Flamsteed Astronomy Society

‘Cosmic Explosions, Dark Energy and the Fate of the Universe’ by Dr Mark Sullivan - February 13, 2012

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In the 1990s, two teams used high redshift supernovae to measure how fast the universe is expanding. The supernovae were fainter than expected, and therefore must be further away, and it was concluded that something extra must be pushing them. The extra 'something' is dark energy. Einstein was not so crazy; he was right to introduce the cosmological constant, but for the wrong reasons.

Dark energy appears to be driving an accelerating universe, and a huge international effort is being made to understand dark energy. In an image of an area of the sky four times the size of the full moon, 0.5 million galaxies have been discovered, but this includes only 20 interesting supernovae, so being able to deal with huge volumes of data is the key to this research.

After showing a pie-chart illustrating that about 70% of the universe is Dark Energy, Mark said that nobody has the faintest idea what dark energy is!


Mark presented an interesting graph plotting the scale of the universe from the big bang to the present with three curves. After the big bang there was a marked deceleration in the early period, followed by a steady acceleration over the passage of time to the present day.

Looking ahead, Mark demonstrated theories predicting either a steep acceleration (the big rip) where matter is torn apart by the expansion of the universe, or (if dark energy theory is incorrect) a sharp deceleration (the big crunch) with the universe contracting into a hot dense state, similar to the big bang.

Another scenario is the big freeze with the universe expanding and cooling forever, until the universe expands to such a point that heat death occurs (not enough heat to sustain motion).


This is one of the biggest unknowns in physics.

The Mount Palomar 48” telescope is looking for supernovae every night and generates a vast number of supernovae candidates, but this is a human recognition task (better than computers!) in which amateur astronomers can participate through the Galaxy Zoo.

All of us can help to identify the best candidates using a yes / no decision tree which is accessed via http://supernova.galaxyzoo.org/ After logging on, there is a tutorial showing how to take part, and the dates of the next observing run.

This was a brilliant lecture delivered with a very clear and structured approach which everyone found truly absorbing. Mark concluded by answering questions.


Chris Sutcliffe

A change in the expansion rate of the universe about 7.5 billion years ago may be due to a mysterious dark force that is pulling galaxies apart.

Hunting for supernovae in Galaxy Zoo

Palomar-QUEST survey looking for supernovae explosions

High redshift supernovae deviate from the straight line, suggesting they are further away than expected