97 Fun Facts About Black Hole

What is the boundary around a black hole beyond which nothing can affect an outside observer called?

Event horizon: to a distant watcher, anything falling toward it seems to slow and freeze at the edge, never quite crossing, as its light fades away.

What is the name of the supermassive black hole at the centre of the Milky Way?

Sagittarius A*: thick dust hides the galaxy's centre from ordinary telescopes, so astronomers found it in 1974 by its radio waves, which pass straight through.

The first photograph of a black hole, released in 2019, showed the object at the heart of which galaxy?

Messier 87: a century before the photo, astronomers had spotted a strange straight ray poking from its core, now known to be a jet of gas blasted out by that black hole.

Which physicist is credited with popularising the term "black hole" in 1967?

John Archibald Wheeler: by his own account he kept saying "gravitationally completely collapsed object" in a lecture until someone in the audience suggested "black hole", and he took it up.

If the Sun were swapped for a black hole of equal mass, what would Earth's orbit do?

Stay the same: gravity depends on mass, not size, so Earth would keep circling exactly as before, only in the cold and dark. A black hole pulls no harder than the star it replaced.

Which English clergyman-astronomer proposed in the 1780s that a body could be too massive for light to escape?

John Michell: he pictured light as tiny particles that a star's gravity could slow, so a big enough star would drag its own light back and stay invisible.

Karl Schwarzschild found the first exact solution of Einstein's equations while serving in which First World War army?

Germany: a volunteer in his forties, he posted the solution to Einstein from the Russian front, and a surprised Einstein replied that he had not expected the exact answer to be so simple.

An "Einstein-Rosen bridge" in the maths of black holes goes by what popular name?

Wormhole: Einstein and Nathan Rosen described the shortcut in 1935, but later work showed it would pinch shut too fast for even light to get through.

How does the temperature of Hawking radiation depend on how heavy the black hole is?

Inversely proportional to mass: the lighter a black hole, the hotter it glows, so as one evaporates it heats up and shrinks ever faster, ending in a final burst.

Which object, discovered by a rocket-borne detector in 1964, became the first widely accepted black hole?

Cygnus X-1: a blue giant star there whirls around an unseen partner every 5.6 days, and that partner proved far too heavy to be anything but a black hole.

Kip Thorne collected a year's subscription to which magazine when Hawking conceded their black hole bet?

Penthouse: Hawking called the bet an insurance policy, because if black holes turned out not to exist and his life's work was wasted, he would at least win four years of Private Eye.

Which 2014 film sends its crew to planets orbiting a supermassive black hole named Gargantua?

Interstellar: physicist Kip Thorne wrote the equations behind its black hole, single frames took up to 100 hours to render, and the results were accurate enough to yield published scientific papers.

The 1979 film The Black Hole was the first movie from which studio to receive a PG rating?

Walt Disney: the film began years before Star Wars as Space Station One, a disaster movie in space in the mould of The Poseidon Adventure, and was shelved and reworked before it was shot.

Which Seattle band released the 1994 hit "Black Hole Sun"?

Soundgarden: singer Chris Cornell said the title came from a TV news anchor he misheard, and that he wrote the whole song in his head on the drive home.

Muse's 2006 single "Supermassive Black Hole" was written by which member of the band?

Matt Bellamy: the frontman's song turned up in the 2008 film Twilight, whose author Stephenie Meyer is a devoted Muse fan and has named the band as an inspiration for her novels.

Squeezed into a black hole, the Sun would have a Schwarzschild radius of roughly what size?

3 km: the real Sun is about 700,000 km in radius, so it would have to be crushed more than 200,000-fold, and it is far too light ever to collapse that far on its own.

The no-hair theorem describes a stationary black hole by mass, electric charge and what third number?

Angular momentum: that is, its spin. "No hair" means everything else about what fell in is lost from view, so a black hole made of matter and one made of antimatter would look exactly alike.

Who found the exact solution of Einstein's equations for a rotating black hole in 1963?

Roy Kerr: the New Zealander was 29 when he cracked it, and because the stars that collapse all spin, his is the solution that describes the black holes actually out there.

What is the region around a rotating black hole in which it is impossible to stay still called?

Ergosphere: space is dragged around the hole so hard that nothing inside can hold still, yet it lies outside the point of no return, so an object can dip in and leave carrying off some of the hole's spin energy.

Where around a black hole can gravity bend light into a full orbit?

Photon sphere: light there can circle the black hole several times before escaping, and physicists expect it to draw a thin, bright ring around the hole's dark shadow.

Roger Penrose won a 2020 Nobel for showing black hole formation is a robust prediction of which theory?

General relativity: Einstein never believed his own theory's black holes could be real, and it took Penrose, ten years after Einstein's death, to prove that they really can form.

A black hole's gravity bends the light of stars behind it, an effect astronomers name after which optical device?

Lens: the effect has exposed what looks like a lone black hole drifting through our galaxy, invisible itself, when it slid in front of a distant star and made that star brighten for months.

Which astronomer became only the fourth woman to win the physics Nobel, in 2020?

Andrea Ghez: for over two decades her team followed stars whipping around something unseen at the galaxy's centre. Only Marie Curie, Maria Goeppert Mayer and Donna Strickland had won before her.

Which observatory first directly detected gravitational waves on 14 September 2015?

LIGO: the waves came from two black holes colliding over a billion years ago, a crash that turned about three Suns' worth of mass into ripples in space within a fraction of a second.

In 2008, critics went to court to stop which machine, fearing it would create a black hole that swallowed the Earth?

The Large Hadron Collider: the case was thrown out, and physicists noted that cosmic rays have struck Earth at far higher energies for billions of years, and the planet is still here.

The English clergyman who imagined light-trapping stars in the 1780s also designed the apparatus later used for what?

Weighing the Earth: he built a delicate twisting balance for the job but died before using it, and it ended up with his friend Henry Cavendish, who finished the famous experiment in 1798.

Which celebrated astronomer told a 1935 meeting there should be a law of nature to stop stars collapsing so absurdly?

Arthur Eddington: he was mocking a 24-year-old colleague's proof that heavy dead stars must keep collapsing. The young man was right, and Eddington's scorn may have set the idea back by decades.

The 1.44-solar-mass limit worked out by a future Nobel laureate applies to what kind of star?

White dwarf: a 19-year-old student worked the limit out in 1930 on the voyage from India to England, showing that a dead star any heavier cannot hold itself up and must collapse further.

NASA's Chandra space telescope, launched in 1999, is named after which physicist?

Subrahmanyan Chandrasekhar: NASA ran a worldwide naming contest, and the winning entries came from an Idaho high-school student and a California teacher. The Raman among the options, also a Nobel winner, was his uncle.

Which Space Shuttle, later lost in an accident, carried the Chandra telescope into orbit?

Columbia: five seconds after liftoff an electrical short knocked out two engine controllers, and only their backups kept the climb going. Eileen Collins, the first woman to command a shuttle, was in charge.

In the 2009 Star Trek reboot, which substance creates the black hole that destroys Vulcan?

Red matter: the villain drops it down a shaft drilled to the planet's core. As astronomer Phil Plait pointed out, a real black hole made by crushing the entire Earth would be only about the size of a marble.

The word "quasar" is a contraction of what phrase?

Quasi-stellar radio source: the first ones were radio signals traced to what looked like faint stars on photographs. Many quasars found since are radio-quiet, so the full name no longer even fits.

Roughly how far from Earth is the black hole at the centre of the Milky Way?

26,000 light-years: the Milky Way's disc is about 100,000 light-years across, so we live roughly halfway out from the middle, in the quiet suburbs of our galaxy.

The detectors that first caught two black holes colliding measure the ripples by firing what down 4 km tunnels?

Laser beams: Einstein, who predicted the ripples, thought them far too faint ever to detect, yet the laser light reveals a tunnel changing length by less than a ten-thousandth of a proton's width.

Roughly how massive is the Milky Way's central black hole?

About 4 million Suns: all of it is packed into a space no bigger than our solar system, which astronomers worked out from how fast nearby stars whip around it.

About how massive is the black hole shown in the famous first photograph, released in 2019?

6.5 billion solar masses: the heavier a black hole, the bigger its shadow, and this one's bulk makes it one of the largest in our sky, which is why it was picked for the first picture.

"Spaghettification" describes what happening to an object that falls toward a black hole?

Being stretched thin by tidal forces: gravity tugs far harder on the near end of a falling body than on the far end. Oddly, the biggest black holes are the gentlest, and an astronaut could drift into one intact.

In 2004 Hawking conceded a bet to John Preskill with an encyclopedia of which sport?

Baseball: the wager was over whether information that falls into a black hole is lost for good, so the forfeit was an encyclopedia. Preskill is a big baseball fan, and Hawking joked that he should really have handed over the ashes.

Which Stephen Hawking book stayed on a British bestseller list for 237 weeks?

A Brief History of Time: Hawking set out to write a physics book that would sell in airport bookshops, and it worked. The book was translated into some 40 languages and sold millions of copies.

In 2022, which European star-mapping spacecraft revealed the nearest black hole then known, about 1,600 light-years away?

Gaia: it caught a Sun-like star wobbling around something ten times its mass that gave off no light at all. This black hole is dormant, feeding on nothing, so only that wobble gave it away.

Astronomers understand quasars to be what kind of object?

Feeding supermassive black holes: the black hole itself is dark, but the gas swirling into it glows so fiercely that a quasar can outshine its entire home galaxy a hundred times over.

Black holes bigger than stellar ones but smaller than the giants in galactic cores are called what?

Intermediate-mass: astronomers call them the missing link between small black holes and giants, yet they are fiendishly hard to find. One strong candidate betrayed itself by tearing apart a star that strayed too close.

Hypothetical primordial black holes are thought to have formed when?

Soon after the Big Bang: within the first second, pockets of hot matter may have been dense enough to collapse directly, no dying star required. The smallest would have evaporated long ago, but bigger ones might still be out there.

The hot gas spiralling into a black hole shines most strongly in which part of the spectrum?

X-ray: friction superheats the gas until it glows in X-rays rather than visible light. Earth's atmosphere soaks those up, so the telescopes that hunt black holes this way, like NASA's Chandra, have to work from orbit.

The note from the Perseus cluster black hole detected by Chandra in 2003 is how many octaves below middle C?

57: a piano spans only about seven octaves, so no ear will ever catch this B-flat. The black hole's outbursts push pressure waves through the hot gas around it, which Chandra saw as ripples.

What likely makes galaxy OJ 287 flare roughly every 12 years?

Two supermassive black holes orbiting each other: astronomers think the smaller one crashes through the disc of gas around its giant partner twice every 12 years, and each plunge sets off a flare brighter than a trillion stars.

Penrose's 1969 cosmic censorship conjecture proposes that singularities formed by collapse are always what?

Hidden behind an event horizon: an exposed or "naked" one would put a place where physics breaks down in plain view, and the theory could no longer predict what happens next. So nature, Penrose guessed, plays censor.

How does the average density inside a supermassive black hole compare with a stellar black hole's?

Much lower: a black hole's width grows in step with its mass, so its volume balloons far faster than the mass inside. Averaged out, the very biggest are less dense than water.

Who first argued in 1972 that black holes should have an entropy proportional to their surface area?

Jacob Bekenstein: two years later Hawking's discovery that black holes glow with heat confirmed the hunch and fixed its missing constant at exactly one quarter. The formula now carries both their names.

Katie Bouman led development of which algorithm for imaging black holes, first presented in 2016?

CHIRP: Bouman unveiled it in 2016 to stitch a picture from telescopes scattered across the globe. The famous 2019 image was in fact made with other methods, by four teams working blind to one another so no one's hunch could shape it.

The light in the first black hole photo left about 55 million years ago, when dinosaurs were what?

Already extinct: the asteroid struck 66 million years ago, so the light set off about ten million years later and has been travelling ever since. The photo shows the black hole as it was then, not as it is today.

Stellar black holes are typically the remnants of what event?

A supernova explosion: only the heaviest stars end this way. While the star's core collapses inward to form the black hole, the blast around it can outshine an entire galaxy for days or even months.

What do physicists' equations predict lies at the very centre of a black hole?

A singularity is a point where matter is crushed to infinite density; it may be a real object or just a sign the theory is incomplete, and astronomers do not yet know which.

Astronomers have watched the star S2 lap a giant black hole in roughly how long?

16 years is all S2 needs, so telescopes have followed it right round; on its 2018 closest pass it hit almost 3% of light speed and gravity shifted its light to longer wavelengths, just as predicted.

A black hole just hot enough to out-radiate the cosmic background and shrink would weigh roughly as much as what?

The Moon marks the line: a black hole of about that mass glows at the 2.7 kelvin of the cosmic background, so anything star-sized soaks up more than it gives off and keeps growing.

What do astronomers call the glowing whirlpool of superheated gas that spirals around a feeding black hole?

Accretion disk light is how astronomers find black holes: the hole itself emits nothing, but the gas circling it grows hot and bright before it falls in.

Which physicist co-wrote the 1939 paper showing a heavy enough dying star must collapse into a black hole?

Robert Oppenheimer and his student Hartland Snyder published it on 1 September 1939, the very day the Second World War began, and it was scarcely noticed at the time.

How did the telescopes behind the first black hole photograph send their data for processing?

On hard drives by plane, a low-tech method engineers jokingly call a sneakernet. The drives went to centres such as MIT's Haystack Observatory, where computers lined the recordings up.

Squeezed small enough to become a black hole, the whole Earth would be roughly the size of what?

A marble: all of Earth's mass would have to fit inside a radius of about 9 millimetres, a figure physicists call the Schwarzschild radius.

If the Milky Way's central black hole sat where the Sun is, how far out would it reach?

Short of Mercury: astronomers calculate the black hole is about 14 million miles across, so it would sit comfortably inside the innermost planet's orbit despite its enormous weight.

Stephen Hawking's memorial stone, carved with a black hole equation, lies in which London church?

Westminster Abbey received Hawking's ashes in 2018, interred in the nave beside the grave of Charles Darwin.

For a clock placed close to a black hole, what happens to time compared with clocks far away?

It runs slower: the stronger the gravity, the more time drags, an effect Einstein predicted and precise clocks at different altitudes have since confirmed.

Why will the Sun never collapse into a black hole when it runs out of fuel?

Too little mass: only a star about 20 times heavier than the Sun leaves a core weighty enough to collapse that far. The Sun will swell into a giant instead.

NASA says the smallest black holes may be the size of an atom yet have the mass of what?

A mountain packed into a speck is NASA's picture of a primordial black hole, a kind that remains a theory because none has yet been found.

Which neighbouring spiral galaxy hides a central black hole far heavier than the Milky Way's own?

Andromeda's central black hole packs in roughly 140 million Suns, and the galaxy around it lies about 2.5 million light-years away.

Which astrophysicist and planetarium director wrote the 2007 essay collection Death by Black Hole?

Neil deGrasse Tyson assembled the book from columns he wrote for Natural History magazine between 1995 and 2005.

Which space telescope, launched in 1990, found giant black holes in the cores of most galaxies?

Hubble found the hidden giants so reliably that astronomers could tie each one's mass to the properties of the galaxy around it.

Which city-sized remnant is left when a collapsing stellar core is too light to become a black hole?

Neutron star material is so dense that a matchbox of it would come to about 3 billion tonnes. A remnant above roughly three Suns cannot hold itself up and collapses further.

Stephen Hawking predicted in 1974 that black holes are not eternal but will very gradually do what?

Evaporate they must, Hawking showed, because black holes leak a faint glow of particles. One as heavy as the Sun would take far longer than the universe has existed to vanish.

The 1780s idea of a star that traps its own light leaned on whose theory of light as tiny particles?

Isaac Newton's light particles, the argument ran, would be pulled back by a star's gravity the way a thrown stone is, so a heavy enough star could hold on to them.

When two black holes spiral into each other, as detectors first saw in 2015, what is left behind?

A single larger one: the first collision ever recorded joined black holes of 36 and 29 Suns into one of 62, with the missing three radiated away as gravitational waves.

A black hole is an extreme warp in the four-dimensional fabric that physicists call what?

Spacetime, in Einstein's picture, is bent by anything heavy, and a black hole bends it so steeply that every path inside leads further in.

What do astronomers call the thin streams of plasma some black holes fire out at near light speed?

Jets emerge along a black hole's poles and carry off much of the energy of the gas swirling inward.

Many black holes betray themselves by stripping hot gas from what kind of close neighbour?

A companion star locked in a tight pairing gives the game away: its stolen gas heats up and glows fiercely on the way in, lighting up an object that is otherwise invisible.

A telescope at which remote, bone-dry spot helped photograph the Milky Way's central black hole?

South Pole air is thin, bitterly cold and very dry, which leaves little water vapour to blur the faint millimetre waves the dish collects.

The first black hole ever photographed sits in a giant galaxy within which zodiac constellation?

Virgo hosts the galaxy, a supergiant elliptical that contains several trillion stars.

Which Indian city's notorious prison reportedly gave collapsed stars the name black hole?

Calcutta's Black Hole was notorious as a cell prisoners entered and never left alive, a comparison one physicist reportedly drew in the early 1960s.

What name is given to a quasar whose stream of particles happens to point almost directly at Earth?

Blazar is a blend of the names BL Lacertae and quasar, coined in 1978. Looking straight down the stream makes such an object appear far brighter than it otherwise would.

Which brilliant flashes from deep space are thought to mark a massive star imploding into a newborn black hole?

Gamma-ray bursts were first picked up in 1967 by Vela satellites, which had been built to catch covert nuclear weapons tests.

A 2021 image of the first photographed black hole used polarised light to map which invisible feature?

Magnetic fields show up in the image as swirling lines around the bright ring, and such fields are one proposed engine for the outflows a black hole can launch.

What do astronomers call the lightless central patch of a black hole image, about twice as wide as the hole?

The shadow forms because light passing too close is swallowed while light a little farther out is bent around the hole, which enlarges the lightless patch.

The twin detectors that first sensed colliding black holes sit in Washington state and which other state?

Louisiana's detector at Livingston caught the wave seven milliseconds before its twin about 3,000 kilometres away at Hanford.

ALMA, a giant array that helped photograph a black hole, sits high in which South American desert?

Atacama's Chajnantor plateau lifts the array's 66 dishes to about 5,000 metres above sea level.

The Keck telescopes, which tracked stars circling the Milky Way's black hole, stand on which Hawaiian volcano?

Mauna Kea puts the twin telescopes 4,145 metres above the Pacific, and their sharp vision let astronomers follow individual stars around the unseen object.

Thick dust hides the Milky Way's centre, so astronomers track stars near its black hole in which kind of light?

Infrared light slips through the dust that blocks nearly all visible light from the heart of the galaxy, which is how decades of stellar orbits there were recorded.

Stephen Hawking showed that black holes glow faintly by applying which branch of physics to them?

Quantum mechanics makes a black hole behave like a warm object, Hawking showed, radiating particles as though it had a temperature.

Which French mathematician independently suggested in 1796 that a big enough star could be invisible?

Pierre-Simon Laplace floated the idea in a book speculating on how the Solar System formed, and supplied the mathematics only when another astronomer asked for it.

Which Max Planck astrophysicist shared the 2020 physics Nobel for tracking stars around the Milky Way's centre?

Reinhard Genzel's group spent decades following how stars move at the heart of the galaxy, motion that betrayed an unseen and extremely compact object.

Which MIT physicist shared the 2017 physics Nobel for pioneering the detectors that heard black holes collide?

Rainer Weiss realised such an instrument would need arms kilometres long, and he received half of the prize money while his two co-winners split the rest.

What name describes how a spinning black hole twists nearby space around with it, an effect derived in 1918?

Frame-dragging grows stronger the closer you get to a spinning mass, and near a black hole it sweeps gas and light around in the direction of the spin.

Which quasar, first logged as a faint blue star in Mexico, hides one of the heaviest black holes known?

TON 618 is short for Tonantzintla 618, its entry in a Mexican observatory's catalogue, and estimates of its black hole run to tens of billions of Suns.

Which object, bright enough to see through a 6-inch amateur telescope, was the first quasar ever identified?

3C 273 outshines its entire host galaxy more than sixteen times over, which is how light from billions of light-years away still reaches a backyard telescope.

What do physicists call a hypothetical black hole made from pure light rather than matter?

Kugelblitz is German for ball lightning: enough radiation aimed at one spot would warp space so strongly that the energy traps itself, with no ordinary material required.

Which French astrophysicist drew the first simulated image of a black hole in 1978 using India ink?

Jean-Pierre Luminet fed the mathematics to an early computer and inked the result himself. Four decades later the first real photograph bore out his predictions.

Astronomers time which natural cosmic clocks to catch a gravitational hum likely made by giant black hole pairs?

Pulsars tick so steadily that a passing gravitational wave shows up as pulses arriving slightly early or late. In 2023 several teams reported evidence of the hum.

Which Bell Labs engineer, hunting telephone static in the 1930s, first detected signals from our galaxy's centre?

Karl Jansky traced the hiss to the heart of the galaxy, yet his employer could not justify the cost of studying it any further.

The ripple from the first black hole collision ever recorded shifted the detectors by a thousandth the width of what?

A proton's width divided by a thousand: in proportion, that is like the distance to the nearest star beyond the Sun changing by the breadth of a single hair.