I’ve good news to report. A supernova discovered by Chinese observers last Tuesday in the galaxy NGC 3972 in the Big Dipper has become bright enough to see with modest equipment. Many dozens of supernovae or exploding stars are discovered every year in galaxies beyond the Milky Way, but most are too faint to see through the average telescope.
Not so with supernova 2011 by. By good luck, the Chinese observers spotted it some 10 days before it was predicted to reach peak brightness. At the time, the ‘new star’ was already bright and located in a relatively nearby galaxy, upping the chances it would get even brighter and become an easy target in smaller telescopes. Currently shining at magnitude 13.4 and still rising, the star is within range of 6-inch telescopes from dark, rural skies and 8-inch or larger scopes under moderate light pollution.
2011by – pronounced ‘Bee-Why’ rather than ‘by’ – got its name because it’s the 77th supernova discovered this year. Astronomers name supernovae after letters in the alphabet. The first discovered in the year 2011 is called 2011 A. After 2011 Z, letters are doubled up for the next series, so we get 2011 aa, ab … az and then 2011 ba, bb … bz and so on through 2011 zz. Add them up and you get slots for 702 supernovae in a year, a number that I’m quite sure has never been touched. 241 supernovae have been reported thus far this year.
There are several types of supernovas, but this one is what astronomers call Type Ia. Before it exploded, 2011 by was an impossibly faint white dwarf star invisible in even the largest telescopes. White dwarfs are typically the size of planets, but contain a sun’s worth of matter. When one is orbited closely by a companion star, the dwarf’s gravity is strong enough to pull hydrogen gas, the main ingredient of stars, from the companion. The gas piles up on the surface of the dwarf until the its mass reaches a critical limit of 1.4 times the sun’s mass.
When that occurs, the star begins a process of catastrophic nuclear fusion – burning if you will – and becomes so incredibly hot, it heats up and explodes in one titanic blast. The energy released in the explosion causes the star to grow some 5 billion times brighter than the sun, bright enough to see across millions of light years. Considering that 2011 by’s home galaxy is 55 million light years away, that’s one brilliant beacon!
I hope you’ll find the photo and maps useful for locating the supernova. NGC 3972 is a rather dim, 12th magnitude galaxy; the supernova looking like a ‘star’ pinned to its northern edge. In 8-inch scopes and larger, it’s a very cool sight, especially when you realize what you’re looking at. To follow 2011 by’s progress through photos and brightness changes, I highly recommend David Bishop’s Latest Supernovae site.
OK Bob, that’s great if you own a decent telescope. What’s out there we can see with just our eyes? Allow me to recommend a farewell look at Sirius, the brightest star in Canis Major the Great Dog and brightest in all the sky. Sirius is still visible early this month but will disappear in the twilight glow in a couple weeks for observers living in mid-northern latitudes. Look for it twinkling away in the southwest an hour after sunset in the darkening sky. If your location allows, you might also spy nearby Betelgeuse and the Belt of Orion. Don’t wait too long – if you do, you won’t see these shiny objects again until mid-August at dawn.