What’s the biggest explosion in the universe?

The universe explodes.

Or some parts are. The night sky may appear calm, even serene, but this masks events of catastrophic and almost unimaginable magnitude. Across the galaxy and even in the cosmos itself, immense bursts of energy are occurring that could easily vaporize our planet. Fortunately, space is vast and the distance between these events is terrible and we reduce what we see to a faint glow, usually. It is very rare for our Earth to be directly hit by such explosions, but it does happen, but with usually minimal effect.

As Douglas Adams wrote in The Hitchhiker’s Guide to the Galaxy, “Don’t panic.”

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That said, some of these events may be at the origin of a few little worry. How concerned you should be about a given cosmic paroxysm depends on how powerful it is – and therefore how close it is to posing a planetary danger. With that in mind, let’s run through the Rogues’ gallery of astrophysical assaults, ranking them in order of destructive potential.

Locally, the sun is capable of some epic tantrums. Solar storms are flares that release some of the energy stored in the sun’s powerful magnetic field. These can create intense, localized explosions called solar flares, or much more powerful and dangerous coronal mass ejections, which spread over a much larger volume. Both generate high-energy subatomic particle explosions that can impact Earth’s magnetic field, causing widespread problems such as power outages, loss of satellites, and more.

They also create spectacular auroras, so there’s at least one benefit.

How much energy is released during such an event? In just a few hours in 2003, the most powerful solar flare ever measured directly released as much energy as the entire sun did in about a fifth of a second. This may not seem like much, but it is equivalent to simultaneously detonating about 17 billion megaton nuclear bombs. While it’s not enough to, say, melt the world, it’s still a phenomenal event.

Fortunately, solar storms of this magnitude are rare and can miss Earth even when they occur, but we still need to take them seriously.

Also remember that these are the First of all and therefore the smallest explosions on our list. Things get pretty apocalyptic from here.

When the sun eventually runs out of nuclear fuel and dies, in about seven billion years (mark your calendars), it will undergo a series of short-lived flares and eventually disappear, cooling for several billion more years. But some stars are much more tumultuous.

A white dwarf is the core of a star that was once like the sun, now exposed to space. This object is massive and tiny, giving it Herculean gravity. If it is in orbit around a normal star, it can siphon off material which then accumulates on the surface of the white dwarf. If enough material accumulates, it can be compressed so hard that it triggers nuclear fusion. The result is a very powerful explosion called a nova. When it explodes, it can emit as much energy as the sun for several centuries.

I will note that there are also recurring novae, which explode again and again, some even millions of times.

Even though novae are powerful, some stars Really go out with a bang. A supernova occurs when a massive star ends its life. The stellar core collapses, releasing a truly staggering amount of energy that causes the star to explode; in an instant, several octillion tons of matter are thrown outward at an appreciable fraction of the speed of light. The total energy released can be millions of times that of a nova, enough to eclipse an entire galaxy of billions of stars.

A nova-like situation can also become a supernova: if enough material accumulates on the surface of a white dwarf, the ensuing explosion can be so large that it tears the star itself apart, coincidentally exploding with an energy roughly the same as a core-collapse supernova.

Being near a supernova can ruin your day. It’s not clear exactly how far away you need to be to have a detrimental effect on our planet, but about 160 light years of space between us is probably a good estimate. This happens quite rarely, but close calls to have It happened: radioactive elements were found in seafloor material that could only be created in a supernova, meaning that a few million years ago at least one star flipped its lid close enough to Earth to spray us with a few hundred tons of mildly radioactive material. It’s not really dangerous – we’re still here, after all – but it’s sobering to think that something so powerful could hit us from more than a quadrillion miles away.

We have also been hit by a cosmic monster more recently. In December 2004, astronomers were shocked when a huge burst of energy swept across Earth, shaking up our planet’s magnetic field and increasing the ionization of its atmosphere. The culprit was a magnetar, a super-magnetized neutron star located about 50,000 light years away. For reasons still poorly understood, these ultradense objects – each about the mass of our star, squeezed into a strange, city-sized ball of degenerate quantum matter – experience starquakes in which the matter on the surface moves much like an Earthquake. This shift may only be a centimeter or so, but the enormous mass and ridiculously strong gravity (billions of times that of Earth!) release large amounts of energy, mostly in the form of gamma rays and

Black holes are also on this list, surprisingly. Core-collapse supernovae can form stellar-mass black holes, and the birth announcement is strong: A gamma-ray burst is the impulsive release of supernova-level energy, but instead of exploding in all directions, the burst is concentrated into a pair of tightly focused beams. These are more dangerous and more remote than the previous items on our list; less than 6,000 light years away, it becomes risky. They are so intense that they can be seen at incredible distances; one of them, called GRB 080319B, erupted 7.5 billion light years from Earth. Yet, even from so far away, he was briefly visible with the naked eye!

Sometimes stars get too close to a large black hole and gravity can tear them apart. Called tidal disruption events, these also erupt with energies close to those of a supernova. Astronomers have discovered quite a few, all (so far) fortunately in very distant galaxies.

But it’s hard to beat when two supermassive black holes collide. This can happen when two large galaxies collide; their central monsters can eventually merge, creating a larger black hole. When this happens, a substantial fraction of their mass, around 10%, is instantly converted into energy. This amount of energy is enormous, path beyond what the human mind can comprehend; the explosion resulting from the merger of two black holes of one billion solar masses emits as much energy as the sun in three billion trillion years. This number stopped me in my tracks; my brain started to panic and spin in circles in my skull. It’s much more than the energy emitted by every star in the entire universe. This is literally the most powerful bong since the big one.

Why didn’t we see one of these explosions? All this energy is emitted as invisible gravitational waves, ripples in the structure of the universe. These giant waves get weaker with distance, and such mergers are rare enough that they tend to occur billions of light years away.

This all sounds rather violent, doesn’t it? But keep hope! There is a cycle in the universe. When stars explode, they create and disperse heavy elements such as iron, calcium, etc., all of which are necessary for life as we know it, and in fact, your blood and bones exist because of these explosions. Supernovae can also compress interstellar gas around them, contributing to the formation of new stars; black hole flares can do the same.

These cosmic explosions can ostensibly herald a catastrophic end, but they can also usher in a new beginning. I find this rather comforting.