Archive for February, 2010

Scary Childrens’ TV

Posted in Personal with tags , on February 24, 2010 by davidnm2009

Anyone else remember the Groke?

Probably/maybe the scariest thing ever seen in a kid’s show. In fact, I first came across the Groke in the book Moominland in Winter, which I must have been all of about 9 when I read. It scared me senseless … although to be fair I had a worse reaction to ‘Watership Down’, which I’ve actually blanked from my memory. (I watched the intro sequence again on YouTube a few weeks ago. Even now, it’s still pretty horrific…)

Sunday Story Time

Posted in SF, Writing with tags , , on February 21, 2010 by davidnm2009

Abbey Manor – from 2006, but I still like this one. I sent it to Interzone, although they didn’t bite. (Possibly not surprising – this version has been edited to get rid of Eggregious Semi-Colon Disease.)

(This was inspired by my experiences working in the fields of local government and mortgages. I’d write a book about them except I doubt that anyone would believe a word of it…)

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Mystery #3: Where do cosmic rays come from?

Posted in Astronomy with tags , on February 18, 2010 by davidnm2009

Cosmic rays are one of the most wonderfully-baroque, mad-science things in astronomy. They’re exotic. They’re mysterious. They offer no quarter to common sense. And they’re also misnamed.

They’re actually, strictly speaking, particles rather than ‘rays’. Around 90% of them are free protons, with most of the rest being helium nuclei. There’s just a whiff of other stuff in there, namely heavier elements. They come in from space, zap themselves into our atmosphere, smash into the atoms therein and create particle showers that things like the MAGIC telescopes can pick up.

In the early 20th Century, it was believed that they actually came from inside the Earth, released by the radioactive decay of elements in its crust. Then an Austrian physicist called Victor Hess did a remarkable experiment involving an early scintillation counter and a hot air balloon. He showed that counts actually went up with increasing altitude, which was entirely inconsistent with the ‘Earth radioactivity’ hypothesis. This meticulous work ultimately earned him the Nobel Prize.

(Also, he did useful physics from a hot air balloon. Epic mad-science win?)

The space origin of cosmic rays is no longer controversial. You can see further evidence of it in their composition. The free protons can be considered as ionised hydrogen, in which case the H/He ratio is tending vaguely toward that of the universe as a whole. The ‘metallicity’ of cosmic rays is arguably a little low, but on the other hand many of these things will have been travelling for billions of years and thus will have set off from before much of current star formation had happened.

But where have they set off from, exactly?

Some cosmic rays definitely come from supernovae. Some probably come from stellar winds. Some are believed to be extragalactic in origin. And some are just plain weird.

The highest-energy cosmic ray ever detected was the so-called ‘Oh-My-God’ particle. It paid us a visit on the 15th of October, 1991, where it zapped into our atmosphere somewhere over Utah. It consisted of one proton, with an estimated energy of over 3 x 10^20 electron volts – or about the same as a mid-flight tennis ball. Consider – a single proton, packing in as much kinetic energy as a tennis ball. In principle, if this thing decided to pass through you, it could actually injure you. Remember – that’s one proton.

Ouch.

But the sources of these so-called ‘utra high-energy’ cosmic rays are not well-understood. Or understood at all, in fact. There exists a suspicion that they’re accelerated in the hearts of galaxies, by supermassive black holes. In principle, this should be simple to test – look at the active galaxies in the sky, and see if they correlate with cosmic ray detections.

Unfortunately, it doesn’t work like that.

The problem is magnetic fields. Cosmic rays are charged particles, so they will interact with magnetic fields. And space is full of magnetic fields, even intergalactic space. So, if a cosmic ray travels more than few megaparsecs, its trajectory will almost certainly be scrambled beyond recognition. And sure enough, this is what we see on the sky. The distribution of possible extragalactic cosmic rays is basically random. There exists one small correlation; that’s a cluster of high-energy detections associated with the radio galaxy Centaurus A. It’s located at a distance of 11 megaparsecs, so it’s arguably just barely close enough that a few particles might make it to us undistorted. Other than that, the high-energy cosmic ray sky is just a featureless blur, aside from some activity at the centre of our own galaxy.

So, sadly, the origins of extragalactic cosmic rays are probably never likely to be well-known.

Astronomical Mysteries #2: The Blinking Star

Posted in Astronomy with tags , on February 16, 2010 by davidnm2009

What exactly is going on with Epsilon Aurigae?

Epsilon Aurigae (call it EA for short) itself is a fairly normal F0-type giant star – okay, it’s a giant, so not very normal at all, but normal enough for its type of object. It has a temperature of about 7,000 K and it’s located something like 2000 LY away. So far so unexceptional.

Except for what happens every 27 years.

EA basically goes out.

Well, it’s not quite like throwing a switch. The star isn’t plunged completely into darkness. Rather, the brightness that we see from Earth drops by about 60%. It stays dim for between 640 and 730 days, before brightening back to where it was beforehand. Then, 27 years later, it repeats the performance.

Now, variable stars exist. Some of them vary because something’s changed physically inside the star – pulsating variables are one example, where the star expands and contracts. (That alters its radiating area and temperature, in turn altering its light.) Some variables, like Algol, vary because they are periodically eclipsed by a companion – a dimmer object ‘gets in the way’, essentially.

Thing is, none of these models really seem to fit EA.

Although the star dims, its spectrum doesn’t seem to change much during the dimming. This suggests that its surface temperature hasn’t changed, which would be inconsistent with a pulsating variable. This would tend to suggest that it’s dimming by being eclipse by something. But there are problems here too. First of all, eclipsing binaries are very, very regular – the Newtonian clockwork doing its thing. So why does the period of eclipse wobble back and forward between 640 and 730 days? That’s more than a 14% difference, which is quite significant. If there was a third body in the system, perturbing the second’s orbit, we could perhaps explain it – but why don’t we see the third body?

Also, where is the secondary’s spectrum? We’d expect to see features from it superimposed during the primary’s eclipse – instead all we see is the primary, dimmed. One model attempted to work around this by actually suggesting a transparent secondary – surely one of the weirdest ideas in stellar astronomy?

Also, there’s another big problem – right in the middle of its eclipse cycle, EA actually briefly gets brighter before fading again. That really makes no sense in terms of the eclipse hypothesis – the only way to make it work would be assume a secondary star with a hole in the middle!

We don’t see many* donut-shaped stars in the night sky, needless to say. It’s hard to conceive of how such an object could even exist – one would expect its own gravity to collapse it inwards, quickly filling any hole.

An alternative suggestion has been that the eclipsing secondary is not actually a star but actually a disk of gas, with a hole in the middle. This can resolve some of the above problems, but has issues of its own – like what exactly is holding the disk of gas together? A current hypothesis suggests a disk of gas with a B5-type star embedded in its middle, and with a hole, and oriented so that we don’t actually see the B5 star, and, and….

Yes. The more people look at this object, the more confusing it gets. I think the honest answer is that we currently just don’t know what’s going on with EA.
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*And when I say ‘many’, I mean ‘any’.

Five Astronomical Mysteries

Posted in Astronomy with tags , on February 13, 2010 by davidnm2009

People like to talk confidently about what we do know. And the way some people talk, you’d think we know everything.

Not so.

So, I’m going to do a series of posts on astronomical mysteries over the next few days. Here is the first…

1: Is the Sun binary?
The short answer is probably not. However, perhaps surprisingly, we don’t know this for an absolute fact.

What we do know is that the Sun is certainly not a close binary; two Suns would be hard to miss in the sky! However, the possibility does exist that there might be a wide-separation companion. (‘Wide’ in this context means thousands of AU*.) Wide-separation binaries do exist; take our next nearest stellar system, Alpha Centauri. The inner two stars, A and B, also have a companion in the form of the red dwarf Proxima, which is currently more than a tenth of a light-year closer to us. That’s a huge separation, something like 6000 AU. Wider-separation binaries are also known to exist. (There is a K-giant, L-dwarf binary in the literature with a 15,000 AU separation.)

It is possible that a small and faint companion, like Proxima, might exist at an extreme separation from the Sun. Such an object would certainly be in existing star catalogues – it would have a magnitude between 7 and 12 – but there are lots of red dwarfs in star catalogues. Not every one has a parallax measurement. Also, the object in question would move with the Sun, so it might not appear to have a high proper motion, which would select it out of important catalogues like the Luyten Half-Second.

(Also, a brown dwarf companion would be even harder to spot…)

Surprisingly, there may be a shred or two of indirect evidence to support the Sun-as-binary idea. In the 1980s, some researchers found a few hints of a 26-million year periodicity in mass extinctions. Such a cycle would be too long to be produced by anything terrestrial. They suggested a possible cause – a companion to the Sun, orbiting at around 1 LY out. This object would periodically disturb the Oort Cloud, resulting in a ‘pulse’ of comets falling Sunwards. This would in turn raise the likelihood of the Earth taking a direct hit, leading to mass extinctions…

…Of course, all of that said, there are problems with the hypothesis. One is that no-one’s yet spotted Nemesis. Another is that the periodicity is controversial with geologists.

If the Sun does have a companion, the current generation of wide-field surveys (Pan-STARSS, Wise, LSST and so on) should be able to find it. Also, one would expect it to be in 2MASS somewhere as well. So, this one at least should be soluble sometime soon.

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* Terminology note: 1 AU = the Earth’s mean orbital radius, or about 149,600,000 Km.

A Small Plus

Posted in Personal with tags on February 11, 2010 by davidnm2009

One nice thing about working in research science is that sometimes, you get to hear about interesting things long before the wider world.

That happened today.

*sits back with smug look on face*

Edit several afterwards: it was this that I found out about, by the way.

On Writing

Posted in Personal, SF, Writing with tags , , on February 8, 2010 by davidnm2009

What kind of idiot tries to combine a hard-science PhD with writing a novel?

This one, apparently.

Since it’s now finally heading vaguely toward a denouement, I thought I’d write down some of my thoughts regarding something I’ve been writing.

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