UV(oorwerp) from Space
We have some new results to show off, Hanny’s Voorwerp observed using a space telescope. No, not that space telescope, that’s still coming up (shortly, we hope).
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. Read More…
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!
First Results from Galaxy Zoo 2: Bars in Disk Galaxies
I’m happy to announce that the first paper using Galaxy Zoo 2 data was submitted (to MNRAS) yesterday.
In this work we used an early look at the information you have provided us on the presence of bars in a sample of GZ2 galaxies too look at trends of the bar fraction (basically how likely a certain type of disk galaxy is to have a bar) as a function of other properties.
Examples of barred (top) and unbarred (bottom) galaxies from Galaxy Zoo 2.
In doing this research I’ve learned that bars are really interesting features in disk galaxies. Unlike spiral arms, which are density waves (meaning stars pass in and out of them over the life of the galaxy), the matter in bars (stars and gas etc) actually rotates with the bar. This means that the bar breaks the symmetry of the disk of the galaxy and causes transfer of material both in an outwards along its length. What it boils down to is that bars should have a significant impact on the internal evolution of a galaxy. They have been suggested as a way to build some types of bulges, as a way to fuel star formation in the central regions, and perhaps even fuel AGNs. At the outer ends, the bar can induce ring like structures (see the top middle example) – and might even be responsible for driving spiral structure.
So what did we find? Well we observed a strong correlation between the bar fraction and the colour of the disk galaxy. Redder disk galaxies are much more likely to have bars identified by GZ2 users than bluer disk galaxies.
Bar fraction as a function of galaxy colour. The dashed line shows the overall bar fraction for the whole sample.
We also tried to split the sample by the size of the bulge. We find that disks with large bulges (shown by the red line below) have high bar fractions, and that disks with small bulges (shown by the blue line) have low bar fractions. This split by bulge size also splits the disks into things which are mostly red (large bulge) and blue (small bulge) – as illustrated by the histograms of the colour distribution of the two types of disk galaxies. What’s new here is that we show this also correlates strongly with the presence of a bar.
Top: bar fraction as a function of galaxy colour split into disk galaxies with large bulges (red) and small bulges (blue). The dashed line shows the overall bar fraction for each sub-sample. Bottom: histograms showing the colour distribution of the disk galaxies with large bulges (red) and small bulges (blue).
So we seem to split disk galaxies into two populations – ones that are red, have large bulges and are very likely to have bars, and ones that are blue, have small bulges, and are not so likely to have bars.
This gives an overall picture in which bars may be very important to the evolution of disk galaxies – perhaps more so than has been thought before. It’s very interesting, and I look forward to spending more time with barred galaxies and with the rich data set that you have given us with Galaxy Zoo 2.
We’re already working on more results from the bars using Galaxy Zoo 2, so expect updates soon. Also I just saw some very interesting results on bar lengths using data from the (now completed) Bar Drawing project. Hopefully we’ll have a paper from that soon too. Stay tuned!
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]
Unveiling the Mass of Galaxies with Vera Rubin
This week I am attending a conference at Queen’s University in Kingston (Ontario, Canada) with I think the longest name I have ever seen. It’s called “A Celebration of Vera Rubin’s Life. Unveiling the Mass: Extracting an Interpreting Galaxy Masses.” I was very excited to attend this conference. Vera Rubin has always been a role model of mine (hard to avoid as a women studying galaxies) and as well as her the list of speakers includes many people who’s work I know and respect. It also has the advantage of being held in Kingston where a close friend (and fellow astronomer) from graduate school is now living with her very new baby.
This morning the introductory talks did not disappoint. We heard anecdotes from Vera Rubin about her work as a young scientist just trying to interpret the observations she was making on the rotation curves of galaxies (observations that provided the first strong evidence for dark matter in galaxies). She talked about a 1962 paper she did with students measuring the rotation curve of the Milky Way, and her regrets on not noticing that dark matter must have been present when she measured a similar “flat” rotation curve for the Andromeda galaxy 13 years later. She further impressed me by dating another anecdote (about discovering a galaxy in which the stars rotated in two directions) by the year her youngest child learned to walk (1961). Not only is Vera Rubin an incredibly successful and famous astronomer, but she managed to have 4 children (at least one of whom followed her into astronomy) during the period she did most of her famous work. Wow! I got to talk with her a little bit this morning at coffee, and she’s also a very nice person.
As well as enjoying the many talks by leaders in the field of galaxy evolution, I am presenting a poster on my work on dust reddening of Galaxy Zoo spirals which you have heard about several times before (eg. Blue Sky and Red Spirals, and from when I presented it at the 2009 European Week of Astronomy). This work has relevance to the masses of galaxies as dust is a significant source of error on estimates of the total mass of stars in a galaxy – at the simplest level dust hides the stars.
I was encouraged to share my poster on this blog, so if you wish to have a closer look at it you can download it (pdf). Of course this poster is aimed at explaining my work to other astronomers not to a general audience. If you have questions about it I encourage you to first look at my more general explanation of the work Blue Sky and Red Spirals and I am also happy to answer questions in the comments below.
One little details which is not explained in the poster is that the images of galaxies on both the right and left are not random. On the right I show edge-on spiral galaxies ordered from bluest (at the bottom) to reddest (at the top). On the left I show all face-on galaxies, also ordered in the same way. My definition of blue versus red comes from a measured difference in the brightness seen through 2 filters (in this case the SDSS g and z filters), so is not always obvious to the eye – also remember that it is the average colour of the whole galaxy, and some have significantly different colours in their centres to in the outskirts. However one of the interesting results coming from this work is that even though on average dust reddens galaxies as they become more inclined (as they go from face-on to edge-on) some face-on galaxies are much redder than some edge-on galaxies. This shows that while dust is important to the colour of a spiral galaxy it is clearly not the most important factor. This is very good news for those of us interested in red spirals as an evolutionary stage!
If anyone is in the Kingston area there will be a public lecture at 8pm tomorrow night given by Prof. Sandy Faber. It’s on the Queen’s Campus in the Biosciences Building, Room 1101. I include the poster below. Sandy Faber was a student of Vera Rubin’s and gave a very nice review talk this morning about her early work on dark matter during this time. I encourage you to attend if you are able – I think it will be a very nice public astronomy talk.
Galaxy Zoo 