Dueling bright supernovas in M95 and NGC 4790 kick off new season

Two bright supernovae in galaxies M95 and NGC 4790 are currently visible in small to moderate-sized telescopes. North is up, west to the right in both pictures. Credits: Martin Mobberley (Ieft) and William Wiethoff

60 million years ago a supergiant star exploded in the galaxy NGC 4790 in Virgo. 22 million years later another overgrown and underfed supergiant star ended its life in the galaxy M95. After all that time traveling through space, the light from each explosion arrived within two days of each other in the skies over planet Earth. What a joy to see them both in their final glory.

Supernova 2012 aw has been getting most of the attention lately, because it was discovered in a bright galaxy not far from the planet Mars in Leo. Most supernovae are caught on the rise to maximum light. This one was no exception. 2012 aw was first spotted at 15th magnitude (dim!) by Paolo Fagotti and Alessandro Dimai of the Italian Supernovae Search Project, and independently by Jure Skvarc (Crni Vrh Observatory, Slovenia) on March 16. A day later it rose to 13th magnitude which put it within range of many amateur telescopes. Today March 21, the supernova still hovers at around 13th magnitude, though it’s uncertain if it will brighten further or plateau.

Stay back! An artist's view of a supergiant star undergoing core collapse to become a supernova. Credit: ESO

Studying its light with a spectrograph, an instrument that drags a fine-toothed comb though a star’s light to determine its chemical makeup, speed of rotation and the like, astronomers discovered that M95’s supernova is a Type IIP. Type II tells us this was a supergiant star that used up all the available nuclear fuel in its core. With nothing left to burn, the star’s internal “furnace” shut down, gravity took hold and the whole works collapsed in upon itself at speeds up to 45,000 miles per second.

When the outer layers reached the core, they crushed it into a dense ball of subatomic particles and sent a powerful shock wave back towards the surface that helped tear the star apart, creating a supernova. New radioactive forms of elements like nickel and cobalt were created by the tremendous pressure of the explosion; their decay into stable forms releases energy that contributes to the supernova’s light. The “P” by the way stands for plateau. Type IIP supernovae level off in brightness more slowly, plateauing for a time before fading away.

Galaxies M105, NGC 3384 and NGC 3389 in Leo. Although composed of billions of stars like our Milky Way, most scopes see them as hazy patches. They're too far to resolve into individual stars. Credit: Jim Misiti

A supernova is really the only way beginning and amateur astronomers can see a star in another galaxy. Galaxies beyond the Milky Way system – which includes our nearby satellite galaxies the Magellanic Clouds – are too far away for most telescopes to resolve into stars. All those billions of stars in the thousands of galaxies visible in amateur telescopes look like pale white fuzz that remind me of cocoons. Not so when a supernova blows. We finally get to see across the light years at an individual star waving farewell.

To get an idea of how bright the supernovae in M95 and NGC 4790 are, take a look at Arcturus, the bright star in the northeastern sky found below the arc of the Big Dipper’s Handle. If you placed either SN 2012 aw or SN 2012 au at Arcturus’ distance of 34 light years, each would shine at better than magnitude -15 or a full magnitude brighter than the full moon. Image all that light squeezed into a point in the sky. Think how bright that would be and the shadows it would cast at night. What power!

Just before a supergiant star blows it has a core made of iron that cannot "burn" to create energy to power the star. Gravity takes hold and the star collapses. Supergiants are several hundred times larger than our sun.

I was asked today whether you can see M95’s supernova in a small, 4-inch telescope, and the answer is yes – if you observe from a dark sky inĀ  good seeing (steady, non-turbulent air) using higher magnifications (150x). The limit for a 4-inch is 13.2 magnitude. A 6-inch scope is better and it should be easy in an 8-inch. By good fortune, the star is far from the galaxy’s center where it might otherwise be camouflaged by a haze of spiral arms.

But what about SN 2012 au? Let’s not pass it by. After all, it’s even brighter than the one blazing in M95. This Type II supernova is nearly dead center in NGC 4790 in Virgo and currently shines at 12.7 magnitude or nearly a half-magnitude brighter than 2012 aw – well within the 4-inch limit. The reason it might be overlooked is that 4790 is a smaller, fainter galaxy and not as easy to find. Try using this finder chart for NGC 4790 from this earlier blog. Once you spot the galaxy, you can’t miss the supernova.

Finder charts and other details on M95 are HERE and HERE. David Bishop, keeper of the Latest Supernovae site, always has updated information on current supernovae bright and faint.

9 Responses

  1. John

    I’m continually surprised that I have trouble seeing things down to 13 with my 8″ SCT. Maybe my eyes really aren’t just good (I do wear glasses, but observe with them off), or maybe there’s too much light pollution in Central CT for this. I found M95 last night, but that 12.2 star right near it was just on the edge of what I could resolve. The 10.2 was easy.

    M95 was extremely faint at 8pm and a little puffball at about 10pm. I could only spot “something” where the SN was by moving the fine controls on my scope up and down…suddenly there was a little light.

    I don’t believe my scope needs collimating, as stars brought out of focus are uniformly round. I’ve never cleaned my lenses or scope for fear of scratching, but they aren’t excessively dirty.

    1. Profile photo of astrobob

      Hi John,
      Thanks for detailed observation. I think it can be helpful to others trying to find the supernova. Seeing down to a limiting magnitude depends on several things:
      amount of light pollution, if there’s any haze or thin cloud, steadiness of the air, whether the telescope optics have cooled down, sensitivity of the eyes (degree of dark adaption, age of the observer) and observer experience. I used to think I could only reach 14th magnitude in my 10-inch, but with practice and excellent skies and seeing, I can usually dig down to about 15.3.

  2. John

    I’d be curious if others with 8″ scopes in similar light-polluted areas have seen anything. I also had a streetlight off to my side to contend with, so I’m sure my eyes weren’t as adjusted to the dark as they could have been.

  3. markan

    I saw it with my 8″ reflector on the 21st from a Bortle 4 site I use, so not really light polluted. I found I needed higher power (125x) to to see it. On the AAVSO chart I was using there was a magnitude 13.9 reference star that was only visible with averted vision so that’s about my limit. The supernova was brighter, but not by much. It was best viewed with averted vision as well. I could only see the core of M95 so the supernova itself looks like it’s adjacent to the galaxy.

    1. Profile photo of astrobob

      Thanks for writing in with your sighting. Using higher magnification really helps when trying to see a faint star. I start low to locate the galaxy and then increase as needed until the SN shows as clearly as possible. Current brightness of the M95 supernova is 13.0.

      1. mintaka77

        Great to hear you guys are seeing it, I’ve tried with a 12 inch Dob, 18mm and 9mm eyepiece (up to 170x therefore) but no joy. The only star I can see away from the two blurs of M95 and M96 forms an equilateral triangle with the two galaxies. Scope is freshly perfectly laser collimated. Not sure what magnitude of this star is – Skies are fairly dark here but may be a lot of moisture in the air tonight. I’ve realised I need a star atlas more detailed than Sky Atlas 2000 which only goes to magnitude 8.5 to distinguish the equilateral triangle star from the supernova. There was also another even fainter star on the other side, forming a kind of kite shape with the two galaxies, that I could just see with averted vision. What would be a recommended more detailed star chart to use? It’s the first time my trusty Sky Atlas 2000 hasn’t been sufficient ….

        1. Profile photo of astrobob

          You should see the supernova well in a 12-inch Dob under decent skies. Last night it was easy at 64x in a 15-inch scope. Be sure you’re focused closely on M95. SN 2012 aw is quite close to the galaxy compared to a field of view that would include M96. Distance from M95’s nucleus is under 2 arc minutes. Using an AAVSO chart, I estimated its magnitude at 13.1. Try using the telescopic sketch in my earlier blog on the supernova here: http://tinyurl.com/7nwysk3
          There’s also a photo finder chart there. Let us know how it goes and good luck!

  4. Bill Gucfa

    Hello Bob,
    Just a quick message to let you and the others know I’ve seen Sn2012aw in M95.
    My method is using a 6″ Antares refractor, an old Sony 5mp DSC F-707 and a Canon T1i. I used the Sony afocal with a 40mm eyepiece on the scope to find the field and object. In a light polluted sky I can reach 13th mag. (or 14, under excellent conditions). When I’m sure where I am, I switch cameras to the Canon and use the same afocal technique. A single exposure is used with both. Thirty seconds with the Sony and no limit but usually close to 1 minute with the Canon to achieve around 14th mag (dimmest stars in the field).
    For those having trouble seeing this magnitude visually I highly recommend this method. Of course the scope must have an accurate drive for success!
    I’m going for Sn2012au next chance!
    If there are any questions on my method please ask!
    Clear skies! Bill

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