“When I had satisfied myself that no star of that kind had ever shone before, I was led into such perplexity by the unbelievability of the thing that I began to doubt the faith of my own eyes.” –Tycho Brahe
When we look out at galaxies throughout the Universe, we find that every so often — about once per century — a bright star flares up so brightly that it can, for a brief amount of time, outshine the entire rest of the galaxy!
What’s going on, of course, is not that a star is brightening, but that the very atoms composing a star are undergoing a runaway chain reaction of nuclear fusion, creating the infamous phenomenon known as a supernova!
In perhaps one of the worst strokes of luck, we haven’t seen a supernova go off in our own galaxy since the invention of the telescope! The last one, in fact, went off in 1604, and has long since faded from view. But thankfully, it isn’t just in visible light that we can learn about these objects: we can turn a myriad of telescopes sensitive to different wavelengths at the regions of sky where these supernovae were recorded, and see what they look like today!
The 1604 supernova was the last one visible from Earth with a human’s naked eye, and is shown here in a composite of visible light, X-rays, and infrared. We know, from the lack of a strong X-ray source (neutron star or black hole) at the center, that this explosion was probably a Type Ia, where a white dwarf star either merges or accrues enough matter and goes supernova!
Same deal for the one prior to that: SN 1572.
Visually unspectacular, the ultra-hot remnants of the exploded star have been blown off into space at breakneck speeds of thousands of kilometers per second, and are so hot that they emit X-rays! There’s also dust, present throughout the galaxy, which gets heated by the supernova explosion; that’s what glows in the infrared.
This supernova remnant, as you will immediately notice, looks nothing like the prior two, and for a good reason: it’s an entirely different type of supernova! The famed Crab Nebula, also known as Messier 1, wasn’t formed by a white dwarf getting too massive, but rather by an ultra-massive star burning through all of its nuclear fuel and dying in a core collapse supernova, blowing off tens of solar masses worth of material!
The collapsed core of this star has created a pulsar, one of the most spectacular clocks in the Universe, and bested for timekeeping purposes only by our atomic clocks on Earth!
Prior to that, there was the brightest supernova ever recorded on Earth: the one of 1006.
By this point, you should be able to tell that this was once a white dwarf and not a supermassive star, and you’d be correct! After 1,000 years, the “bubble” produced by this explosion is actually light years in size, and if it were our star that exploded like this, the edge of the bubble would be halfway to Alpha Centauri by now!
Again, just from looking at the X-ray image, 2000 years later, you can tell this was a white dwarf that exploded, and not an ultra-massive star.
But looking at these images got me curious: how much fun would it be to take a look at these supernova remnants in visible light only, like watching snapshots from a slow-motion cosmic fireworks show? Let’s go to the pictures!
From nearly 2000 years ago, the supernova remnant RCW 86 (from the 185 supernova) still has a small section of the outer “bubble” visible in visible light, as shown in red, above. Like the very end stages of a fireworks display, this is the last bit that would be visible with unmodified human eyes. (The blue is shocked X-ray gas.)
But apparently, a thousand years doesn’t necessarily change things all that much.
The 1006 supernova is nearly invisible in optical light, save for a thin ribbon and some very faint gas along the outer shell. (And, of course, all the stars visible in the image, too!) But the 1054 supernova, the only one we talked about as being a remnant from a supermassive star instead of from a degenerate white dwarf (that’s not a snark; they really are degenerate), has an entirely different story to tell.
That gorgeous image of the Crab Nebula I showed you earlier? That was entirely a visible light image! The outer layers of gas, rich in some of the lighter heavy elements — oxygen, carbon, nitrogen — create some beautiful, contrasting colors in the nebula as they get superheated and strewn across interstellar space.
But there’s a very rich story to be told in a myriad of wavelengths, as you can clearly see, from the bright X-ray source at the core to the warm dust traced out by the infrared telescopes. Visible light still tells a rich story for the Crab Nebula because of the sheer amount of gas and dust, as well as the energy that was released into it.
The 1572 supernova, with almost no gas and dust, tells a very different story.
Sure, they found the leftover, Sun-like star that got blasted by its companion which went supernova nearly 500 years ago, but visible fireworks? Not a trace.
So there’s some variety here, and this is well-exemplified by the 1604 supernova.
Not a bubble or a ribbon, but just a small region of the remnant contains some visibly glowing gas.
It seems like the one thing that’s missing — that I’d want to know about, anyway — is a supermassive explosion where that hot, visible dust were somehow stripped away. What would that look like?
Well, there weren’t any naked-eye supernova that have occurred in our galaxy since 1604, unfortunately. But in the late 17th Century, there was a supernova that occurred, and while its remnant is very faint optically, it’s the loudest radio source (right, Nicole?) in our galaxy: Cassiopeia A!)
Located an estimated 11,000 light years away, this supernova remnant is already over 10 light years across, making it larger than the Crab Nebula in just a third of the time! With the strongest radio source (other than the Sun) in our galaxy, there must be either a fantastic neutron star or black hole at the center.
But today, I wanted to show you the fireworks.
Not from a simulation or visualization, though. The incomparable Hubble Space Telescope has an amazing, long-exposure photograph of the visible light left behind from this supernova explosion, which you have got to see, because it truly shows you why I call these explosions “cosmic fireworks.”
This is fantastic! If you have all day, I suggest you play around with the full, amazing-resolution version. I did, and so I decided to make it a little more interesting for you, by zooming in, bit-by-bit, to one of the most interesting spindly regions inside this amazing stellar show.
Let’s focus first on the bubble.
And now let’s take a look at the triple-layered structure atop that bubble. Look for little “columns” or “pillars” where some regions of space have greater densities of gas and/or dust than others.
And finally, let’s zoom in to focus on that green region you see.
As always, click on any of the images on this page to get the fullest-resolution version available, and I hope you enjoyed the fireworks show! It’s been far too many centuries since the last visible supernova in our galaxy; will we get one in our lifetime? As the Count of Monte Cristo concludes:
all human wisdom in contained in these two words: wait and hope.
Until then, enjoy the show!