Follow the reluctant adventures in the life of a Welsh astrophysicist sent around the world for some reason, wherein I photograph potatoes and destroy galaxies in the name of science. And don't forget about my website, www.rhysy.net
Science, someone told me recently, is a business. This bold assertion made me too angry to respond because I've seen first-hand what happens if you try and run an observatory as a business, and it just plain doesn't work. Science is not a business. Nor is it art, or politics, or journalism, or a religion, or anything else. It's it's own thing, but like most enterprises it does have some aspects of all of those. Today I'm going to explore a few of those and look at how science and other endeavours relate to each other.
Is science a religion ? Actually screw this one, I can't be bothered.
I'vewrittenfartoomuch to bother repeating myself as to why science isn't dogmatic to go through all that again. Simply put, if you think science clings fervently to its beliefs, you are deluded. Nor does religion refuse to admit its mistakes either, though both religious fundamentalists and individual, highly intelligent scientists can and do sometimes behave like this. No amount of devout atheism will save you from being a blithering idiot - or, more to the point, from having any irrational beliefs at all. But I really don't want to dwell on this today, so just go and watch the movie Contact. Don't worry, I'll wait. Just don't bother bringing this up in the comments because I'm not in the mood, OK ?
Fair enough. What about the arts ?
You might not necessarily think that science has much in common with art either, but you'd be wrong. As explained previously, the humanities courses can be an essential tool in developing rational thinking. I'll get to the most obviously relevant form of this - journalism - in a minute, but even the purely creative arts share important aspects with science. And I don't mean the more obvious overlap of scientific illustrations, which have to be able to inform as well as (in a sense) entertain - I mean something much more fundamental.
Problem solving is not so very different to creativity. This is especially important in theoretical physics, where thinking up radically new concepts is the key to making breakthroughs, but it's also essential to be able to come up with new ways of analysing data or doing new tricks with old technology. Finding new interpretations of old data is also tantamount to being creative.
These similarities mean that sometimes the process of doing both science and the arts can be very similar. Both require large amounts of time to do nothing but thinking (and in the case of science at least, an awful lot of background reading). Inspiration can't be forced - you cannot make people have new ideas. You can, however, encourage them. Science and art are both sometimes highly elaborate forms of play, to explore the question, "what if I did it this way...", or better yet, "what does this button do ?" Such thinking intrinsically demands a liberal, reasonably informal atmosphere. Insisting that people are at their desks during some particular set of hours and only talk to each other during scheduled meetings makes absolutely no damn sense whatsoever.
And art and science sometimes both require large amounts of trial and error and sheer patience. Scientific productivity is hard to measure in any case (more on that later), but it simply cannot be evaluated at all on hourly, daily, or even weekly timescales. Above all, both require the freedom to fail - to spend years on something that may very well be utterly useless without worrying that it might end careers if nothing useful turns up*.
* Recent example - this project took a full seven years to complete, and it could easily have been the case that we would have found nothing interesting whatsoever. So you can take your hourly timesheets and file them where the sun does not shine, thanks.
You might say, "Well, in science a negative result is always useful, and in art, paintings that people hate today might be seen as masterpieces eventually." And that's partially true. Sometimes results in science also aren't recognized as significant until centuries after their inception. And, sometimes, like terrible works of art, they are just god-awful and done by people who are simply very, very stupid.
On the other hand there are plenty of pictures of Jesus, but very few that could be described as "a very hairy monkey in an ill-fitting tunic", so maybe this one wasn't such a waste after all.
The point is that sometimes there's just no way to know in advance if your research will be a load of tripe or lead to the invention of electrical power. To invest only in research you believe is more likely to have practical benefits is the sign of a small mind bereft of vision. You cannot innovate without taking risks. With science, the payoffs - electricity, radio, television, communications satellites, hurricane prediction, the internet, fewer diseases, greater food production, cheap global travel - are so stupendously important that I'm continually amazed by the ongoing need to justify science expenditure at all. It just makes no sense to me whatsoever. Perhaps it's because these things are such an integral part of our daily lives that we don't often think of them as scientific advances.
And no, I don't care about the typo.
Of course science isn't quite the same as the arts. Scientific freedom of thought has to be constrained by observational evidence, whereas the imagination of an artist has no such limits. Scientists can question whether the observations were done correctly, but that's as far as you can go - if your theory predicts that a plane will fly and it doesn't, well that's tough on you. Art on the other hand has no such clear objective measurement.
Journalism then.
Good journalism is the search for truth, no matter how unpleasant it may be or how many people want to stop you from exposing it (excepting perhaps cases where that might endanger innocent people). Similarly, good science is about the search for truth no matter how crazy it might seem or how opposed it may be to any and all ideologies.
Bad journalism, on the other hand, is all about making a sale : telling people what they want to hear or what evokes such a strong emotional reaction that they can't help but feel it's correct. It's much more about who than what or why. Similarly, bad science is about only going for easy, non-controversial results, never considering alternative ideas, interpreting the evidence to mean what you already think it should mean, and deliberately trying to agree or disagree with specific people rather than their ideas.
Sorry Augustine, but that's total rubbish. If it was true we wouldn't have people still claiming the Earth is frickin' flat or refusing to use vaccines. Maybe natural selection will kill off those idiots eventually, but it's a slow and unnecessary process. Bad journalism and bad science (and bad science communication) can be immensely damaging practises.
Good science is a lot like good journalism. The major difference is that science isn't about people, it's about specific things and general trends : the ability to say, "if I do this, given these conditions, then that will always happen." Journalism, on the other hand is usually only about discovering what happened in the past in a very specific circumstance, rather than what might happen next. Journalist's predictions are (often simply because the number of variables is so large) only speculation, even if they are very well-informed speculation, whereas established scientific results are always true. Heating up lead to ~350 C will always melt it - unlike in politics, it doesn't matter what the mood of the experimenter was or whether they'd gained enough support of their peers.
There's also a curious difference between science and journalism when it comes to impartiality. It's usually the job of a journalist to communicate the findings of experts to the public rather than present their own opinions, at least when it comes to making predictions. But it is not always the job of a scientist to be impartial. Scientists are supposed to be objective, which is not the same thing.
Suppose some imbecile of a politician decides that astrology really works. It's the job of a journalist to interview both the politician, scientists, and possibly members of the public to inform people what those groups believe, not to decide who's right and who's wrong. But it is exactly the job of a scientist to decide what's right and what's wrong, to tell you what the evidence says. When the case is a decisive as this, being impartial is not being objective at all, because astrology objectively doesn't work. It doesn't matter if you disagree, you're wrong. Science is not a democratic process.
Not quite true : you do need people's opinions on facts, but we'll get back to that soon.
It's the job of a scientist to form an opinion based on the evidence. As usual it all comes back to this : the beliefs of science are evidence-based and provisional. But for established results which have mountains of evidence (or even irrefutable proof) backing them up, objectivity and impartiality could not be further apart : a scientist who believes the Earth is flat is an oxymoron.
When it comes to cutting-edge research, however, it's another story entirely. Scientists should, of course, try and assess the evidence in an unbiased way. But that does not mean they shouldn't form an opinion about it, only that they should be prepared to change that opinion given different evidence. Of course, when there is very good opposing evidence to an idea, scientists should be honest enough to state, "this is my opinion, but for an alternative you should talk to that guy." But you cannot expect scientists not to express their opinions at all, which brings us neatly on to the next area.
Or, Galaxies Behaving Badly...
I've been itching to write this post for a while. They say the first one's always the hardest, and that's certainly true of astrophysical papers. Much toil has gone into this over the last year or so on the paper alone, but the results are not only very interesting, they're also pretty.
If we could see the hydrogen gas in the galaxy M33, it would appear around five times larger than the full Moon.
The super-short version is that we've found a new hydrogen cloud (not shown above, you'll have to keep reading for that) near to the Triangulum galaxy. It's the largest, most massive cloud that's been found there in over 30 years, and it's ring shaped. We have no idea why it's a ring, let alone what the cloud actually is. A giant starless galaxy ? A huge shell of hydrogen somehow thrown out of the galaxy ? Nothing seems to work. But to understand why this is so difficult to explain, read on.
(Note that I could have given this the clickbaiting title of "Arecibo Scientists Baffled By Giant Hydrogen Cloud" or, "Find Out Why Astronomers Can't Explain This Huge Celestial Ring" or even, "One Young Scientist Went Looking For Galaxies And You Won't Believe What Happened Next". But I didn't, because I am not a moron.)
As usual, the first part is an introduction. If you'd rather skip straight to the new results, scroll down to the "Hydrogen Hunting" section.
Trouble in the Neighbourhood
At first glance, our Local Group of galaxies is a somewhat dull place. Our Milky Way is like a great galactic introvert, hanging out with just a couple of close friends (Andromeda and Triangulum - also known as M31 and M33) and steering clear of heaving nightclubs like the Virgo cluster. Or so you might think.
The Local Group (left) compared to the nearest rich galaxy cluster (Virgo, right). The field of view - about 6 million light years - is the same in each case; the galaxy sizes have been exaggerated by a factor of twenty. Galaxy images come from the Sloan Digital Sky Survey. Small galaxies in the Local Group are shown as faint transparent fuzzy patches. You can just about see Andromeda flying past, but good luck spotting the tiny Triangulum.
But look a little closer and the Local Group turns out to be less of a fancy soiree and more of a rowdy house party. True, there are only three giant galaxies, whereas the Virgo cluster has many hundreds (possibly thousands). If you count smaller (dwarf) galaxies, the Local Group still only has around a hundred at most - it's nowhere near as crowded as a cluster, but we haven't got to the good stuff yet.
I've already described how the numbers and orbits of those dwarfs aren't anything like what we expected (have a look here, points 5 and 6). In short there aren't anywhere near as many dwarfs as models predict, and while they should be buzzing around the giant galaxies like a swarm of bees, they're actually orbiting in loose planes at right-angles to the discs.
So the Local Group is maybe like some sort of non-conformist hipster club where no-one tells anyone what to do. But that's just what we see in the visible light. When we look at the atomic hydrogen gas* using radio telescopes, things get even stranger - and messier.
* See link for details, but remember that atomic hydrogen can only be seen using radio telescopes - so colours are false.
Two major features dominate the group. The first, and most spectacular, is the Magellanic Stream shown above - a huge stream of hydrogen gas that runs halfway around the sky. Possibly more. Whenever observations get more sensitive, it seems we find it's even longer than we realised.
Most - possibly all - of this gas seems to have come from the Magellanic Clouds, two nearby dwarf galaxies. Exactly how the gas got into this peculiar configuration is not well understood, but probably has something to do with how the two galaxies are interacting with each other whilst orbiting the Milky Way. The stream isn't spectacular just because it's close though. At well over half a million light years, it's one of the longest hydrogen streams known.
Fading between an optical image of the Magellanic Clouds and the hydrogen data which shows the gas stream.
The second feature is another, much fainter stream linking Andromeda and Triangulum. This is another dramatic structure at 850,000 light years long. It's also one of the faintest hydrogen streams known, and was only detected by a survey of exceptionally high sensitivity and low resolution. So, unfortunately, there aren't any pretty pictures of this one.
So whereas the Local Group has three large galaxies and two hydrogen streams which are nothing less than awesome in extent, the Virgo cluster may have thousands of galaxies but it's only got four major streams. Looks like it's a win for the hipster house party, then. Of course the Virgo cluster has its own weirdness, but that's another story.
To understand the new results, there's one other important feature of the Local Group you need to know about. Although the main part of the Magellanic Stream doesn't go anywhere near Triangulum, a bunch of smaller clouds do. Could there be some connection between the Magellanic and the Andromeda streams ? I dunno. M33 and M31 are a lot further away than the Magellanic Clouds and the stream would have a really weird, sharp kink in it, so it could just be a complete coincidence.
Probably the best map of the stream produced to date, from a paper by Nidever et al. 2010. M33 is just above Wright's Cloud (which we'll talk about soon).
Hydrogen Hunting
Now that we've got the proper context, the new results. Most of the smaller galaxies in the Local Group are orbiting the Milky Way and Andromeda. Only one is believed to be associated with Triangulum, and that's not certain. Together with all these crazy streams (especially the M33-M31 stream), back in 2006 it seemed like a good idea to look at the hydrogen in and around M33 as part of the Arecibo Galaxy Environment Survey, AGES. This is one of the most sensitive atomic hydrogen surveys ever performed, so if there's anything interesting, AGES is what will find it.
"If all else fails, point a 300m telescope at it."
It took us five years to complete the observations - without any guarantee that we'd detect anything interesting in the end. That's the problem with a telescope that can't be steered much, but it isn't normally this bad. The difficulty was that the survey area is at the absolute northern limit of where Arecibo can see, so often we could only observe it for an hour a night. Factor in that other projects sometimes get priority, the fact that we can't see the region at all for more than half the year, and various equipment failures, and five years doesn't seem quite so bad.
Five years of stating at computer screens...
More staring at screens...
Everybody look serious now. Come on people, this is science.
Occasional bouts of madness began to set in...
... which were usually solved with late-night Dominion sessions.
Sometimes even the ALFA receiver went a little nuts and had to be taken down for repairs.
Most of the people above didn't do observations of M33. In fact most of the time we just did it by setting up a script and going home.
After all this, what did we find ? Well, firstly that the hydrogen of Triangulum is considerably more extended than what the last major survey of the area had revealed. Some of the "clouds" that ALFALFA had found turned out to just be slightly denser parts of this larger disc. Also, the disc is really quite faint - so faint, according to earlier work, it should be ionized. But it isn't. You could call it, "The Hydrogen Cloud So Large It Shouldn't Exist", if you want to clickbait it*.
* But don't. It's not the only hydrogen detection known below the ionization threshold nor the first such discovery.
Animation showing the hydrogen in M33 at different sensitivity levels. If your sensitivity isn't very good, all you'll see is the densest gas in the stellar disc. Go a bit deeper and you'll see things are a lot more extended, and part of the disc (upper right) is warped. Go as deep as AGES and you'll see that even this extended component is actually just part of something even larger.
There's one more brief digression I must make for the sake of non-regular readers. Hydrogen observations depend on frequency - that is, how fast something is moving towards or away from us. Which means our radio maps are actually 3D data cubes. They're very cool to look at (and extremely useful, as we shall see), but velocity is not the same as distance. For example some of the hydrogen in M33 has the same velocity away from us as does the hydrogen in parts of the Milky Way. So in these data cubes it can look as though the hydrogen in M33 and the Milky Way overlap each other - but in reality they're actually separated by over a million light years.
M33 is the big bright thing in the middle. Some hydrogen from the Milky Way can be seen as the big flat thing at one edge of the cube.
Anyway, although the new observations showed that some clouds weren't clouds at all, they also found new ones that pretty much exactly balanced out the numbers. Just enough to agree with how many satellite galaxies models of galaxy evolution predict there should be... but none of them have any stars !
Could these be the "missing satellites" that people have been searching for for so many years ? It's not impossible, but I doubt it. Firstly, it doesn't seem very likely that only this one galaxy happens to have the right number of companions and they just happen to be made of gas rather than stars - the model's so badly broken for other galaxies, fixing it with this one wouldn't really help. Secondly, the motions of gas in the clouds don't match the model predictions*. Thirdly, they're not distributed like the predicted "swarm of bees" at all - they're found in a distinct band. There's a hint that some of these clouds are actually linked together and part of a much larger structure.
* This is a debatable point though. More precisely, models predict how fast the gas should be moving within galaxies, and also how it's moving - that is, they predict it should be rotating. The observations say the motions are random. But a new paper has just been submitted saying that maybe the motions should be random after all.
Some of the clouds we detected with AGES (M33 is right in the middle, but at a different velocity so it's not visible here). Notice that there aren't any clouds in the top half of the survey area. Though it is awfully strange that the number of clouds is almost exactly enough to account for the missing satellites.
And two of the clouds are much, much bigger than the others. One of them - Wright's Cloud, which we mentioned earlier - has been known about since 1979. The most popular explanation is that it's part of the Magellanic Stream, or at least related to it in some way. Although it's not that close to the main stream, it does seem to follow those smaller clouds heading from the stream towards M33. It's a bit strange though, since Wright's Cloud is far larger than any other cloud at that distance from the Magellanic Clouds.
Now, 36 years later, we can reveal another giant cloud right next to Wright's Cloud that no-one had ever detected before. Well, that's not quite true. Parts of this new cloud had been found by ALFALFA. But our new observations were more sensitive over a larger area, and they've revealed that these clouds are actually just a small part of a much larger ring :
The centre of M33 (not shown) is just above and to the right of the ring.
We're calling this Keenan's Ring after "Princess"Olivia Keenan who discovered it and did most of the hard work of writing the paper. There isn't really any convention for naming hydrogen clouds, but if we get this in common usage it will probably stick. After all, it sounds a lot better than its catalogue designation AGESM33-31.
Map of all the clouds in the area. Keenan's Ring is at about as large as M33 and yet no-one knew about it until now.
So what the heck is it ? It all depends on how far away the cloud is, which we can't measure directly. If it's as far away as M33, then the thing is about 60,000 light years across - as big as the hydrogen of M33 itself ! And that would be seriously strange, because there's no obvious way to form a stonkin' great ring of hydrogen gas like this. Models show that you can do it through colliding galaxies, but M33 doesn't look as though it's had any kind of major collision recently. The gas in the Ring appears to be completely separate to the gas in M33.
The full data cube. Colours are arbitrary - blue was chosen to highlight the gas in the Milky Way, which fills the entire field of view. Orange shows everything else. M33 is the big orange blob in the middle. Wright's Cloud is the brightest-looking orange cloud which is cut off by the edge of the survey area. Keenan's Ring is visible, as are a bunch of other smaller clouds. The data looks noisier around the Ring and the Cloud, but this is just an artifact due to how the data was visualised.
Because this gas cloud is so dang large, could it be a giant, failed galaxy ? A tempting idea. Although M33 doesn't seem to have collided with anything recently, there is a strange "warp" in its hydrogen disc, and Keenan's Ring is on exactly the opposite side of the galaxy. Which is what you might expect if a giant object had come sailing past. Also, the densest gas in the Ring is closest to M33, suggesting that M33 is exerting a gravitational influence on it (which isn't the case for Wright's Cloud, which has a higher density in its center).
But this idea doesn't really work. Although there is a small velocity gradient (the gas on one side is moving at a different speed to that on the other) across the Ring, which is often a sign of rotation, it's far smaller than for M33 (~30 km/s compared to ~180 km/s). A galaxy as large as M33 really ought to be rotating as fast as M33 - if it isn't, then it isn't as massive, so it's far less likely to explain the warp. And if it was massive, that would make the predictions of the models of how many galaxies there are even worse, not better.
It also doesn't seem a likely coincidence that Keenan's Ring and Wright's Cloud are at almost exactly the same velocity. If Wright's Cloud is really just another part of the Magellanic Stream, then it seems probable that Keenan's Ring is as well. This, in my opinion, is the most likely explanation. But it's not without major difficulties either. Why in the world should there be two massive clouds near the end but significantly offset from the main stream ? And if it's not a coincidence that Wight's Cloud is part of the Magellanic Stream because it's so close, then surely by the same token it's at least equally likely to be associated with M33 in some way as well ?
No-one seems to have any answer to this. And it's also worth remembering that Wright's Cloud and Keenan's Ring are at different velocities to the other clouds detected in this area, suggesting that they might have different origins. Yet they're also very different to each other. Wright's Cloud is larger, much more massive, doesn't show any signs of a velocity gradient, has an irregular structure, and is denser in the centre. Keenan's Ring does have a velocity gradient (albeit a small one), is much denser on one side than the other, and is of course ring shaped.
And perhaps the most difficult question to answer applies to any scenario : why is it a ring ? A disc, well, that's fine - could be a giant galaxy, or just a cloud, whatever. An amorphous blob like Wright's Cloud - yeah, also possible, could be interacting with all the other clouds and M33, no problem. But there's no obvious reason why the gas in the middle should be missing. Where's it gone ?
Could it just be that the "ring" is a bunch of clouds which happen to line up and look like a ring ? Not likely. That would require an extremely unlikely chance alignment of clouds - there's no reason you'd expect the central region to be underpopulated just by placing clouds at random. And although the velocity gradient is small, it does have one. If it was a bunch of random clouds, you'd expect the velocity of each cloud to be different. But the velocity of the gas across the Ring varies quite smoothly from one side to the other, which you wouldn't expect if it was made of separate clouds. It's possible, but not credible.
Map showing the velocity of the gas at each point in the Ring
Honestly we really just don't know what this is. Supernovae explosion are known to blast holes in the hydrogen, but if it's close to M33 then the hole is about ten times larger than any other known holes. Nor are there any obvious star clusters (massive stars aren't thought to be able to form in isolation), so if it's inside our own galaxy the Ring would be much smaller but probably just as strange. And it would be one heck of a coincidence if this structure just happened by chance to not only be so close on the sky to Wright's Cloud but at such a similar velocity.
Like all the most interesting discoveries, this one poses a lot more questions than it answers. Which, if you ask me, makes it five years well spent.
Of all the allegations made against mainstream science, the charge of "false consensus" is the one that's the most worrying. The idea is that we all want to agree with each other for fear of being seen as different, or worse, that we will lose research funding for being too unconventional. Maybe individual scientists are sensible enough, but apparently some sort of "herd mentality" creeps in which can override the ordinarily sensible scientific method. It's this charge, more than any other, which I find has the most truth to it, and therefore the one I'm the most concerned about.
As far as the idea that scientists like conformity goes, that's just wrong. Wrongity wrongity wrong wrong wrong wrong wrong. Wrong.
This idea ties very closely with the idea that scientists are close-minded, which I've written about extensively here and also here. But to be fair, there is a difference between saying, "scientists prefer ideas that agree with what they already think" and saying, "scientists never consider any ideas that disagree with existing theories". The above links already deal with that, though I'll come back to it a little bit later. Today I want to focus on the question : do we at least merely prefer things which conform to established ideas ? The answer of course is no, absolutely not : but with very important provisions.
The media is awash with "scientists make breakthrough discovery !" articles, which I've also already railed against here. But, nonetheless, scientists do like discoveries. That's what science is for. And you can't make a discovery, by definition, which isn't in some way new. But you can make discoveries which are expected (boring, but useful) as opposed to those which are unexpected (exciting, but confusing).
My big gripe with the mainstream media (traditional newspapers and television channels) is that far too little care is taken in determining whether a new "discovery" is really true and a lack of interest in alternative explanations. Most recently, that gives us the headline, "Scientists may have found giant alien `megastructures' orbiting star near the Milky Way [never mind that the star is actually in the Milky Way, not near it]" in the Independent (a paper I otherwise have a lot of respect for), as opposed to the far more modest original "The Most Mysterious Star in Our Galaxy" in the Atlantic.
I want an extension for Chrome that replaces the "aliens" dude with this image.
Yes, adorable kitty, aliens are a possible explanation. But they are not the only explanation by any means, and even the scientist proposing that we have a look for radio signals (not an unreasonable prospect) says that aliens aren't the most likely explanation by a long shot. Whereas the media likes exciting ideas (or any kind of excitement at all*, really), scientists like exciting discoveries : i.e. things which are both contrary to existing paradigms, are observationally verified, and have few alternative explanations. * I'm linking to that newspaper and not any particular story on the grounds that it's a safe bet the headline won't be genuinely exciting. At the time of writing, it reads, "FELLAINI SENT ME PICTURES OF HIS TACKLE !".
The "alien megastructures" are currently only an idea, not a discovery. They are one explanation, others haven't been ruled out yet. Hence the media gets excited, while scientists react more like this :
Let's not lose sight of the fact, though, that many of these exciting "discoveries" are proposed by scientists, which ought to knock the closed-minded charge on the head.
I am also reminded of the case of superluminal (faster than light) neutrinos, which had the media up in arms and scientists sighing lethargically. The original statement by the scientists (which amounted to, "hey, this looks odd, we think it's probably wrong but we can't figure out why, so we thought you all should check it") was perfectly reasonable, as it is in the current case ("if we're going to look for aliens at all, this would be a good target") and completely different to the media hype ("EINSTEIN DISPROVED ! DR WHO IS A DOCUMENTARY !").
BICEP2 provides another great example. Here, scientists were looking for a signature of inflation, a very mainstream idea, infinitely more so than aliens building Dyson spheres. Yet when it was proposed that this had been found, the scientific community reacted with strong skepticism - and later this very important mainstream "discovery" turned out to be mistaken. It's a wonderful case of skepticism at its best, questioning even things which agree with mainstream theory. So no, we don't just attack findings which disagree with the consensus. We attack the consensus itself as a matter of course - that's why it's the consensus !
The reason all this matters is because whenever something is presented as a "discovery" when it actually isn't, or when at least equally valid explanations aren't discussed or are marginalised, it makes scientists dismissing the alternatives look like they're doing so because it doesn't fit with the cosy "false consensus" world view. Clickbaiting has a lot to answer for. But then, "Promising new target for SETI" doesn't sound as exciting as "OMG ALIENS !"
But what about when unconventional discoveries turn out to be correct ?
There's not much evidence that Lord Kelvin really said, "X-rays will prove to be a hoax", but they werefound by accident.
Well then that's when we do get excited ! Decades ago, no-one had any reason whatsoever to think that dark matter existed. A few people made claims that the stars weren't moving as conventional theory said they should, but the evidence wasn't great. Only in the 1970s did the observational data become good enough that there was really no getting away from it, and guess what ? Mainstream science changed its mind, even though our theory of particle physics didn't predict anything obvious that could explain dark matter.
More recently, no-one had any reason to think that dark energy existed. Then along came the results of two supernovae surveys, and suddenly we found that the expansion of the Universe was accelerating. Again, mainstream science changed its mind, even though none of our theories gave an obvious explanation for the cause of the acceleration. And in this case, despite still not knowing why the acceleration is happening, the discovery led to the award of a Nobel Prize - which is a pretty clear sign of excitement, in my book.
The idea that scientists don't like non-conformity is like saying that we don't want a revolution, that we somehow think that breakthrough discoveries are a bad thing. But discoveries are the name of the game, so this is basically saying that scientists hate their job. If you've ever talked to a scientist for more than five minutes, I very much doubt you'll agree that this is the case.
It's not that we hate exciting discoveries. It's that we hate getting excited about things which aren't true. Everyone wants to make a name for themselves by making a killer breakthrough (see BICEP2 above), but no-one wants to be remembered as the moron who gave way to premature publication (also see BICEP2 above).
Still, while I think the above dismisses any notion that we don't like excitement or unconventional discoveries, I haven't really addressed the charge that we prefer discoveries which agree with existing ideas. Maybe breakthrough discoveries aren't being entirely shot down, just suppressed and held back longer than they should be.
Well, OK, if scientists don't hate excitement, do they at least prefer to be dull ?
No, but it's good practise not be over-enthusiastic. Science is a slow, careful, and often tedious process. The big breakthroughs are undeniably exciting, but much rarer than the day-to-day process of research. We don't have Star Trek level computers yet. We can't just say, "Computer, run a simulation of solar flares with the observed magnitudes of all flares detected in the last 100 years and compute the probability of disruption to satellite communications in the next six months." The best we've got in terms of automatic language recognition is Siri, and she's not very helpful.
No, we've got to actually look through old records for the data, decide on the best sort of simulation to run, apply for time on a supercomputer to run it, investigate the vulnerabilities of satellites to electronic disruption, etc. etc. etc. for ourselves. Computers are a long way off from replacing researchers.
Science is dull by necessity. Without doing all that work, you can't get to the exciting results. We prefer exciting results which are true, but it's only by doing all those dull tasks, and making all those boring, expected discoveries, that we stand any chance of being sure we've found an exciting result when something interesting crops up. You can't know what's unusual without first knowing what's normal. And you do have to take a certain satisfaction in doing rather a lot of repetitive tasks, otherwise the process would be unbearable.
I personally have long since lost count of the number of times I thought I'd seen something really interesting in a data cube, only to find that it was either a mistake I'd made or a problem with the data itself. 95% of these never even made it to the stage of "I should check with someone else" because I was able to dismiss them very quickly. It wasn't particularly rewarding, but it's a necessary part of the process.
No-one ever gets excited when a paper that's nothing but a catalogue of detections comes out. It's simply that it's not possible to get to the excitement without doing the gruelling legwork. Real science is not much like movie science.
In short, if science appears to be boring and conformal, that's because science is hard. This relates closely to the clickbaiting articles I mentioned earlier : there is a widespread misconception that science is only interesting when it's exciting. The most notable, prominent exception in the mainstream media to this is David Attenborough. The man could easily hold my attention for a full hour talking about nothing except the mating habits of snails, and I'd be absolutely riveted. Yet at no point would I ever feel the urge to leap from my seat, punch the air and shout, "YEEEAH ! SNAIL SEX IS MORE AWESOME THAN SALMA HAYEK WATER SKIING WITH NINJAS AND LASER KITTEN SHARKS !".
Which is not to say I don't find Salma Hayek (with or without ninjas laser kitten sharks) exciting... just that if I have to choose between a Salma Hayek movie and an Attenborough documentary, it's a tough choice.
Soo... you're saying the false consensus idea is just wrong then ?
Thus far the idea of a false consensus looks to be on very shaky ground. Science is often dull and conformal, but only as a means to the exciting breakthrough discoveries which are possible. Revolutions that completely overturn long-standing theories certainly do happen, just rarely. That's because : 1) We want to be sure we're correct because we hate wrong conclusions; 2) A theory that lasts a long time has stood up to a lot of tests, making it (by definition) a very good theory and therefore harder to disprove; 3) The process of doing science is long and tedious.
I say forget trying to make people excited about science all the time, because it isn't usually exciting. Get them interested instead.
Which is not to say it isn't sometimes very exciting indeed.
The perception that we're all trying to agree with each other largely rests on the media constantly promoting things which are exciting but not true as though they were true, which results in scientists having to repeatedly explain why they're not true, making us look like we disagree because we don't like it.
Aren't you being a bit idealistic ?
So far I've painted a very rosy picture. In the real world, scientists are fallible human beings. They lie, cheat, steal, fornicate, drink, take drugs, rape, murder, create weapons of mass destruction, become assassins, vote for the Conservative party, listen to Celine Dion, and use their enemies skulls as drinking cups. Well... probably not that last one. And apart from the WMD bit, you could say the same for people of any vocation.
As with discrimination in any situation, the question to ask is : does this really represent a wider problem ? Are we seeing a flaw in the system, or just flawed individuals ?
The above is a wonderful piece of satire, but it does emphasise a mood among certain elements that the climate consensus must, somehow, despite all the robustness of the scientific method, either be wrong or just not really exist.
When I encounter reasonable people on the internet, and explain to them what I do and my personal experiences of the scientific method, they sometimes respond with something along the lines on, "Well, of course I didn't mean you, Rhys. I meant that lot. Those darn climate scientists. They're not allowed to publish anything that disagrees with their precious theory."
If that's so, then it's completely at odds with my own experience of the scientific process. I know a number of people personally who hold and publish results which are radically different to the mainstream (some are well-respected figures, some are... not). I'm also aware that human failings do cause problems with the scientific method : sometimes paper referees are overly-harsh, sometimes they will let shoddy work through on a nod if a famous name is on the author list.
(You will have to forgive me, but for obvious reasons I'm not going to name names.)
But the allegation of a false consensus is wholly different. That's saying that almost everyone, everywhere, in every institute, refuses to publish something because they think that either a) it won't get past the referee; b) if it does get past the referee, it will damage their reputation; c) never even considers the possibility / hates the idea in the first place because they're so darn closed-minded.
Options A and B are swiftly dealt with : not every publication is peer reviewed. Conference "proceedings" (the written summary of a conference) are rarely reviewed, and even when they are the review process is not supposed to be as strict as for a regular journal. Consequently they're often much more readable, but not as detailed or as reliable, than regular publications - but I've never seen a proceeding article that differed radically from the reviewed version*. As for option B : nah, also silly, I know plenty of people who don't give a hoot about their reputation - even at the expense of their funding.
* And I'll add that even in refereed articles, you can generally say whatever you like as long as you make it clear when you're speculating.
Option C, however, is more serious - because I do know people who are so closed-minded that they refuse to consider certain ideas. That includes people who are so ultra-mainstream they think we've basically got everything licked and laugh in the face of alternatives, and people who are so anti-mainstream they think their silly pet theory has trumped Einstein. Individual scientists are certainly capable of being dogmatic.
But the idea that the system as a whole is so closed is pure nonsense. MOND isn't a mainstream theory, but papers get published on it all the time (26 papers so far this year with MOND in the title). No less a mainstream institution than the Monthly Notices of the Royal Freakin' Astronomical Society has published papers on cyclic extinction events (an idea that's been controversial for thirty years or so), at least twopapers about dark matter causing the untimely demise of the dinosaurs, and recently one has been submitted about aliens building megastructures around that star. And the equally respected Astrophysical Journal published one this year about looking for Dyson spheres via the Tully-Fisher relation, for crying out loud.
Maybe it was a passing Dyson sphere, deflected by the dark matter in the galactic disc, that disturbed the Oort cloud and sent in the comet that killed the dinosaurs. Yeah.
If all that's still not enough to kill off the idea that controversial ideas aren't considered, look no further than the late, great Sir Fred Hoyle. A man who, amongst other things, believed the Universe was eternal (he hated the now-mainstream Big Bang theory) and that life didn't arise on Earth (which is still not settled today*). Yet few would dare label him as anything less than a great scientist - which his knighthood attests to. The idea that there is some sort of mass silencing of ideas or publication of those ideas looks to me to be utterly ridiculous.
Obviously I write everything with the bias of an astronomer. I can't do anything else. All I can say is that if climate scientists really are behaving as their detractors allege, then they are acting in a way that's preposterously alien to me.
(As far as media excitement is to blame, it works both ways for climate change. Without being a climate scientist, experience of this process in astronomy tells me to be way both of scientists claiming they've solved everything through a natural mechanism, and of those claiming we're all going to die by 2050 due to methane eruptions and there's absolutely nothing we can do about it)
Didn't you say you were worried about a false consensus ? It sounds like you think it's almost impossible.
Indeed. So why do I say that there's any truth at all in the allegation of a false consensus ? Three reasons :
1) Big science
CERN played an important role in the invention of the internet (which alone more than justifies the money spent on it), but only as a spin-off, not as a direct result of the research being done.
We need big facilities. There's simply no other way to test some theories. The problem is that big facilities are great for testing specific things, but large teams of people are absolutely lousy as a means of proposing new ideas. Everyone has to play ball to make the project work - you simply can't have three hundred people pulling in different directions; a consensus must be enforced or nothing will get done. It's hardly a true consensus if you only admit people into your group who already agree with you. Smaller groups and individuals are much more free to come up with new ideas.
Of course not all big facilities operate in the same way. Instruments like the LHC are designed to do a few specific tasks by enormous groups of people. Telescopes are generally run as observatories which are operated and maintained by a single largeish group, but usually used by dozens of much smaller external groups who have no vested interest in that particular facility, theory or even subject (Arecibo does everything from the atmosphere to distant galaxies; ALMA looks not just at molecular gas in other galaxies but also the Sun).
Big, open-time telescopes (which anyone can apply to use) are a great example of combining the power of big instruments with the creativity and flexibility of small groups. Sometimes we also need large, dedicated facilities to test single specific ideas - the trick is not to let those facilities dominate the world of science. For more on this, see this essay by noted "I love dark matter !" astronomer Simon White.
2) Publish or perish
Assessing people by their number of publications makes very little sense (disclaimer, I'm biased). Not all papers are created equal; no individual is ever perfectly objective and everyone makes mistakes. But worse, if your career depends on publishing as much as possible, you're innately encouraged to write mediocre papers that the journals can't refuse to publish but which don't actually advance science in the slightest. It may look great on paper if you've got twenty papers but it doesn't mean a thing if they're all crap.
Perhaps we need a new publication system which recognises that yes, pretty much all research needs to be published, but differentiates between style and content more precisely. Cataloguing observations is essential, but is a fundamentally different task to inferring what they mean. Currently authors options are either a) a regular journal or b) publishing in the overly-prestigious Nature or Science. There's not much middle ground. Maybe there should be more. We don't necessarily need more journals, just more sections within journals to differentiate content.
3) Science by grant
If you're a tenured professor, you yourself can do pretty much whatever research you want. At the postdoctoral level this is rarer : you're often expected to work only on a specific project*. Frequently this is because your source of funding comes not directly from your research institute or university, but an external grant agency. Your hands are tied; if you come up with a brilliant idea that's nothing to do with what you work on, you probably won't have time to pursue it because your funding doesn't permit it.
* I'm not, though as a student I didn't have time to write my own galaxy-finding code so I did it during some late-night observations. It worked pretty well, and became an important part of the resulting publication and thesis. As a postdoc, I initially didn't have time to work on my data-viewing code, so I did it at home when I was bored. Eventually it became a paper in its own right. Sometimes discoveries happen when you're most free to play around without fear of failure.
Which sucks. Professors tend to spend a lot of time teaching, managing students, and writing grant applications to hire new staff. They fit whatever research they can in around this. Consequently we have this strange system where the ones doing most of the work are the ones least free to innovate, and the ones doing the least frontline research have the most experience. The solution ? End the grant system. Give more money to universities to hire staff as they see fit. Trust in scientists to do their job and don't tie their hands by external agencies.
The grant system isn't exactly causing a false consensus, because it doesn't enforce finding only specific conclusions. But it does limit thinking and stifle innovation, which is false consensuses' ugly cousin.
Conclusions
If there is any scientific discipline in which the public might legitimately say, "well you would say that wouldn't you, you're a scientist", it is not astronomy. There are so many examples both past and present of astronomers throwing out crazy ideas and getting them published that the idea of a false consensus looks absurd. So if you throw out an idea and every astronomer shoots it down, here's a thought : maybe it really is just because your idea is bonkers.
But even in astronomy we've seen how there can be flaws in the system. Astronomy has always been a big science, nothing wrong with that provided things are managed correctly. All we need to avoid on that front is relying exclusively on huge research teams, which are ill-suited to innovation. The publication and grant cultures are more damaging.
To some extent these problems are a result of trying to quantify the unquantifiable. You can't put a number on how good a scientist someone is, and it's a mistake to try. If you've written a lot of papers, that means you're good at writing papers. It tells you nothing about the quality of the work. And yes, I have an example in mind of a famous group who do publish some genuinely outstanding research but a lot more mediocre stuff as well, though I'm not going to name names.
The grant system is similarly a result of trying to do science like it's a business : this person shall work on project X, this one on project Y, we shall all be in work 9-5, we'll never take coffee breaks, etc., the most important thing is that we have productive output, gotta keep the taxpayers happy. But running a scientific institute in this way (as some would like) is ultimately self-defeating. Allowing people to work how and when they choose and publish when they want to publish does not mean you can't evaluate their performance, but it does mean that you can't reduce them to their number of publications.
Science and the arts have something in common : to do either of them well, you need to innovate, to think creatively. You can't force new ideas by chaining someone to a desk. You can't guarantee that they'll happen at all, but you can encourage them through getting people to talk to each other, by fostering a free-thinking, informal atmosphere. Most importantly of all, they need to feel free to fail, to pursue crazy ideas that might take months and end up being useless. To really innovate, you need to take risks. Grant-based research, which expects this many results about this project, is not suitable for this.
Those societies in which seriousness, tradition, conformity and adherence to long-established - often god-prescribed - ways of doing things are the strictly enforced rule, have always been the majority across time and throughout the world.... To them, change is always suspect and usually damnable, and they hardly ever contribute to human development. By contrast, social, artistic and scientific progress as well as technological advance are most evident where the ruling culture and ideology give men and women permission to play, whether with ideas, beliefs, principles or materials. And where playful science changes people's understanding of the way the physical world works, political change, even revolution, is rarely far behind.
- Paul Kriwaczek, Babylon
To summarise then, here are a few ways to avoid a false consensus and demonstrate this to the public :
Be more interesting and less exciting. The media desperately need to learn that the most exciting solution is not usually the correct one, nor the one favoured by the majority - and those two facts are not unrelated. False excitement is at least partly to blame for this image of the false consensus / closed-minded attitude.
Do more outreach. That's always good advice. In particular ram it down people's throats that the findings of science are evidence-based and provisional. Tell people about the methods, not just the results.
Teach people about statistics in primary school. When a few scientists dissent from the prevailing opinion or make controversial statements, that does not automatically make everyone else wrong or even more likely to be wrong.
Emphasise controversies where they do exist. They are an asset to science, not a danger.
Don't rely exclusively on large teams at big facilities. Smaller groups are much more flexible and innovative.
End the "publish or perish" culture. More publications does not guarantee better science is being done, and can in fact lead to exactly the opposite.
End the grant-based funding process. To be innovative, scientists must be free to take real risks, to pursue projects with no guarantee of success. They must be free to play, to try things on a whim for no other reason than to see what will happen, not because some bureaucrat thought it would look good to tick a box on a form.
"Atomic hydrogen is the reservoir of fuel for star formation." "Neutral hydrogen is a galaxy's fuel tank." These stock phrases are a mantra I fall back on for beginning both public outreach and journal articles. But are they accurate ? A recent paper has got me wondering if we've got something terribly, terribly wrong. It seems that when galaxies merge, although star formation rates increase, the gas really doesn't do a lot at all. It's a bit like pulling the plug out and not seeing the water level drop.
We Need To Talk About Hydrogen - Well, I Do, Because They Pay Me Money To Look For This Stuff, But You Can Just Listen If You Like.
Atomic hydrogen (HI, pronounced, "H one" since it's a Roman numeral 1, not an I) is the simplest element there is. One electron orbiting one proton. That's it. Electrically neutral overall, since the proton and electron have equal but opposite charges, it should be as simple as you can get.
In reality things can be a great deal more complicated if you want to bring quantum into it, which I don't. Anyway this simple picture is good enough for what I'm going to discuss here.
That picture is a little over-simplified for what we'll need though. For example, two hydrogen atoms can bond to form an H2 molecule :
The electrons from each atom are now associated with both protons, forming a covalent bond.
Or the hydrogen can have its electron stripped away by an energetic photon (i.e. light, often near hot young stars) to become HII (confusingly also pronounced "H two"), which is really just a cloud of protons and unbound electrons. It can even gain an electron to become the negatively charged hydride ion, though this is not thought to be important in astronomy.
The current working model (I would not call it a consensus by any means) is that it's usually only the H2 that's important in forming stars. Atomic hydrogen is generally so hot (1,500 - 10,000 Kelvin) that its own internal pressure prevents it from collapsing into stars. Molecular hydrogen is colder, which means it's less able to hold itself up and more prone to collapsing. That view is by no means certain, and there are some hints that in some circumstances, HI can indeed collapse into stars without forming molecular hydrogen first.
When we go looking for atomic hydrogen, we mostly find it in blue, star-forming galaxies (they look blue because the most massive stars are blue and don't live long).
Random sample of galaxies detected by their hydrogen emission from a large survey. True, many are red, but when you look at them more closely they usually have blue star-forming regions as well.
Looking in more detail, we see "holes" in the atomic hydrogen, where it looks as though the gas has cooled to become molecular and is forming stars. We also see a few cases where there's atomic hydrogen but no star formation. And that's the (simplified) version of why we think atomic hydrogen is usually just a sort of reservoir : ultimately it will cool into molecular hydrogen and form stars, but it doesn't normally form stars directly.
OK, That's Enough About Hydrogen, Please Tell Me About These New Results Now Or I Will Become Cross.
When galaxies merge, the gas collides and things get seriously messy. Not for nothing was a Hubble press release entitled, "Galaxies Gone Wild !"
Needless to say, galaxy collisions and mergers are complicated. But generally if the galaxies both contain gas, collisions result in a massive increase in star formation as the gas compresses and cools. So the atomic hydrogen becomes molecular hydrogen which becomes stars, and everyone's happy, right ?
Oh, would that 'twere that simple. The new paper shows that when you stick two galaxies together, the atomic hydrogen does sod all. Well, it might get splashed about a bit, but its mass doesn't decrease and in fact it might even increase slightly. Which as far as the "fuel reservoir" idea is concerned is like being poked in the eye with a sharp stick.
How Do We Know This ?
Galaxy collisions are slow, grand affairs that can last for billions of years - so we can't just watch galaxies merge and see what their HI does. The metaphor that's usually used is that if you want to learn about how trees grow, you look at many different trees. So it is with galaxies. By finding enough isolated galaxies and galaxies which have already merged, the authors try to look at what happens to the gas statistically.
That's not any easy process. After the merger happens, a lot of information about the original galaxies gets lost. So unfortunately there's just no way to know what sort of galaxies were involved in the original collision. But most mergers are thought to occur between spiral galaxies (because these are far more common, except in galaxy clusters), and spiral galaxy gas content doesn't vary very strongly depending on their precise morphology.
What the authors do is define a sample of post-merger galaxies, then for each of these they find isolated galaxies which have the same mass in stars. Then they measure the gas content of all the galaxies in both samples using existing data from the ALFALFA survey and their own Arecibo observations (They've got me to thank for that since I supervised Derik Fertig (second author on the paper) at an Arecibo summer school. The fact that the other authors are far more experienced senior astronomers has, obviously, absolutely nothing to do with it whatsoever).
What they find is that the amount of gas is the same in both samples. That is, a galaxy with a billion stars that's quietly minding its own business has the same amount of gas as a post-merger of a billion stars. Even though new stars are forming*, somehow the gas just nonchalantly sticks its hands in its pockets and goes, "meh".
* Before the galaxies merged they would have had less than a billion stars in total.
It's not quite as simple as that though. It's not terribly likely that all of the mergers are formed from equal-mass galaxies. And less massive galaxies tend to have higher gas fractions - that is, more gas relative to their stars. So if you stick two unequal-mass galaxies together, and none of the gas gets turned into stars, you'd expect the gas fraction of the post-merger object to be a bit higher that a normal galaxy of the same stellar mass.
There isn't really a handy analogy for this, so let's make one up. And let's bring Worf back into it, why not. Suppose Worf goes to a party at Starfleet headquarters and brings a bottle of strong Klingon blood wine. Captain Picard is making do with regular human wine. When his glass is half-empty, a waiter asks if he wants a top-up. Worf, however, is honour-bound to offer the captain a refill from his blood wine instead. If Picard chooses the blood wine, he'll end up with a stronger drink than if he accepts the regular wine, even though the same amount would have been added.
It's the same with gas fractions. Smaller galaxies are more "potent", they contain more gas per star, so merging them with a larger galaxy is like topping up orange juice with vodka. You'll get a lot more drunk that way.
As long as one bottle is of Klingon blood wine, obviously.
When reading the paper I thought to myself, "man I could sure use a glass of wine right about now !". But then I thought, "well, maybe you could account for the mergers of unequal-mass galaxies by choosing random galaxies from the isolated sample and adding up their stellar and gas masses". Lo and behold, the authors did exactly that in the next paragraph ! What they found was that the difference in gas fractions of the initial galaxies would increase the gas fraction in the post-mergers quite considerably, not by a very dramatic amount but easily enough that they should have been able to measure it in their sample.
So, does that mean that some of the gas is being consumed after all ? The gas fraction may not have changed, but it is less than if you stuck two unequal-mass galaxies together. Well, maybe, though it seems a bit suspicious that all of those tremendously complex processes that happen during the merger just bring the gas fraction down to that of a normal, isolated galaxy. We had a saying during the undergraduate course on general relativity : it all cancels and equals nought - an awful lot of work needed to find out that nothing's happening.
At this point the team turn to numerical simulations to figure out how much gas should be consumed by star formation. This is perhaps the weakest aspect of the paper. Ideally, they'd set up their own simulations and track the evolution of the atomic and molecular gas and the stars, but this is tremendously difficult to do. We're talking about many months (or more) of extra work, so it's perfectly understandable that they don't do this.
Instead they use an existing set of simulations which are (it must be said) vaguely-described here (again this is understandable since that publication is only a letter, not a full article). What they do is track the total mass in stars, then use the known gas fraction relation (from observations of isolated galaxies) to calculate how much atomic hydrogen there is during the whole merging process (presumably because the simulation itself doesn't distinguish between the different forms of hydrogen we discussed earlier).
What they found by doing this is that the star formation process shouldn't change the gas fraction much at all. So the fact that the post-mergers don't have as much gas as expected can't be due to star formation.
But that assumes that there really is a decrease in the gas content as the galaxies merge. Now I mentioned earlier that there was some suggestion that the gas fraction actually increases a little bit from the mergers. That's a little more tentative. The thing is, not every galaxy in their sample had detectable atomic hydrogen at all, but the detected fraction of the post-mergers was double that of the isolated galaxies of the same stellar mass. That is, if you randomly choose a post-merger and an isolated galaxy of the same mass, you're much more likely to detect gas in the post-merger than the isolated galaxy. Which suggests that post-mergers actually have higher gas fractions than their parent galaxies did.
Another important factor is that the ALFALFA survey isn't as sensitive as we might like. That means it's only detecting particularly gas-rich objects which, say the authors, reduces the expected difference in gas fractions between the isolated and post-merger galaxies - so their calculated differences are probably too large. Many of their isolated galaxies that have no detected gas from ALFALFA probably do contain some gas, just not enough to be detectable. When you run the numbers, say the authors, that means that it's very possible that smashing galaxies together increases both their star formation rate and their gas content.
Which is a lot like pulling the plug out and seeing the water level rise. It's weird.
Believe me, if you Google image search "weird" you'll get far stranger stuff than this.
What ? How Could This Happen ?!? What Does This MEAN ?!?!?!?! To summarise, it seems that when galaxies merge their atomic gas content remains (at best) unchanged, even though part of their gas is turned into stars. Simulations suggest that the fraction that forms stars is very small, but it looks plausible that the atomic gas content actually increases, somehow.
One thing this study doesn't look at directly is the molecular gas, which is what we think is more directly responsible for star formation. Could it be that the stars which form as a result of the merger do so from the existing H2, perhaps due to the shock of the collision increasing the density ? Unfortunately, say the authors, previous studies have found that the molecular gas content also increases during mergers, so, nope.
It just seemed really wrong not to include a picture of the famous merging "Antenna" galaxies in this post somewhere, so here we go.
But before we go saying, "a wizard did it !", the authors suggest a possible explanation for where this extra gas comes from. Galaxies, it's thought, may be surrounded by large halos of ionized hydrogen. Just how much is not known. Normally it could be slowly trickling down, keeping the reservoir's topped up, but during a merger it might cool more rapidly. Simulations say that's possible, so, maybe. Whether this is the correct explanation or if it's due to something else entirely, we just don't know.
If it's true, then atomic hydrogen is just the middle step in the process - a complex system of dams rather than just one reservoir. It's not a totally unprecedented idea, but it will mean quite a rethink. We'll have to wait and see what other observations and simulations have to say : this one study is important, but not enough by itself to prove what's going on.
Then there are elliptical galaxies. They're thought to be formed by mergers, as this rather nice simulation shows :
But they usually don't have any atomic hydrogen. Where's it gone ? And yet, sometimes they do - occasionally they have very large amounts of it. It's a mysterious mystery, right enough. As usual, we need more data. But the more we learn about galaxies, the more complicated they become. Eventually, perhaps, we'll have enough data and good enough theories to have a real explanation. For now, we're still learning. And that's fun.
