Black Holes

Abell 2261
Credit: X-ray: NASA/CXC/Univ of Michigan/K. Gültekin;
Optical: NASA/STScI and NAOJ/Subaru; Infrared: NSF/NOAO/KPNO

The mystery surrounding the whereabouts of a supermassive black hole has deepened.

Despite searching with NASA's Chandra X-ray Observatory and Hubble Space Telescope, astronomers have no evidence that a distant black hole estimated to weigh between 3 billion and 100 billion times the mass of the Sun is anywhere to be found.

This missing black hole should be in the enormous galaxy in the center of the galaxy cluster Abell 2261, which is located about 2.7 billion light years from Earth. This composite image of Abell 2261 contains optical data from Hubble and the Subaru Telescope showing galaxies in the cluster and in the background, and Chandra X-ray data showing hot gas (colored pink) pervading the cluster. The middle of the image shows the large elliptical galaxy in the center of the cluster.

Shifu Zhu

Shifu Zhu, a 5th-year graduate student of Astronomy & Astrophysics at Pennsylvania State University, is our guest blogger for this post. He received his B.S. in Astronomy from the University of Science and Technology of China (USTC) in 2013. He received his M.S. in Astrophysics from USTC in 2016.

“So, the answer to the nature of the X-ray emission from radio-loud quasars is simpler than we previously had thought,” I said to myself after staring for a while at our new correlations between how bright radio-loud quasars are in X-ray and ultraviolet light.

The term “quasar” was originally coined for bright radio sources that look like stars in visible-light images, i.e., quasi-stellar radio sources. Shortly after their discovery, researchers realized that quasars are supermassive black holes (with masses of millions to billions of times that of the Sun) feeding on material that is gravitationally attracted to them. Notably, despite this strong gravitational attraction, some material can also be ejected in powerful jets, narrow streams of material shooting away from the supermassive black hole in opposite directions. These jets are fueled by material in an “accretion disk” falling towards the black hole.

Sagittarius A*
Credit: NASA/CXC

The winners of the 2020 Nobel Prize in Physics were announced this week: a trio of astrophysicists won for their work — both theoretical and observational — of black holes. Two of the three, Dr. Andrea Ghez of the University of California at Los Angeles and Reinhard Genzel of the Max Planck Institute for Extraterrestrial Physics in Germany — were cited “for the discovery of a supermassive compact object at the center of our galaxy”.

There are black holes throughout our Galaxy and across the Universe, but the one at the Milky Way's center, known as Sagittarius A* (Sgr A*), is particularly fascinating. At a distance of about 26,000 light years from Earth, Sgr A* is the closest supermassive black hole to us. Both Ghez and Genzel have spent decades tracking stars and clouds of dust near Sgr A* to learn more about the black hole and its environment.

Erini Lambrides

We are delighted to welcome Erini Lambrides from Johns Hopkins University (JHU) in Baltimore Maryland as a guest blogger. She is the first author of a paper in the Astrophysical Journal that is the subject of our latest press release. Erini is a PhD candidate at JHU in the Department of Physics and Astronomy and will be defending her thesis next year. Prior to starting her PhD, she spent a year as a research assistant at Gemini Observatory North, and a year as a research assistant at the American Museum of Natural History in NYC. She got her BS with Honors in Physics at the University of Rochester. She was awarded a NASA Maryland Space Grant Fellowship to fund her PhD and outreach efforts. Her research is focused on quantifying the extent and impact of AGN-host galaxy co-evolution.

When one normally thinks of the scientific method, the following mantra rooted in elementary school days comes to mind: The Question, The Research, The Hypothesis, The Data, The Conclusion. Neatly lined, linear steps that seemingly underpin the entirety of humanity’s quest for knowledge about our physical world. I learned this when I was ten years old, but nearly twenty years later, as I trundle along my own scientific journey, I’ve learned that the steps of the scientific method more resemble an M.C. Escher painting.

My group and I have recently completed work on a peculiar class of astrophysical objects: growing supermassive black holes that are embedded in a thick cocoon of gas and dust. This work is exciting because we discovered that this particularly difficult-to-observe class of objects can be detected in greater numbers than previously thought. However, when I started this work, my goal was not to find these objects, nor was it even about this class of objects!

This article appeared on NASA.gov, written by NASA public information officer Elizabeth Landeau, based on a press release from Keck Observatory.

Examples of Einstein ring gravitational lenses taken with the Hubble Space Telescope.
Credit: NASA/ESA/SLACS Survey Team: A. Bolton (Harvard/Smithsonian), S. Burles (MIT), L. Koopmans (Kapteyn), T.Treu (UCSB), L. Moustakas (JPL/Caltech)

Determined to find a needle in a cosmic haystack, a pair of astronomers time traveled through archives of old data from W. M. Keck Observatory on Mauankea in Hawaii and old X-ray data from NASA’s Chandra X-ray Observatory to unlock a mystery surrounding a bright, lensed, heavily obscured quasar.

This celestial object, which is an active galaxy emitting brilliant amounts of energy due to a black hole devouring material, is an exciting object in itself. Finding one that is gravitationally lensed, making it appear brighter and larger, is exceptionally exciting. While slightly over 200 lensed unobscured quasars are currently known, the number of lensed obscured quasars discovered is in the single digits. This is because the feeding black hole stirs up gas and dust, cloaking the quasar and making it difficult to detect in visible light surveys.

By combining data from telescopes with supercomputer simulations and virtual reality (VR), a new visualization allows you to experience 500 years of cosmic evolution around the supermassive black hole at the center of the Milky Way.

This visualization, called "Galactic Center VR", is the latest in a series from astrophysicists, and is based on data from NASA's Chandra X-ray Observatory and other telescopes. This new installment features their NASA supercomputer simulations of material streaming toward the Milky Way's four-million-solar-mass black hole known as Sagittarius A* (Sgr A*). The visualization has been loaded into a VR environment as a novel method of exploring these simulations, and is available for free at both the Steam and Viveport VR stores.

MAXI J1820+070
Credit: X-ray: NASA/CXC/Université de Paris/M. Espinasse et al.; Optical/IR:PanSTARRS

Astronomers have caught a black hole hurling hot material into space at close to the speed of light. This flare-up was captured in a new movie from NASA's Chandra X-ray Observatory.

The black hole and its companion star make up a system called MAXI J1820+070, located in our Galaxy about 10,000 light years from Earth. The black hole in MAXI J1820+070 has a mass about eight times that of the Sun, identifying it as a so-called stellar-mass black hole, formed by the destruction of a massive star. (This is in contrast to supermassive black holes that contain millions or billions of times the Sun's mass.)

Andrew King

We are pleased to welcome Andrew King from the University of Leicester in the United Kingdom as a guest blogger. Andrew is the author of a paper that is the subject of our latest press release. He graduated in Mathematics from the University of Cambridge (UK), and then researched there for his PhD in General Relativity. After postdoctoral positions in London and Hamburg, he moved to the University of Leicester, where he is now Professor of Theoretical Astrophysics. He is a long-term visitor at the Anton Pannekoek Astronomical Institute in the University of Amsterdam, and Visiting Professor at Leiden Observatory. His interests include ultraluminous X-ray sources, accretion and feedback involving supermassive black holes, and how this affects their host galaxies.

A few months ago, Giovanni Miniutti from ESA's Center for Astrobiology in Spain, and collaborators observed that X-ray emission from the low-mass nucleus (that is, a relatively small black hole at its center) of the galaxy GSN 069 brightened by factors of about 100 roughly every 9 hours, staying bright for about an hour each time before returning to the faint state. From the X-ray spectrum — the intensity of X-rays at different wavelengths — they deduced that the X-rays came from an accretion disk around the central black hole of the galaxy, which has the rather low mass of about 400,000 times that of the Sun. I was intrigued by these observations: the eruptions implied that a lot of mass was being fed into the accretion disc every 9 hours, and the reasonably stable period suggested there was something in a very close orbit around the black hole.

Chris Reynolds

We are pleased to welcome Chris Reynolds as our guest blogger. Chris is a professor in the Institute of Astronomy at the University of Cambridge in the United Kingdom, and led the study that is the subject of our latest press release. He received his Bachelors degree in Physics and Theoretical Physics from the University of Cambridge in 1992, and continued in Cambridge to graduate with his PhD in astronomy in 1996. He then moved to the University of Colorado Boulder for five years as a post-doctoral fellow and Hubble Fellow, before joining the faculty of the University of Maryland's Department of Astronomy. In 2017, after 16 years as a professor at the University of Maryland, he was lured back to Cambridge to take up the position of Plumian Professor of Astronomy and Experimental Philosophy. Chris is a high-energy astrophysicist who mainly works on the properties of supermassive black holes, although he has taken a detour into particle physics with his latest work, which is the subject of this blog post.

A little over 200 million light years from us lies the Perseus cluster, a swarm of a thousand galaxies trapped within the space of just a couple of million light years by the gravitational field of a massive ball of dark matter. This gravitational field doesn't just confine the galaxies. It also holds onto an atmosphere of hot (40-60 million Kelvin) gas that fills the space between the galaxies; this matter is known as the “intracluster” medium. At the center of all of this lies the unusual galaxy NGC1275, and at the center of this galaxy is a supermassive black hole that is driving powerful jets out into the intracluster medium. When my team observed the active galactic nucleus (AGN) in NGC1275 with the Chandra X-ray Observatory in late 2017, we thought that our focus would be the properties of this black hole and how it interacted with its surroundings. Little did we know that we'd be publishing a paper on particle physics, setting the tightest limits to date on light axion-like particles with implications for string theory!

Ophiuchus Galaxy Cluster
Credit: X-ray: Chandra: NASA/CXC/NRL/S. Giacintucci, et al., XMM-Newton: ESA/XMM-Newton;
Radio: NCRA/TIFR/GMRT; Infrared: 2MASS/UMass/IPAC-Caltech/NASA/NSF

We are pleased to welcome two guest bloggers, Maxim Markevitch and Simona Giacintucci, who led the study described in our latest press release. Markevitch, an expert on galaxy clusters X-ray studies, got his PhD at the Space Research Institute of the Russian Academy of Sciences. He worked on ASCA X-ray data in Japan, then at the Chandra X-ray Center for the first 10 years of Chandra operations, and is now at the NASA Goddard Space Flight Center. He received the AAS Rossi Prize. Giacintucci, the lead author of the study, is an expert in radio phenomena in galaxy clusters. She got her PhD at Bologna University. She was a postdoc at the CfA and an Einstein fellow at the University of Maryland, and is now at the Naval Research Lab.

Galaxy clusters are colossal concentrations of dark matter, galaxies, and tenuous, 100-million-degree plasma. This plasma — gas where the electrons have been stripped from their atoms — slowly loses heat by emitting radiation in the form of X-rays. Around the central peaks of many clusters, where matter concentrates, the plasma gets dense enough* to cool quite fast, on a timescale shorter than the cluster's lifetime (a few billion years). The higher the plasma's density, the more X-rays it emits and the faster it cools. As it cools down, it contracts and becomes denser still, and so on, entering a runaway cooling process. Left unchecked, this process should deposit vast quantities of cold gas in the cluster centers.

We know for a fact that the plasma cools down because we do observe those X-rays — but we don't find nearly as much cold gas in the cluster centers as such runaway cooling must deposit. This has been a puzzle for a long while, and the solution the astronomers converged upon is that there must be some source of additional heat in the central regions of clusters — their “cores” — that doesn't let the plasma cool below 10 million degrees or so.

Early Chandra X-ray images of galaxy clusters pointed to the likely source: the supermassive black holes (SMBH) that sit in the centers of the cluster central galaxies, pull in the surrounding matter, and eject a tiny part of it (just before it sinks irretrievably into the black hole) at nearly the speed of light back into the surrounding gas. Where those jets hit the gas, they blow huge bubbles in it, stir it, generate shocks like sonic booms, etc. (all of these features have been seen in the Chandra images of the cluster cores). The current wisdom holds that these processes together supply the needed heat to prevent runaway cooling from occurring, but at the same time are not so powerful that they blow up the whole plasma cloud, implying some kind of a gentle, self-regulated feedback loop may be occurring.