Join ABC Stargazing Live at Siding Spring observatory in the search for supernovae!

The team at the SkyMapper Telescope at Siding Spring observatory in Australia have teamed up with ABC Stargazing Live to get you to help out in the search for supernovae. We are observing an area of sky ~1,000 times larger than the full Moon every night!

How do we find Supernovae?

Supernovae are "transient events", they shine very brightly for weeks and then fade away. A good way of finding transient objects in the sky is to compare an "old" or "reference" image to a "new" image. If a bright object appears on the "new" image which was not visible a month ago we have found a transient event! Usually we call this process subtraction, which is literally subtracting the new image from the old, so if you have a particular star or a galaxy in the "new" and "old" image there will be no event (transient) in the "subtracted" image.

Supernovae will usually appear like point sources (small white dots of light). They can occur near or in galaxies. Some don't seem to be in a galaxy (usually the galaxy is too faint to be seen or is not close to the supernova) and others can be seen in their galaxy like:

Transients can be supernovae but also stars that vary their luminosity, Active Galactic Nuclei (AGN) found in the centres of a galaxies, and even asteroids passing by! Remember, we are taking snapshots in time with our telescope. So once we find a transient candidate, which you can do in this page, we have to figure out what type of object this is. We then go to get the spectrum of the object using a special type of telescope called a spectrograph.

Supernovae as the Deaths of Stars

Supernovae are the explosive, violent deaths of stars. A single supernova can outshine its entire host galaxy for a period of a few short weeks before it fades away forever. In the image below the "blue" dot is a single star exploding as a supernova (SN2012fr), outshining millions of stars in this galaxy.

Credit: Brad Tucker and Emma Kirby (Mt. Stromlo Observatory/ANU) and Carlos Contreras (Las Campanas Observatory).

Most of the elements heavier than iron are forged in these short explosions. Over the course of billions of years, supernovae have shaped galaxies, filling them with atoms that lead to planets and life. Supernovae are also incredibly useful for measuring distances in our Universe.

Supernovae are all unique. The explosion depends on the way the star or stellar system ends its life, which can produce “normal” or “weird” explosions. We can classify broad types of supernovae by studying the rainbow of light they emit, known as the spectrum. The spectra of different types of supernovae have characteristic brighter and darker sections in their spectrum, known as emission and absorption lines respectively. The spectral lines depend on the different elements produced in the supernova, so act like a fingerprint. Each type of supernova has an expected spectral fingerprint.

We can analyse the spectra using instruments known as spectrographs, which break up the light into rainbows. Some supernova spectral lines belong to left over hydrogen and helium. Other supernovae that are produced by the death of massive stars, that are around 10 times the mass of the Sun, contain lots of heavy elements larger than iron that were produced by nuclear fusion in the explosion.

The two main types of supernovae are known as core collapse and thermonuclear supernovae. Core collapse supernovae mark the deaths of massive stars, as they run out of fuel. Core collapse supernovae produce extremely dense objects such as neutron stars and black holes, alongside beautiful nebulae. Thermonuclear supernovae are the detonations of compact objects, known as white dwarfs, caused by either two white dwarfs colliding, or material falling onto the white dwarf from a companion star. The thermonuclear explosions are incredibly bright and play a critical role in modern cosmology.

Although we can classify supernovae with spectroscopic classification, every case will be slightly different. Supernovae with large variations can lead to some exciting discoveries, so keep an eye out for peculiar looking supernovae!

##How do we use supernova to measure the age of the Universe?##

When we search for supernovae, there are many different types we can find. A special type of supernovae explode at the same brightness wherever they are in the Universe. These are called Type 1a supernovae and we can compare how bright they appear to us, to how bright they should be to work out how far away they are. We can also split the light from a supernova into its component parts using a prism in order to work out how much that light has been stretched by the expansion of space on its way to us on Earth. Using both the distance of a supernova and this measure of the expansion of space, we can work out the rate at which the Universe is expanding. From this we can work backwards, to rewind time, and work out how old the Universe is.

Astronomers have been doing this calculation for decades with ever increasing numbers of supernovae. Every time we find another supernova, our calculation of the age of the Universe gets more precise. By helping to classify images on Supernova Sighting you will be contributing to on going scientific research to help understand the Universe in which we live. This is a field of research called cosmology.

Supernovae as Tools for Cosmology

Cosmology is the study of how the Universe evolves over time. The tools of cosmology are bright objects that can be seen far across the Universe. Supernovae, which are often about 5 billion times brighter than the Sun, can be seen from billions of light years away. In particular, we are interested in type Ia supernovae which tend to all behave in a similar way, shining very brightly to a known luminosity and then fading away. They are known as ‘standard candles’ because we know how intrinsically bright they should be, allowing us to calculate their distance based on how bright they appear to us here on Earth. Type Ia supernovae are identified by having no hydrogen or helium in their spectrum but strong evidence of silicon (produced in the explosion).

Type Ia supernovae were used by two competing teams of scientists to measure the Universe's rate of expansion, leading them to find that the rate of expansion is accelerating. This discovery was surprising because gravity, the main force shaping the Universe as a whole, is (in our daily experience) only attractive. The accelerated expansion is like throwing a ball into the air and watching it shoot off towards the Moon rather than coming back down to the ground. The unknown cause of the phenomenon is commonly referred to as "dark energy", and its discovery won the 2011 Nobel Prize in Physics for Prof. Brian Schmidt (ANU), Prof. Saul Perlmutter (Berkeley) and Prof. Adam Riess (Johns Hopkins).

Understanding dark energy is now a major international research enterprise, with many new telescopes, surveys, and missions dedicated to the problem. The SkyMapper Transient Survey is searching for type Ia supernovae and using them to study the expansion of the Universe, with this project you are invited to participate in the search using real telescope images!

The Different Types of Supernovae

Supernovae and other transient events are usually classified with information from a telescope with a spectrograph. This telescope splits the light into different wavelengths (colours) to obtain a spectrum. This spectrum will tell us the chemical decomposition of the object, allowing us to accurately identify it.

Unlike stars or galaxies, features in supernova spectra are very broad (due to the large speeds at which the explosions eject material) and often overlap with each other. They also change with time, as layers of material expand and become transparent to reveal deeper layers (the star’s interior) underneath. Getting the most out of a new supernova requires that it be found and classified as early as possible.

To ensure access to spectroscopy, the SkyMapper team uses the ANU 2.3m telescope at Siding Spring and collaborates with the Public ESO Spectroscopic Survey of Transient Objects (PESSTO) and LCO.

SkyMapper

The SkyMapper Southern Sky Survey is a project to make a digital map of the southern hemisphere, much like the Sloan Digital Sky Survey (SDSS) did for the northern hemisphere. SkyMapper is located in Siding Spring Observatory in Australia. Alongside the Southern Sky Survey, SkyMapper is conducting a search for supernovae and other transients. This Transient Survey covers a large area of the southern sky (2000 Square Degrees) and is optimised for the discovery and follow-up of low-redshift (nearby) type Ia supernovae to constrain cosmic expansion and peculiar velocities. The images that you will find in this project have been freshly observed from the telescope within the last few days so that we can detect supernova candidates as early as possible. SM cover image courtesy of J. Calcino

The SkyMapper telescope

The SkyMapper telescope was constructed by EOS. It has a modified Cassegrain design, featuring:

• A 1.35m primary mirror
• A 0.71m secondary (on 5 axis hexapod mount)
• A 0.56m aspheric corrector
• Two additional spherical correcting elements

All transmissive optics are made of fused silica to ensure optimal UV throughput. The telescope is housed in a dome that is 11.5m tall and 6.25m in diameter, located near the summit of Siding Spring Mountain, at The Australian National University's Siding Spring Observatory.
SkyMapper observes the sky in a custom-made set of filters optimised for studying extremely old, nearly metal-free stars; high-redshift quasars; and supernovae.