Tag Archive | x-rays

Chandra X-ray Observations of Mergers found in the Zoo Published

I hope you all had clear skies during the Transit of Venus. If not, it’ll be over a hundred years before you get another chance…. and in Zoo-related news, the Transit of Venus is an example of one way we find planets around other stars. We look for a dip in the brightness of the star as a planet moves across it from our point of view. Want to know more? Head over to the Planethunters blog, or put in some clicks looking for transits yourself!

So, in actual Galaxy Zoo news, I am very happy to report that the latest Galaxy Zoo study has been accepted for publication in the Astrophysical Journal. As we blogged a while back, we got Chandra X-ray time to observe a small sample of major mergers found by the Galaxy Zoo to look for double black holes. The idea is to look for the two black holes presumably brought into the merger by the two galaxies and see if we find both of them feeding by looking for them with an X-ray telescope (i.e. Chandra).

The lead author of the paper is Stacy Teng, a NASA postdoctoral fellow at NASA’s Goddard Space Flight Center and an expert on X-ray data analysis. In a sample of 12 merging galaxies, we find just one double active nucleus.

Image of the one merger with two feeding black holes. The white contours are the optical (SDSS) image while the pixels are X-rays. The red pixels are soft (low energy) X-ray photons, while the blue are hard (high energy) photons. You can see that both nuclei of the merger are visible in X-rays emitted by feeding supermassive black holes.

We submitted the resulting paper to the Astrophysical Journal where it underwent peer review. The reviewer suggested some changes and clarifications and so the paper was accepted for publication.

You can find the full paper in a variety of formats, including PDF, on the arxiv.

So what’s next? We submitted a proposal, led by Stacy, for the current Chandra cycle. To do a bigger, more comprehensive search for double black holes in mergers to put some real constraints on their abundance and properties. We hope to hear about whether the proposal is approved some time later this summer, so stay tuned and follow us on Twitter for breaking news!

X-ray observations of IC 2497 in the can!

As we tweeted about and as Chris noted in his blog post about the Zooniverse success at the American Astronomical Society meeting in Austin TX, half of the Chandra X-ray observations of IC 2497 (the galaxy next to Hanny’s Voorwerp) have been executed and so with bated breath we awaited the results.

From previous X-ray observations with Suzaku and XMM, we know that the quasar that lit up Hanny’s Voorwerp is dead, and that there’s just a weak source in the center of IC 2497 where the black hole lives and some evidence for hot gas. So we had turned to Chandra to figure out what was going on in the center of IC 2497. To puzzle apart the faint black hole at the center and the gas around, and Chandra has the sharpest X-ray eyes in the sky.

We got the notification from the Chandra X-ray Center that the observations had concluded and that we could have a preview of the raw frame. Bill and Chris happened to be near, so after Chris finished his talk on the latest Planethunters.org results (two new planets!), we got together in (possibly) the exact same spot where Chris and Bill viewed the first spectrum of the Voowerp at another AAS meeting in Austin four years ago.

Chris (left), Kevin (right)

From left to right: Bill, Kevin, Chris, all looking at the data.

So, without much further ado, here’s what we got:

Well that’s a bit underwhelming!

Or not!

First, we know that we have a bright source, so we can study the X-ray data in detail. Also, this is just a JPEG screenshot, so we can’t even zoom in and change the scaling to see if there’s anything else there. We don’t even know which way is North, so we don’t know where the Voorwerp is. So for now, all we can do is wait for the actual raw data to be available. This should take a few days. Stay tuned….!

The Sudden Death of the Nearest Quasar

When I told Bill Keel the results of the analysis of the X-ray observations by the Suzaku and XMM-Newton space observatories, he summed up the result with a quote from a famous doctor:

“It’s dead, Jim.”

The black hole in IC 2497, that is.


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).

Now it is possible to hide such a floodlight. You just put a whole bunch of gas and dust in front of it. If there’s enough material, no light even from a powerful floodlight will get through. Imagine pointing it at a solid wall – even the brightest floodlight in the world will be completely blocked by the wall. In the realm of quasars, such a barrier is usually made up of the torus of material (gas and dust) spiralling in towards the black hole and settling into an accretion disk. So you can have quasars that are feeding at enormous rates and being correspondingly enormously bright, but our line of sight is blocked.

So there are two possibilities of what could be going on with IC 2497 and the Voorwerp:

1) The quasar is “on” but hidden by lots of gas and dust, or

2) The quasar switched off recently, but because the Voorwerp is 70,000 light yeas away, the Voorwerp is still seeing the quasar –  after all, even light takes a while to travel 70,000 light years. This would make the Voorwerp a “light echo.”

So how do we distinguish between the two possibilities? The best way is to look at a part of the electromagnetic spectrum that generally has no trouble penetrating even thick walls: X-rays!

If the quasar in IC 297 is feeding, then we should see the X-ray light it is emitting even through the thickest barriers. That’s why we asked for observations with Suzaku and XMM-Newton. It took many months to gather and analyze the data before we were ready to write up a paper and submit it to the Astrophysical Journal as a Letter. The referee report was challenging but positive, and the Letter got accepted rapidly. The pre-print is now out on arxiv: http://arxiv.org/abs/1011.0427

So what did we find? We found something, but it isn’t a quasar. With the X-ray data, we can definitely rule out the presence of a quasar in IC 2497 powerful enough to light up the Voorwerp. We do however see some very weak X-ray emission that most likely comes from the black hole feeding at a very low level. Compared to what you need to light up the Voorwerp (the floodlight), the black hole currently puts out 1/10,000 of the required luminosity. That’s like trying to illuminate a sports stadium at night with a candle.

We can therefore conclude that the black hole in IC 2497 dropped in luminosity by a factor of ~10,000 at some point in the last 70,000 years. This implies a number of very exciting things:

1) A mere 70,000 years ago (a blink of an eye, cosmologically speaking), IC 2497 was a powerful quasar. Since it’s at a redshift of only z=0.05, it’s the nearest such quasar to us. Since IC 2497 is so close to us, and the quasar has switched off, it means that images of IC 2496 are the best images of a quasar host galaxy we will ever get.

2) Quasars can just switch off very quickly! We didn’t know they could do this before, and the fact that they can is very exciting.

3) Maybe the quasar didn’t just switch off, but rather switched state, and is now putting out all its energy not as light (i.e. a quasar), but as kinetic energy. That’s an extremely intriguing possibility and something I want to investigate.


We put out a press release via Yale. You can find it here.

Chandra Program to study Galaxy Zoo Mergers approved

Good news, everyone!

Earlier this year we submitted a proposal to use the Chandra X-ray Observatory to observe a set of merging galaxies in X-rays. The target list for Cycle 12 has just been released, and with a bit of scanning, you can find a set of targets with names like “GZ_Merger_AGN_1”. These targets are a set of beautiful merging galaxies discovered by YOU as part of Galaxy Zoo 1 and the Merger Hunt. The 12 approved targets are here:


These 12 mergers are all very pretty, but they have something else in common: they all host active galactic nuclei (AGN) – feeding supermassive black holes at their centers. X-rays are great for finding such hungry black holes, but we already know that all 12 of these mergers are AGN, so why observe them again? We’re looking for a mythical rare beast: the binary AGN!

Only a handful of these objects are known and they were discovered by chance. We believe that every massive galaxy has a supermassive black hole at its center and so when two galaxies merge, then there should be two black holes around for a while, that is, until they merge. The goal of our Chandra study of these 12 mergers is to systematically search for binary AGN in merging galaxies to work out what fraction of them feature two feeding black holes. Knowing whether such phases are common or not is important for understanding how black holes interact with galaxies in mergers and what exactly happens to them as they plunge towards the center of the new galaxies where they are doomed to merge and form a single supermassive black hole.

As usual, it may be quite a while before we get the data. The observing cycle won’t start for a while and takes about a year. Since our observations are short and we don’t have any time constraints (they’re galaxies, they don’t move!) the Chandra operators will most likely schedule our observations in between longer projects and time sensitive observations and so we won’t know when they will happen. Of course, once we do get the data, we’ll definitely update you.

Oh and you might notice some of the targets in the Merger Zoo in the near future. We’ll need your help to fully understand them….

XMM-Newton is observing Hanny's Voorwerp TODAY!


Hi all,

Just a quick note – our observations of IC 2497 and the Voorwerp have been scheduled for today and are taking place now. Since we’re observing in the X-rays, our “quick snapshot” to see what is going on actually takes almost a whole day. XMM-Newton‘s eye isn’t very sharp, so we won’t get a pretty picture. What we will get however is a really great spectrum of the X-ray emission of the black hole in IC 2497 (if it’s munching on stars and gas) and perhaps also the hot gas in the Voorwerp.

We won’t get the data right away though. First, the folks at the European Space Agency (esa) who are controlling XMM need to check out whether the data is OK and do some basic processing on it. Only then can they send it to us to have a look and that may take a few weeks.

Stay tuned!


Voorwerping, Part 1

I’m working on the Suzaku data that we’ve obtained on IC2497, the galaxy next to Hanny’s Voorwerp. X-rays, especially the really energetic ones that Suzaku is able to detect are probably the best way to probe whether the black hole in a galaxy is actively feeding or not. Shanil Virani and I are currently working on the data reduction and analysis, which is quite challenging. Early indications are that the data will show us some really exciting things, but the problem is that they make us really scratch our heads. It may yet take us quite a while to see if we understand what’s going on and we may have to pick the brains of a theorist or two. So, stay tuned….