The answer really is 42

As if we needed any further proof that Douglas Adams was a bloody genius. If you haven’t read his fantastic Hitchhiker’s Guide to the Galaxy series, turn off your computer this instant, get down the bookshop and start reading. For the humans among you, you’ll remember that the mighty supercomputer Deep Thought pondered for 7.5 million years to come up with the answer to Life, the Universe and Everything. His answer was 42. This prompted Arthur Dent and friends to go off in search of the real question to which this was the answer, as that was rather beyond Deep Thought at the time.

Douglas Adams
Douglas Adams – bloody genius

Well, in one of those truth is far stranger than fiction moments, the universe is providing the question for us after all. For some time now scientists have been trying to estimate the weight of the universe. It seems like one of those cunning ploys to get indefinite funding from some mug, but there’s actually good reason for the research. Knowing the weight of the galaxy, the amount of matter it contains, is key to solving important astronomical problems.

Astrophysicist Ken Freeman is particularly interested in the nature of so-called dark matter. Unlike the “ordinary matter” of stars and planets, scientists don’t really know anything about the nature of the invisible material that, along with “dark energy”, they estimate makes up 96 per cent of the universe.

Serious questions abound with regard to dark matter. What is it? How is it distributed across the universe? Does it really even exist? That last question is particularly relevant.

“That’s worth knowing,” said Professor Freeman, an astrophysicist with Mt Stromlo Observatory and the Australian National University’s Research School of Astronomy and Astrophysics in Canberra. Let’s give Prof Freeman this week’s Understatement of the Week trophy.

Along with colleagues in Australia, Europe, the US and Britain, Freeman decided to “weigh” a galaxy. How’s that for a lofty goal? This is the description as reported in the The Daily Telegraph:

While it’s possible to estimate the mass of the entire universe, accurately measuring galaxies, particularly distant ones, is another matter.

The problem is there’s no good way to quantify all the dark matter in such galaxies, thus making it difficult to total all the matter, dark and ordinary.

So Professor Freeman and his colleagues chose the Milky Way.

“Because we’re inside our galaxy, we can get a more reliable measure of the dark matter content than we can for galaxies outside,” he said.

To do so, the group first estimated the “escape velocity” of the galaxy – the speed stars passing near the sun needed to attain in order to escape its gravitational pull.

It did so using the line-of-sight, or radial, velocity of stars crossing the central rotating disc of the galaxy.

The data was collected by the 1.2m Schmidt Telescope of the Anglo-Australian Observatory at Siding Spring, NSW.

The escape velocity, calculated at between 544km/sec and 608km/sec, allowed the team to calculate the Milky Way’s mass and weight, as well as the amount of dark matter: 94 per cent.

And the net result of all this? Where’s the connection to Adams’s magical number of 42? Well, it’s slightly tenuous actually, but why let the truth get in the way of a good story. It turns out that our galaxy weighs three times 10 to the power of 42kg. Or a number written as 3 followed by 42 zeroes. Ooh, spooky!

Whatever, Douglas Adams was still a genius. Vale, Douglas.

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