Dual Supernovae Light Up June Nights: Part 1
By: Bob King | June 8, 2016
Supernovae are popping up everywhere! Two stars flamed out millions of years ago and at least one is an easy catch right now in amateur telescopes.
Type Ia Supernova 2016coj in NGC 4125 is now bright enough to see in amateur telescopes.
You'll find it 11.7″ NE of the galaxy's nucleus. NGC 4125 lies about 72 million light-years from Earth.
William Wiethoff
Recent years have seen a blizzard of new supernovae discoveries from dedicated robotic searches by both amateurs and professionals. If you have any doubt, David Bishop's excellent Bright Supernova site lists 3,471 reported in 2015. Already this year, we're up to 2,910!
Sorting through them to find visual candidates takes more time that it used to, but I'm not complaining. Among the ubiquitous 18th- and 19th-magnitude candidates there are always a few bright enough to spot in an 8-inch or larger telescope. On May 28th, two new exploding stars were discovered, SN 2016coj in NGC 4125 (a 10th-magnitude elliptical galaxy in Draco) and SN 2016cok in the bright spiral M66 in Leo, by the automated Lick Observatory Supernova Search (LOSS).
SN 2016coj's initial brightness of ~15.5 magnitude didn't immediately shout "Hey, look at me!" But in recent days, the Type Ia supernova brightened steadily to its present magnitude of 13.6, making it fair game for 10-inch and even 8-inch telescopes.
Several nights back, I took a look at the host galaxy in my 15-inch (37-cm) reflector. Its location near a 6th-magnitude star a short distance north of the Big Dipper's bucket made the finding easy. When I used 142×, the supernova presented itself almost immediately as a "second nucleus" about 11.7″ northeast of the true nucleus, a tiny kernel of light buried in the galaxy's core. When the seeing steadied, the supernova stood out crisply, a sharp point compared to the slightly fuzzy galactic nucleus. Here before me eyes was the end of a life, a white dwarf blown to bits in a tremendously powerful explosion brought on by ... weight gain.
Out With a Bang
This illustration shows the stages of a Type Ia supernova explosion like that in SN 2016coj.
From left: a white dwarf accretes matter from a close companion until it reaches a super-critical
state when it exceeds 1.4 solar masses; a thermonuclear explosion ensues, wiping out the star;
and an expanding cloud of debris is all that's left.
NASA / CXC / M. Weiss
After feasting on its close companion star's atmospheric gases, the Earth-sized star accumulated enough material on its surface to exceed the Chandrasekhar Limit of 1.4 solar masses and undergo rapid gravitational collapse. Dire consequences followed as a runaway fusion reaction from the crushing heat and pressure raced through the star, destroying it in one titanic blast.
Since then, SN 2016coj has continued to brighten and should be an even easier target by the time you read this. Meanwhile, SN 2016cok in the familiar galaxy M66 in Leo has taken another path.
Another Dwarf Bites the Dust
Supernova 2016cok (beween the tick marks) was discovered in the bright, nearby galaxy M66
in Leo on May 28th, the same day as SN 2016coj was discovered. Unlike the latter, SN 2016cok's
brightness has remained nearly constant at about magnitude +16.5. The new object is located 61″
east and 34″ south of the galaxy's nucleus in an outer spiral arm. East is up and north at right.
Gianluca Masi