The weather’s been shocking here for weeks but finally there was a clear evening on Sunday. Unfortunately I’d left my telescopes at work so thought I’d experiment with my SLR camera.
I live only a few miles from Manchester city centre so skies are light polluted to say the least. The Plough was visible from the backyard of our house sitting just above the rooftop. I set up my camera on a mini tripod, pointed it in roughly the right direction (somewhere above the line joining the Pointers to the Pole Star) and took a 30 second exposure.
With no clever mount to correct for Earth rotation, in 30 seconds all the star images trail left to right. However, a quick check with Stellarium let me spot the star patterns and sure enough there were the fuzzy blobs of galaxies M81 and M82.
Of course this is no claim for astrophotographer of the year but I quite enjoyed the back to basics challenge of city skies and minimal equipment. It’s possible to see the star towards the top end of M82, but unfortunately these images are not good enough to see SN 2014J. That will have to wait until the next clear night when I’m in close proximity to my telescopes.
Why the fuss?
As soon as the discovery of 2014J hit the newsfeeds of the internet, telescopes around the world and in space were being directed towards it. But why the fuss?
SN 2014J is a Type Ia supernova. These are thought to be the explosions of white dwarf stars, either as a result of accretion of gas from a companion star, or from a merger with another white dwarf. Type Ia’s can be used as standard candles to measure distances in the Universe, famously resulting in the Nobel-Prize winning discovery in 1998 of the accelerating expansion of the Universe. Something that simply wasn’t expected.
The cause of the acceleration is unknown although we’ve dubbed it dark energy, in honour of the other major component of the Universe we don’t understand – dark matter. To find out more, astronomers need to see very distant (and hence faint) supernovae, far off in the Universe and far back in time. This will allow us to measure how the expansion has changed over time and so pin down the properties of dark energy.
But if we are to understand Type Ia supernovae themselves, then nearby examples which can be studied in detail are essential, and SN 2014J is the nearest Type Ia since 1972. [In fact, it was so bright it wasn’t picked up on the automated searches for fainter, more distant objects and was discovered by chance by staff and undergraduate students in the University of London Observatory.] Our telescope and instrument technology has been revolutionised since the 1970’s, so 2014J promises to be a major source of information over the coming months and years.
A deluge of supernovae
The Central Bureau for Astronomical Telegrams (CBAT) designate confirmed supernovae using letters. The first 26 of the year are named with capital letters, so 2014J in galaxy M82 is the 10th supernova of 2014. After Z the designation moves to two lower case letters aa, ab, ac…az, then ba, bc, bd… etc. In 2013 the CBAT list got to supernova 2013hw, the 231st (26+7×26+23) supernova of the year. By the way, these supernovae are all in other galaxies – there hasn’t been one seen to explode in our Milky Way since Kepler’s supernova in 1604 (although the youngest remnant discovered dates from about 1870).
Of course you’d expect the rate of supernova discoveries to increase year on year as technology improves (each galaxy might have a supernova only every 50 years say, but there are billions of galaxies out there and automated searches are now the norm). It had been a while since I’d checked how many supernovae were discovered each year and I thought 231 last year seemed a bit low compared to what I remembered. So I took the CBAT list and plotted the numbers since 1980.
Now that seems a bit strange. Surely there can’t be fewer supernovae being discovered each year?
According to the Latest Supernovae website, maintained by David Bishop since 1997, at least part of the explanation is that some of the current supernova search projects are not submitting all their discoveries to CBAT for naming. Bishop’s website aims to compile a complete list of all supernovae from various sources. Using the numbers for all supernovae from his annual statistics pages the discovery rate is, as one might expect, steadily increasing.
The automated surveys are indeed driving the increase in supernova discovery. The peak in numbers around 2006 was largely due to the Sloane Digital Sky Survey supernova search (SDSS-II SN). This operated from July 2005-July 2008 and was responsible for finding ~500 Type Ia’s and 80 core-collapse supernovae – all of which were reported and appear on the CBAT lists. For example, in the peak CBAT year of 2007, 573 new supernovae are listed of which 228 were down to SDSS.
Using Bishop’s list, 2013 had most supernovae with 1100. Out of these, 400 were discovered by the Catalina Real-Time Transient Survey, 146 by the OGLE-IV programme, 137 by LaSilla-QUEST and 117 by the Palomar Transient Factory.
Upcoming instruments will increase the discovery rate even further. For example:
- the Dark Energy Survey, which began on 2013 Aug 31, will discover 4,000 new supernovae over the next five years;
- the Gaia spacecraft (which released its first test image today) is expected to discover about 6,300 supernovae over its 5-year mission;
- the Pan-STARRS project expects to discover more than 10,000 supernovae per year;
- whilst the incredible Large Synoptic Survey Telescope (LSST) will find thousands of new supernovae every single night!
The next decade is going to provide a deluge of supernova discoveries, hopefully bringing us closer to solving the problem of dark energy.