Ist die Galaxie strukturlos und rund, ohne Anzeichen einer Scheibe? Hat die Galaxie einen Bauch in ihrer Mitte? Wie rund ist die Galaxie? Gibt es Anzeichen fuer einen Balken der durch die Mitte laeuft? Gibt es Anzeichen fuer Spiralarme? Und viele Fragen mehr zu Galaxien, die euch sicher bekannt vorkommen – alles jetzt auf Deutsch. Also – viel Spass beim “clicken”!

One by one, all the stars appear
As the great winds of the planet spiral in
Spinning away, like the night sky at Arles
In the million insect storm, the constellations form

On a hill, under a raven sky
I have no idea exactly what I’ve drawn
Some kind of change, some kind of spinning away
With every single line moving further out in time”
- Brian Eno, “Spinning Away”

Well if you ask me, what you’ve drawn there Brian is a “Polar Ring” galaxy.

Polar ring galaxies, unlike all other galaxies in the Universe, are made up of two distinct parts. In the centre we have a normal galaxy and around the outside we have a “golden chain” of stars and gas clouds. This ring is perpendicular to the “silver plane” of the host galaxy disk, rotating over the poles, and so it’s known as a polar ring.

So how are polar rings formed? Polar rings are thought to form when two galaxies gravitationally interact with each other. We believe that “one by one, all the stars appear” as they are stripped from a passing galaxy and “spiral in” to produce the polar ring we see today. Polar rings, although not quite as rare as smoke rings, are pretty hard to find. According to “New observations and a photographic atlas of polar-ring galaxies”, about 1 in every 200 lenticular galaxies (a type of galaxy between an elliptical and a spiral) have these “golden chains” of stars and gas spinning around them. Below is a selection of some of my favourite polar rings from the Galaxy Zoo:

The Zooites have done fantastically well at finding Polar Rings and you can see all of their incredible finds on the Possible Polar Ring thread on the Galaxy Zoo forum.

My Ring of the Week this week is the stunning pair of interacting galaxies Arp 87. Located in the constellation Leo, approximately 300 million light years away from Earth, Arp 87 gives us a fantastic insight in to exactly how polar ring galaxies are formed. The image on the left is the Galaxy Zoo Arp 87 image and on the right is an image taken by the Hubble Space Telescope. We can clearly see the galaxy on the left gravitationally stripping away the stars and gas from the spiral galaxy on the right.

Unfortunately for Brian Eno, his hypothesis of a “golden chain” of stars that “spiral in” a “silver plane” came a full 23 years after the first polar ring galaxy was identified by J. L. Sérsic in 1967.

However, perhaps someone else had already had a genuine polar ring premonition a full 78 years before Sérsic’s discovery…?

- “Starry Night” 1889, Vincent Van Gogh

The Hubble image is part of a collection of 59 images of merging galaxies released on the occasion of its 18th anniversary on April 24, 2008. (NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University))

More to the point – when do you see the pretty pictures? That’s slightly complicated. We’ve been torn between two worthy goals. One one hand, the Zoo team has tried to show the process of science as openly as possible (Voorwerp fans recall seeing a lot of early ideas hashed out on the forum and unfolding on the blog). On the other, if the images are as spectacular as we expect, there might be a unique chance to get a lot more attention for the Zoo if we can make a big public image release, supported by NASA and ESA. The problem is that news organizations want, well, news, so they all have to get it at the same time rather than reproducing something that’s been crawling around the Web already. That means if we show a nicely processed color image, or a set of black-and-white images someone could use to make a color image, on the forum or blog, the image would already be out in public and news interest would drop. After a long discussion with the STScI public-outreach people and among ourselves, the best solution we can find is to talk about the science as it unfolds, show what we can without jeopardizing the image release, and work as rapidly as the science allows toward a public release (which might well attract thousands of additional Zooites).

Soon after the initial results showed what a fascinating object Hanny’s
Voorwerp was proving to be, it was entered in the observing schedule for NASA’S GALEX satellite (GALaxy Evolution EXplorer). Alex Szalay, who belongs to both the GALEX and Galaxy Zoo science teams, played a key role in making this happen). Alex has interesting career parallels with Brian May, but that’s another story.

GALEX was designed to make the first sensitive ultraviolet survey of most of the whole sky (skipping only areas where there are such bright stars that they would damage the detector array), with a major goal of tracing the recent evolution of galaxies. The ultraviolet spectral range gives a lot of leverage for this, since this is where the most massive and recently-formed stars are brightest (unless they are hidden by dust). Its 50-cm telescope couples to microchannel arrays to show a 1.2-degree patch of sky at once. Not only does it obtain images, in two bands at once (near- and far-UV), but can obtain the spectra of everything in the field of view by inserting a grating-prism combination (grism). They have a very nice sky browser – GALEXView – which will show you the UV-color images for any piece of sky GALEX has observed, and give you object lists and file retrieval options. GALEX observes in orbital night, for about 45 minutes of each orbit, because the tiny residual atmosphere even at its altitude creates a UV glow (which became best known as “Shuttle glow”) when encountering fast-moving objects, and this glow impairs sensitivity just like light pollution on the ground.

With its wide field, GALEX is very good at capturing large objects,and particularly large diffuse objects (such as the Voorwerp). It observed IC 2497 and its surroundings for 1.7 hours in the imaging filters, and for nearly five hours for the spectra. The spectra look odd compared to most we use in astronomy, where we analyze only the light coming through a narrow slit or a tiny optical fiber. Here, the entire field of the telescope is spread out, letting spectra overlap where they may, so big galaxies have big fuzzy spectra where one wavelength from one side overlaps a different wavelength from the other side, and both are overlapped by the light of the “blank” sky at yet a different wavelength. This technique – slitless spectroscopy – is hard to use from the ground because of light pollution and airglow. But in the UV, the background sky brightness in space is so low that the main limitation is confusion as spectra from different objects land atop one another. For these observations, all the data were taken with the spacecraft rolled so that the spectra of Hanny’s Voorwerp would cleanly fit between those of neighboring objects (such as the galaxy IC 2497). Even so, it just barely fit.

Here are some views of the data. First, a color UV image (where blue means brighter in the far-UV, such as hotter stars). Compare that to the SDSS image of the same area. The GALEX image isn’t as sharp (what you get from covering such a wide area at once with a single detector), but you can easily see how different the UV sky looks from the visible-light appearance. For example, the spiral galaxy to the southeast has really blue arms, and its central bulge almost vanishes in the ultraviolet. Stars come and go between the images depending on temperature. More to the point of our story, Hanny’s Voorwerp is brighter than IC 2497 at these wavelengths. We knew that much already – early on, the Swift satellite observed it in both UV and X-rays, giving us a somewhat sharper view at one UV wavelength.

IC 2497 field in UV with GALEX

IC 2497 field from SDSS matching GALEX image

Where does all that UV radiation come from? That’s the point of observing the spectrum – it will tell whether that comes from ionized gas, light from the AGN in IC 2497 scattered from dust grains mixed with the gas, or maybe even stars that used to belong to a galaxy which has been shredded by a gravitational encounter with IC 2497. The UV spectra aren’t much to look at compared to the optical data, but they can be informative. Here are the far- and near-UV spectra as they look when the GALEX data are all added together:

GALEX far-UV spectrum of Voorwerp

GALEX near-UV spectrum of Voorwerp

Each object gives a spectrum making a horizontal streak. The spectrum of IC 2497 shows up just above the Voorwerp’s, and the blue galaxy to its southwest spreads just to its south in the spectra. We could see right away that a couple of strong emission lines show up in the far-UV data, smeared out by the large size of the Voorwerp. To get some numbers, we folded in the wavelength corresponding to each location and the sensitivity of the GALEX system at each wavelength, to get this
composite spectrum from both data sets:

GALEX UV spectrum plot of Hanny's Voorwerp

We’re missing some of the wavelengths at the ends of each piece, where the sensitivity of the system is so low that statistical “noise” is amplified and even minor contamination from surrounding objects makes a huge difference in the result. But we do see some of the emission lines accompanying gas ionized by quasars and their kin, which are familiar to Zooites who look at high-redshift quasars. They are marked
with their expected locations at the redshift of Hanny’s Voorwerp. C IV and He II are unmistakeable, each blurred by the size of the emitting cloud. An optical line of He II
at 4686 A was one of the things that put us on the trail when we got the first optical spectra, and in the UV there is a stronger one. This stronger line, emitted at 1640 A, plays the same role for He⁺⁺ that Hα does for ionized hydrogen, at 1/4 the wavelength because the binding energy of a single lone electron depends on the square of the charge in the nucleus (2 instead of 1, comparing H and He).

It’s also interesting that the spectrum doesn’t go to zero between the strong emission peaks. Sources of this continuum could include the recombining hydrogen (except at the very short UV end), dust grains scattering the light of the AGN toward us, or young stars in the Voorwerp for example, if its gas originated in a galaxy disrupted by a tidal encounter). I don’t think these data let us distinguish yet how much of each there might be, but its brightness in the UV bodes well for seeing lots of interesting detail in a Hubble ultraviolet image. More shortly on the Hubble data!

When not doing research, Manda loves traveling the world and enjoys good food, good wine and the company of good friends. If she ever finds more hours in the day (or less of a need to sleep), she hopes to take up dancing again and start working on her first novel!

• How did you first hear about Galaxy Zoo?

I saw the Galaxy Zoo papers on astro-ph of course when they were first coming out. However, I only decided to get involved later when my PhD supervisor, Prof. Ofer Lahav mentioned it to me while I was at UCL. We were working together on using machine learning algorithms such as artificial neural networks to estimate the redshifts of galaxies from their colours. Ofer mentioned that he had used the same neural network tool to classify galaxies with collaborators in the early nineties. He also knew Chris Lintott from having been his PhD co-supervisor at UCL so we decided to start working together on applying machine learning to the Galaxy Zoo data.

• What has been your main involvement in the Galaxy Zoo project?

I led the machine learning paper which showed that the Galaxy Zoo classifications can be used as a “training set” in order to supervise the learning of automated morphological classifiers such as artificial neural networks. Once these networks have been “trained” using the human classifications, they can be used to automatically classify much larger data sets.

• What do you like most about being involved in Galaxy Zoo?

The best thing about being involved in Galaxy Zoo is the mass appeal of any work carried out on the project. I have always believed in the importance of communicating science not just to fellow researchers but also general members of the public so that they hopefully find it interesting and feel inspired to pursue some aspect of it themselves. The Galaxy Zoo project provides a wonderful forum through which to communicate interesting science to many many members of the public while at the same time getting them involved to contribute to the projects themselves.

• What do you think is the most interesting astronomical question Galaxy Zoo will help to solve?

I think one very unique aspect of Galaxy Zoo is the sheer size of the data set that has now been classified by eye. This means we can actually make a lot of statistically significant statements about the nature of our Universe. For example, what fraction of elliptical galaxies don’t live in overdense regions of the Universe? What fraction of them are blue? In addition, the discovery of unusual classes of objects such as the Green Peas will pose as yet undefined questions. This to me is the most fun part of doing science. You often don’t know what the best questions are to ask before you’ve stumbled upon an answer!

• How/when did you first get interested in Astronomy?

I first became interested in astronomy when I was about ten years old. I still remember the day actually. We were visiting the Kennedy Space Center in Orlando on a family holiday in Florida. I was so inspired and fascinated by everything I saw and just contemplating the vastness of space and the many things we didn’t know about it, I couldn’t imagine not wanting to find out more. Ever since that day I have wanted to be an astrophysicist. I should also mention that were it not for my brilliant physics teacher at sixth form college, I probably would never had the confidence to pursue an academic career. He would spend most of his lessons making us read New Scientist and watching Horizon and I think this is when I developed an appetite for scientific research and began to appreciate the creativity and independence it affords.

• What (if any) do you think are the main barriers to women’s involvement in Astronomy?

I think there probably were many barriers to women in astronomy ten maybe twenty years ago. However, I do feel that today this is much less of an issue. For example, I don’t think astronomy is any longer a male dominated subject and the situation here is much better than in other areas of physics. That is not to say that there aren’t many barriers to pursuing an academic career. For example the need to move around frequently for postdoc positions often means people have to make very tough choices. However, in my experience there are many men who worry about this too and many women who don’t so I don’t think this is a barrier that is specific to women by any means!

Having said that, one problem that I do think faces women in astronomy today is the lack of female role models. There are very few female astronomers in very senior academic positions and even fewer who have chosen to have a family. This does sometimes make me doubt if I can pull off both having a successful academic career as well as a family because there are so few examples of women who have actually achieved this! I hope this will change though in years to come.

• Do you have any particular role models in Astronomy?

I think there are so many people in astronomy (both men and women) who are inspiring in different ways that it’s very hard to single out just a few of them. I’ve learned different things from all the different people that I have interacted with so far in my research career and they’ve all been valuable lessons to learn!

• Zooites:
  • Hanny Van Arkel (Galaxy Zoo volunteer and finder of Hanny’s Voorwerp). Hanny’s interview in het Nederlands.
  • Alice Sheppard (Galaxy Zoo volunteer and forum moderator).
  • Gemma Couglin (”fluffyporcupine”, Galaxy Zoo volunteer and forum moderator).
  • Aida Berges (Galaxy Zoo volunteer – major irregular galaxy, asteroid and high velocity star finder). Entrevista de Aida en español.
  • Julia Wilkinson (”jules”, Galaxy Zoo volunteer. Frequent forum poster, and member of irregular and HVS projects).
  • Els Baeton (”ElisabethB”, Galaxy Zoo folunteer. Frequent forum poster, and member of most of the spin-off projects!). Els’s interview in het Nederlands.
  • Hannah Hutchins (Galaxy Zoo volunteer, forum poster and co-creator of Galaxy Zoo APOD)
• Researchers:
  • Dr. Vardha Nicola Bennert (researcher at UCSB involved in Hanny’s Voorwerp followup and the “peas” project). Vardha’s Interview auf Deutsch.
  • Carie Cardamone (graduate student at Yale who lead the Peas paper).
  • Dr. Kate Land (original Galaxy Zoo team member and first-author of the first Galaxy Zoo scientific publication; now working in the financial world).
  • Dr. Karen Masters (researcher at Portsmouth working on red spirals, and editor of this blog series.)
  • Dr. Pamela L. Gay (astronomy researcher and communicator based at Southern Illinois University).
  • Anna Manning (Masters’ Degree Student in Astronomy at Alabama University working with Dr. Bill Keel on overlapping galaxies)

We’re almost done – just one more Zooite and one more researcher to come in the series!

Yes, to dance beneath the diamond sky with one hand waving free,
Silhouetted by the sea, circled by the circus sands,
With all memory and fate driven deep beneath the waves,
Let me forget about today until tomorrow.”
- Bob Dylan, “Mr Tambourine Man”

After last week’s leisurely cruise through 450 million light years to Mayall’s Object, this week I take you on a flying tour across the local Universe to view the spectacular galactic jewels known as “Smoke Rings”.

Smoke Rings, like all collisional ring galaxies, are formed when a smaller galaxy hits bull’s-eye into the centre of a larger disk galaxy. The impact creates a density wave, throwing matter out into a ring shape. With the help of the Zooites I’ve found just 12 Smoke Rings in the Galaxy Zoo and so these amazing objects are very rare indeed. You can see 4 of them below:

There are two things you’ll notice about these galaxies:

Firstly, all of the smoke rings we’ve found are blue in colour. This is because as the shock wave expands into the disk, it triggers the birth of large numbers of high mass stars. Massive, young stars are extremely hot and so the light that they radiate is bright blue.

Secondly smoke rings, by definition, have no central nucleus. Answering the question of why smoke rings have no obvious nucleus is not as simple as it may sound but we believe that smoke rings are created in one of the following situations:

1. The original target galaxy had no substantial nucleus to start with
2. Or the angle and position of impact was such that the nucleus was thrown out into the ring
3. Or the nucleus was destroyed by the impact

Smoke rings are incredibly important as they are shining blue clues as to how galaxies collide. My Ring of the Week this week is Arp 147 - a perfect example of the way that smoke rings allow us to turn back the clock and stare deep into the Universe’s distant past.

Arp 147 is located in the constellation Cetus over 400 million light years from Earth. The image on the left is the Galaxy Zoo Arp 147 image and on the right is an image taken by the Hubble Space Telescope. We can clearly see the “bullet” galaxy on the left and, on the right, the bright blue ruins of the original “target” galaxy. What makes Arp 147 so special is the unusual reddish-brown spot at the bottom of the ring and we believe that this marks the exact position of the original nucleus of the “target” galaxy. From the positions of the bullet, the smoke ring and the red spot we can rewind time over millions of years and simulate exactly how these two galaxies collided.

So as we “dance beneath the diamond sky” it is the smoke rings, beautiful in their simplicity, that make the “foggy ruins of time” crystal clear.

The Hubble image is part of a collection of 59 images of merging galaxies released on the occasion of its 18th anniversary on April 24, 2008. (NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University))

And it makes a fiery ring

Bringing hurt to the heart’s desire

I fell in the ring of fire”

- Johnny Cash

Before I venture any deeper into the mysterious world of Ring Galaxies, I thought I would give a quick introduction to the archetypal ring galaxy – the “Collisional Ring”.

Collisional Rings are formed when a smaller galaxy crashes through the centre of a larger galaxy. Just as throwing a stone into a pond creates an outwardly moving circular wave, a gravitational density wave is generated at the point of impact throwing matter out into a ring shape. Most Collisional Ring galaxies manage to hold onto a nucleus in the centre of the ring but sometimes the disturbance is so large that the nucleus is completely destroyed. Thanks to the work of Zoo members I have so far found about 125 Collisional Rings in the Galaxy Zoo (and still searching…!) so we can safely say that Collisional Rings are quite a rare phenomenon.

It is incredibly rare to see the galaxy collision actually taking place so my Ring of the Week this week is a fantastic Collisional Ring seen just after impact. Nick-named ‘Mayall’s object’, this ring is located in the constellation of Ursa Major, approximately 450 million light-years away. The image on the left is the Galaxy Zoo image and on the right is an image of the same galaxy taken by the Hubble Space Telescope. You can clearly see the elongated “bullet” galaxy blasting through the disc, creating a huge raggedy ring of stars.

The Hubble image is part of a collection of 59 images of merging galaxies released on the occasion of its 18th anniversary on April 24, 2008. (NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University))

Hannah Hutchins lives in England with her Grandmother and her hamster, “Hubble”. At just 15, she’s by far the youngest entrant in our “She’s an Astronomer” series, providing us with some perspective from the next generation of astronomers. Hannah is homeschooled and currently studying for her IGCSEs. As well as being a frequent contributor to the forum, she is the co-creator of the Galaxy Zoo APOD. As well as Galaxy Zoo she’s involved in all sorts of astronomy projects, including the Young Astronomers blog.

• How did you first hear about Galaxy Zoo?

On the BBC News Website in August 2008. I read an article about Hanny’s Voorwerp and when they mentioned Galaxy Zoo I was immediately interested! I went onto the website and was hooked from then onwards.

I classify galaxies, chat on the forum and I write Object of The Days (OOTD). Alice got me into writing the OOTD’s, which is when I discovered that I loved to write.

Knowing that I’m helping science. It’s fantastic because I don’t have to be an adult in university doing astrophysics or something to be able to contribute to science like this. It has also turned my interest in astronomy into a passion and I could never live without it. I’m now determined to go to university to study astrophysics. It’s also great to be part of such a friendly community! I finally found friends at the zoo who shared my interests.

There are so many to choose from! I have a soft spot for the Voorwerpjes though, It’s amazing how AGN (active galactic nuclei) belt out all that radiation which then ionize huge gas clouds, it creates some spectacular images.

My earliest memory of having an interest in astronomy was sitting on my bed when I was around four years old flicking through an astronomy book called ‘Spacewatching: The ultimate guide to the stars and beyond’, I remember staring in wonder at pictures of nebulae and reading aloud the titles in the book. My grandparents bought it for me at a sale along with a book about Comets after I pestered them for them. I think those where my very first astronomy books.

I’m not really sure, but I know from my experience of school (though rather a short experience, I only lasted a couple of terms in secondary school for instance because I wasn’t happy with the education I was getting) that there is sometimes an attitude where it is bad to have an interest in science and maths, they have to be viewed as so very boring. I think that is because it’s taught so badly at school, it shuts down any interest.

There are so many fantastic people in astronomy, but I don’t really have a role model.

• Zooites:
  • Hanny Van Arkel (Galaxy Zoo volunteer and finder of Hanny’s Voorwerp). Hanny’s interview in het Nederlands.
  • Alice Sheppard (Galaxy Zoo volunteer and forum moderator).
  • Gemma Couglin (”fluffyporcupine”, Galaxy Zoo volunteer and forum moderator).
  • Aida Berges (Galaxy Zoo volunteer – major irregular galaxy, asteroid and high velocity star finder). Entrevista de Aida en español.
  • Julia Wilkinson (”jules”, Galaxy Zoo volunteer. Frequent forum poster, and member of irregular and HVS projects).
  • Els Baeton (”ElisabethB”, Galaxy Zoo folunteer. Frequent forum poster, and member of most of the spin-off projects!). Els’s interview in het Nederlands.
• Researchers:
  • Dr. Vardha Nicola Bennert (researcher at UCSB involved in Hanny’s Voorwerp followup and the “peas” project). Vardha’s Interview auf Deutsch.
  • Carie Cardamone (graduate student at Yale who lead the Peas paper).
  • Dr. Kate Land (original Galaxy Zoo team member and first-author of the first Galaxy Zoo scientific publication; now working in the financial world).
  • Dr. Karen Masters (researcher at Portsmouth working on red spirals, and editor of this blog series.)
  • Dr. Pamela L. Gay (astronomy researcher and communicator based at Southern Illinois University).
  • Anna Manning (Masters’ Degree Student in Astronomy at Alabama University working with Dr. Bill Keel on overlapping galaxies)

Still to come in the series – a few more Galaxy Zoo volunteers and researchers. We’re not quite done yet!

Because of Valentine’s Day, we decided to pick an unusual galaxy for our target today.  As you can see, it looks very similar to a Valentine’s Day heart.   If you look carefully at it, you can see it is actually two “collisional ring galaxies” that overlap each other.   In general, we know that collisional ring galaxies are created when an intruder galaxy passes near the center of a target galaxy.  The orbit has to be nearly perpendicular to the plane of the unperturbed galaxy’s disk.    During the close passage, the extra gravity of the intruder draws in the orbiting stars and gas.   After the intruder leaves, the stars spring out in a circular wave like ripples in a  pond.   Since the gas from the original galaxy is compressed into rings as well, most of the star formation in these systems tends to be in the outer ring of the galaxy.

Collisional ring galaxies are rare beasts, and one of my favorite types of interacting systems.   This is the first example that I have ever seen of two ring galaxies created in the same collision.   It seems like creating this type of system should be possible, but we aren’t sure how to create models that closely reproduce this beautiful system.   As always, we need your help!

The challenge will be to find a collisional ring galaxy that close matches the heart-shaped rings of the real system.   The star in the upper left is almost certainly a red herring  (or rather a red dwarf star) that has nothing to do with the collision.  Try using the explore feature until you find a few close examples of double ring galaxies, and then use the enhance feature to tune it further.   This approach works pretty well for most of the systems we have played with, although you have to be patient!   We played with this system on our computers, and found some models that had two rings but didn’t reproduce the heart-shaped structure of this system.  We know from experience that you can do better.   Please make sure to save your work at the end so we know which system is the best of your best!

In a few weeks, we will present the best model or models in this blog.  We will also present some of the models you found of the other galaxies.   We should have a few other surprises coming up soon as well.

The Valentine system is also a gift from all of us at the Zooniverse to our incredible volunteers.   We couldn’t do this science without you.  As always, thanks for your on-going contribution to our project and the rest of the Zooniverse.

-John