At the start of this year, our paper on bulgeless galaxies with growing black holes was published. These galaxies are interesting because each is hosting a feeding supermassive black hole at its center, a process typically associated (at least by some) with processes like mergers and interactions that disrupt galaxies — yet these galaxies seem to have evolved for the whole age of the universe without ever undergoing a significant merger with another galaxy. In fact, they must have had a very calm history even among galaxies that haven’t had many mergers. If these galaxies were people, they’d be people who had grown up as only children in a rural town where they always had enough food for the next meal, but never for a feast, who never jaywalked or stayed out in the sun too long, and whose parents never yelled at them — because it was never necessary. Sounds boring, perhaps, until you see the screaming goth tattoo.
We see the evidence of the tattoos — rather, the growing black holes — by examining the galaxies’ optical spectra. But how do we know they’ve had such calm histories? You told us. Galaxy Zoo classifications revealed that, once you account for the presence of the bright galactic nucleus, these galaxy images have no indication of a bulge. And bulges are widely considered to be an inevitable byproduct of significant galaxy mergers, so: no bulge, no merger.
Of course, that’s a very general statement and it begs many follow-up questions. For instance: what counts as a “significant” merger? These galaxies had to have grown from the tiny initial fluctuations in the cosmic microwave background to the collections of hundreds of billions of stars we see today, and we know that process was dominated by the smooth aggregation of matter, but just how smooth was it? If two galaxies of the same size crash together, obviously that’s a merger, and that will disrupt both galaxies enough to create a prominent bulge (or even result in an elliptical galaxy). If one galaxy is half the size of the other, that’s still considered a “major” merger and it almost certainly still creates a bulge. But what if one galaxy is one-quarter the size of the other? One tenth? One hundredth? At what level of merger do bulges start to be created? Simulations tend to either not address this question, or come up with conflicting answers. We just don’t know for sure how much mass a disk galaxy can absorb all at once before its stars are disrupted enough to make a detectable bulge.
However, we may be able to constrain this observationally. Galaxy Zoo volunteers are great at finding the tidal features that indicate an ongoing or recent merger, and the more significant the merger, the brighter the features. Mostly the SDSS is only deep enough to detect the signs of major mergers, which are easier to see, but which settle or dissipate relatively quickly. In a more minor merger, on the other hand, the small galaxy tends to take its sweet time fully merging with the larger galaxy, and with each orbital pass it becomes more stretched out, meaning faint tidal features persist. The Milky Way has faint stellar streams that trace back to multiple minor mergers. But if we want to see their analogs in galaxies millions of light-years away, we’re going to need to look much deeper than the SDSS does.
So we were thrilled when we got time on the 3.5-meter WIYN telescope. Of the six nights we got, 2 are set aside for infrared exposures to make sure these galaxies aren’t just hiding bulges behind dust, and the other 4 are for ultra-deep imaging to see what (if any) faint tidal features exist around some of these bulgeless galaxies. If we find tidal streams, we can use their morphologies and brightness to help us figure out the size of merger they indicate (by comparing to simulations). If we don’t find any, then these galaxies really have had no significant mergers, and the growth of supermassive black holes via purely calm evolutionary processes is confirmed. (Long live the vanilla farm kid with the wicked tattoo!)
So how’s it going so far? Reasonably well: conditions haven’t been perfect, but until tonight we hadn’t lost much time to full clouds or dome closures. Tonight, though there’s not a cloud in the sky, there’s so much dust in the air that the domes are closed to prevent damage to the optics. Obviously I’m sad about that — it means we’ll miss one of our targets — but in between various incantations to the gods to clear the air so we can re-open, I’m working on an initial reduction and stacking of all the images I’ve taken over the past couple of days, so that I can (hopefully) give everyone a sneak peek at the results soon!
I’ve been both excited and nervous about my trip to Kitt Peak. I’m excited because observing is fun and the science is cool, but the program I have planned is also technically challenging and uses a brand new instrument, which is a little scary.
In addition, although I’m plenty experienced with data, I haven’t done a lot of hands-on observing. My PhD thesis used Hubble data, and Galaxy Zoo uses both Hubble and SDSS data — neither of which you take yourself. Because observing is a useful skill for my profession, I made sure to get some experience while I was in grad school, but this is my first solo run to collect data for my own project. I’m here to get very deep images of some of our bulgeless AGN host galaxies, so if it doesn’t work out I’m probably going to be heartbroken. And clouds or technical issues are one thing, but I’ll be even more upset if I fail because I make a mistake that a seasoned observer wouldn’t have. I don’t want to let the Galaxy Zoo participants down! So I’ve been reading the instrument manuals and scouring papers that have done similar work in the past. The pressure is on.
I arrived the night before my first night so that I could “eavesdrop” and start to learn the new instrument on the 3.5-meter WIYN telescope, called pODI. Eventually it will just be the One Degree Imager, but for now it’s only partially complete — which is fine for me, as I only need a fraction of the total area ODI will eventually cover. But Kathy Rhode, who studies globular clusters in nearby galaxies, has slightly larger targets:
This is just one of many images Kathy took, all of which will eventually be combined to fill in the chip gaps and get rid of the usual artifacts. The instrument is working very well — it’s a good thing instruments don’t get as tired as their observers!
For my own first night, I was assisted by a startup person, an ODI system scientist who knows the instrument backwards and forwards. He walked me through everything, and stuck around to make sure my science observations were starting off right. He was joined by two others, both software gurus who are either writing code for ODI or for similar instruments. Along with Doug, the veteran telescope operator, there was a lot of expertise in the room. They were very patient as I asked all my questions (and made some suggestions — the software is still in progress), and my first science exposure of the night looked exactly as I had hoped:
Okay, like I said, pODI is a little bit more area than I need at the moment. Here’s a zoom in to the central detector grid:
So. Why am I observing these objects? What am I hoping to learn? More soon… for now it’s the start of my second night, and I have to get started on calibrations!
John Wheeler once summarized General Relativity as “Matter tells space how to curve, and space tells matter how to move.” While that is a handy description, and while there have been many textbooks written, lectures given and websites constructed to explain this, the quote itself doesn’t address what happens to the light streaming through the universe as it encounters the warped space curved by matter.
The simple answer is: it curves too, and Einstein’s equations provide predictions for exactly how it works. In fact, observations of the bending of starlight around the Sun were one of the first implemented tests of General Relativity, and it passed with flying colors. On the scale of the Universe, the Sun isn’t that massive, but it’s massive enough to bend the light just a little, and by exactly the amount the equations predicted.
Those equations say that more matter in the same place is more likely to produce a strong lens effect, distorting and magnifying a background source. So what happens when you have a *lot* of matter, say, in a big galaxy or a cluster of galaxies?
Some pretty impressive configurations, which are rare but which humans are best at finding — hence Space Warps, the Zooniverse’s newest project and our astronomical project sibling. Co-lens-experts Phil Marshall and Aprajita Verma joined us during this hangout to describe how they use gravitational lenses to weigh galaxies. In particular, they can tell the difference between Dark Matter and “matter that’s dark” — the former being the exotic particles that are very different from stars and gas and planets and people, and the latter being normal matter that isn’t bright, such as brown dwarf “stars” that never actually ignited.
Note: Google+ was feeling a bit out of sorts, so the first minute or so of the broadcast was cut off, during which time Bill Keel showed us the first known image of a gravitational lens, from 1903. We went on to talk about all of the above, and more besides, including the importance of simulated lenses, why the images Space Warps uses are specially tuned to help us find lenses, and how the science team (which includes citizen scientists from Galaxy Zoo!) plan to turn our clicks into discoveries.
Notice my swapping of pronouns to “we” — I’m not on the Space Warps science team, but I’ve done nearly 100 classifications now myself! I can’t wait to see the results start to come in from this project.
Not too long ago we announced that Galaxy Zoo has gone open source – along with several other Zooniverse projects. Part of that announcement was that it is now possible for anyone to translate the Galaxy Zoo website into their own language and have that pulled back into the main site. We love translation at the Zooniverse! Using GitHub (our code repository) means we can open up the translation process to everyone.
I’ve been answering a lot of emails about how this process works so I thought I would outline a tutorial here on the blog. If you’re familiar with GitHub, much of this will be stuff you already know. You will need a (free) GitHub account which you can get at github.com.
This tutorial also shows only one way for this process to work. It is also possible to clone the Galaxy Zoo repo on your own machine and run the app locally to test it out. That will no doubt help with checking the translation and understanding the context of all the translatable text; however, this guide shows a way to translate Galaxy Zoo that does not require you to install any additional software or run any code.
After you have completed the tutorial, you’ll have a new language file to translate. This bit is up to you and everyone works differently. You might want to use a nice Text Editor to help you out (we like lots of them, such as Text Wrangler, Textmate and Sublime Text 2). We are working on ways to assist with making this part less painful (for example, by auto-translating from Google Translate) and will blog when we do. Galaxy Zoo is about 1,000 lines of text and about 8,000 words. You can see a sample here:
The text shown in green here is the index keys used in the code and these must not be changed. We’ve tried to name them such that they are meaningful; to aid translation, they are grouped. The text shown here in red is the text that needs translating. It is important to keep the file structured correctly, with a return after each entry and keeping indentation as shown. If you only edit the red text in quotes you’ll be fine. This file is a CoffeeScript file, if you’re interested.
NOTE: If you are happy running Ruby scripts there is is a script to create a JSON file from the current translation. You can find this script here. If you’re working on your own machine you might find this easier]
When you have a completed translation, or when you’ve gotten as far as you can, you’ll need to send us the file by making a ‘pull request’. Make sure all your changes are saved and committed to your repo. You’ll find a ‘Pull Request’ button at the top of the forked repo in your account. Clicking this button shows something like this screen:
Sending the pull request alerts us that you have a file you want to add to the main Galaxy Zoo site. We’ll check that the code works and then find another speaker of your language who can read the translation and verify both that it works and that Galaxy Zoo will still make sense to native speakers. We’ll keep you posted via GitHub.
This process is not simple but it is possible to create translations without installing any code on your own machine. If you are comfortable with GitHub then just fork the repo and work locally, pushing back changes and sending the pull request when you’re ready. We’re keen to hear from people who are trying this and what languages they’re working on.
Good luck with your translation, and thank you! Hopefully we can open up Galaxy Zoo to many more people around the world.
See the video of our latest hangout here (or, if you prefer, click to download the podcast version):
Spiral galaxies are seemingly endless sources of fascination, perhaps because they’re so complex and diverse. But why does spiral structure exist? Why do some spiral galaxies have clearly defined spiral arms and others have flocculent structure that barely seems to hold together? What’s the difference between a 2-arm spiral and a 3-arm spiral? How many kinds of spirals do we actually observe? And what is happening to the stars and gas in spiral galaxy disks?
All of the above questions are related to a question we got right at the end of our last hangout: what is the significance of the number of spiral arms? Determining how many spiral arms a galaxy has is hard, and is often subjective — so why bother?
It’s a good question. Part of the reason spiral arm classification & count is a challenge is that it often depends on the wavelength at which you observe a galaxy. New stars tend to form along the spiral arms, whereas older stars have time to spread out into more uniform orbits. So ultraviolet observations of a galaxy, which tend to pick out the new and bright stars, often highlight the spiral arms much more strongly than longer-wavelength observations, which see more light from older stars.
It’s not quite that simple, though. As you get to longer and longer wavelengths, you start to pick up the heat radiated by clouds of gas and dust, which are often stellar nurseries — and often trace spiral arms. At a wavelength of 21 centimeters you can detect neutral Hydrogen, which provides raw material for the cooling and condensation of gas into cold, dense molecular clouds that form stars in their densest pockets. Each wavelength you observe at provides a glimpse at a different targeted feature of a spiral galaxy.
Including our own, of course: we live in a spiral galaxy (though how many arms it has, and whether it’s flocculent, is a matter of debate), and it provides the best means of studying star formation up close. When studying other galaxies, it’s easy to get caught up in the race to discover the biggest, the smallest, the farthest and the most extreme, and forget that our own Universal neighborhood is pretty amazing too.
For example, one of the most famous nebulae in the world was recently imaged by one of the most famous telescopes in the world — again — but this time in the near-infrared. The Horsehead Nebula is a well-known feature in the Orion star-forming complex, and the new Hubble images provide a great opportunity to learn even more about this region that has been studied for hundreds of years. How thick and cold is the gas and dust in the nebula? How long will it take for it to dissipate under the harsh radiation of the bright, young stars near it? What’s going on behind it?
The near-infrared view from HST is sort of the sweet spot in this spectacular space — the wavelengths aren’t so long that the resolution suffers, but they are long enough that you see through a bit more of the clouds than in the optical. So you see more of the structure of the cloud itself, and more of where it’s thin and thick. If you zoom in, you can even see distant galaxies peeking through! And not just on the edges: in some parts you can see galaxies through the middle of the nebula. Wow. This image alone contains spiral galaxy insights big and small, near and far, from the very distant universe and right in our own backyard.
Note: right at the end of the hangout, we again got another great question from a viewer that we didn’t have time to answer. So stay tuned for the next hangout when we just might have a thing or two to say about dark matter, dark energy and new projects!
I enjoy days where we get to use questions from the public to meander our way through the Universe. Our latest live hangout saw us discussing the latest update to the Galaxy Zoo site — made based on your clicks! — and doing a live, collective classification on a few example objects from our Hubble sample that we hope represent the kind of things you’ll be seeing more of from now on.
We debated, for example, whether this galaxy’s central “feature” was a bulge or a bar:
Whether this relatively featureless galaxy’s blue smudge indicates a voorwerp:
And how many spiral arms this galaxy has:
We also talked about the origin and importance of dust in galaxies, and just what a green pea would look like in the Hubble data. Green peas are galaxies with incredibly high rates of star formation. They’re rare in the local Universe, but how rare do we think they were billions of years ago, at the epoch we’re looking back to with Hubble?
And, for that matter, what were the stars like then? Astronomers very broadly group stars into three populations depending on their composition. The very earliest stars were made from the primordial elements forged during the Big Bang — almost entirely Hydrogen and Helium, nearly devoid of anything else (we call “anything else” a metal, including elements like Carbon and Oxygen). The next generation of stars had some metals, but the Universe has been around long enough that those stars (even the lower-mass ones that live for a long time) are past their prime and a new generation, one with compositions generally like our Sun, are now in their heyday.
Naturally, though, since the Sun is our First Star, we call its generation Population I. The slightly older stars, many of which are still around and living in our galaxy and others, are Population II; and the very massive rockstars of the early universe that have all died out are called Population III. So “Pop III” were the first stars — a slight reversal, but labels and names that seemed like a better idea at the time than with hindsight are nothing new in Astronomy. (Exhibit A: the magnitude system. Exhibit B: “planetary nebula“.)
Bonus: green peas, voorwerpjes, and planetary nebulae are just three of the phenomena that (at least in part) glow green to human eyes because of one particular frequency of light emitted by Oxygen at a certain temperature, an atomic transition seen only rarely on Earth but fairly often in the Universe.
Also, did you know that dust grains are the singles bars of the atomic universe, allowing atoms to meet and combine into molecules and cooling the gas clouds they live in — which in turn helps new stars form? Heating and cooling, gravity and pressure, and the interplay between atoms, molecules, and radiation are all a part of what gives us this amazingly diverse Universe. We understand quite a lot of it given that we are such a tiny part of it, but what we know is dwarfed by what we don’t. And that’s just the way astronomers like it… we love a challenge and we’re glad to have as much help as possible sorting things out.
Here’s the hangout video:
Way back in August I gave a evening (public) plenary talk about “The Zoo of Galaxies” at the 28th General Assembly of the International Astronomical Union. I wrote a couple of blog posts about it at the time (here and a bit more here). Just this week I got word that the video is now available, so here it is:
To go with this I have also posted the “proceedings” (a write-up based on my talks) which will be appearing in the 16th Volume of “Highlights of Astronomy”. This is available on the arxiv. It’s not supposed to be a transcript as such, but if you watch both the video and read this I think you’ll see they’re quite similar.
Astronomers always want better images. Sometimes it’s possible right away; other times doing better requires new technology and/or waiting for the next generation of telescopes. We have both kinds of “fuzzy blobs” in Galaxy Zoo, and during this hangout we showed several examples. For a couple of hangouts now we’ve been meaning to address some of the most frequently asked questions about the faintest, most distant galaxies we ask volunteers to classify:
- what are they?
- why are the images so fuzzy?
- can we get better images of them now or in the future?
Given the data we have, the short answer to the first question is that we don’t yet know for sure — and, perhaps most importantly, we don’t need to know all the details. We can learn quite a lot from classifying even faint, fuzzy objects. Some of the faint galaxies on Galaxy Zoo are among the most distant galaxies ever imaged by the Hubble Space Telescope, and we don’t necessarily expect them to look like galaxies we see more nearby, so classifications from our volunteers are helping us to understand them even when we don’t have all the information we might want.
And what would it take to give us the information we want? What’s the future of astronomy after Hubble? How can we get better data than we have right now? Do we need to go into space to do it? (And what else are we working on right now, anyway?) Answers given in the video:
This is a great time to be working on Galaxy Zoo: there’s plenty to classify and analyze, and — of course — plenty to discuss. So stay tuned for next time!
Note: for those who prefer audio only, here’s a link to the podcast version.
Just a quick note to point out a new paper based on Galaxy Zoo classifications appeared on the arxiv this morning (and just accepted to MNRAS): The Differing Star Formation Histories of Red and Blue Spirals and Ellipticals, by Rita Tojeiro et al.
In this work we took samples of galaxies split by their morphological classifications (from you all, and actually going back to the original Galaxy Zoo project) as well as by their optical colour. With the help of an Ogden Trust undergraduate summer student (Joshua Richards) we then compiled the average star formation histories of these samples, based on fits of star formation models to the Sloan Digital Sky Survey spectra of the galaxies (previously published and called VESPA, or “VErsatile SPectral Analysis” by Rita).
Our main result was that red spirals differ in their star formation histories from blue spirals only in the last billion years or less. We also find that blue ellipticals have very similar star formation histories to blue spirals. We show some results about the dust and metal (astronomers metal) content of the galaxies as well. I think it’s a nice project and I’m very happy to see it finally finished and published.
Thanks again for the classifications.
I remember going to a lecture as an undergraduate wherein my professor compared what astronomers do to a hypothetical alien crew on a fast-moving ship that can only take one photo of the Earth as it passes by. We can assume they have a special camera that can see through buildings, but otherwise they just get one photo of, say, a major city, and from that they have to try and learn as much as they can about the human race. How hard would it be to discover that our species has two genders? Or that both of them are required to propagate the species, but only one gives birth? Would it be possible to figure out the whole human life cycle? To discover what disease is? To distinguish between genetics and culture (nature and nurture)? Just having one picture is limiting, but with careful study you can learn more than you think.
The professor was drawing an analogy with the Hertzsprung-Russell diagram in particular, which we’ve talked about before on our hangouts: to make it, you record the color and the luminosity of all the stars you can and plot them up against each other, one point per star. The stars group together in interesting ways in particular areas of the diagram, and it turns out that from this diagram alone you can recover an enormous amount about the life cycles of a population of stars (for example, in a star cluster, a neighborhood of our own galaxy, or a nearby galaxy). You can learn even more if you couple the diagram with spectra of stars from different parts of it. Studying stellar populations has helped us understand the fundamentals of what kinds of stars exist, how they are born and die, and how many stars of any given mass are likely to develop in a galaxy in relation to stars of different masses. That last thing is called the Initial Mass Function (IMF for short). Essentially it says that, when stars form in groups, more low-mass stars form than high-mass stars. Put that together with what we know about how much brighter high-mass stars shine and how much faster they die than low-mass stars, and you can start to understand how whole populations of stars in galaxies form and evolve.
And we can apply our studies of nearby galaxies and groups of stars to galaxies we observe much farther away. It’s a good thing, too, since most galaxies are far enough away that our current telescopes can’t resolve individual stars. We just get the sum of the light from all the stars. That combined light is sometimes made up of multiple populations of stars that formed in groups at different times and now all live together in a particular galaxy. Taking that single picture combining the light from billions (often hundreds of billions) of stars and using it to learn about the stars’ masses, ages and histories is an important process, and there are several ways to do it: one way combines models of stellar populations made by forming and evolving many stars in a computer simulation. This is sometimes called Stellar Population Synthesis, or SPS.
On today’s live Hangout, we once again let your questions guide us as we talked about IMFs and what they have to do with SPS and measuring the stellar masses of galaxies. The work that laid the foundations for today’s study of galaxy stellar populations was done in large part by women (Bill mentioned Beatrice Tinsley, for example), which is fitting since today is International Women’s Day. We talked about that too, and about diversity in general in astronomy. Just as you can learn a lot from even one snapshot of a galaxy, you can do a lot with just a bit of mindfulness about being an ally for diversity (Kyle noted on Twitter that World Day for Cultural Diversity is May 21), be it equality for women or for any other minority groups in science, or indeed any field.
Here’s the audio-only version of the Hangout: click to listen to mp3 version.
And the video:
We’ll post about our next hangout soon; in the meantime, keep those questions coming!