Black Holes Press Kit

Black Holes 1 Contents

Preface 3 Overview and History 4 Black Holes in Theory 6 How Big can a Black Hole be? 7 Stellar-mass black holes 7 The heavyweights: supermassive black holes 8 The enigma of ULXs 10 Microscopic black holes 11 Birth of a Black Hole 12 The traditional recipe: stellar collapse 12 Tradition and innovation: gamma-ray bursts 14 The puzzle of supermassive black holes 15 Weighing Black Holes 16 Stellar-mass black holes 16 Supermassive black holes 16 Motion of stars 16 Motion of gas 16 Reverberation mapping 17 Secondary methods 17 Black Hole Research at ESO 18 ESO’s current black-hole instruments 18 Future plans 18 ESO Achievements — List of Black Hole Related ESO Press Releases 19

2 Black Holes Cover: The Milky Way spans the sky above Paranal as the VLT peers out towards the Galactic Centre | ESO/ Yuri ­Beletsky

Back cover: Artist’s impression of a black hole | ESA/Hubble

Left: Spiral galaxy NGC 253 seen edge-on 13 million light-years away in this image taken with the Wide Field Image at the La Silla Observatory | ESO

Preface

The existence of black holes has been What are black holes? How do they theorised for more than 200 years. Ini- form? How can they be studied if nothing tially just a philosophical idea, there is can escape them? This guide aims to now strong evidence that most, if not all answer these questions, giving a general galaxies contain black holes millions or overview of the theoretical and observa- billions of times heavier than our Sun. tional achievements of the last century in Black holes themselves cannot be black hole science. observed since, by definition, no light can escape them, but astronomers can study The ESO telescopes and astronomical the effects of black holes on their sur- community have greatly contributed to roundings. the investigation of black holes. The place of ESO in the frame of such discov- eries will be revealed in this short tour of the past and future of one of the most exciting fields of modern astrophysics.

Black Holes 3 Overview and History

Lasciate ogni speranza, o voi When all the sources of nuclear fusion in remarkable discoveries by observing the ch’entrate (Dante Alighieri, Divina a star are exhausted, there is nothing to effect of black holes on their surround- Commedia) prevent the star from collapsing. ings at ultraviolet, optical and infrared wavelengths. Do black holes exist? You may argue that Abandon all hope, you who enter if they do not emit any radiation it is The concept of an object so massive and here (Dante Alighieri, The Divine impossible to detect them. This is indeed dense that nothing can escape from its Comedy) true for isolated black holes, but luckily fatal grip was first proposed at the end of there are black holes that swallow gas, the 18th century, extrapolated from New- Nothing can escape from a black hole: modify the trajectories of nearby stars or ton’s law of gravity. However the true anything that crosses the boundary have a stable life close to a companion black hole revolution occurred only with known as the event horizon becomes star. The study of the effects that these Einstein’s theory of general relativity trapped. Even light is not fast enough to black holes have on the surrounding gas (1915). This theory states that matter escape. The reason that nothing can and stars gives information about the curves spacetime. The denser the matter, escape a black hole is its enormous grav- black holes themselves. Observations the larger the curvature. According to itational pull. Black holes a few times from Earth and from space are per- Einstein, mass and energy are equivalent, more massive than the Sun can form at formed at every wavelength: from radio to and so even massless phenomena, such the ends of the lives of massive stars. gamma rays. ESO telescopes have made as light, are affected by gravity.

4 Black Holes The centre of the Milky Way and its supermas- sive black hole seen in near infrared with the VLT at Paranal | ESO/S. Gillessen et al.

From there the step to black holes is allgemeinen Relativitätstheorie. Black as smaller stars do, but to collapse into short. By 1916 Karl Schwarzschild had holes are a direct consequence of gen- something denser (such as white proved that black holes work as a solu- eral relativity; however Einstein himself dwarfs and neutron stars). tion to Einstein’s equations. did not believe that they could exist. – In 1939, the American physicists Robert – A year later, in 1916, the German physi- Oppenheimer and Hartland Snyder pre- In the past few centuries, black hole cist Karl Schwarzschild proved that dicted that black holes could, in princi- physics has made many major break- black holes are a solution to Einstein’s ple, form in nature from the collapse of throughs: equations in spherical symmetry. massive stars. – In 1784, the eclectic English geologist Schwarzschild’s solution is for a non- – In 1974, the British theoretical physicist John Michell, followed in 1796 by the rotating black hole, while in 1963, the Stephen Hawking considered quantum French mathematician Pierre-Simon de New Zealand mathematician Roy Kerr effects and discovered that quantum Laplace, proposed the existence of so- found the theoretical solution for rotat- black holes are not as black as classi- called dark stars, which would exert a ing black holes. cal black holes: they emit thermal radia- gravitational pull strong enough to lock – The Indian–American astrophysicist tion. in light. Subrahmanyan Chandrasekhar first – In 1915, Albert Einstein published his speculated in 1930 that the fate of mas- The term “black hole” was coined in 1967 first paper on general relativity: Zur sive stars may not be just to cool down, by the American physicist John Arichbald Wheeler.

Black Holes 5 Black Holes in Theory

In theory, black holes are simple to think that black holes rotate: if they until it evaporates. This effect is important describe. Just three parameters are suffi- formed from a rotating collapsing star or for very tiny black holes, but astrophysi- cient to characterise them fully: mass, from the merger of two neutron stars they cal black holes are very massive and they angular momentum (describing their rota- must have preserved their rotational would need a time much longer than the tion) and electric charge. Compared to energy. Moreover they can spin up age of the Universe to evaporate. stars, from which they form, these are thanks to successive interactions. very few characteristics, leading physi- cists to say that “black holes have no It was once thought that black holes do hair”. Astrophysical black holes are even not emit anything. However, Stephen simpler, as they have no charge: if they Hawking pointed out that if quantum were charged, they would be quickly effects are taken into account, they can neutralised by the surrounding plasma. radiate thermal energy and particles. This Hawking radiation carries energy away Schwarzschild’s solution to Einstein’s from the black hole and reduces its mass equations describes a black hole that is (E = mc2). Therefore a black hole shrinks not rotating, while Kerr’s solution is for rotating black holes. It is reasonable to

Artist’s impression of Cygnus X-1, a black hole 10 000 light-years from Earth and five times the mass of the Sun | ESO, NASA, ESA/Hubble

6 Black Holes How Big can a Black Hole be?

In principle there is no limit to the size of Black holes of different masses have the Stellar-mass black holes a black hole: it can be as light as a same basic properties (they all have no feather or as heavy as a few billion Suns! hair). They are expected to display differ- A billion stellar-mass black holes exist in Their size varies accordingly. A black hole ent behaviours only because the typical our galaxy, the Milky Way, according to with a mass equal to that of the Sun lengths and timescales involved are pro- standard galactic evolutionary models. would have a radius of three kilometres. portional to the mass and because black Their masses are estimated to be Furthermore the radius of a black hole holes of different sizes exist in different between three and twenty solar masses. scales in proportion to its mass. So a environments. In the next section we Some will be isolated black holes, others typical stellar-mass black hole (ten times quickly review the different weight black holes lying close to normal stars. the mass of the Sun) would have a radius classes. Such coupled systems are called black of thirty kilometres, and a supermassive hole X-ray binaries, or microquasars, in black hole (e.g., one million solar masses) cases where they emit a relativistic pair of would have a radius of three million kilo- jets. The bright X-ray emission comes metres. from a disc of gas that is sucked from the normal star and spirals towards the black hole’s event horizon, like water spiralling down a plughole.

Black Holes 7 The heavyweights: supermassive black The AGN extend only over a few light- tion is the term used to describe this fatal holes minutes or light-days: they are less than attraction: the gas rotates towards the one ten-millionth the size of their host event horizon, building an accretion disc. Where do we find supermassive black galaxy, but they are hundreds of times While the gas spirals in, its energy is con- holes? At the centre of a galaxy! The core brighter than the whole galaxy. The con- verted into heat and starts to shine of many galaxies is exceedingly luminous, sensus is that AGN are powered by a brightly, producing the observed extreme and often across all wavelengths. These central supermassive black hole. luminosities over the entire electromag- brilliant central regions are called Active netic spectrum. Part of the matter Galactic Nuclei (AGN). Quasars (QUASi- Supermassive black holes are not iso- escapes the fate of being gulped down stellAR radio sources), QSOs (Quasi Stel- lated: they sit at the centre of galaxies into the black hole, by being carried away lar Objects) and blazars all belong to this and they attract the matter in their vicinity in two highly collimated radio jets that class of objects. with their strong gravitational field. Accre- emerge close to the inner edge of the disc.

Artist’s impression of an Active Galactic Nucleus, with a supermassive black hole emitting two jets of energy and parti- cles | A. Simonnet, ­Sonoma State University

8 Black Holes Image of the central region of the Milky Way with an artist’s impres- sion of the bright gas surrounding the central black hole | ESO

Flare detection from the centre of the Milky Way using adaptive optics on the VLT at Paranal | ESO

In less active galaxies, such as our own our galaxy, about 27 000 light-years from The next generation of telescopes, like Milky Way, the black hole at the centre is Earth. The motion of the stars in its vicin- ESO’s planned European Extremely starving, as there is not much matter ity provides the best empirical evidence Large Telescope (E-ELT), will probe scales around it. It is therefore much less bright for the existence of a supermassive black of less than a few parsecs (~ 10 light- than an AGN. hole (eso0846). years) in the very central regions of galax- ies out to cosmological distances of The best evidence for the existence of Over the past decade a correlation ­hundreds of millions of light-years, allow- supermassive black holes comes from between the mass of a galaxy and the ing us to trace the build-up of supermas- within the Milky Way: thanks to ESO tele- mass of its central black hole has been sive central objects in galaxies when the scopes, astronomers are now convinced observed. For these properties to be Universe was as young as a quarter of its that a black hole, with a mass of a few related, a number of mechanisms must present age. million solar masses and called Sgr A* be at work over nine orders of magnitude (Sagittarius A star), sits at the centre of in scale, from galaxy environments to the “sphere of influence” of the black hole.

Black Holes 9 Artisit’s impression of a black hole inside a binary system | ESO

The enigma of ULXs This is the limiting case, assuming spheri- Intermediate-mass black holes could rep- cal symmetry, when the gravitational resent a link currently missing between Today, more than 200 ULXs are known. force acting in towards the black hole stellar-mass black holes and supermas- ULXs stands for UltraLuminous X-ray equals the radiation force acting out- sive black holes and they could serve as sources: they are “ultra” because their wards. Hence the mystery: are ULXs seeds in the early Universe for the forma- apparent X-ray luminosity is above the powered by intermediate-mass black tion of the supermassive black holes that maximum possible luminosity for stellar- holes (100–1000 times more massive we see today. There is a lot of effort mass black holes. Under normal condi- than the Sun) or is their high luminosity going into the search for intermediate- tions accretion onto a stellar-mass black due to stellar-mass black holes that mass black holes. hole cannot supply radiation over some accrete above the Eddington limit? limit, known as the Eddington luminosity.

10 Black Holes Microscopic black holes time the temperature and pressure were up of the Large Hadron Collider (LHC) so gigantic that they could have these microscopic black holes received a The world of black holes is full of sur- squeezed matter down to a singularity: lot of attention as they might be pro- prises: there may be black holes smaller however only primordial black holes of duced during particle collisions at the than a flea and lighter than a feather and about a billion tons could have survived LHC. However, they would immediately tiny black holes could one day be pro- until the present day; the lighter ones disintegrate again, and would therefore duced in the laboratory. would all have evaporated. not have time to accrete matter and cause any macroscopic effects. Primordial black holes may have existed The lightest black holes are called ele- during the early stages of the Universe, a mentary black holes, as they would be few moments after the Big Bang. At that like elementary particles. With the start-

Colour-composite image of the spiral galaxy NGC 1097 taken by the VLT | ESO

Black Holes 11 Birth of a Black Hole

The traditional recipe to make a black The traditional recipe: stellar collapse the end nothing can counteract gravity hole needs a single ingredient: a very and the whole mass is squeezed into a massive star at the end of its life. More The life of a star is a continuous struggle point of zero volume and infinite density. recently another mechanism has been between gravity and pressure radiation. This point is called a singularity. Physi- found, the collision and merger of very Gravity compresses the star, while the cists say that the singularity is not dense objects, such as neutron stars. radiation due to nuclear fusion pushes its “naked”, in the sense that it is surrounded matter outwards. When the fuel is by a boundary, called an event horizon. Black holes that form through these exhausted, the star stops burning. Hence what is left at the explosive end of mechanisms usually have masses three the life of a very massive star is a singu- to ten times greater than the Sun and If the star doesn’t have much mass — larity surrounded by an event horizon — they are called stellar-mass black holes. like our own Sun — it will become fainter, a black hole. In theory black holes of any size can cooling down as a white dwarf. However exist. Supermassive black holes of a mil- if its initial mass is about eight times that lion to a billion times the mass of our Sun of the Sun, it will collapse, bounce back are found at the centre of (almost) all and detonate in a supernova. Neutron massive galaxies. How they form is still stars form in this way. And if the original not fully understood. mass exceeds about 25 solar masses, at

12 Black Holes Artist’s impression of the enormous energy released in a gamma-ray burst, associated with stars as they collapse into black holes | ESO

Image from ESO’s Giga- Galaxy Zoom project, displaying the central part of the Milky Way | ESO/S. Guisard

Initial Stellar Mass Final Stellar Mass End Product

Less than 8 M Less than 1.4 M White dwarf

8–25 M 1.4–3 M Neutron star

Greater than 20–25 M Greater than 3 M Stellar-mass black hole

Black Holes 13 Tradition and innovation: gamma-ray GRBs have been detected in two fla- Short GRBs seem to arise from a new bursts vours, both related to the formation of a mechanism of black-hole birth: namely black hole: long (when the burst is longer the dazzling merger of two compact In the last decade, a lot of evidence has than about two seconds) and short. objects. Black holes and neutron stars been collected indicating that the most are called compact objects, simply energetic blasts in the Universe, gamma- Bohdan Paczynski and Stanford Woosley because they are made up of enormous ray bursts (GRBs), may be connected to were the first astronomers to propose amounts of matter compressed into a rel- the birth of black holes. Since their dis- that long GRBs could be connected to atively tiny space. The prevailing model covery in the 1960s, GRBs have posed a stellar collapse. Today, this long-sus- for short GRBs links them to the fusion of challenge to astrophysicists. They are pected connection (eso9847) is well- two neutron stars or a neutron star and a sudden and intense flashes that occur established (eso0318). The dominant black hole that were orbiting close to randomly in space and time and they interpretation suggests that a black hole each other. The result of this collision release in a few seconds more energy forms in a hypernova (a rare type of would be a black hole and a brief but than the Sun during its whole life. A less supernova) explosion. Such a newborn intense burst of gamma-ray emission. energetic X-ray, radio and optical after- black hole is not isolated: it is surrounded The analysis of the optical afterglow sin- glow follows the first emission in the by a disc of matter spiralling in and has gled out this theory from many others gamma-ray band. The afterglow is two jets. The interaction of the jets with (eso0533). extremely useful to investigate the prop- the gas expelled in the detonation is erties of these elusive explosions. thought to be the responsible for the long GRBs.

14 Black Holes The puzzle of supermassive black holes Population III, may have been 100–1000 tries to understand one of the two proc- times more massive than the Sun and esses has to consider both. A fascinating While the formation of stellar-mass black would have collapsed to black holes with challenge for astrophysicists! holes is fairly well understood, it is not masses of a few hundred up to thou- clear how black holes as massive as a sands of solar masses. million to a billion times the mass of the Sun could have formed and have already One possible scenario for the formation been in place at a time when the Uni- of supermassive black holes is that these verse was less than 1 billion years old seed black holes of intermediate mass (current age 13.6 billion years). Super- merged to form more massive black massive black holes cannot form through holes, which grew to build up into the the collapse of a single star. The forma- supermassive black holes observed tion and growth of supermassive black today. The growth is regulated mainly by holes is the subject of intense discussion. accretion. An important aspect in the life Observations and computer simulations of supermassive black holes is their inter- indicate that when the Universe was action and co-evolution with the host gal- 200–400 million years old it was inhab- axy: the formation of stars in the galaxy ited by stars brighter, hotter and more and the accretion process onto the cen- massive than the next generation. This tral supermassive black hole influence first generation of stars, usually called each other strongly and any theory that

Artist’s impression of energy jets from a black hole creating a galaxy | ESO

Black Holes 15 The centre of the Milky Way | ESO

The Milky Way’s central     supermassive black hole   has been weighed by   measuring the proper   motions of stars in its   vicinity | ESO   6JU$    ǥ KHFGSC@XR

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Weighing Black Holes

Astronomers can measure the masses of hole. The speed is encoded into the time Modelling the orbits of these stars black holes by studying the material that variability of the light emitted by the requires the presence of an unseen mass orbits around them. So far, two types of accretion process onto the black hole, of four million times the mass of the Sun black hole have been identified: stellar- where material from the companion star (eso0846). mass (just a few times heavier than our is transferred to the black hole (eso1004). Sun) or supermassive (about as heavy as For more distant galaxies it is not possi- a small galaxy). But black holes might ble to resolve individual stars, but a close exist in other mass ranges as well. These Supermassive black holes group of stars can be used to trace the are the most common techniques for kinematics. Building a dynamical model measuring the masses of black holes. Motion of stars for the galactic nuclei then allows astron- omers to find the best match for the The best evidence for the existence of a observations by varying the mass of the Stellar-mass black holes supermassive black hole is provided by black hole. the centre of our own galaxy. Astrono- The mass of a stellar-mass black hole mers have monitored the movements of can be derived by measuring the speed the individual stars at the Galactic Centre of a companion star orbiting the black very carefully for almost twenty years.

16 Black Holes Composite image of the jets shooting from the central black hole of the Centaurus A galaxy | ESO/WFI (Optical); MPIfR/ESO/APEX/A. Weiss et al. (Submillime- tre); NASA/CXC/CfA/R. Kraft et al. (X-ray)

    Velocity map of the molecular hydrogen line     emission and the stellar motion around the     nucleus of Centaurus A | ESO/N. Neumayer et     al./M. Cappelari et al. BRDB @Q l  l 

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l  l  l  l  l          l  l  l          @QBRDB @QBRDB

l  UJLR   l UJLR 

Motion of gas Reverberation mapping the dark central mass can be extracted by reverberation mapping. Gas orbiting the black hole can also be Some active galactic nuclei show very used as a kinematic tracer for the gravita- broad gas emission lines that originate tional field. This method can be easily from regions very close to the black hole. Secondary methods applied to active and non-active galaxies. The lines appear broad because they In some cases, the orbiting gas radiates come from gas that is orbiting the black There are now a couple of well-estab- maser emission that serves as an alterna- hole at very high speeds from a small lished relations between the mass of the tive dynamical indicator for the central region that cannot be spatially resolved. supermassive black hole and some more masses. This is a very reliable mass trac- Astronomers detect the direct radiation global properties of the surrounding gal- er as maser emission originates from very from the central source and with some axy, like mass, luminosity, stellar velocity close to the central supermassive black time lag, indirect radiation reflected from dispersion or light concentration. These holes and enables astronomers to meas- the clouds in the broad-line region. The scaling laws are often used to estimate ure the enclosed mass very accurately. time lag reveals the distance of the masses of supermassive black holes in Maser emission is however not so com- clouds in the broad-line region to the galactic nuclei, as it is often easier to mon in galactic nuclei and this method is black hole. Combining the distance of the measure the global properties of the host only applicable to some sources. gas clouds with their measured width, galaxy.

Black Holes 17 Black Hole Research at ESO

ESO’s current black-hole instruments FLAMES (Fibre Large Array Multi Element accuracy of the observations by a factor Spectrograph, VLT) is used for multi-fibre 10 to 100 over what is currently possible. GROND (Gamma-Ray burst Optical/ high spectral resolution spectroscopy. This combination has the potential to Near-Infrared Detector) on the MPG/ESO directly test Einstein’s theory of general 2.2-metre telescope takes images simul- VIMOS (VIsible Multi-Object Spec- relativity in the presently unexplored taneously in seven colours. It is mostly trograph, VLT) has a large field of view region close to a black hole. used to determine the distances of and can take many spectra simultane- gamma-ray bursts. ously. The millimetre interferometer Atacama Large Millimeter/submillimeter Array FORS on the Very Large Telescope (VLT) VISIR (VLT Imager and Spectrometer in (ALMA) will have enough sensitivity and at Paranal is an imager and spectrograph the InfraRed) studies the dust emission angular resolution to shed light on the that allows very sensitive follow-up around black holes. growth of supermassive black holes. observations of gamma-ray burst after- ALMA will be able to trace the motion of glows to be made as well as mass meas- MIDI (Mid-InfrareD Interferometric Instru- molecules in the close vicinity of black urements for stellar-mass black holes. ment, VLT) combines the light of two tele- holes out to cosmological distances, scopes for very high spatial resolution when galaxies and black holes were in NACO (VLT) is a near-infrared imager and studies of galactic nuclei. the process of formation. spectrograph equipped with a powerful adaptive optics system, which allows very AMBER (Astronomical Multiple BEam The E-ELT will probe scales of less than a sharp observations of even dust- Recombiner, VLT) combines the light of few parsecs (~10 light-years) in the very enshrouded black holes. three VLT telescopes and works in the central regions of galaxies out to cosmo- near-infrared for even better spatial reso- logical distances of hundreds of millions SINFONI (VLT) is an integral field unit lution. of light-years, allowing us to trace the spectrograph equipped with an adaptive build-up of supermassive central objects optics system that allows unprecedented in galaxies when the Universe was as studies of the stars and gas that are Future plans young as a quarter of its present age. orbiting black holes. The next major advance will be to com- ISAAC (VLT) is an imager and spec- bine the light from the four 8.2-metre VLT trograph in the near-infrared and can Unit Telescopes — a technique known as peer through the dust in active galactic interferometry — with an instrument nuclei. called GRAVITY. This will improve the

Artist’s rendering of the future ALMA array of antennas in the Chilean Andes | ESO/NAOJ/ NRAO

18 Black Holes ESO Achievements — List of Black Hole Related ESO Press Releases

2010: A stellar mass black hole much fur- 2008: Combining data from ground- and 2007: Discovery of the first known triplet ther away than any previously known was space-based telescopes reveals that the of quasars. This close trio of supermas- detected with ESO’s Very Large Tele- jets of the gamma-ray burst called GRB sive black holes lies about 10.5 billion scope. (eso1004) 080319B were aimed almost directly at light-years away towards the Virgo (The the Earth. (eso0828) Virgin) constellation. (eso0702) 2009: A new scenario for the co-evolu- tion of black holes and galaxies has 2008: Discovery of a supernova that has 2006: Discovery of a new kind of cosmic emerged from observations at ESO’s VLT: collapsed into a black hole and produced explosion related to gamma-ray bursts black hole outflows might trigger the for- a jet, which is typical of much more that seems to arise when a newly born mation of stars. (eso0946) ­violent events, the so-called gamma-ray black hole swallows most of the matter bursts. This represents an important con- from its doomed parent star. (eso0649) 2009: ESO’s ISAAC instrument at the VLT nection between the most violent has identified the gamma-ray burst GRB ­phenomena observed in the Universe. 2005: Confirmation that the formation 090423 as the most distant known object (eso0823) mechanisms for short and long gamma- in the Universe. (eso0917) ray bursts are different. Short gamma-ray 2008: Using ESO’s VLT astronomers bursts are the result of the merger of two 2008: Astronomers have scrutinised the could uncover the true colour of the compact objects, while long ones mark inner parts of the disc around a super- accretion discs in quasars. (eso0821) the death of a massive star. (eso0541) massive black hole 10 billion light-years away, and have confirmed current models 2008: Astronomers observed four 2005: Observations with NACO at ESO’s of accretion discs. (eso0847) gamma-ray bursts on the same day (19 VLT give new insight how black holes are March 2008), with one of them being the fed by their surrounding material. 2008: In a 16-year-long study, using sev- most luminous object ever observed in (eso0534) eral of ESO’s telescopes, a team of the Universe. (eso0808) astronomers has produced the most 2005: First observations of the visible detailed view ever of the surroundings of 2007: At ESO’s La Silla Observatory, light from a short gamma-ray burst show- the supermassive black hole at our gal- astronomers have measured the velocity ing that these short, intense bursts of axy’s centre. (eso0846) of the explosions known as gamma-ray gamma-ray emission originate from the bursts. The material is travelling at the collision of two merging neutron stars. 2008: Astronomers have used APEX and speed of more than 99.999% of the (eso0533) the VLT simultaneously to study the vio- velocity of light, the maximum speed limit lent flares from the supermassive black in the Universe. (eso0726) 2005: Using ESO’s VLT and the Hubble hole in the centre of the Milky Way. Space Telescope (HST) astronomers dis- (eso0841) 2007: Triggered by the Swift satellite, covered a quasar without a host galaxy. ESO’s VLT has observed two gamma-ray (eso0529) 2008: Unique observations of the flicker- bursts merely minutes after the explo- ing light from the surroundings of two sion. The data show that these powerful black holes have shown that magnetic explosions are linked to the death of fields must play a crucial role in the way massive stars. (eso0717) black holes swallow matter. (eso0836)

Design of the E-ELT | ESO

Black Holes 19 Black Holes Press Kit

20 Black Holes