What's the blue stuff below?

Anyone?‘ asked Hanny from the Galaxy Zoo Forum. She came across a weird blue blob that none of us could really make any sense of. It’s right next to a rather massive galaxy that might be a spiral or a somewhat disturbed galaxy.

Hanny’s Voorwerp, the mystery blue blob

A highly scientific illustration.

At first, we had no clue. The mystery blob didn’t have a spectrum, so we couldn’t tell much about it at all. It could be in our Milky Way, it could be as distant as that big galaxy, or it could even be at the edge of the universe. Bill Keel enhanced the SDSS image a bit (see below) to reveal the intricate structure of what became known as ‘Hanny’s Voorwerp’ (object).


The five different SDSS bands (g,u,r,i,z), note the intricate structure in the g-band image.

The object seems to be very bright in the g-band image and virtually absent in the others. This led us to think that it must be an emission line object, i.e. an object which emits most of its light only in very specific atomic transitions. This usually means that what we are seeing is ionised gas, rather than stars. Still, it could be anything. Bill Keel kindly also obtained a multi-colour image with the 0.9m SARA telescope at Kitt Peak. The three colours here are much closer to what human eyes would see, so as Bill pointed out, it’s actually much more appropriate to call it the mystery *green* blob.


BVR image from the SARA telescope.

We’ve managed to contact a friend of ours who is currently observing at the 4.2m William Herschel telescope in La Palma and convinced him to take a spectrum of the Voorwerp for us. It shows us that the Voorwerp is…. *drumroll* at the same distance as the big galaxy. This implies that it’s really rather huge and luminous.What does all this mean? What is the Voorwerp? That’s not too clear yet. We have to properly analyse the spectrum to understand what exactly is going on. It’s likely forming stars at a huge rate, ionising lots of gas and making it shine. We’re also trying to get a deeper image to see if there’s evidence of an interaction between the big galaxy and the Voorwerp.So what’s next? We’ll have to do a lot of work to understand this mystery blob better. Right now, the Voorwerp is only slightly less mysterious than when we started, but I have a feeling that it’s going to be really good fun figuring out what is really happening here. It also shows the power of Galaxy Zoo and of having you guys go through the images by eye. If Hanny hadn’t spotted it and asked, we’d never have known about it!

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18 responses to “What's the blue stuff below?”

  1. Rick Williams says :

    I think I’ve figured it out!!! Check this link out at HubbleSite

  2. Hanny says :

    I think Chris beat you to that! Have a look at his website too..

  3. Chris says :

    We need to do some more work but I don’t think we have exactly the same sort of thing; I was in the press conference where that was announced and from memory I think their source is much brighter in the near-UV than ours is. We do need to check though…

  4. Adam Primus says :

    Has the object actually been classified i.e. have an official catalogue number or something, & is there any chance the name “Hanny’s Voorwerp” will ever become more than it’s un-official title?

  5. starry nite says :

    Way to go Hanny!

  6. Chris says :

    It has a long SDSS classification number, but we’re certainly referring to it as a Voorwerp. Let’s see if we can get that into a paper…

  7. FermatsBrother says :

    Hi folks – Where can I access the individual g,u,r,i,z images of SDSS objects (like those above)?

    Fermats Brother

  8. NGC3314 says :

    You can get the individual FITS images in ugriz from the object explorer pages. Midway down in the left-hand frame, the bottom link under PhotoObj is “FITS”. That link leads to a page which lets you click for individual filtered images (or the combined atlas images, which IIRC are stacked into a 3D FITS form). This gets you a fairly large chunk of the scan, with the original x,y axes at skew angles to RA and declination axes. (I was pleased to find that, for examples, DS9 will rebin during display to align them with coordinates if requested).

  9. xxfubsyxx says :

    Wow, its rather interesting isn’t it. Well done for reasearching into it.

  10. Brian Whittaker says :

    http://cas.sdss.org/astro/en/tools/explore/obj.asp?id=587736525907034357 has several blue blobs around the edge, one on the south is quite prominent. Remotely similar??

  11. Chris says :

    Although they look similar, they’re equally bright across all of the SDSS colours, which is very different from the Voorwerp.

  12. Ruben says :

    587726032234741807 is also a blue blob-thing, but it’s part of the same galaxy in the picture, right? I’ve seen they’re almost as common to find as mergers.

  13. Chris says :

    That object’s pretty bright in each of the SDSS colours, whereas the Voorwerp is much brighter in ‘g’ than in any of the others. It’s a crucial difference, distinguishing an object shining by starlight from an object dominated by emission lines like the Voorwerp. The moral of the story? Look for the specific shade of blue!


  14. David Sale says :

    In the top left portion of the “BVR image from the SARA telescope.” (blueblob2-1.jpg) on this web page is a line that is very similar to the “blue blob”. This line is diagonal and “intersects” the very bright object also in the “top left” corner of the picture. This line is a little fainter than the “blue blob” Any idea what that is?

  15. James M. says :

    I would like to mention though. If this was just a mas of brilliant blue stars that weighs 10 of thousands of solar masses, wouldnt we see a some type of lensing effect. As well why would an object so massive have little to no effect upon the density wave of its “nearby” spiral galaxy. from the observations thus far it seems that this object has very little mass compared to its neighbor. Very strange.

    I suppose that this is a super dense, but not super massive, collection of gasses that is being ionized by its neighbor.

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