57 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.