Ring of the Week: Arp 147
“Then take me disappearin’ through the smoke rings of my mind
Down the foggy ruins of time…
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:
- The original target galaxy had no substantial nucleus to start with
- Or the angle and position of impact was such that the nucleus was thrown out into the ring
- 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))
Ring of the Week: Mayall's Object
“Love is a burning flame
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))
A Valentine's Day Challenge
We’ve been a little quiet over at Merger Zoo recently. In the first three months of this project, you have viewed nearly two million simulations for nearly 40 different galaxies. Of these two million, you have picked about 30000 galaxies that we have been doing further investigations on. In short, we have been extremely busy because of all your hard work!
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
Happy Valentine's Day!
Ellipses are red,
Spirals are blue*
But a heart-shaped ring galaxy?
Haven’t a clue!
My name is Georgia Barrie and I’m a Masters student at Oxford University. I’m currently working on a research project with Chris Lintott, attempting to explain the formation of the elusive ring galaxies. Thanks to the work of Galaxy Zoo users, I am now in possession of the biggest catalogue of ring galaxies in the World. Having looked through each of the three and a half thousand galaxies classified as rings by Galaxy Zoo users, I am lucky enough to have seen some of the weirdest and most wonderful galaxies in the Zoo. Rings come in all shapes and sizes and over the next few weeks I will share with you some of the most beautiful, unusual and mystifying rings in our Universe.
As today is Valentine’s Day I will start with this astounding heart shaped merger. This beautiful object was first discovered by teckborg on July 26 2007 and was posted on the forums shortly afterwards by ALKA on August 14. It looks as though this galaxy is made up of two intertwined ring galaxies with one ring appearing to be red and the other appearing to be quite blue. We’ve calculated that this galaxy is about 600 million light years away but the formation of an object like this is, quite literally, a mystery.
For something as baffling as this we really need your help. Today the Heart Galaxy is our featured merger and we need you to help us simulate how this incredible galaxy could be created. To get involved go to the Galaxy Zoo Mergers site and, who knows, you may be the very person to solve this cosmic mystery!
If you want to hear more about the Heart Galaxy then I will be talking about this amazing discovery live on Monday’s Breakfast Show, BBC Radio Oxford.
*The Galaxy Zoo team has just recently discovered a population of red spiral galaxies. Click here to find out more!
Red spirals at night, astronomers' delight
We heard a few days ago that our paper on red spirals has been accepted by the journal. Not only is this another success for Galaxy Zoo science, but it’s a tribute to the hard work of Karen who led the effort. What with the first Zoo 2 paper being submitted and a few other distractions as well it’s been a very busy week for her.
The paper itself is another variation on what should be becoming a very familiar theme for those who have followed Galaxy Zoo science: colour and shape are not the same, and tell us different things. To recap slightly, as young, massive and short-lived stars are blue, colour is a measure of what’s happened recently. The blue spiral arms in the galaxy pictured below, for example, mark sites of recent star formation.
It was known long before Galaxy Zoo that most of the star formation in our local Universe takes place in spiral galaxies, and so they tend to be blue whereas ellipticals are often red. In looking at the blue ellipticals and now the red spirals, it’s clear that interesting things happen when this rule is broken.
Before we can work out what’s going on though, we have to find our red spirals, and this is trickier than it sounds. If we weren’t careful, then our sample would get contaminated by edge-on systems, which appear redder because of the effect of the dust that scatters light which travels through the disk. As this paper uses only Zoo 1 data, we just selected the roundest spirals assuming that this would get rid of those pesky edge-on systems; we also insist that Zooites were able to identify a direction to the spiral arms.
It turns out that 6% of spiral galaxies are red, which I think is higher than most would have guessed before this project. So how did a substantial number of spiral galaxies come to turn red? What caused them to cease forming stars and become what the paper title calls them : ‘Passive red spirals’?
One important clue is understanding where this process happens. It turns out that the greater the density of the environment a spiral finds itself in (that is, the more neighbours it has) the more likely it is to be red…but only up to a point. Once we find ourselves near the core of a cluster of galaxies, the number and fraction of red spirals drops dramatically. So whatever it is that is causing the spirals to turn red must be more likely in the outskirts of galaxy clusters, but relatively rare outside this particular environment.
The story is, as ever, a little more complicated than that. If it was the environment that was driving the dramatic change from blue to red, then we’d expect the properties of the red spirals to depend on the environment. We might find that those in the densest environments were redder than their (still quite red) counterparts further out, for example. But we don’t. We don’t see any connection between the properties of the red spiral and the environment they find themselves in.
In my next blog, I’ll look at what we do know about this mysterious population of galaxies unearthed by your hard work. Until then, if you want the gory details, you can find the latest version of the paper over here.
How to find black holes?
The first step in trying to understand the connection between black holes and galaxies is finding them. But black holes are, well, black. In fact, you might say their blackness is their most defining feature.
So, how do you find them? It turns out that when they’re feeding on infalling gas and dust, a massive black hole can turn into the brightest object known in the whole universe – a quasar!
As the gas and dust falls towards the black hole, it settles into a disk around it, and as it moves in, friction in the disk heats up all the matter in it to such temperatures that it stats shining. In this way, black holes can be very bright, or quite dim, depending in part on how much matter they are munching on.
There are many ways to find feeding black holes and for the Galaxy Zoo paper on black hole growth, we used the emission lines that AGN (active galactic nuclei, or feeding black holes) cause when the light coming from the accretion disk shines on some other gas floating around in the host galaxy and makes that light in turn emit light with a very particular signature that we can detect by carefully analysing the spectra.
Black holes – why do galaxies care, anyway?
Now that our paper on AGN host galaxies (galaxies whose black holes are feeding) is out, I will write a few blog posts about what we found with your help. But before we start, a little background.
Why do black holes matter? We now believe that at the centers of most, if not all galaxies, there is a supermassive black hole. We call these black holes “supermassive” to distinguish them from stellar mass black holes that were formed in the deaths of massive stars. These supermassive black hole can be as heavy as a million or even a billion solar masses.
So you might think that these enormous black holes can wreak havoc in their host galaxies. However, galaxies are even bigger, much bigger than these black holes. In general, the black hole makes up about 0.1% of the mass of its host galaxy making really just a drop in the bucket.
In fact, their gravitational sphere of influence is tiny compared to the size of the whole galaxy and so they generally don’t affect anything but their immediate surroundings. As far as the galaxy as a whole is concerned, the supermassive black hole at its center might as well not be there.
But why is the mass of the black hole always some fraction of the galaxy mass (or to be more precise, bulge mass)? How does the black hole even know how big the galaxy is? Why does the mass of the black hole correlate with the mass of the galaxy bulge (the M-sigma relation)? It’s almost as if they somehow grew together….
Bar drawing project complete!
GZ2 Galaxy with Bars drawn by users.
Bar project stage 1 complete!
Dear all, we’d like to thank everybody for making the bar drawing project such a success. We now have enough data to perform some reliable, new & very exciting science.
The site will remain open (for future inspection), but the votes will no longer we recorded. We’d like to take this opportunity to draw your attention to other interesting galaxy zoo and zooniverse projects.
We’ll keep you posted about future publications.
Once again, we’d like to thank you all!
Best Regards,
Ben [and on behalf of Karen and Bob with the bar drawing team]
Finishing off the Peas Documentary
Dear all,
Many moons back, a large group of Zooites travelled to Oxford to make nearly all of a documentary about Galaxy Zoo, and especially peas, with PulseProject. It was a terrific success, and there’s just one more thing they’d like to do before it’s ready. Can you help?
Colin, who interviewed us all, wants to make a montage of about 30 zooites from around the world. He’d like you to Skype him, or to send him a brief video recording of yourself, along with your latitude and longitude. All you need to say is your name, and that you’re a zooite. For example, “My name is X and I classify galaxies at Galaxy Zoo” or “My name is Y and I am a zooite”. (Either your real name or your zoo name is fine.)
When you connect to him, you’ll get a blank screen – he may need to text you to let you know that he’s there watching. It’s so that his part doesn’t interfere with the recording. His Skype name is colincmurphy and his e-mail is colin@pulse-project.com. He’d love to hear from you.
You don’t have to have come to Oxford for that meet-up or to have had any particular involvement with the peas. Being a zooite is the main thing!
There is a copy of this message on the zoo forum if you’d like to see more discussion. Please let me know of any questions, and I’ll answer them if I can and contact Colin if I can’t.
I hope to see our peas, Oxford and the wonderful science of Galaxy Zoo in PulseProject’s documentary soon – and you as part of it!
Alice
Galaxy Zoo paper on AGN host galaxies accepted!
Dear all,
I am happy to tell you that after a lot of work and a long peer review process, the Galaxy Zoo paper on AGN host galaxies (galaxies whose supermassive black holes are feeding) has finally been accepted by the Astrophysical Journal.
I’ve blogged about it before when we submitted it last year. The paper itself has gotten a lot longer than I initially thought it would be because the morphologies we got out of all your clicks revealed quite a few things that we really didn’t expect, and that we weren’t sure how to explain. I’ll keep this blog post short, but I’ll try and follow it up with more details on what your clicks enabled us to to find, and (maybe also) what it means about growing black holes and how they affect the galaxies that they live in.
One of the more interesting things we found were these galaxies whose black holes are growing. In many ways, these galaxies resemble our own Milky Way…
In the meantime, you can get a PDF copy of the paper here, or off astro-ph when it appears there tomorrow night (January 19th).
Galaxy Zoo 