Herschel opens its eye!

The entire universe in blog form
June 19 2009 9:44 AM

Herschel opens its eye!

Herschel, the largest far-infrared telescope ever launched into space, has taken its first image!

Herschel spies M51

Phil Plait Phil Plait




That's M51, better known as the Whirlpool Galaxy, a nearby spiral galaxy (well, 25 million light years is close on an intergalactic scale). It's face-on to us, allowing us to see its magnificent spiral arms and all the structure therein. Herschel is sensitive to far-infrared light, much lower energy than what our eyes can see. In galaxies, the brightest emitter of that kind of light is dust located near and in between stars, and dust is created by stars when they are born (and when massive ones die). Star birth happens in the spiral arms of these kinds of galaxies, so when Herschel looked at M51 that's what it saw: the spiral arms outlined by the warm dust within them. The brights spots are where dust is being warmed by young, massive stars. It's falsely colored blue in the image, meaning it's the highest energy flavor of IR light Herschel sees; to our eyes it would still be invisibly far in the infrared.

Herschel’s mirror
If you're used to Hubble images, this one looks a little fuzzy. That's because the resolution of a telescope -- that is, how well it can resolve small objects -- depends on the size of the mirror and the wavelength of light it sees. Optical light, the kind we see, has a far, far smaller wavelength than infrared, so images in optical light have much higher resolution, and look sharper.

But for science, we want to know how much better Herschel does than previous far-infrared telescopes, and that depends on its mirror. Herschel wins here by a lot: its mirror is 3.5 meters across! Spitzer, the NASA observatory that has been taking such wonderful IR images of celestial objects, has a mirror less than a meter across, so Herschel's eye is far sharper. Compare!

Herschel and Spitzer compared

You can see that Herschel's view of M51 is a lot sharper than Spitzer's at these long wavelengths. This means that with Herschel, astronomers will have a better infrared view of the sky than ever before. [Update: To be clear, Spitzer was not optimized for wavelengths this far in the IR, so its resolution in that image above is actually not as good as what it could do at shorter IR regions; for example check out this stunning M51 image taken by Spitzer in the nearer infrared to see what it can do!]

And this is just the first image, a test of the telescope's abilities. In the coming weeks, months, and years, we'll be seeing far more from this new eye in the sky, and I am very much looking forward to seeing what it sees.

Tip o' the dew cap to Amanda. Image credits: ESA and the PACS consortium (Herschel images), and NASA/JPL-Caltech / SINGS (Spitzer image)