra, Hubble, Spitzer, and other observatories. The observations are so deep that we can study the evolution of black holes and their host galaxies 12 billion years in the past, when the Universe was less than 15% of its current age.

Illustration: NASA/Swift/A. Simonnet, Sonoma State Univ.

An international collaboration of scientists, using data from Chandra and other X-ray telescopes over two decades, has shown that the “weather” around some black holes is stormier than previously thought.

The research, which appears in the January 22th issue of the journal Nature and is available on the arXiv, looked at 21 outbursts in X-rays from 12 X-ray binaries, that is, systems where a stellar-mass black hole is in close orbit with a companion star.

SDSS J1354+1327

Using data from several telescopes including NASA's Chandra X-ray Observatory, astronomers have caught a supermassive black hole snacking on gas and then "burping" — not once but twice, as described in our latest press release.

This graphic shows the galaxy, called SDSS J1354+1327 (J1354 for short) in a composite image with data from Chandra (purple), and the Hubble Space Telescope (HST; red, green and blue). The inset box contains a close-up view of the central region around J1354's supermassive black hole. A companion galaxy to J1354 is shown to the north. Researchers also used data from the W.M. Keck Observatory atop Mauna Kea, Hawaii and the Apache Point Observatory (APO) in New Mexico for this finding.

Chandra detected a bright, point-like source of X-ray emission from J1354, a telltale sign of the presence of a supermassive black hole millions or billions of times more massive than our sun. The X-rays are produced by gas heated to millions of degrees by the enormous gravitational and magnetic forces near the black hole. Some of this gas will fall into the black hole, while a portion will be expelled in a powerful outflow of high-energy particles.

Chris Russell

We welcome this guest post from Christopher Russell of the Pontifical Catholic University in Chile. Dr. Russell was the creator of the new immersive movies that allow viewers to explore the center of the Milky Way in 360 degrees. In this post, Dr. Russell provides the backstory of how he came to make these innovative movies.

I went to a Galactic Center meeting in Australia in July 2016, where I saw an Occulus Rift (a high-end virtual reality, or VR, setup) display by Chi-Kwan Chan (Univ. of Arizona). With the Rift, you plug it into your computer (so much more powerful rendering than available with a phone) and your position actually determines what is rendered. So if you walk left, right, forward, or backward, you are actually walking through the simulation and therefore seeing a different perspective. The thought of visualizing one of these Galactic Center simulations in this fashion was immediately apparent. Then we talked about 360/VR videos; what is required from the goggle side, computer specs, rendering programs, etc.

The day after the meeting, I went snorkeling, and unfortunately the Ziploc bag I put my phone in to keep it waterproof failed. Not one of my brightest ideas, I must say. But when I was looking for a new phone, the one I wanted (Galaxy s7) had two available promotions: get a free 256 GB memory card (useful, but not really fun), or the Samsung Gear VR goggles (definitely fun). I chose the latter, so now I could at least view 360-degree videos in their native format, and so would be able to view one of the Galactic Center if I could figure out how to make it.

What would happen if you took two galaxies and mixed them together over millions of years? A new image including data from NASA's X-ray Observatory reveals the cosmic culinary outcome.

Arp 299 is a system located about 140 million light years from Earth. It contains two galaxies that are merging, creating a partially blended mix of stars from each galaxy in the process.

However, this stellar mix is not the only ingredient. New data from Chandra reveals 25 bright X-ray sources sprinkled throughout the Arp 299 concoction. Fourteen of these sources are such strong emitters of X-rays that astronomers categorize them as "ultra-luminous X-ray sources," or ULXs.

These ULXs are found embedded in regions where stars are currently forming at a rapid rate. Most likely, the ULXs are binary systems where a neutron star or black hole is pulling matter away from a companion star that is much more massive than the Sun. These double star systems are called high-mass X-ray binaries.

Dr. Edwige Pezzulli

It is a pleasure to welcome Edwige Pezzulli as a guest blogger. Edwige led the black hole study that is the subject of our latest press release. She is a Ph.D. student at the University la Sapienza in Rome (Italy), under the supervision of Raffaella Schneider. During her Ph.D., she spent several months at the Institute d’Astrophysique de Paris (IAP) in France. She has mainly worked on the study of the origin and properties of the first black holes in the Universe.

“As an adult, I’d like to be sent into a black hole!” This is my first memory from childhood on the topic of space.

Since then, I have studied and discovered a lot more about black holes, and yet they still fascinate me in the same way. Considered, for many, the most exotic objects ever discovered, supermassive black holes are the tip of the iceberg of the “dark” side of the Universe. Supermassive black holes are behemoths located in the centers of galaxies and can be among the most luminous sources ever known, from the radiation of surrounding material.

In particular, observations of the Universe’s earliest supermassive black holes, with masses about a billion times that of the Sun, open the door to many questions, especially this one: how did these monsters form in such a short time?

Astronomers find black holes with similar masses in the present-day universe, but these black holes have grown to their enormous size over a much longer period of time – about 13.8 billion years – compared to those that formed about a billion years after the Big Bang. In order to tackle the question of how supermassive black holes formed in the very early Universe, it is imperative to make numerous observations of the light they generate while pulling in, ie accreting, matter as they grow.

CXO J101527.2+625911

Supermassive holes are generally stationary objects, sitting at the centers of most galaxies. However, using data from NASA's Chandra X-ray Observatory and other telescopes, astronomers recently hunted down what could be a supermassive black hole that may be on the move.

This possible renegade black hole, which contains about 160 million times the mass of our Sun, is located in an elliptical galaxy about 3.9 billion light years from Earth. Astronomers are interested in these moving supermassive black holes because they may reveal more about the properties of these enigmatic objects.

This black hole may have "recoiled," in the terminology used by scientists, when two smaller supermassive black holes collided and merged to form an even larger one. At the same time, this collision would have generated gravitational waves that emitted more strongly in one direction than others. This newly formed black hole could have received a kick in the opposite direction of those stronger gravitational waves. This kick would have pushed the black hole out of the galaxy's center, as depicted in the artist's illustration.

NGC 4696

At the center of the Centaurus galaxy cluster, there is a large elliptical galaxy called NGC 4696. Deeper still, there is a supermassive black hole buried within the core of this galaxy.

New data from NASA's Chandra X-ray Observatory and other telescopes has revealed details about this giant black hole, located some 145 million light years from Earth. Although the black hole itself is undetected, astronomers are learning about the impact it has on the galaxy it inhabits and the larger cluster around it.

In some ways, this black hole resembles a beating heart that pumps blood outward into the body via the arteries. Likewise, a black hole can inject material and energy into its host galaxy and beyond.

By examining the details of the X-ray data from Chandra, scientists have found evidence for repeated bursts of energetic particles in jets generated by the supermassive black hole at the center of NGC 4696. These bursts create vast cavities in the hot gas that fills the space between the galaxies in the cluster. The bursts also create shock waves, akin to sonic booms produced by high-speed airplanes, which travel tens of thousands of light years across the cluster.

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.