Cosmic Monsters: Black Holes and the Images That Finally Revealed Them

This graphic series shows a computer simulation of a black hole from multiple stages — plasma slowly falling toward the hole with a magnetic field visible as white lines, the plasma accelerating as it falls, and the final moments before material crosses the event horizon from which no light can return. Magnetic fields play a crucial role in black hole accretion: they enable the transfer of angular momentum outward through the disk, allowing matter to spiral inward, and they help launch relativistic jets of material perpendicular to the disk plane that can extend millions of light-years into space.

This artist's concept shows a black hole with its accretion disk and a jet of hot plasma extending outward. Using NASA's NuSTAR space telescope and the ULTRACAM camera at the William Herschel Observatory, scientists measured the spin of a stellar-mass black hole in a binary system with unprecedented precision. Black hole spin is a fundamental property that, unlike mass, is difficult to measure but contains crucial information about how the black hole formed and has evolved. Rapidly spinning black holes have larger ergospheres — regions where spacetime itself is dragged around by the rotation — and produce more energetic jets.

Blue dots in this COSMOS field image mark galaxies found by NuSTAR, NASA's Nuclear Spectroscopic Telescope Array, to contain supermassive black holes emitting high-energy X-rays. NuSTAR spotted 32 such black holes in this single field, adding them to a catalogue of hundreds detected across larger surveys. Most of these are "Compton-thick" black holes — objects so heavily obscured by surrounding gas and dust that they are invisible in optical and soft X-ray surveys, detectable only at the hard X-ray energies that NuSTAR specialises in. Before NuSTAR, this entire class of active galactic nuclei was largely unknown.

This animation illustrates the technique of reverberation mapping — also called echo mapping — which uses the time delay between X-ray variations from a black hole's corona and the corresponding reflections from its accretion disk to map the disk's geometry. The technique is analogous to using the echo delay of a sonar pulse to measure distances underwater, except that here the "sonar" is X-ray radiation from a corona of superheated plasma above the black hole, and the "echo" is the reflection off the accretion disk thousands of kilometres below. Different delays correspond to different disk radii, building up a three-dimensional picture of the disk structure.

When two black holes collide, they release enormous energy in the form of gravitational waves that propagate through the fabric of spacetime — literally squeezing and stretching space as they pass. On September 14, 2015, the LIGO detector in the United States recorded the signal from two black holes colliding 1.3 billion light-years away: a chirp lasting less than a second, rising in frequency as the black holes spiralled inward, then a single pulse as they merged. It was the first direct detection of gravitational waves and the first observation of two black holes in the act of merging — confirming a century-old prediction of Einstein's general relativity.

On June 15, 2015, NASA's Swift telescope caught the onset of a rare X-ray outburst from the stellar-mass black hole in the binary system V404 Cygni — its first major outburst in 26 years. As gas from a companion star falls toward the black hole, instead of flowing smoothly into the event horizon it piles up in an accretion disk, eventually triggering a runaway process that releases an enormous burst of X-ray energy before settling back into quiescence. V404 Cygni's 2015 outburst was the brightest X-ray transient event observed by Swift since its launch in 2004, attracting observations from telescopes around the world.

When a star passes too close to a supermassive black hole, tidal forces shred the star — a process called a tidal disruption event, or TDE. As the stellar debris falls toward the black hole, some of it forms an accretion disk and some is launched outward as a relativistic jet, producing a dramatic flare of radiation detectable across billions of light-years. This artist's concept illustrates the moment of disruption and the subsequent jet launch. TDEs allow astronomers to study black holes in otherwise quiescent galaxies that have no ongoing accretion — the equivalent of detecting an otherwise dark room by waiting for something to fall into it.

The beautiful spiral galaxy RX J1140.1+0307 in the Virgo constellation presents an intriguing puzzle: its nucleus is far less luminous than would be expected given its known black hole mass, and the variability pattern of its X-ray emission is inconsistent with standard accretion physics. Some astronomers proposed that this galaxy harbours an intermediate-mass black hole rather than a supermassive one — a class of black hole whose existence was, until recently, purely theoretical. Intermediate-mass black holes, if they exist in significant numbers, would help explain how supermassive black holes grew so quickly in the early universe.

This illustration shows another perspective on a tidal disruption event: the moment when a star's gravity is overwhelmed by the black hole's tidal forces as it passes too close, the star stretching into a long stream of debris before wrapping around the black hole and partially accreting into it. TDEs produce optical, ultraviolet, and X-ray flares that can outshine the entire host galaxy for months before fading. Modern time-domain astronomy surveys like the Zwicky Transient Facility are detecting TDEs at an increasing rate, building statistical samples that help constrain the properties of black holes in otherwise unremarkable galaxies.

This graphic series shows a computer simulation of a black hole from multiple stages — plasma slowly falling toward the hole with a magnetic field visible as white lines, the plasma accelerating as it falls, and the final moments before material crosses the event horizon from which no light can return. Magnetic fields play a crucial role in black hole accretion: they enable the transfer of angular momentum outward through the disk, allowing matter to spiral inward, and they help launch relativistic jets of material perpendicular to the disk plane that can extend millions of light-years into space.

This artist's concept shows a black hole with its accretion disk and a jet of hot plasma extending outward. Using NASA's NuSTAR space telescope and the ULTRACAM camera at the William Herschel Observatory, scientists measured the spin of a stellar-mass black hole in a binary system with unprecedented precision. Black hole spin is a fundamental property that, unlike mass, is difficult to measure but contains crucial information about how the black hole formed and has evolved. Rapidly spinning black holes have larger ergospheres — regions where spacetime itself is dragged around by the rotation — and produce more energetic jets.

Blue dots in this COSMOS field image mark galaxies found by NuSTAR, NASA's Nuclear Spectroscopic Telescope Array, to contain supermassive black holes emitting high-energy X-rays. NuSTAR spotted 32 such black holes in this single field, adding them to a catalogue of hundreds detected across larger surveys. Most of these are "Compton-thick" black holes — objects so heavily obscured by surrounding gas and dust that they are invisible in optical and soft X-ray surveys, detectable only at the hard X-ray energies that NuSTAR specialises in. Before NuSTAR, this entire class of active galactic nuclei was largely unknown.

This animation illustrates the technique of reverberation mapping — also called echo mapping — which uses the time delay between X-ray variations from a black hole's corona and the corresponding reflections from its accretion disk to map the disk's geometry. The technique is analogous to using the echo delay of a sonar pulse to measure distances underwater, except that here the "sonar" is X-ray radiation from a corona of superheated plasma above the black hole, and the "echo" is the reflection off the accretion disk thousands of kilometres below. Different delays correspond to different disk radii, building up a three-dimensional picture of the disk structure.

When two black holes collide, they release enormous energy in the form of gravitational waves that propagate through the fabric of spacetime — literally squeezing and stretching space as they pass. On September 14, 2015, the LIGO detector in the United States recorded the signal from two black holes colliding 1.3 billion light-years away: a chirp lasting less than a second, rising in frequency as the black holes spiralled inward, then a single pulse as they merged. It was the first direct detection of gravitational waves and the first observation of two black holes in the act of merging — confirming a century-old prediction of Einstein's general relativity.

On June 15, 2015, NASA's Swift telescope caught the onset of a rare X-ray outburst from the stellar-mass black hole in the binary system V404 Cygni — its first major outburst in 26 years. As gas from a companion star falls toward the black hole, instead of flowing smoothly into the event horizon it piles up in an accretion disk, eventually triggering a runaway process that releases an enormous burst of X-ray energy before settling back into quiescence. V404 Cygni's 2015 outburst was the brightest X-ray transient event observed by Swift since its launch in 2004, attracting observations from telescopes around the world.

When a star passes too close to a supermassive black hole, tidal forces shred the star — a process called a tidal disruption event, or TDE. As the stellar debris falls toward the black hole, some of it forms an accretion disk and some is launched outward as a relativistic jet, producing a dramatic flare of radiation detectable across billions of light-years. This artist's concept illustrates the moment of disruption and the subsequent jet launch. TDEs allow astronomers to study black holes in otherwise quiescent galaxies that have no ongoing accretion — the equivalent of detecting an otherwise dark room by waiting for something to fall into it.

The beautiful spiral galaxy RX J1140.1+0307 in the Virgo constellation presents an intriguing puzzle: its nucleus is far less luminous than would be expected given its known black hole mass, and the variability pattern of its X-ray emission is inconsistent with standard accretion physics. Some astronomers proposed that this galaxy harbours an intermediate-mass black hole rather than a supermassive one — a class of black hole whose existence was, until recently, purely theoretical. Intermediate-mass black holes, if they exist in significant numbers, would help explain how supermassive black holes grew so quickly in the early universe.

This illustration shows another perspective on a tidal disruption event: the moment when a star's gravity is overwhelmed by the black hole's tidal forces as it passes too close, the star stretching into a long stream of debris before wrapping around the black hole and partially accreting into it. TDEs produce optical, ultraviolet, and X-ray flares that can outshine the entire host galaxy for months before fading. Modern time-domain astronomy surveys like the Zwicky Transient Facility are detecting TDEs at an increasing rate, building statistical samples that help constrain the properties of black holes in otherwise unremarkable galaxies.