SN 1885A The Last Supernova in Messier 31
It has been well over a hundred years since the last visual supernova has been seen in the Andromeda Galaxy when in August of 1885, SN 1885A went off. On August 21st, 1885, SN 1885A reach magnitude 5.85, and then by six months later had faded down to magnitude 14. Observations made at the time, with light curves fall in line that SN 1885A was a Type Ia Supernova event. You can read about SN 1885A over at Wikipedia at this LINK or at the centennial review article written in 1985 at this LINK which is a PDF link. SN 1885A is an interesting study of a supernova that is suppose to be a Type Ia. The SN, reached maximum brightness, around magnitude 5 to 6 rather quickly and then rather quickly, more quickly than a typical Type Ia supernova does, went to being undetectable about 5 to 6 months later (most Type Ia SN take much longer to totally fade in brightness). This led some to believing that this wasn't a SN at all, perhaps just a shedding of a thin Helium shell that caused a massive outburst or explosion, but left the white dwarf there (see The Nature of S Andromeadae (SN 1885A) at this LINK).
For example, SN 1885A had a sudden rise to maximum light on the night of August 21st, 1885. The SN was not seen on the night of August 16th and so from August 16th to August 21st, 1885 "the rise time from 3 mag below maximum to maximum is thus ~ 4 days." The scale for most Type Ia to reach maximum is ~14 days + 2 days. So SN 1885A rose rapidly, very rapidly when compared to other Type Ia. Also, SN 1885A declined from maximum at a mean rate of 0.10 + 0.01 mag. day while the mean for 8 SN Type Ia is shown to be at 0.065 + 0.007 mag day. So there are some things about SN 1885A that are unique or different to it when compared to known Type Ia SN. We also know that SN 1885A came from a "low mass progenitor due to its location in M31, which was about 16" from the core, which is an area of new new star growth and old star populations. Thus this combined with a low luminosity means that SN 1885A was a white dwarf in a binary system." The conclusion of Roger A. Chevalier and Philip C. Plait (I believe The Bad Astronomer) is that SN 1885A fits a model by Woosley, Team and Weaver where a thin shell of Helium detonates leaving a remaining white dwarf intact and spreading out an Iron (Fe) rich gas from the explosion.
In the article An Unusually Fast-Evolving Supernova (LINK) Dovi Poznanski, Ryan Chornock, Peter E. Nugent, Joshua S. Bloom, Alexei V. Filippenko, Mohan Ganeshalingam, Douglas C. Leonard, Weidong Li,and Rollin C. Thomas show that SN 2002bj was a new type of Supernova Type I that had a quick rise to maximum luminosity, a quick decline from maximum, and lines of helium in its spectra but no lines of iron. Sounds like SN 1885a a lot. Here two binary white dwarfs are exchanging helium and eventually, the larger white dwarf, surpassing the Chandrasekhar limit of 1.4 mass, detonates the helium shell, much like a nova but extremely more intense and brighter, leaving the white dwarf there in place. That would go a long way to explaining SN 1885a and SN 1939b. I also think it makes major sense since SN 1885A occurred so far in toward the core of Messier 31, where new star formation was not occurring and thus the chances of two white dwarfs being a binary pair are more than possible, and in truth, probably likely. For me I find this fascinating because it shows that in the science of Astronomy, knowledge continues to grow and be unwoven/discovered, as we learn more, see deeper and with more detail and can put the science and math to work to reach factual conclusions. If you want to learn more of SN 1885A I suggest these links:
Supernova 1885A Professor from Ca State Sonoma
RN (Recurrent Novae) M31N 2008-12a
Now for the exciting news that has been out for some time, but something I just recently discovered. There is a very exciting candidate that has been identified for being the next Supernova in Messier 31, the Andromeda Galaxy. It is called RN M31N 2008-12a. The RN is for recurrent Novae since it has gone off in 2008, 2009, 2011, 2012, 2013 and 2014. It is believed the nova was missed in 2010 and studies on transient X-ray sources were detected in 1992 and 1993 near this position and in September 2001, X-ray sources at this site were also detected. thus as pointed out in their 2014 paper A remarkable recurrent nova in M31 - The optical observations, (LINK) M.J, Darnley, S.C. Williams, M.F. Bode, M. Henze, J-U. Ness, A.W Shafter, K. Hornoch, and V. Votruba show that this actual binary pair of a white dwarf and a Red Supergiant Star have been exchanging material and the white dwarf has been blowing off some of that material for at least the last twenty years! Because of the faintness of the eruptions and their quick rise to maximum (around 18 to 18.5 mag) and their rapid decline back to below 21 mag., it is highly likely that there have been a significant number of missed eruptions.
Since this binary pair have been having short time duration between eruptions, these and other astronomers know that this is a "unique system." To quote from the above article "Such a short (~ 1 year) recurrence time can be expected from a system with al ow critical mass for ignition, which requires a high mass white dward. Further to accumulate enough mass for ignition within a short time, a high mass accretion rate is needed." The paper also shows that from a previous study done and model created, this is possible but only with a WD or white dwarf star that is very close to the Chandrasekhar limit of 1.4 solar masses. This binary pair then is exchanging material at a rapid rate, the white dwarf companion has to be very close to the Chandrasekhar limit of 1.4 solar masses, and thus is soon, in astronomical terms, going to be ready to detonate as a Type Ia supernova! Again from the article above is a summation:
"The five known eruptions of this nova over the past five years (2008, 2009, 2011, 2012, 2013, 2014) indicates that we have a very fast He/N nova with a decline time of about 4 days. These observations when combined with the X-ray detection in 1992, 1993 and 2001 indicate that this system has a remarkably short ~ 1 year recurrence time. This points to a system having a very high mass white dwarf with a high accretion rate. A search of the Hubble Space Telescope data shows a candidate progenitor system, most likely containing a RGB secondary (RG-nova) and a bright accretion disk."
So what does this mean for us amateurs? First, if your a supernova hunter, I would put the coordinates of this system and pair in your nightly survey's IF your telescope can reach down that low (around mag. 18 to 19). The coordinates from the article are 0h 45m 28.80s for RA and Dec. is +41 degrees, 54', 10".1 If your a visual observer I tried to give a very general idea where this object is in Messier 31. It is out in an outer arm of Messier 31 and thus why one star would most likely be a white dwarf, having gone through its journey on the Hertzsprung–Russell diagram to ending up as the white dwarf in this binary and the other, entering its last stages on the Hertzsprung-Russell diagram as a giant star. Here is where I estimate the region of the this system is located if your wanting to watch it.
Above you will notice Messier 110 at the top of the screen. If you move to the right, you can see a triangle of 3 bright stars near the green eclipse line that shows M31. I've circled them in the red circle. The green line is going under the star on the left side, HIP 3432, and then in between the two bright stars that make the base. The top star in that base is HIP 3510 and the bottom one is TCY 2805-11695-1. You are aiming for the bottom left star, TCY 2805-11695-1
Now you can see a closer view of the three stars listed above. Go to the top star, HIP 3510 and then
On the image above (now realize, I took the RA and Dec and tried to get close, close not exact to where this system is so at least if your visually trying for this as a SN, you know where to look but who knows, I may have totally blown it) you can see where you star hop starting at the TCY 2805 star and move up to that top star.
A closer view:
This shows the star hop above to star 4 and then if you go to star 6 which is UNSO J0044126 + 421849 magnitude 16.5 (so faint, very faint) you are at RA 0h 45.080 and Dec 42 degrees, 23.899 which is a tad closer to the system.
So if I am wrong and someone makes a better finder chart for the system, please let me know so I can delete this. If it is close, let me know as I would like to know that also. I believe I am in the general location and if looking will spot it. I will give it a shot in terms of getting to the location in the next couple of nights when I am observing at my dark site location. Please realize this object is close, very close to going supernova, but close is relative in Astronomical terms. It probably has already blow of course, and the light could reach us tonight, tomorrow, next week, later this month, next month, next year or a few thousand or hundred of thousands of years depending when it actually triggers. If your in the area though why not take a look and see if you can capture it. It may be your first SN captured though I am sure the professionals are watching it with equipment that will capture it before a visual observer can but one never knows. It is a very interesting object regardless and fun to learn about. May the stars shine bright as you observe our wonderful night sky.