NAMdudno

Hello from the (surprisingly) sunny North Wales seaside town, Llandudno! I’m here, along with around 500 other astronomers, for the Royal Astronomical Society’s National Astronomy Meeting, which began on Sunday night and continues until Thursday lunchtime. The conference centre is right on the seafront which is a little distracting.


Sunny Wales

I’m not giving a talk this year (had quite enough of that at last year’s meeting) but I am helping out on both the LOFAR-UK and Herschel & Planck Telescope stands. I was even roped into helping to build the Herschel stand on Sunday afternoon, but I think the end result looks pretty good:

Those are the quarter scale Herschel and Planck Telescope models you can see – the real satellites (the ones currently in space) are four times bigger.

It’s been an interesting meeting so far. However, the wifi can be a little flaky; my connection’s just dropped out and lost the rest of this post! Here instead is what I can remember from it:

1. The mysterious object in the nearby galaxy M82 remains mysterious. It’s looking more likely that it’s something like the microquasars we see in our own galaxy (which was the the likeliest explanation last year) but still more data are needed.

2. A combination of astronomy and history suggests that the supernova Cassiopeia A may have gone off several decades earlier than previously thought – in the early 17th century – and fortuitously coincided with the birth of the future Charles II.

3. A peryton is both a winged yak which casts the shadow of a man and a type of radio interference that can be mistaken for an extragalactic radio burst.

4. Schoolchildren are going to be manning a global network of telescopes for Global Jet Watch – a new project to monitor microquasars in our galaxy.

5. Plants growing on a planet with two dim, red dwarf type, suns could have black leaves so that they can use as much of the light they’d produce as possible for photosynthesis.

Oh, and one more thing I’ve found out. The planned Overwhelmingly Large Telescope (OWL) actually already exists in North Wales, but it’s a lot less impressive than I’d been led to believe:

If this has whetted your appetite for astronomy news keep an eye on the Royal Astronomical Society’s page, or follow the #nam2011 hashtag on twitter for minute-by-minute updates.

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Pluto gets hot(ter)

You know Pluto, a Kuiper Belt object and a previous planet. It’s made of rock and ice, not just water ice but also nitrogen, methane and carbon monoxide ice. Like all planets (and Kuiper Belt objects) Pluto is on an elliptical orbit. However its orbit is much more elliptical than any of the eight planets in the Solar System. This means its distance from the Sun varies by up to 40% during its “year”. As the amount of energy received from the Sun is greater the closer you are to it, large changes in temperature occur over the course of one orbit. 

So what happens when Pluto gets closer to the Sun and heats up? It boils. Well actually it sublimates meaning the gases change from solid directly in to a gas. This means that when the ex-planet is near the Sun and hot, it is warmed up and gases are released from the surface forming an atmosphere. When it is far away it gets colder and those gases can freeze back on to the surface.

Luckily for astronomers wanting to study it, Pluto made its closest approach to the Sun in 1989. This means it is still pretty warm and so it has an atmosphere which can be studied. However this is not a simple thing to do.

Pluto and Charon, its largest moon. Credit: NASA

Pluto is a long way away and pretty small. Hence observing the tiny silver of atmosphere around it is difficult. The simple trick is to wait for Pluto to pass in front of a background star who’s brightness can be monitored. Subtle changes in the star’s brightness provides valuable information about the icy body’s atmosphere. This doesn’t happen often but luckily it is passing through the plane of the Galaxy which means the number of background stars is very high. So this combined with the fortunate timing of its closest approach means the rather jammy folk who study Pluto can look at its atmosphere when it is warm in detail every few years when it passes in front of a star. One such event happened in June 2006. A study based on this found that the atmosphere had warmed by 1.2-1.7 degrees Celsius compared to a previous close encounter with a star in 1988 (although it’s still about 170 below zero). It also detected the atmosphere up to about 135km.

So to a paper which came out today. Astronomers based in St Andrews, Scotland and on the Big Island of Hawai`i used the James Clerk Maxwell Telescope on Mauna Kea to probe the upper atmosphere of Pluto. It’s been thought for a while that there could be part of Pluto’s atmosphere which extends to a few thousand kilometres. This study looks for the telltale traces of carbon monoxide. They have a clear detection of carbon monoxide and use the shape of the spectral line to estimate the temperature and hence the height above the surface this gas would lie at. It turns out to be over 3000km above the surface of Pluto (compared to Pluto’s solid radius of 1153km), much higher than the denser lower atmosphere detected when it passed in front of a star in 2006. The researchers also find a very slight shift in the wavelength of the spectral line, opening the possibility that Pluto may have a comet-like tail.

All this provides an interesting preview of the sort of results NASA’s New Horizons missing which will arrive at the frigid sphere in 2015. While Pluto isn’t significant enough to be considered a planet, it’s certainly still fascinating astronomers.

J. S. Greaves, Ch. Helling, & P. Friberg (2011). Discovery of carbon monoxide in the upper atmosphere of Pluto MNRAS arXiv: 1104.3014v1

Young, E., French, R., Young, L., Ruhland, C., Buie, M., Olkin, C., Regester, J., Shoemaker, K., Blow, G., Broughton, J., Christie, G., Gault, D., Lade, B., & Natusch, T. (2008). VERTICAL STRUCTURE IN PLUTO’S ATMOSPHERE FROM THE 2006 JUNE 12 STELLAR OCCULTATION The Astronomical Journal, 136 (5), 1757-1769 DOI: 10.1088/0004-6256/136/5/1757


Investigating the unexpected

One of the most interesting things in science is finding something unexpected in your data, and this is exactly what happened to a group of astronomers when they looked at the objects present in their large radio sky survey.

Before I get to what they found though, we’re going to need a little bit of background (don’t worry, there’s not much). These days when astronomers look at a large patch of sky with a particular telescope they tend to chose a bit that other people have looked at before at a different wavelength. Objects in the Universe emit light at many wavelengths, from gamma-ray through optical to radio, so combining observations from several complementary surveys gives a more complete picture of what’s going on up there. A consequence of this approach is that once you have one set of data for a particular source you can predict how it will look in another, assuming your guess as to what kind of source it is is correct.

So, to get back to the astronomers and their radio survey, the unexpected things they found were infrared-faint radio sources. These are objects which, as their name suggests, are bright at radio wavelengths but very, very faint when they looked for them in the infrared. Normally, radio sources like this are active galactic nuclei (AGN), but the lack of an infrared detection is weird.

What are they then? Well, in the words of this post’s referenced paper, “Are the infrared-faint radio sources pulsars?”. A pulsar is the rapidly rotating remains of an exploded star in our own galaxy, from which we see regular radio pulses of the right sort of brightness to be candidates for these mystery objects; Niall gives a longer description of them here. Unfortunately when the astronomers looked into this hypothesis they found that their odd infrared-faint radio sources weren’t pulsing, and the answer to their title question is no.

This paper is a great example of how a non-detection in science can also be useful. The paper authors may not have pinned down just what infrared-faint radio sources are, but they’ve managed to rule out something they aren’t.

ResearchBlogging.orgA. D. Cameron M. J. Keith, G. Hobbs, R. P. Norris, M. Y. Mao, & E. Middelberg (2011). Are the infrared-faint radio sources pulsars? accepted by MNRAS arXiv: 1103.6062v1