…..And the rocks melt wi’ the sun


Happy Burns Day everybody. While I contemplate my failure to acquire a haggis and some Irn Bru in Honolulu, I thought I may as well find a tenuous link between Burns and astronomy.

Robert Burns was not only a poet in his own right, he was also an important librarian of Scots traditional songs. Sometimes he would add his own input to the lyrics, sometimes he wouldn’t. One of the songs he catalogued was My Love is Like a Red, Red Rose,

O my Luve’s like a red, red rose
That’s newly sprung in June:
O my Luve’s like the melodie
That’s sweetly play’d in tune.

As fair art thou, my bonnie lass,
So deep in luve am I:
And I will luve thee still, my dear,
Till a’ the seas gang dry:

Till a’ the seas gang dry, my dear,
And the rocks melt wi’ the sun;
I will luve thee still, my dear,
While the sands o’ life shall run.

And fare thee weel, my only Luve
And fare thee weel, a while!
And I will come again, my Luve,
Tho’ it were ten thousand mile.

Here’s Eddi (It’s got to be-ee-ee-ee-ee-ee-ee perfect) Reader singing it while some people wander by and bend down in the background.

So what part of this song made me think of astronomy? This part,

Till a’ the seas gang dry, my dear,
And the rocks melt wi’ the sun

That line has always made me think of the eventual fate of the Earth.

When the Sun stops burning Hydrogen in its core, it will expand to over a hundred times its current size. This period in its evolution is known as the red giant phase. It’s possible that during this phase the Earth will be swallowed up by the Sun. Whether this will happen is a matter of debate but this paper from a few years back came up with some possible answers.

So the first part,

Till a’ the seas gang dry, my dear,

Well it is possible that the seas will dry up if the Earth becomes so hot that it can’t support liquid water. The region around a star where a planet can exist with liquid water is called the Habitable Zone. The paper tries to estimate at which point the Earth will cease to be in the Habitable Zone and hence cease to have seas and oceans. It’s sooner than you’d think. Not only will the Sun become a red giant once it stops burning Hydrogen, it also evolves during its Hydrogen burning lifetime, getting brighter as time goes on. The paper uses the latest models of stellar evolution to estimate the point when the Earth will get too hot to have liquid water on its surface. This isn’t an easy calculation as greenhouse gases in the atmosphere will have some effect, but the authors reckon the Earth’s oceans could possibly disappear in about a billions years. Long before the Sun becomes a red giant.

And so to the final part,

And the rocks melt wi’ the sun

Well again it isn’t just a case of working out when the Sun will get to the size when it will engulf the Earth. When the Sun evolves it will lose mass meaning the orbits of planets in the solar system will get larger. It’s probable due to this that the Earth’s orbit will lie outside the maximum size of the Sun. However, another effect comes into play. When the Sun gets to the red giant phase its rotation rate will slow and the surface will get close to the Earth’s orbit. The Earth’s gravity will deform the Sun slightly, leading to a bump on its surface. As the Sun will be rotating more slowly than the Earth will orbit it, the bump will lag behind the Earth and produce a drag on it. This will pull the Earth towards the Sun. The authors calculate that, combined with the drag of the Earth moving through the Sun’s atmosphere, the Earth will be sucked into the Sun in about 7.6 billion years.

So,

Till a’ the seas gang dry, my dear,
And the rocks melt wi’ the sun

Or in one billion or 7.6 billion years.

Schröder, K., & Connon Smith, R. (2008). Distant future of the Sun and Earth revisited Monthly Notices of the Royal Astronomical Society, 386 (1), 155-163 DOI: 10.1111/j.1365-2966.2008.13022.x


A little light reading

Finished reading Niall’s post on weird things seen by Kepler? Still need somewhere to go to extend that procrastination a little bit further? How about this week’s Carnival of Space, hosted this week by the Noisy Astronomer? If that’s not enough, Neurotopia lists the 50 best science posts published in the Open Laboratory over the past year. Phew, reading that lot should keep anyone busy for a while.


What the hell are these things?

You know the drill, I find a paper detailing some wonderful discovery, waffle a bit of background and then give a glib summary of the conclusions. This is a bit different, this is the scientific process snow leopard caught outside it’s den, looking for a kill. Because the answer here is, “We don’t know”.

You might have heard of the Kepler telescope, it’s up there, looking for planets around other stars and maybe other things. It searches for planets by staring at a field with a lot of stars in it. If a planet orbiting one of the stars has an orbit with just the right alignment it can (once per orbit) get in the way of some of the light from the star, causing it to appear dimmer. Conversely, when the planet is on the other side of its orbit, the star can eclipse it, but given planets are much dimmer than stars, the effect on the measured brightness is small.

However, today this paper came out detailing two very strange discoveries. These are two objects, orbiting around two stars where the smaller object going behind the star causes a bigger dip in brightness than the smaller object passing in-front of the star. This means the smaller object must be pretty bright and as the authors calculate, pretty hot too. Using the data from the light curves of the star-object systems, they are able to calculate estimates for the size and temperature of these objects. One is between a fifth and a quarter of the Sun’s radius and about 9000°C, orbiting the parent star every 5 days. While the other is about a twelfth of the Sun’s radius, 10000°C and goes round its parent object every 23 days. To put these numbers into context, Jupiter is about a tenth of the Sun’s radius and a typical gas giant planet in the sort of orbits these objects are in would have temperatures below 2000°C.

So these objects are much, much hotter than they should be. So what are they? Well the authors speculate that they could be the hot remnants of stars stripped of their outer atmospheres. When stars age they puff up. If stars are in binary systems that are close enough, the binary companion can remove the outer layers of the star, leaving a small hot core. Perhaps this is one of these objects.

Strange, seemingly new classes of objects such as this will attract a lot of follow-up studies. The primary goal will be to work out what mass these objects are, the authors produce an estimates of the masses based on interactions between the objects, but an RV mass will be much more accurate. This will require measurements of the parent stars’ radial velocity.

So the conclusion of the paper, don’t know. Possibly the most interesting conclusion you can have in science.

Jason F. Rowe, William J. Borucki, David Koch, Steve B. Howell, Gibor Basri, Natalie Batalha, Timothy M. Brown, Douglas Caldwell, William D. Cochran, Edward Dunham, Andrea K. Dupree, Jonathan J. Fortney, Thomas N. Gautier III, Ronald L. Gilliland, Jon Jenkins, David W. Latham, Jack . J. Lissauer, Geoff Marcy, David G. Monet, Dimitar Sasselov, & William F. Welsh (2010). Observations of Transiting Hot Compact Objects Submitted to ApJL arXiv: 1001.3420v1


We are now on twitter

Just a quick note to say that we are now on twitter. We’ll be tweeting to let you know when we have a new post up obviously, but also if we find something interesting and we want to share it quickly.

To follow us add allinthegutter (thwarted by annoying character restrictions on usernames!) To let you know who is writing a tweet, we’ll put the first letter of our names before each one. There’s also a nice list of tweets in the sidebar and tweet buttons on all the posts.


A new, bigger kind of boom

This post was chosen as an Editor's Selection for ResearchBlogging.org


Firstly apologies that this post may seem a bit behind the times given that it’s based on an article that was in Nature a month ago. I don’t read Nature too often as I’m too cheap to buy my own subscription and the only other way to read it would be going into the institute’s library which is full of grad students who make me feel old. However the article in question appeared on the arXiv this week.

As you probably know, stars sometimes blow up completely. These massive explosions are known as supernovae. They rarely happen in our Galaxy (maybe one a century), but look at enough galaxies and the chances are you’ll see one. Most supernovae fall into two main types, Type Ia supernovae and core collapse supernovae. In the former a white dwarf explodes, probably after gaining mass from a companion in a binary system. In the latter a massive star fuses elements in its core until it has an iron centre. Fusing iron nuclei together won’t produce energy, so the star must have some other way of supporting it. However if the star is sufficiently massive (above about 8 solar masses) as stars that have iron cores are, it has no other way to support itself and hence its core collapses, leading to an explosion of the star. There is however a third possibility.

A very massive star is supported against collapse by high energy photons (particles of light) which provide a pressure to push again gravity. However if the star is hot enough this mechanism can go horribly wrong. In a strange quirk of particle physics when photons are produced with a high enough energy, they can turn into an electron and its antiparticle, a positron. This process leads (with a few complex steps) to the star’s core becoming unstable and collapsing. This happens long before the star would have time to form an iron core. Such an event is called a Pair Instability Supernova (PISN) and only occurs with a star more massive than about 140 solar masses.

And so this article claims that a recent supernova (SN 2007bi) found in a dwarf galaxy has all the characteristics of a PISN. The authors followed the supernova for 18 months and also took spectral observations. Supernovae get bright and then fade away with time. The authors note that this event closely matches the expected light curve and maximum brightness for a very high mass progenitor with a core mass of about 100 solar masses and a total mass double that. They also examined the object’s spectrum and found that the event produced an extremely high amount of radioactive nickel. In fact the authors believe the explosion produced more than seven solar masses of radioactive nickel. This is another pointer that the event was a PISN.

It isn’t 100% certain that this was a PISN, another paper on the subject suggests the galaxy this explosion occurred in was not the type of environment PISN supernovae can happen in. However given the maximum brightness and spectrum of this event it is possible this is the first observation of a very big kind of boom.

Gal-Yam A, Mazzali P, Ofek EO, Nugent PE, Kulkarni SR, Kasliwal MM, Quimby RM, Filippenko AV, Cenko SB, Chornock R, Waldman R, Kasen D, Sullivan M, Beshore EC, Drake AJ, Thomas RC, Bloom JS, Poznanski D, Miller AA, Foley RJ, Silverman JM, Arcavi I, Ellis RS, & Deng J (2009). Supernova 2007bi as a pair-instability explosion. Nature, 462 (7273), 624-7 PMID: 19956255


Brrrrr….


I know, I know, it is winter, it’s not that weird to get cold weather in winter, everybody moans about a little bit of snow, but really there’s more than just a little bit around at the moment:

The chilly image above comes from the Earth-observing Terra satellite (credit: NASA/GSFC, MODIS Rapid Response) and it shows the worst snowfall to hit the UK in 30 years (according to the news!) which means that I’m allowed to complain, just once, that my feet are FREEZING!

Not everyone in Britain has spent the past two days refusing to leave their flat. Watch the video below to see what a group of engineers at National Instruments did in their lunch hour (and make sure you don’t miss Rich’s health & safety briefing at the end).


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