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

Pleas for the future of physics education

Two interesting videos were posted yesterday on the problems with the current state of high school physics education. The first is an open letter to Barack Obama from Minute Physics, pleading for the US physics curriculum to include results more recent than the Civil War:

In the second Nottingham academics, and regular contributors to the Sixty Symbols video series, give their views on the situation in the UK:

Personally I found the concepts taught in my school physics courses much easier to grasp once my teachers explained them using the proper maths (mainly calculus!)

Alpha Centauri, a quick biography

So you’ve probably heard the exciting news, that a small, earth-mass planet has been identified around one of the components of Alpha Centauri. It’s the nearest neighbouring system to our Sun. Despite that it isn’t the brightest star in the sky (that’s Sirius), also it’s a southern star so is not very familiar to those of us who live in the Northern hemisphere. In-fact I didn’t see it until I was 28 and had moved to Hawai`i. Here’s a picture I took of it rising above Kilauea.

Alpha Centauri over Kilauea

Alpha and Beta Centauri rising over Kilauea. Alpha Centauri is itself a double star with a planet around one of them and a wide third star in the system called Proxima Centauri.

Because it was so far south, Alpha Cent. wasn’t well studied by early European astronomers. In the 1830s Thomas Henderson, the first Astronomer Royal for Scotland measured its distance using trigonometric parallax. This was the first distance measurement to a star other than the Sun. However he hesitated in publishing the result and Bessell scooped him to the first published distance to a star (61 Cygni).

The system itself actually consists of three stars. The two brightest components appear as a single source to the naked eye. The two stars orbit each other at a distance about 17-18 times the Earth-Sun distance. There’s third star in the system, Proxima Centauri. It’s 100 times too faint to see with the naked eye and while the two brighter components are of similar mass to the Sun, Proxima is less than an eighth of that. That said for people like me who study low mass stars, it’s still not that low mass. It was discovered by another Scot, Robert Innes who worked as a wine merchant in Australia before taking up astronomy fulltime. Simply, he found a star with a similar motion across the sky to Alpha Centauri and given their close positions (yet it’s still 17,000 times the Earth-Sun distance from Alpha Centauri AB), deduced they were a pair. This is what I do a lot in my research, but I use large catalogues produced by data pipelines, he used many painstaking measurements by hand. Sometimes I feel like modern astronomy is cheating. One interesting side-note, this double star with a wide companion set-up seems to be more common than a single star with a wide low mass companion. A rather nice  recent paper by Peter Allen and others quantified this and indicated that this may say something about how these systems form.

A quick note about the planet. It appears to be too close to the star to sustain liquid water and hence life. This system has a fairly complicated Habitable Zone. The planet is orbiting the smaller of the two stars but it will also be heated by Alpha Centauri A. Duncan Forgan wrote a paper about this earlier this year saying the difference will be small but will induce oscillations of a few degrees. Also sometimes on the surface of the planet Alpha Centauri B will have set but the planet will still be lit by Alpha Centauri A. This will of course change as the two stars orbit each other. Duncan has a nice blog post about the paper where he also talks about sleeping rhythms on a hypothetical planet around Alpha Cent B. When Alpha Centauri A is on the other side of Alpha Centauri A from the planet I guess sunset will look a bit like that on Tatooine. Although with a different brightness ratio between the two stars.

So it’s Alpha Centauri has a planet. It isn’t able to support life, but maybe there’s another one in the system that can. What this discovery makes me think of is Civilisation. No, not the noted BBC TV series, but the classic Sid Meier strategy game. One of the victory conditions was to send a spacecraft to Alpha Centauri. I never got that far, on more difficult levels my civilisation would die in the Bronze Age and in the harder levels I’d get bored of nuking phalanxes in about 1900 and give up. However if I hadn’t given up perhaps I could have built a ship to head for what the Nature press release calls a “scorched barren rock”.

I think we learned something today……..

A week ago I posted about some of the videos that had been made at .astronomy4. The video I was involved in (Sh*t Astronomers Say) has so far got over 5,000 hits. I find that a little scary and it’s been odd having colleagues asking me questions on desk head-butting techinques. While this wasn’t a video with an agenda, I think there is a lesson to be learned from the post. In other words, I think we learned something today……

You remember the end of He-Man where in an earnest tone Ram-Man would explain that it’s bad to ram things with your head or Beast-Man would tell you not to put lit fireworks in your mouth*. Anyway, this is a bit like that. During the drafting of Sh*t Astronomers Say, we basically made a big list of things that we heard a lot. In many cases we added things because they are frequently done and they are annoying. Some things are annoying and are trivial, others get in the way of astronomers doing and communicating science.

The main bugbear for me was a lot of the stuff that went in to the talk section. I hate going to talks, sitting somewhere in the middle to back of the room and then not being able to see anything. The number one problem is with plots. About the worst thing you can do with a plot is jsut take the version from the paper and then slap it up there. Normally the axes will be unreadable for half the audience and often the datapoints will be a confusing jumble. Then there’s the issue of colour schemes, many are headache-inducing but often they just confuse the audience. Remember that about 8% of men and 0.4% of women are colourblind so avoid reds and greens that may be indistinguishable (I’m biased here as I’m red-green colourblind). Finally the last point, the organisors have been very nice to give you a slot to talk in, don’t outstay your welcome. There’s nothing worse than someone bringing 30 slides to a 10 minute talk and proceeding to go over each one in great detail. OK maybe regicide is worse but it’s borderline.

Was there a particular bugbear of your’s in the video? Feel free to comment on it below.

One thing before I outstay my welcome, we are going to have a go at a crowdsourced follow-up. Below are the details,

Did we leave out your personal favorite saying? Want to contribute to a new, crowdsourced version of Sh*t Astronomers Say? Send submissions to astronomerssay@gmail.com by August 31! We’ll accept any video+audio formats compatible with iMovie – you can even record with PhotoBooth! (You have a Mac, right?!?!) Please keep videos under 30 seconds and leave enough space between sayings for editing. Include your name, institution, occupation (undergrad/grad/postdoc/faculty/etc) and filming location so we can give you proper credit and estimate the diversity of contributions. We can’t guarantee we’ll be able to use every submission, but we’ll do our best!

*OK I made up the last one, but the Ram-Man one is real

When astronomers get video cameras……

Last week I (along with 49 others) attended the 4th installment of the .astronomy conference. Part of the conference was a Hack Day where people went off and designed useful bits and bobs for astronomy. One example was the Zoonibot which is designed to monitor the Planet Hunters forum to help users with classifications have posted.

For the hack I was involved with we did a video. What better way to promote the science of astronomy than with in-jokes.

Also doing a video production were Amada and Nicole who made a response to the silly,  shallow and demeaning “Science it’s a a Girl Thing” video. As you can see there’s is a lot slicker than ours which indicates they actually know how to use iMovie properly.

Science: It’s Universal from amanda bauer on Vimeo.

And yes, I know the sound is only on one side.