An Extra-galactic Halloween
At a pumpkin carving event yesterday, we (a group of people from Yale astro) tried to come up with an appropriate theme for our pumpkin. Naturally, we decided on the Hubble Sequence of galaxy morphology:
Elliptical
Lenticular
Early Spiral
Late Spiral
Irregular
And the artists…
A Train-wreck in Pisces
This weeks OOTW features Lightbulb500’s OOTD posted on the 22nd of October 2010.
SDSS J233604.04+000447.1
1 billion light years away a cosmic train-wreck of two merging galaxies is taking place, throwing stars out in streamers stretching out for thousands of light years in a flurry of gravitational disruption. Deep within this train-wreck at least one super massive black hole has awakened as a result of the infalling matter from the merger, making it a Seyfert 1 galaxy according to SIMBAD.
A seyfert 1 galaxy is a galaxy host to an AGN (Active Galactic Nucleus). The matter falling into the black hole forms an accretion disk which in turn creates massive jets of plasma as the disk emits huge amounts of radiation as a result of friction. This radiation gets concentrated into jets of plasma that beam out for thousands of light years!
The angle of the jets mostly determines what type an AGN is. There are several types such as the Blazars, the Seyfert 1’s, seyfert 2’s and so on. This galaxy is a seyfert one so the jet is beaming out at around 30 degrees so that it’s not quite facing us directly. A blazers jet would be facing directly at us, and the jets of a seyfert two would be at pointing 90 degrees away from us.
Eric F Diaz commented in the OOTD thread and asked if the galaxy is a polar ring or not, and Lightbulb500 set up a poll to see what everyone thought.
A polar ring galaxy is where a galaxy punches through the centre of another and as a result this creates a ring. This ring sorrounds and orbits the galaxy at its poles, creating wonderful images like this:
Mrk 1477
The Smiling Lens
This weeks OOTW features Jean Tate’s OOTD posted on the 20th of October 2010.
This is SDSS J103843.08+484916.1. It’s a gravitational lens in Ursa Major that Jean calls the ‘Smilie’; and you can see why!
So what is the cause of the arcs around the central galaxies?
Gravitational lensing is due to the curvature of space. Think of a bowling ball on a trampoline, the trampoline is the fabric of space and the bowling ball is the mass – say a cluster of galaxies – bending it. The more mass the bowling ball has the more it will bend the trampoline, and the same goes for objects in space.
The arcs are in fact distorted images of a galaxy that is lurking behind the central galaxies you can see in the image; you can see it much clearer in this Hubble images here. The light from the galaxy behind has followed the curvature of space caused by the huge mass of the central objects, making the light bend around the galaxies as arcs.
The left golden fuzzy has a redshift, Z, 0f 0.426, making it around 4.5 billion light years distant. The galaxy that forms the arcs however could be much further away.
Hunting Voorwerpjes
The discovery of the Voorwerp is definitely still keeping us busy as we’re trying to understand it. To recap what we know: the Voorwerp is a bit of a giant hydrogen cloud next to the galaxy IC 2497. The supermassive black hole at the heart of IC 2497 has been munching on vast quantities of gas and dust and, since black holes are messy eaters, turned the center of IC 2497 into a super-bright quasar. The Voorwerp is a reflection of the light emitted by this quasar. The only hitch is that we don’t see the quasar. While the team at ASTRON has spotted a weak radio source in the heart, that radio source alone is far too little to power the Voorwerp. It’s like trying to light up a whole sports pitch with a single light bulb – what you really need is a floodlight (quasar). We’ve been working hard on the X-ray observations that will give us a final answer whether there’s a quasar clevely hiding in IC 2497, or whether the black hole has somehow abruptly stopped feeding.
In the meantime, what we want to know is if there are more Voorwerps, or if Hanny’s Voorwerp is all we have in the local universe. This turns out to be harder than it sounds because asking a computer to go search a massive data set like Sloan for smudges that have this weird blue-purple-y colour is rather difficult. In fact, the Computer said ‘no.’ Fortunately, we could ask you folks to find weird blue-purpley-y stuff around galaxies because such a vaguely phrased question of a human makes sense. And you found more Voorwerps. Since they’re smaller, we dubbed them Voorwerpjes, or `Little Objects’ in Dutch (I look forward to the day that ‘Objects’ are a class of astronomical objects!).
Bill and his team have been taking a look at all the potential Voorwerpjes that you found and many of them are similar to the Voorwerp in the sense that they are clouds of gas lit up by an accreting black hole. All these clouds, like the Voorwerp, are many tens to hundreds of thousands of light years away from the centers of the galaxies they surround. So like with the Voorwerp and IC 2497, we know for a fact that the black hole was feeding tens to hundreds of thousands of years ago. What we’d like to know is if they are still feeding. If not, then clearly black hole meals can end rather abruptly (10,000 years is nothing to a billion solar mass black hole). If that’s the case, then black hole feeding is stranger and less stable than we previously thought….
To find out, we submitted a proposal, again to our friend XMM-Newton, to take X-ray snapshots of the galaxies with the top Voorwerpjes. Fingers crossed that we get the time.
A Cataclysmic Delight
This week’s OOTW features Jean Tate’s OOTD posted on the 6th of October
This is SDSS J120231.00+450349.1; a Cataclysmic Variable star in the constellation Ursa Major.
Cataclysmic Variables are stars in a binary system, with one white dwarf and another star of varying type. The white dwarf steals matter from its companion as it orbits closely, often completing an orbit within hours! As the white dwarf pulls the matter off its companion it surrounds itself with an accretion disk mostly made of hydrogen. If this CV was observed in the X-ray or UV you’d see it as strong sources in both wavelengths, as both X-rays and UV are being strongly emitted from the accretion disk!
As the name suggests this CV varies in brightness, getting brighter for a period as the accretion disk falls onto the white dwarf, setting off nuclear fusion at the stars surface.
Jean Tate found this CV to be of ZZ Ceti type, which are stars that pulsate, swelling from one size to another. Jean Tate writes:
In the H-R diagram, there is a thing called the instability strip; stars which fall in this strip pulsate (move in and out, usually radially) … and that pulsation is used, in Cepheids, as a key ‘standard candle’ in the cosmic distance ladder. Some white dwarfs pulsate; some which pulsate are called ZZ Ceti stars, after the variable ZZ Ceti: they are hydrogen WDs (classified as DA), and because they are variable, DAV stars (helium WDs (DB) can be variable too; they are DBVs. I don’t know if carbon (DQ) or metal (DZ) white dwarfs can pulsate).
I highly recommend reading her OOTD for a lot more information; and for details on the spectra!
Post-starburst galaxies paper submitted!
Today’s blog post is from Ivy Wong:
Hello Zoo-ites! I’m a work colleague of Kevin’s and I just recently submitted a Galaxy Zoo paper too. I just wanted to let you know all about it because I also wanted to thank you all for the great work which you’ve done in classifying so many galaxies. I am quite excited by the results and hope that it will be published soon. My research interests spans from understanding the processes of star formation to the evolution of galaxies and the Universe as we see today.
Ivy’s research assistants
The Galaxy Zoo paper that I just submitted consists of nearby galaxies which appear to be transitioning from being star-forming to passively-evolving galaxies. In particular, I looked at a sample of post-starburst galaxies (PSG). These PSG had a recent burst of star formation but they have since ceased forming stars. Thanks to the compilation of all the morphology classifications and the merger votes produced by the Zoo-ites, we were able to determine that most of these PSG have an indeterminate morphology with a higher fraction of interaction than regular spirals or ellipticals. It is possible that these interactions were responsible for the burst of star formation as well as the disturbed galaxy morphology.
The majority of PSG are low-mass but most of their stellar distribution already resemble those of ellipticals. However, they are still somewhat “green” and will likely turn red once the starlight of the youngest population of stars start to fade. Therefore these nearby PSG will probably end up as redder, low-mass and more passively-evolving galaxies. This result agrees with previous works asserting that the most massive and passively-evolving galaxies were formed at earlier times in the history of the Universe.
Sombrero and the Ultra-Compact Dwarfs
This week’s OOTW features Jean Tate’s OOTD posted on the 28th of September.
This is M104, otherwise known as the Sombrero galaxy. Lurking in the picture above hanging in front of the galaxy’s halo and blending in with all the stars of our galaxy is a strange little thing; an Ultra-Compact Dwarf (UCD) called SUCD1 :
UCDs are very compact objects, with millions of stars crowded into a small area as small as 200 light years across! They are rather luminous, showing up on the SDSS as star-like points. The UCDs have been observed in the Fornax cluster, which you can read about in the papers linked to in Jean Tate’s OOTD.
These objects are currently the subject of a lot of debate; are they dwarf galaxies or aren’t they?
Jean Tate summarises this, calling into question if the dwarfs are galaxies or more like globular clusters:
The jury is still well and truly out; however, UCDs do fit several (elliptical) galaxy scaling relationships better than they do globular cluster ones. But perhaps the most intriguing thing is that at least some UCDs seem to have mass-to-light ratios which suggest lots of dark matter, just like dwarf ellipticals (globular clusters seem to have essentially no dark matter) … so perhaps UCDs are not dwarf ellipticals because they are so close to massive cD (giant elliptical) galaxies?
This very interesting paper by Michael Hilker et al includes some very interesting scenarios as to how the UCDs form, including the UCDs being remnants of the centres of galaxies, or the result of globular clusters merging or that they are indeed dwarf galaxies! The paper also researches whether UCDs have dark matter haloes or not.
Black hole hunter finds quarry!
The care and feeding of black holes in galaxies has been a major focus of Zookeeper Kevin’s work. Checking his research publications shows at least a dozen journal papers dealing with black holes, whether seen actively accreting and shining as active galactic nuclei, or lurking quietly in less spectacular galaxies. Now I can reveal that, thanks to new technology, black hole hunting has become dramatically easier. Witness this documentation from a site visit – only one building over from Kevin’s office. I didn’t see what kind of delivery vehicle this needed.
Kevin finds black holes!
Galaxy Zoo Supernova Paper Submitted!
I’m pleased to let you know that the first Galaxy Zoo Supernova paper has been submitted to Monthly Notices of the RAS. This is a brief paper describing the supernova zoo, and analysing the classifications that you all made over May-July earlier this year.
Over that period, nearly 14,000 supernova candidates from the Palomar Transient Factory were classified by some 2500 of you, usually within a few hours of the data reaching the website. When we compared some of those classifications to those made by experienced astronomers, we found a excellent level of agreement: 93% of all confirmed supernovae over that period were identified correctly by the volunteers at Galaxy Zoo Supernovae (and usually more quickly than astronomers in PTF would be able to!). Galaxy Zoo Supernova continues to play a major role in classifying supernovae for PTF.
If you’re interested in the gory details, you can find the article here.
On to the next paper!
Mark
The Distant Globular of Camelopardalis
This week’s OOTW features JeanTate’s OOTD posted on the 22nd of September.
This object has the inventive name of F46 and it lives in the constellation Camelopardalis. It’s not a star, but is in fact a cluster of stars; a globular cluster. It’s not in our galaxy unlike most globular clusters we observe in the night sky, but lies 11 million light years away in the outskirts of NGC 2403; a spiral galaxy that William Herschel discovered in 1788.
Globular clusters are balls of thousands of old stars gravitationally bound to each other. They orbit their galaxy around the centre, but instead of following the normal path that most stars take – such as in the disks of spiral galaxies – they orbit their galaxy in the galactic halo, which stretches out farther than what is visible in the image above as a sphere, placing the globulars as much as 100,000 light years away from the centre.
F46, being magnitude v 18, is the brightest globular in NGC 2403. But there are plenty more unseen (as far as I can tell) in this SDSS image which you can see in this lovely Hubble image here. Our own galaxy has around 150 or so globular clusters, but many more galaxies have a much higher number; elliptical galaxies for instance have thousands!
You can find many beautiful images and spectra in the MAST database here, and at the Hubble Legacy Archive here!
Galaxy Zoo 