A record-breaking brown dwarf: as cold as ice and just 6 lightyears away

About a year ago I wrote about how Kevin Luhman at Penn State had discovered a pair of brown dwarfs that were the just 2 parsecs (about 6 lightyears) from the Sun. Well he’s gone and done it again, discovering another brown dwarf at about 2pc, only this time it’s colder, much, much colder.

A decade and half ago, we astronomers (being rather odd) were getting very excited about some new odd objects we were finding by looking at the sky in infrared light. These brown dwarfs bridged the gap between very low mass stars (which can go down to about 8% of the mass of the Sun) and giant planets like Jupiter (with a mass of about 0.1% of the mass of the Sun). Brown dwarfs can’t fuse hydrogen in their cores so they don’t have a stable brightness like stars do and hence cool with time. This means that a very cold brown dwarf could be very low mass or just very old. Anyway, the things we were getting excited about 15 years ago had temperatures of about 1100C. At this point the cloud physics of these objects change dramatically, their upper atmospheres clear and their colours in near-infrared light changes significantly.

A decade or so went along and we started to get more excited as we crept to lower and lower temperatures, getting down to about 400-500C. Then we got a stroke of luck, Kevin Luhman (yup, same bloke) published the discovery of a really cold brown dwarf around a dead star called a white dwarf. This has a temperature of 25-80C, so between a pleasant summers day and a hot cup of tea. This object was joined by a few other slightly hotter objects which formed a newly defined class of cold brown dwarfs, the Y dwarfs. These big balls of gas about the size of Jupiter could have water clouds in their atmospheres.

So now we have a new coldest brown dwarf. It was found by looking at images from the WISE satellite which studies the universe in mid-infrared radiation. Nearby stars and brown dwarfs move slowly across the sky compared to background stars due to proper motion. This can be pretty slow, a very nearby star might move at one arcsecond per year, about the apparent angular speed of a tortoise walking at the distance of the Sun. So Luhman looked for objects that had moved a lot between different WISE images and found one which he published last year. This was a pair of cool brown dwarfs with temperatures of about 1100C. Now he’s published another that is moving even faster, about 8 arcseconds per year. Despite this, it is about the same distance as the previously published one, 2.2pc (a bit more than 6 lightyears). This distance was determined by follow-up Spitzer Space Telescope observations using a trick called trigonometric parallax.

So what is this thing? Well, we know it is bright in the mid-infrared, light which it is difficult to observe from Earth and which is way beyond what the human eye can see. And that’s where the observations of it stop, well not really, we can tell a bit about this object from what we don’t see, near-infrared light. Luhman’s new object was observed by the VISTA telescope in Chile a few years back. Well I say observed, it didn’t see it, neither did Luhman’s follow-up observations with Gemini. But from those observations one can set a limit of how bright this object is in the near-infrared and hence constrain its properties. Luhman used these along with his measurement of how bright the object was in the mid-infrared to find that the temperature was -48 to -13C, colder than ice on Earth, you’d even struggle to play at Lambeau Field in those temperatures. Not that this is a solid, icy planet, it’s about 3 to 10 times the mass of Jupiter and about the same size. It’s also a bit warmer than Jupiter which has an effective temperature at the top of its clouds of about -160C.

What more will we find out about it? Who knows. Last year’s spectacular Luhman discovery sent astronomers into a frenzy, studying the weather on the objects, even mapping its clouds. This one will be harder as the object is so cold and faint, but I’m sure observers will be furiously writing proposals to observe this immediately. Wait, why am I blogging? I should be proposal writing. And I’m sure this object will be one of the first things the mid-infrared JWST will look at when it launches.


Enceladus!!!

Enceladus!!!


EU protection could be boon for Monaco’s science sector

A political manoeuvre by the government of Monaco could lead to disaster for large scientific facilities, but would be a boon for the economy of the small principality. The European Union has protected products from specific geographic regions for over 20 years. As a result, anything designated as a “Protected Designation of Origin” (PDO) can only be produced in a defined geographic region. This has resulted in champagne only being produced in the appropriate region of France, protection for the economically important Cornish pasty industry and has been a lifeline to traditional Arbroath Smokie factories which make up 40% of the economy of the Angus region of Scotland. The Monégasque government has applied (as an EU associated country) to allow its distinctive “Monte Carlo” name for casinos to be afforded the same status. The principality believes this will protect its exclusive brand from competition from down-market amusement arcades.

Monte Carlo, soon to become major centre for European research. Credit: Wikipedia

This application could have wide-reaching implications in the scientific community. Traditionally, large-scale simulations which rely on random number generation have been termed “Monte Carlo” a brand which would fall foul of the PDO designation. Large EU-based scientific institutions could now be faced with a choice, close down their computer simulation departments, or move them to the tiny city-state on the Mediterranean coast. Mark Ofchane, professor of computational astrophysics at the Irish National Space Agency says this could lead to funding problems for many departments. “Governments fund Big Science based on our ability to train the next generation of young minds for the modern workforce,” he said, “Now we have to tell the politicians that our students will be sunning themselves in glamorous Monaco rather than slaving away in subterranean labs across Northern Europe”.

The move has resulted in big plans to expand the currently tiny science research-base in Monaco. Count Simeon Poisson-d’Avril, the Monégasque science minister, has announced plans to build a new “Science City” on the outskirts of the capital. Named after a wealthy benefactor, the Hastings Metropolis will allow Monaco to fully explore the probability space offered by the influx of scientists. “We see this as a massive step up,” the Count said, “Maybe there will be some steps down in future, but we are confident these will be only part of determining the probability of us gaining the maximum economic benefit from this move.”


Don’t call me Colin

Recently the International Astronomical Union decided that planets might start getting named after things. Previously they’d been given a lower-case letter after the name of their host star. Now they could get other names, something that inspired this memorable XKCD cartoon.

Well it turns out some of the planets aren’t terribly happy about the prospect too. In-fact Gliese 581d is pretty miserable about the idea of getting a dull or bizarre name, especially if you decide to name it after your cat, Colin. Gl 581d is a planet that’s a bit more massive than the Earth orbiting a faint, red star in the constellation of Libra. It might have a temperature that means it isn’t too hot or too cold to have liquid water (the so-called “Goldilocks zone“). This means it might have life. All it wants is to get a nice mythical name like the planets in the Solar System, preferably Norse but any pantheon would do. It really doesn’t want to be called after a celebrity or your mum or Permadeath, just a nice normal, mythical name. It’s been bombarded by comets for a billion years so don’t you think it deserves a break?
Be careful however, there are some mythical names are a bad choice, particularly Vulcan. This was a planet proposed around the Sun to explain the unusual orbit of Mercury. However it wasn’t there, the change in Mercury’s orbit was due to a subtle gravitation effect that wasn’t properly understood until Einstein came along with his theory of General Relativity.

Sometimes people have named stars for monetary or patriotic reasons like Herschel originally naming Uranus “George’s Star” after the British king at the time, so steer clear of that. Also a lot of asteroids have unusual names like Moomintroll, and it isn’t keen on that either. So please give a planet a break and name it something sensible.

Thanks to @ruthangus for doing the drawing, @emilulu and Russ for helping record this at AMNH, @astrodrian for lending me his guitar, @noisyastronomer for her camera and to .astronomy and the NERD Centre. The video was partly inspired by “Hey There Andy Murray” by Far-In Jim.

The audio file is also on Soundcloud.


A really, really nearby brown dwarf binary

OK I’m going to break my blogging silence and my aversion to blogging in my subject area to post about a really cool result that came out earlier this week.

Looking up at the night sky you see a hodge-podge collection of stars, perhaps a few thousand of the hundreds of billions of stars in the Galaxy. Some are extremely bright types of star that are really far away. Others like the Sun’s nearest neighbouring system Alpha Centauri are fairly run of the mill but appear bright because they are so close. But not all stars close to the Sun can be seen with the naked eye. Take Barnard’s Star, the second closest system to the Sun, it’s situated roughly twice as far away from us as Alpha Centauri but because it’s a red, faint type of star, it’s over 6,000 times fainter and 25 times too faint to see with the naked eye. This means that even though some stars are very close to us, they are so faint that we need to use a few tricks to pick them out from bright background stars.

One of the best tricks to use is to take a picture of the sky and look back a few years later and compare the positions of stars. Stars move around the Galaxy with different orbits and hence every star has a velocity with respect to the Sun. Due to their closeness, nearby stars appear to move  more compared to background stars (their proper motion). This is simply a perspective effect, they aren’t actually moving through space faster. Hence if you look for stars moving quickly across the sky, chances are a lot of them will be near the Solar System. This isn’t simply a matter of cartography, if you want to pick out a population of faint objects, your best bet is to look close-by.

And that’s exactly what Kevin Luhman did. By taking the positions of objects observed by the WISE satellite, he found one which stuck out. It moved across the sky pretty fast and was very bright in infrared light. Looking back at images taken by other surveys he also found it detected there. This often happens in astronomy, sometimes you find an object nobody had noticed was interesting before but which may have been first detected 50 or even 100 years ago. Anyway, the object Luhman found was moving across the sky pretty fast. Well actually it wasn’t, nearby stars tend to have their motions measured in arcseconds per year. One arcsecond per year is the same angular speed as seeing the average tortoise walking at the distance of the Sun from Earth. The newly discovered high proper motion object was moving at about 2.8 Solar Tortoises, which is pretty big for stars. Well I say star, but it isn’t, it’s a brown dwarf, well actually not “a” brown dwarf.

Stars are fuelled by nuclear reactions in their core. These work because of the huge temperatures in their cores caused by all the mass above pushing down. It’s like the atomic nuclei in the core are caught at the bottom of a really big rugby ruck*. Anyway, they get so hot that they can sometimes overcome their mutual repulsion and fuse together. However some objects, with masses below about 8% of the Sun can’t reach the appropriate minimum temperature to begin stable fusion and hence are “failed” stars or brown dwarfs. When Luhman took a spectrum of his object, he found it was a brown dwarf, well actually while taking the observation he found that it was actually two brown dwarfs in orbit around one and other. Finally, using the data from the WISE satellite and other surveys he was able to work out its distance from an effect known as trigonometric parallax. This showed the two brown dwarfs are about 6.5 lightyears away, slightly more distant than Barnard’s Star.

My reaction to this was probably like others in my field, “how did we miss this?” Well the answer is simple, the system lies close to the Milky Way. The density of stars on the sky increases sharply as you go close to the plane of the Milky Way, meaning searches of nearby stars are often flooded with spurious candidates. Additionally the gas and dust in the plane make background stars appear redder and faint in the optical but still bright in the infrared. This can mimic the colour of brown dwarfs, again contaminating searches. Brown dwarf searches therefor often avoid the region around the Milky Way to make sure they can have clean samples without wading through a load of junk. Hence the extremely nearby, bright brown dwarf lay undiscovered for decades after it had first been detected.

And that brings me to my last point, this is a really cool discovery yet it hasn’t got the attention it deserves. The third closest system to the Sun was just found, that should at least be on the BBC News front page.

*There are no known instances of a rugby ruck leading to nuclear fusion


StarCraft Science

StarCraft 2 game-play (image from Video Games Blogger)

StarCraft game-play (image from Video Games Blogger)

When I was younger one of my favourite game franchises was the Command & Conquer series, in particular Red Alert (1 and 2). They were real-time strategy, or RTS, games, where you built your base, harvested resources, trained your soldiers, and invested in high-tech weaponry all whilst being attacked by your opponents (either other players, or the computer AI). If I’m honest, my game tactics were always a little shaky. I was more likely to throw everything I had on mad, suicidal, missions against the other team, rather than spending the time to properly invest in the infrastructure of my base. In extreme cases I would even sell all my buildings, spend all the money on infantry and send everyone in. Surprisingly this actually worked. Sometimes.

My friend Tom however, he was good at these games. He always had a strategy. A proper one, not the crazy, oh-my-there’s-a-tesla-coil-right-there-RUN-AWAY!, one that I’d be using. He’s been spending time recently on StarCraft 2, another RTS game where you try to become master of a region of space by colonising planets, displacing the territory of the two other rival civilisations as you go.

Tom’s not just a game player though – he’s also an astronomer. Turns out when you combine gaming astronomers (Tom & his colleague Duncan) with real StarCraft gameplay data and realistic simulations of colonisation, based on our own Milky Way, what you end up with is a model of interstellar species expansion. Unsurprisingly the game is pretty evenly balanced (to prevent any one species or strategy from dominating), but the simulations do suggest that one of the races, the Terrans, tend to win out if they put pressure on their opponents early.

Using game data to investigate real-world problems has been around for a few years now. It began when researchers realised that the spread of a virtual plague in World of Warcraft shared many similarities with the spread of real viruses.

Tom and Duncan’s results aren’t meant to directly relate to how real aliens could be spreading through the Galaxy right now (and they definitely don’t want to give the impression that “…intellects vast and cool and unsympathetic, regarded this earth with envious eyes, and slowly and surely drew their plans against us”). However, they do demonstrate the potential power in-game data has for future work in this area.

You can read more about their work at http://www.roe.ac.uk/~tat/StarCraftScience.html or on Duncan’s own blog here.


Excuses, a pop video and a quasar anniversary

Oh my. I’ve just looked at this, our much-neglected blog, and realised that the last post here was in November. The first thing I feel I should do today therefore is wish you all a very belated Happy New Year! Maybe I should go with a slightly early Happy Chinese New Year! instead.

It may sound like a weak excuse for the lack of activity around here, but we’ve all been really busy this past year. Three quarters of us have changed jobs and moved country, half of us have got married (though not to each other), and Niall’s taken the first steps on the road to pop stardom (though, and possibly in tribute to Beyonce, I’m pretty sure he’s miming):

This week is actually a very good time for me to write something here as last Wednesday was the 50th anniversary of astronomer Maarten Schmidt’s discovery that the apparently star-like object 3C273 was actually located far outside our own galaxy – several billion light years away in fact – and was, at the time, the most distant thing ever observed (thanks to Jen Gupta for the tip off). It came to be known as a quasi-stellar object or quasar, and we now know that it’s a galaxy with an active central massive black hole, which is sucking material down onto it at a voracious rate. It’s star-like appearance is because the light coming from this nucleus outshines the combined light from all the stars within it (as I’ve written about here before). Here’s Maarten Schmidt explaining the significance of this discovery in an interview from 1975:

…I would say that indeed it was, in a sense, the birth of the present era of exotic phenomena, exotic and explosive phenomena in astronomy, with the quasars, the pulsars, the x-ray binaries, the black hole, the 3 deg. background radiation. I mean all these things were yet to come. The quasars suddenly started it and since then just about every two years there has been a major development of another discovery. Astronomy in an accelerated development that is just unbelievable. I mean before 1963 things were so unlike after 1963, there was no way to compare it. So in a sense the agony and the pressure of making a good on-the-spot scientific judgment just in one day essentially, the fifth of February, was a very interesting one. Because we had not been subjected to this yet. Later on it was much easier for people to accept extraordinary things in astronomy because we’ve seen it as I said every two years we’ve seen them. This has come on with about five to six, even with seven different types of phenomena including the gamma ray bursts that you may have heard about. Fantastic things. You never heard things like it in astronomy! And if they came, it was one a lifetime… So it was the beginning of an era that, of course we didn’t know at that time, we couldn’t help but realize that the quasars would play a very important role from then on, it was clear enough.

ResearchBlogging.orgSCHMIDT, M. (1963). 3C 273 : A Star-Like Object with Large Red-Shift Nature, 197 (4872), 1040-1040 DOI: 10.1038/1971040a0


Follow

Get every new post delivered to your Inbox.

Join 871 other followers