Archive for November, 2009

The Waters of Mars

Posted in SF with tags , , on November 17, 2009 by davidnm2009

So, I watched ‘The Waters of Mars’ last night on BBC iPlayer. My overall verdict? Meh.

First off, the good points. 1) Mars. 2) The base, which actually did look a bit space-colony-like. 3) The biodome, which was kind of cool. 4) The Doctor gets called on his dickish-ness. 5) There was a bit of tension and maybe even a degree of actual drama (Cpt. Brooke looks like she’s going to be the villain at first, but actually changes role about halfway through).

And now the bad points. 1) Another re-visit of MR GOD DOCTOR, which seems to be an obsession of Russell T Davies’s. Thank you, Mr Davies, one Jesus was quite enough. Also, the Time Lord Victorious, which could perhaps be re-interpreted as the Time Lord Egocentricous.

Point 2), Gadget Gadget == Stupid Stupid. Why did they ever think that was a good idea?

3) The antagonist, which wasn’t really that scary nor very convincing. If it can magically summon vast quantities of water, apparently without limit, why doesn’t it just do so and flood Mars? Why go to all the trouble of stealing a rocket?

4) The absence of sympathetic characters. Cpt. Brooke was a little bit sympathetic, but not in public. Other than her, the black girl didn’t do anything annoying, but then she got killed off too quickly to have the chance. All of the rest of them came across as poorly-socialised jerks.

5) There were too many plot-holes and foreshadowing fails, like that shot of what looked like a small moon colliding with the Earth. That was never followed up or explained. It just left me vaguely confused.

So, overall, meh. It could’ve been worse and to be fair, I didn’t have anything better to do with that hour. But it still wasn’t exactly stunningly brilliant.

Lovecraftian T-dwarfs

Posted in Astronomy, Space, Speculation with tags , , on November 12, 2009 by davidnm2009

(I need a quick break from writing my First Year Progressian report, so here’s something a little silly…)

Cosmic horror and failed stars possibly aren’t the most obvious mix. However, I think there are parallels.

Consider:

What Man Was Not Meant To Know: brown dwarfs are extremely faint, around maybe a ten thousandth of the Sun’s luminosity. In fact, because they’re so faint, their existence wasn’t confirmed until as recently as 1995 (Gliese 229B). So, they’re a classic piece of ‘what man was not meant to know’. There isn’t a single one that you can see with the naked eye from Earth (unless you’re one of these difficult people who insists on counting Jupiter, of course).

That vague, morbid sense: a brown dwarf is arguably what happens when a stellar embryo has an abortion. They don’t fuse hydrogen (or at least, not in any stable, prolonged way), so they glow through residual heat from their formation. (In technical-ese, they thermalise gravitational potential energy.) According to Burrows et al (2001), they “cool like a rock”. So as time goes on, a brown dwarf gradually fades and dies away, like an abandoned ember, until eventually it will just be a dead ball of frozen hydrogen and helium, drifting lifelessly and forgotten through a darkening universe.

They can be absurdly ancient: all good cosmic horrors are old, long pre-dating Humanity. Metal-poor brown dwarfs in particular are like this. (One of the things in my current candidate sample has an upper age constraint of ~10 billion years, making it potentially twice as old as the Sun.)

They’ll see us off: all good cosmic horrors are largely immune to human agency. Brown dwarfs obviously couldn’t care less about us, and nothing we can currently do can impact on them in any way. Also, although they gradually fade away, the cooling timescales are enormous. A 0.06 M_Sun brown dwarf will take around 1.6 billion years even to evolve as far as T0 [1]. Heavier objects will take even longer. If we imagine a 0.07 M_Sun brown dwarf which forms at the same time as the Earth – so ~4.5 billion years ago – then in 5 bn years time, it will have only got as far as type T6 (surface temperature of maybe ~ 1200 K). Meanwhile, in this time, the Sun will have expanded off the Main Sequence and certainly ended all life on Earth, and maybe even have physically-swallowed the planet.

Ouch.

The complete alienness: lastly, it has to be noted that brown dwarfs are just completely, weirdly different. They’re nothing like the environment we live in. They’re probably even less similar to conditions on Earth than London is to R’Lyeh. Brown dwarfs can range from temperatures where the weather system is made of molten iron droplets to temperatures where it might actually rain liquid water. Their atmospheric pressures are enormous and their surface gravities are hundreds of g. They’re just weird.

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[1] Scientific honesty caviat: this number obviously depends on how far you believe the Tucson et al models. Models of low-mass evolution are still a bit up in the air, in a lot of ways.

Population II – a research primer

Posted in Astronomy, Space with tags , , on November 10, 2009 by davidnm2009

I mentioned something about my day job yesterday. I’ve spent much of today peering at plots and graphs and tables, trying to come up with something sensible to say about the science aims. Not much luck, unfortunately! Oh well, c’est la vie. Writer’s block is a funny thing.

Sometimes, when your brain locks itself down, it’s best to take a step or two back, remind yourself what it’s all about.

My PhD is on brown dwarfs; these are what happens when star formation fails. Why it sometimes fails, we don’t really know. There are various theories, and they’re all flawed. Better yet, none of them fit the data well. Some models can explain some bits, others other bits. (One of my pet theories is there are actually several pathways to brown dwarf formation – we’re not seeing one process but two or three, hence the confused data.)

Anyway, in particular I look at ‘metal poor’ T-dwarfs. The ‘T’ bit means brown dwarfs with temperatures of 1400 K and lower. (If it gets to the T spectral type then it’s definitely not an actual hydrogen-burning star. The situation gets muddled for L-dwarfs, which are hotter brown dwarfs; some of them actually are proper stars, albeit pretty much the coolest and faintest there are.)

The ‘metal-poor’ refers to chemical composition. In astronomy a ‘metal’ is any element heavier than helium. This sounds an odd definition but it actually makes sense. Hydrogen came direct from the Big Bang. So does most of the helium. With the exception of some lithium, though, everything else was made in stars, as by-products of nuclear burning. All the carbon, oxygen and uranium and everything else was either blown out in supernova explosions or it was exhaled on the stellar winds of dying red giants. Although it’s a cliched line, we are indeed ‘made of star dust’. (I know, I shuddered too while I typed that.)

Now, there is an implication hidden in all this. The very first generation of stars, the so-called ‘Population III’, would have contained next to no heavy elements. They would have been pure H/He. But, after these first stars died, they would have enriched the surrounding gas clouds with the first heavy elements. The next stars, the so-called ‘Population II’, started off with small but non-zero metallicities. Then, as some of these stars age and die, they dump more metals back into the Galaxy, leading to the formation of the modern stars, like our Sun – the so-called Population I.

Now, there are no observable Pop III stars (at least, that we know of). It’s thought that they’ve all evolved and died, although some of their light may still be visible in the cosmological background, at extreme red-shifts. Population II, however, still lingers on. You see, the less luminous a star is, the longer it lives. Although fainter stars tend to be less-massive as well, their nuclear burning rate drops off through the floor. The theoretical life expectancy of a red dwarf of (say) 0.1 Sun-masses is on the order of 6,000 billion years(!).[1] Pop II red dwarfs should still be visible – the universe is only 13.7 billion years old, so they should barely even have changed in that time. (In fact, we can still see Pop II stars to spectral types as hot as F – these are the so-called ‘cool subdwarfs’.)[2]

And, if they exist, we should also be able to see Population II brown dwarfs. Now, I said something about brown dwarf formation earlier. Pop II T-dwarfs will have formed under very different conditions from ‘modern’ objects. The structure of the Galaxy was different and so was its chemical composition. One might suppose this would affect formation processes. So, if we can find a robust sample of Pop II brown dwarfs, we can compare their properties to modern ones and see if there are any differences. If we can find differences, then we just be able to shed some light on the actual physics of star formation. Also, it may clue us in as to which processes are active in brown dwarf formation.

…But first we need a decent sample. It’s only in the last few years that the instrumentation has become advanced enough to allow for a survey for such faint objects. Finding and following up candidates is a lot of work. That’s where I come in. Creating that sample is the science aim of my PhD.

So, now you have an idea what it is I do, and why. Next post: why I like T-dwarfs. (Answer: they’re rather Lovecraftian…)

[1] Laughlin et al 1997
[2] Yes, there is an elephant in the room – where are the Pop III red dwarfs?

A Painting

Posted in Art, SF with tags , on November 9, 2009 by davidnm2009

I have a DevArt gallery; which is here.

Here’s an example of the sort of thing I occasionally do:

 

Halloween_web

 

H.P. Lovecraft is a guilty pleasure for me. Yes, it’s cheesy and it’s hack writing, but it’s fun hack writing! I faniced the idea of doing something with a vaguely Lovecraftian vibe – except set on the Moon. And that’s where this painting came from.

Who am I?

Posted in Personal with tags on November 9, 2009 by davidnm2009

Hello. My name’s David. I live in the general vicinity of London – or at least, within the commuter belt, anyway. I’m an astronomer – or, more accurately, I’m a British astronomy PhD student in my late 20’s. The ‘day job’ (and contrary to public impression, it mostly is a day job) involves research on chemically-peculiar brown dwarfs. I’ll probably elaborate on that at some point.

Anyway, this is intended as my little corner of the Web, where I can witter publicly about whatever catches my interest. Astronomy will probably be part of it, although I don’t intend for this to be a science blog as such. Probably this will mostly consist of the odd news story and the occasional bit of current affairs. Probably also the odd bit of artwork. Also I imagine science fiction will come up, given that it’s one of my major obsessions.

Anyway, if you want to say hello, please do!