Dual Supernovae Light Up June Nights

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. 

A Stellar Conclusion

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

Ordinarily, the words "supernova" and "M66" heard in the same sentence would make a deep-sky hunter's blood pressure spike. It was here in February 1989 SN 1989B peaked at 12th magnitude, within range of even a 4-inch. Given the galaxy's relative proximity to Earth of 36 million light-years, any supernovae there have the potential to become bright, but this one has so far remained faint.

Farewell Blast

In a Type II supernova, an aging supergiant star runs out of nuclear fuel in its core, leading to a sudden collapse followed by a rebounding shock wave that rips the star apart. Some Type II events leave a neutron star or black hole remnant.
NASA / CXC / M. Weiss

Discovered by Ohio State's All-Sky Survey Automated Survey for Supernovae (ASAS-SN) at magnitude +16.6, SN 2016cok hasn't gotten any brighter than +16.4 as of June 4th.

It may still be on the rise, though. According to a recent notification from The Astronomer's Telegram, the supernova's spectrum indicates it was caught a few days before maximum.

While a perfect target for astrophotographers, the star presents a tough visual challenge at the moment. Maybe a 24-incher can pry this one loose, but until it cracks magnitude +15.5, I'll be sitting on the sidelines watching with interest.

SN 2016cok is a Type IIp supernova involving the collapse and explosion of an evolved supergiant star. But instead of fading at the regular rate, the IIp variety slows or “plateaus” (hence the p) for many days before resuming its normal decline in brightness. Has the supernova already plateaued or does a "brighter future" lie ahead?

M66 Wide and Detailed

This dual map will help you find the 9th-magnitude spiral galaxy M66 and SN 2016cok located midway between the naked-eye stars Theta (θ) and Iota (ι) Leonis. The left half shows a wide view, the right half is zoomed in. Stars at right shown to magnitude +7.5.
Bob King, Source: Stellarium

You can keep track of the progress of both supernovae at the Bright Supernova site. Click and search for "M66" or "NGC 4125" or go out the next clear night and have a look for yourself. When it comes to stellar explosions, M66 is a real champ with five recorded supernovae to its name since 1973.

Explosion Over the Bowl

Use the bowl of the Big Dipper to navigate to NGC 4125 and its bright supernova. Stars shown to magnitude +7.5.
Bob King, Source: Stellarium

I wish you much success in your supernovae hunt. As you slowly twist the focusing knob to bring SN 2016coj into sharp focus, consider that this pinprick of light shines some five billion times brighter than the Sun while material within the expanding debris cloud rushes outward at 9,500 miles per second (15,300 km/s). How fortunate that you and I just happened to be around to see it 72 million years later.

12 thoughts on “Dual Supernovae Light Up June Nights

  1. Bob-PatrickBob-Patrick

    Bob K.

    Another informative article. I like the Type 1a and Type 2 Supernova graphics with educational captions–very helpful for gray-headed know-nothings like myself. And the reality check in the last sentence keeps me on my toes: “How fortunate that you and I just happened to be around to see it 72 million years later”

    Bob P.

    1. Bob KingBob King Post author

      Hi Bob,
      Thank you very much. We are fortunate to be alive at a time when good equipment is relatively easy to afford and news of new sky phenomena can be quickly shared!

  2. Jim-MayercakJim-Mayercak

    Bob King, I hope you see this. I was showing my wife Lynnelast night’s image of NGC 4215 as per your very recent article. She thinks that she knows you from a pen pal group called Pen Pal World! I imaged last night and got a great shot of the galaxy and supernova. You can see it on my Facebook page. https://www.facebook.com/jim.mayercak Hope to hear from you. Clear Skies… Jim

  3. SNH

    Awesome article – again! I thought that my evening telescope viewing was done with the moon creeping into the sky. But no, now I HAVE to set up to see the SN 2016coj. I was immediately familiar with its host galaxy when I read it because it’s one I saw in my 7×35 binoculars earlier in the spring. Thanks for the link to David Bishop’s website. I have been dependent on the S&T website for SN alerts for many years. Well, I better print off your image of NGC 4125 so that I know right where to find it this evening! Great, just great.

    1. Bob KingBob King Post author

      Good luck tonight! I’ve been in your situation many times. Just when I thought I could get some rest, another comet or SN makes its appearance. Good luck tonight!

  4. Tom Hoffelderrocksnstars

    Yes, another great article! And it also gave me what I’ve been looking for, Dave B’s new website URL, which I hadn’t been able to find for the last week or so!

    I was able to view 2016coj on the 31st in our C14; at 150X it required averted imagination but was obvious at 350X. It was the first SN I’ve seen in 24 months; in the previous 24, I had obseved 16.

    My wife and I did observe 1989B, which was our first supernova, and I have seen 24 since. For me, there is nothing more exciting in the eyepiece than the light of a single star exploding some millions of years ago. The most distant was 2013fw in NGC 7042, which according to NED is ~210 Mly away.

    1. Bob KingBob King Post author

      Excellent that you got to see it. I’ve had a similar experience this past year with supernovae. Although hundreds have been discovered the number you can see visually has been unusually low.

      1. Tom Hoffelderrocksnstars

        Bob, as you’ve probably noticed, Mr. Bishop has another supernova (ASASSN-16fp = 2016coi) listed as brighter than mag 14. It is in UGC 11868, which seems a little unusual since UGC usually implies very distant. However, according to NED, this UGC is less than 60 Mly away, and of course, as with stars, there are two reasons an object can be dim. NGC 7177 is located about half a degree to the southeast and NED has a similar distance for it. Anyway, it looks like there is another one out there within reach of moderate sized scopes!

        1. Bob KingBob King Post author

          Hi rockenstarrs,
          I see that. That one really shot up – now 13.8. And the SN in 4125 has continued to rise and is now 13.1. Happy hunting for scopes big and small!

  5. Dave-MitskyDave-Mitsky

    I observed the bright supernova SN 2016coj in NGC 4125 on Tuesday and Wednesday nights using the 17″ classical Cassegrain at the Naylor Observartory and last night using my 10″ Sky-Watcher Dob, a 12.5″ ATM Dob, and a 20″ Obsession Dob from a “local” dark site. The supernova stood out very well indeed at 463x through the 17″ and at even higher magnification through the 20″. The neighboring galaxy NGC 4121 was also visible last night.

    As expected, I saw no hint of SN 2016cok in M66 through the 17″ on Tuesday night.

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