Archive for January, 2011


Posted in Art, Personal with tags , on January 30, 2011 by davidnm2009

Dark Faculae just passed the 3,000 views mark, which is rather more than I ever expected this to get. (Let alone in barely 18 months, as well.)

So, umm, thanks, everyone! (And roll on 4,000…)

In the meantime, here’s a picture:

The Problem of Entropy

Posted in Science with tags on January 29, 2011 by davidnm2009

I’m fascinated by the whole Creationist thing. Or, more accurately, I’m fascinated by the fact that they’ve latched onto evolution. You see, they really should have latched onto physics instead.

Why do I say that?

Well, let’s have a look…
Continue reading

Surfaced At Last

Posted in Astronomy, Personal with tags , , , on January 26, 2011 by davidnm2009

It’s been a long time in the making, but my paper has finally seen the light of day:

Blue not brown: UKIDSS T dwarfs with suppressed K-band flux (Murray et al 2011)

I got the acceptance e-mail from MNRAS yesterday, so it was time to get a copy onto arxiv. It’s a good feeling, finally having all of that sorted!

Pulsar Planets

Posted in Astronomy with tags , on January 21, 2011 by davidnm2009

Recently, I mentioned Kepler 10b.

One of 10b’s big selling points is its billing as the first definitely, definitely-solid exoplanet – i.e., one made of rock, not a gas giant. But actually, being strict, it isn’t the first definite rocky exoplanet – rather, it’s the first to be found around a main sequence star. As for the actual first, well, that’s a surprise.

In fact, the very first were discovered in 1990, orbiting PSR B1257+12. They orbit a neutron star!

If you’re surprised by this, so was the world of professional astronomy. You see, PSR B1257 is a pulsar – a rapidly-rotating stellar corpse, so dense that it’s composed mostly of neutrons with only a thin ‘normal-matter’ crust over them. It would be as little as only a dozen or so miles in diameter, despite weighing in at several solar masses. Its core density is that of nuclear matter – absurdly high. It has an extremely powerful magnetic field, which focus its rotation into two beams. As the neutron star spins, these beams sweep on and off across our line of sight, making it appear to ‘blink’ – to pulse. Hence the term pulsar.

How could such a bizarre object form? The answer is, violently.

It would originally have been a hot blue star, class O or B, and after only a few short million years that star would have ended its life in a supernova explosion. Supernovae are some of the most violent events that can occur in the modern universe – at least momentarily, the luminosity of a supernova can match the output of the galaxy it occupies. Inside them, temperatures and pressures reach levels not seen since shortly after the Big Bang. Due to their titanic luminosities, supernovae are visible over extreme distances – SN 1987A, which occured in one of Magellanic Clouds, was a naked-eye object despite being located 168,000 light-years away. With modern telescopes, we can see supernovae pretty much as far as we can see galaxies.

And if the Sun went supernova*, we would expect it to boil off the Earth. That’s right – no planet left!

In a nutshell, this is why no-one expected the pulsar planets. Pulsars are just not somewhere you’d ever expect to find a planet. In fact, there was some resistance to the idea within the community – and no wonder, given how basically crazy it is.

Anyway, no-one was expecting to find planets around pulsars. They were spotted by the anomalies they create in the beam – pulsars are some of the most precise clocks in nature. The planets’ gravity tug back and forth on the (ex-)star as they orbit it, causing slight variations in the timings of its rotation. Pulsars are so absurdly precise that even small bodies can be detected, hence the revelation of planets.

Further investigation has revealed a family of planetary bodies around PSR B1257, with one object about as heavy as our Moon, two more that are between 3.9 and 4.3 Earth masses and a fourth and final, miniscule object that may be the first detected dwarf exoplanet.

Also, it emerges that at least one more pulsar has a definite planet – PSR B1620-26. This too is a weird system – the pulsar is binary with a white dwarf, and the planet orbits both of them. The planet in this system is believed to be one the oldest known, perhaps barely a billion years younger than the universe itself.

The existence of pulsar planets leaves a lot of unanswered questions. The obvious one is, how did they get there? One possibility is that they’re what’s left of the cores of gas giants, Jupiter-size and upwards. When the star went BANG!, the outer atmosphere would have been stripped off, leaving behind a tiny nub from the core. However, there is controversy over this model. (An obvious problem with PSR B1257 is the tight spacings of its planets – could that many super-Jovians have stable orbits when so close together?) Another – and perhaps more likely – suggestion is that the system formed in situ, after the supernova had run its course. Perhaps the planets accreted from nova-debris, or from a subsequent interaction with another system.

What it does seem to tell us is that planet formation is a robust process. It can happen in some of the most extreme environments imaginable. This bodes well for the distribution of planets across the rest of the Galaxy.
*Which it can’t: the minimum conceivable mass for a supernova is the Chandraeskhar Limit of white dwarfs, which is 1.44 solar masses. And this is a hard limit, set by the basic physics – a supernova collapse can only occur when the inward pressure of a star’s weight is greater than that which electron degeneracy can support. In practise, a huge amount of material is flung out during a supernova detonation, so progenitor-stars weigh in with at least 8 solar masses.

Rho Aquilae – The Star That Moved

Posted in Astronomy with tags on January 21, 2011 by davidnm2009

I used to live in Exeter. In that town, there’s a famous building, presently located off of Fore Street. It was built some time in the 15th or 16th Centuries, but found itself under threat in the early 1960s from a new road development. In 1961, rather then have this listed building demolished, the Council paid to have it moved. And move it did; the entire house was put on a timber cradle and shifted 70 metres to the bottom of West Street. And there it remains to this day. (There’s a video of the move here.)

One of the occupational perils of astronomy is people wittering about their star signs. Unfortunately, to an astronomer, constellations are next to useless. You see, people tend to assume that stars are like houses – they don’t move. But, as we just saw with Number 16 Edmund Street above, every now and then houses can do exactly that. In fact, unlike most houses, stars are moving all the time. It’s just that this change seems small from the immense distances we see them at. As such, most of these ‘proper motions’ are not visible to the eye over the course of a human lifespan. In fact, most of the constellations haven’t changed much over the course of recorded human history. The zodiacal constellations come to us from the Ancient Greeks and thus haven’t changed much in at least two to three thousand years (with the exception of the odd deletion or border change).

However, over time, the constellations do drift. This is why they’re no use to professional astronomy – they’re no more than line-of-sight effects. Come back in 200,000 or 2,000,000 years and Orion and Ursa Major will be long gone. But of course, very occasionally, notable changes can happen rather faster.

This brings us to Rho Aquilae.

Rho Aquilae is a main sequence star of type A2, which means that it’s pretty similar to Sirius. It’s brighter, hotter and whiter than the Sun. It’s also younger; stars of this type don’t live for more then about a couple of billion years. It’s located 154 light-years away. When it was named centuries ago, it was comfortably inside the borders of Aquila, the Eagle. Unfortunately for the Eagle, however, Rho Aquilae quietly carried on moving. (Bad star – no biscuit!) In 1999, just in time for the Millennium, it crossed over into Delphinus.

So in fact the Eagle’s star has been stolen by the Dolphin. Bad Dolphin. Of course, re-naming Rho Aquilae would just confuse things even more, so it’s kept its old name. However, it does demonstrate the practical limitations of the constellations!

Just Landed

Posted in Art with tags , on January 16, 2011 by davidnm2009

Have a Storm Raven:

I’m slowly finding my way around highlight and bump maps. The amount that you set the displacement to makes a huge difference, and it’s easy to miscalibrate it. I’ve been relatively conservative here, although high levels do give quite an interesting ‘moth-eaten armour’ effect.

(A larger version is over here)

A Broken Shrine

Posted in Art with tags on January 12, 2011 by davidnm2009

Here’s a new painting:

By the way, having the full Moon that close to a sunset is astronomically impossible – believe me, I know! I didn’t let it stop me, though.

Larger version over here, as per usual.

Although this one isn’t fan art, the basic idea was inspired by a computer game, of all things. I’ve been playing a lot of the Myth series by Bungie recently – although it’s rather old, the people at Project Magma have created a modern-operating systems patch. Also, even though it’s an old game, it’s still fun. And the graphics are still acceptably pretty, even a decade on.

Anyway, it sort of seeded the image of an abandoned stone monument in a desolate landscape. So here it is.