It’s a great time to observe the sky if, like most guys, you love explosions. Last week the brightest nova in six years went kaplooie right overhead in the constellation of Delphinus the Dolphin. It was bright enough to appear to the naked eye, although it has now faded to be a marginal object, except through binoculars.
I would love to tell you exactly where to look. But this new dim star is located among three faint constellations: Sagitta, Vulpecula and Delphinus. You’ll never find it.
Still, it’s cool that enough hydrogen gas was sucked from a companion star to the surface of a tiny white dwarf that it suddenly ignited like a giant H-bomb the size of our planet. A nova such as this does not destroy the white dwarf star. Indeed, this collapsed star can start the process of accreting material anew, perhaps to display another nova dozens or hundreds of years hence.
A totally different ballgame is being played out in the lovely spiral galaxy M74. That’s where a supernova is unfolding. This time the cause is the collapse of a massive star, identified before it blew up as a giant with 17,000 times the Sun’s brightness. A supernova explosion destroys the star and any unfortunate planets in the neighborhood.
A supernova goes off in each galaxy once a century, on average. Since there are millions of galaxies easily in view, it’s not that uncommon to observe one erupting someplace. The fun lies when a supernova happens in a nearby galaxy – say, within 100 million light-years of us. That’s what’s occurring right now, a mere 34 million light-years distant.
So to sum up, a nova is now going off overhead in our own galaxy, while a supernova currently blows in a nearby galaxy.
Of course, the first question that comes to mind is: What if a supernova happened in our own Milky Way galaxy? Wouldn’t that be awfully bright – even dangerous?
Could be. We’ve not had a supernova anywhere in our galaxy for over four centuries – none since the telescope was invented. The last happened in 1604 and, interestingly enough, the previous supernova erupted that same lifetime, in 1578: a lot of fun for sky observers like Kepler and Galileo.
In our own lifetimes, the closest happened in our satellite galaxy, the Large Magellanic Cloud; its light first reached us on February 23, 1987. This supernova in the outskirts of the Tarantula Nebula, about 168,000 light-years away, was too far south to be seen from here. I brought a group of people close to the Equator to view it that winter. Had to: It was the only naked-eye supernova in the past 384 years.
As for the Milky Way, we’re watching some pretty hefty stars like Betelgeuse and Eta Carinae, which could pop any time. Our galaxy is overdue.