49 Fun Facts About Supernova

At its peak, a single supernova can briefly give off as much light as what?

A whole galaxy: for a few weeks one exploding star can match the light of the billions of stars around it, before fading over the following months.

When a massive star's core collapses in a supernova, what can it leave behind?

Neutron star or black hole: which one forms depends on how much mass the collapsing core holds, and some blasts leave nothing but a spreading cloud of debris.

Supernovae should light up the Milky Way about twice a century, so why has none been seen for 400 years?

Dust hides them: most of the Milky Way's stars sit behind thick clouds in the galaxy's disc, which block visible light, so blasts on the far side never show up in our sky.

The last supernova seen inside the Milky Way, in 1604, bears the name of which astronomer?

Johannes Kepler: he was one of many who watched the blast of 1604, and his detailed account attached his name to it; none has been seen in our galaxy since.

In which satellite galaxy of the Milky Way did SN 1987A explode?

The Large Magellanic Cloud: the 1987 blast there was the nearest supernova in centuries, so astronomers have been able to watch a star's death and its aftermath unfold in detail ever since.

Astronomers expected a red supergiant, so what kind of star surprised them by exploding as SN 1987A?

A blue supergiant: old photographs showed the doomed star, Sanduleak -69 202, was a hot blue giant, a kind that theory had not expected to blow up, and it had vanished once the blast faded.

Walter Baade coined the word 'supernova' around 1931 with which colleague, who also proposed dark matter?

Fritz Zwicky: he and Baade began using the word in lectures around 1931, and in 1933 Zwicky argued that unseen dark matter must be holding the Coma galaxy cluster together.

The Latin word 'nova', from which supernova derives, means what?

It refers to what looks like a temporary new star; the 'super-' prefix separates these blasts from far fainter ordinary novae.

Seen from China to Europe in 1006, the supernova in Lupus holds which record?

The brightest: it probably outshone every star people have ever written down, far brighter than Venus, and Chinese annals say objects on the ground could be seen by its light at night.

What did the supernova that Chinese astronomers recorded in AD 1054 leave behind?

The Crab Nebula: the blast of 1054 was bright enough to see in daytime, and its debris, about 6,500 light-years away, is still spreading outward today.

Which astronomer measured the 1572 supernova in Cassiopeia so carefully that it now carries his name?

Tycho Brahe: he showed the new star of 1572 lay far beyond the Moon, a blow to the old belief that the heavens never change.

Cassiopeia A marks a blast from around 1680, so what is odd about it?

Nobody reported seeing it: the star blew up inside our own galaxy, yet no certain record survives, though John Flamsteed may have logged it as a faint ordinary star in 1680.

A star that flared in 1885 proved to be the first supernova ever seen beyond the Milky Way, in which galaxy?

The Andromeda Galaxy: several observers noticed the star in August 1885, but only Ernst Hartwig in Estonia realised its significance and reported it, so he is counted as its discoverer.

Supernovae are thought to be a major source of which fast particles that rain down on Earth from space?

Cosmic rays: trapped in the wreckage of an exploded star, protons and other nuclei bounce back and forth across its blast wave until they near the speed of light and escape.

Chinese astronomers recorded the oldest known supernova, which lingered for eight months in AD 185, as what kind of star?

A guest star: the record gives a date and a place in the southern sky, which let astronomers eighteen centuries later match it to the debris cloud RCW 86, probably its remains.

Testing a new camera in 2016, Argentine amateur Victor Buso happened to photograph which fleeting event?

A supernova's first light: his run of short exposures of the galaxy NGC 613 showed a new point of light appear and brighten within about an hour, a moment professionals had long hoped to catch.

Any one galaxy hosts only a few supernovae a century, so how are new ones found weekly?

Scanning countless galaxies: surveys keep watch on so many of them night after night that blasts turn up all the time, though any single one produces only two or three a century.

What does the SNEWS project use to give early warning of a Milky Way supernova?

A network of neutrino detectors: these ghostly particles escape the collapsing core hours before the light breaks out, so detectors around the world can alert astronomers in time to watch.

In the supernova name SN 2003C, what does the C signify?

The third one reported that year: capital letters A to Z cover the first 26, then lower-case pairs such as aa and ab take over, which is how 2005 ran as far as SN 2005nc.

The Sun sits inside a huge cavity of thin gas carved out by a string of ancient supernovae, called the Local what?

Bubble: the first blasts went off over ten million years ago, when the Sun was far away, and only millions of years later did the Sun drift into the cavity they had cleared.

What decides whether a supernova is classified Type I or Type II?

Hydrogen lines in its light: Type II blasts show them and Type I blasts do not, a label read purely off the light, so stars that die in quite different ways can end up sharing the Type I tag.

A strong line of which element in its light marks a supernova as Type Ia?

Silicon: the star burns up in seconds and silicon is among the ash, so its line near 615 nanometres gives the type away, while Type Ib shows helium instead and Type Ic shows neither.

In a Type IIn supernova, the n describes the lines in its spectrum, so what does it stand for?

The narrow spectral lines come from ejecta ploughing into a small dense cloud the star shed shortly before dying.

What feature gives Type II-P supernovae their name?

The brightness holds roughly steady for months as hydrogen in the ejecta recombines; II-L 'linear' types lack it.

What kind of star explodes as a Type Ia supernova?

A white dwarf in a binary: it steals gas from its companion, or merges with a second white dwarf, until runaway fusion blows the whole star apart.

A white dwarf that grows past about 1.4 times the Sun's mass is doomed, a limit named after which astrophysicist?

Subrahmanyan Chandrasekhar: he worked on the limit as a student and Arthur Eddington attacked it in public in 1935, yet the result held and he went on to win a Nobel Prize.

Why are Type Ia supernovae so useful to cosmologists?

They work as standard candles: each one peaks at nearly the same true brightness, so how dim it looks from Earth reveals how far away its galaxy lies.

In 1998 two teams found distant supernovae dimmer than expected, which showed what about the universe?

Its expansion is speeding up: fainter than predicted meant farther away than a steadily expanding universe allows, a shock that earned the 2011 Nobel Prize in Physics.

Supernova surveys of the 1990s pointed physicists to which unseen ingredient, now thought to make up most of the universe?

Dark energy: nobody knows what it is, but it is the name given to whatever is driving the cosmos apart, and it is reckoned to make up more than two thirds of everything there is.

The radioactive decay of which isotope powers a Type Ia light curve?

Nickel-56: it decays to cobalt-56 with a half-life of about six days, and the cobalt's slower decay keeps the wreckage glowing for months.

The star left by the supernova of 1054 spins 30 times a second, flashing like a lighthouse, which makes it a what?

Pulsar: its spin is very gradually slowing, and the energy it sheds that way is almost exactly what keeps the whole cloud of debris around it glowing.

A massive star is doomed once its core turns to which element, whose fusion gives back no energy?

Iron: fusing it soaks up energy instead of releasing it, so the fires that held the star up go out and the core caves in within a second.

A sugar cube of a supernova's collapsed core would weigh as much as what?

A mountain: the collapse squeezes a Sun's worth of matter into a ball about 20 kilometres wide, so a sugar cube of the stuff would weigh around a billion tons.

In a core-collapse supernova, what carries away the vast majority of the energy?

Neutrinos: about 99% of the energy of the collapse streams away in a ten-second burst of these almost weightless particles, and the brilliant light is a minor side-effect.

Only stars of about eight Suns' mass or more die as core-collapse supernovae, so what will our Sun become instead?

A white dwarf: the Sun is far too light to crush its own core, so once its fuel runs out it will shrink to an Earth-sized ember and slowly cool.

Type Ib and Ic supernovae come from massive stars that had already lost what before they blew up?

Their outer layers: fierce winds or the pull of a companion star stripped these stars bare before their cores collapsed, which changes the fingerprint seen in the light of the blast.

Which nearby, well-known red supergiant is on the list of core-collapse supernova candidates?

Betelgeuse: the red shoulder of Orion is probably still tens of thousands of years from blowing, but when it does it should be bright enough to see in daylight.

Which massive star flared so brightly in the 1800s that it mimicked a supernova, yet survived?

Eta Carinae: during its Great Eruption it outshone nearly every star in the sky and threw off many Suns' worth of gas, yet the star itself came through intact.

In 2014 one of the nearest supernovae in decades was spotted from London, quite by accident, during what?

A student telescope lesson: astronomer Steve Fossey was showing undergraduates how to use the telescope when they noticed a new star in the galaxy Messier 82, about 12 million light-years away.

A 2003 study found that a supernova would have to explode within about 26 light-years to destroy much of Earth's what?

Ozone layer: gamma rays from so close a blast would break it down and let harsh ultraviolet sunlight reach the ground, but no star ready to explode lies anywhere near that close.

Chemical traces dated to the supernovae of 1006 and 1054 were reported in samples of what?

Antarctic ice: a core drilled at Dome Fuji showed nitrate spikes dated to both blasts, perhaps because their gamma rays made extra nitrogen oxides in the air, though such links remain disputed.

Much of the universe's gold is now thought to be forged not in supernovae but in collisions between what?

Neutron stars: when two of them collided in 2017, telescopes saw the glow of freshly made heavy elements, gold and platinum among them, flung out into space.

Astronomers found which element to be the most plentiful in the wreckage of the supernova Cassiopeia A?

Oxygen: the wreck is rich in it, and most of the oxygen around us, the air we breathe included, was forged in massive stars and flung out when they died like this.

What can a supernova's shock wave do to nearby clouds of gas?

Trigger the formation of new stars: the blast squeezes the gas until clumps collapse under their own weight, so the death of one star can set off the birth of many more.

The supernova iPTF14hls baffled astronomers from 2014 by doing what for more than 600 days?

Brightening again and again: a normal supernova fades within about 100 days, but this one peaked at least five times, and headlines dubbed it the zombie star.

The blast that ends a massive star's life draws most of its energy not from fusion but from what?

Gravity: the core's fall inward under its own weight releases an enormous burst of energy within seconds, and a small share of it is enough to blow the rest of the star apart.

Unusually energetic supernovae whose jets can set off long gamma-ray bursts go by what name?

Hypernovae: as the huge star's core caves in, jets launched from its centre punch out through the star and shatter it from the inside.

Magnetars left by exploding stars are leading candidates for producing which mystery signals?

Fast radio bursts: these flashes last mere thousandths of a second, and in 2020 one was traced to a magnetar inside our own galaxy, though whether all of them start this way is still debated.

Cassiopeia A's flash passed Earth over 300 years ago, so how did astronomers capture it in 2008?

As an echo off dust: light that set off in other directions bounced off distant clouds and reached Earth centuries late, and its spectrum showed what kind of star had blown up.