Why wait around for Betelgeuse to blow up to see a supernova in your lifetime? If you have a 6-inch telescope and dark sky you can see one right now. Two actually. Both are visible in the western sky at nightfall in the neighboring constellations Virgo and Coma Berenices.
The first of the pair, dubbed SN (for supernova) 2020nlb, was discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) on June 25 in the 10th magnitude galaxy M85. Located in Coma Berenices 60 million light years from Earth, M85 is an elliptical galaxy a quarter again as large our Milky Way. The “M” stands for Charles Messier, an 18th century French astronomer who compiled a list of galaxies, star clusters and nebulae he stumbled on during searches for his favorite prey, comets.
On July 1, Japanese amateur astronomer and prolific supernova hunter Koichi Itagaki nabbed SN 2020nvb in NGC 4457, a spiral galaxy in Virgo located about 55 million light years away. Each of these newly discovered supernovae occurred in a close double star system where a tiny, superdense white dwarf star orbits a normal star like our sun. The dwarf is only about the size of the Earth, but its matter is packed so tightly it has nearly the same mass as the sun. You’d need a huge crane to lift even a thimbleful!
The dwarf’s powerful gravity siphons material from its companion onto its surface until the added weight and pressure of the stolen material initiates runaway nuclear fusion within the dwarf and boom! — it explodes cataclysmically as a supernova.
Like breakfast cereals, supernovas come in a variety of types but are broadly divided into Type Ia (white dwarf explosions in close pairs) and Type II (massive star blasts like Betelgeuse). Both 2020nlb and 2020nvb are Type Ia supernovae, among the brightest “candles” in the universe. In fact, the most luminous supernovae routinely outshine their entire host galaxy! Betelgeuse is a standalone, gigantic star. One day it will run out of nuclear fuel, stop “burning” and then collapse and explode as a supernova as bright as the gibbous moon.
The M85 supernova has been getting brighter and brighter since discovery and now shines at magnitude 12.2, within the range of a 6-inch telescope from a dark sky. It’s located right next to a 13.1 magnitude Milky Way foreground star a short distance north of the galaxy’s center. The NGC 4457 supernova is even brighter at magnitude 11.9 and located a little northwest of the center of the galaxy’s nucleus.
Now that the moon is past full it’s on its way out of the evening sky, so you’ll have the darkness you’ll need to spot these distant explosions. I encourage you to start looking for the pair as soon as it gets dark when they’re highest in the sky and least affected by the atmosphere. Begin at Denebola, an obvious 2nd magnitude star about two fists (20°) high in the western sky at twilight’s end, and star hop to M85. Then use the photo to identify the supernova. Or use Epsilon Virginis. To reach NGC 4457 start at either Porrima or Eta Virginis in Virgo and use the detailed map below to star hop to this galaxy.
Use your lowest magnification while star-hopping. Once you’ve arrived at each galaxy increase the power to 100x or higher to pick out the supernovae. The next part’s the best. You get to imagine that the point of light you see is actually a star in the process of self-destruction, one of the most powerful and creative acts in the universe. Creative? You bet. Supernovae explosions seed interstellar space with lots of elements including familiar ones like iron, nickel, lead and gold. All that material regathers into great clouds of gas and dust called nebulae within which are born new generations of stars … and planets.