Date: June 3, 2011
Title: Herschel Space Observatory Science Update
Podcaster: Haley and Edward Gomez
Organization: Herschel Science Center: http://herschel.esac.esa.int/
Description: Haley and Edward Gomez give their picks of the the latest results from Herschel.
Bio: Haley is an astronomy lecturer at Cardiff University, who does research into the origins of cosmic dust using far-infrared telescopes, including Herschel. Edward is education director for Las Cumbres Observatory, and although he works with optical telescopes he’s a big fan of Herschel.
Sponsor: This episode of “365 Days of Astronomy” is sponsored by — NO ONE. We still need sponsors for many days in 2011, so please consider sponsoring a day or two. Just click on the “Donate” button on the lower left side of this webpage, or contact us at signup@365daysofastronomy.org.
Transcript:
Introduction to Herschel
Hello and welcome to our second podcast on the Herschel Space Observatory for 365 Days of Astronomy. I’m Edward Gomez from Las Cumbres Observatory Global Telescope Network
and I’m Haley Gomez from Cardiff University.
The Herschel Space Observatory has now been observing the sky since its launch two years ago, on 14th May 2009.
Ok, let’s find out a small selection of some of the latest news from Herschel.
No 3. Astronomers find Galaxies galore
For me, one of the most amazing things about Herschel is the huge leap it’s made for detecting galaxies. We’ve gone from a total of a few hundred galaxies observed painstakingly over a period of more than 10 years, to finding literally thousands of galaxies within only two years since Herschel’s launch date. Two major teams are making maps of different regions of the sky with Herschel these are called: the HERMES and Herschel ATLAS projects. The ATLAS will be a whopping 550 square degrees by the time its finished. That’s equivalent in area to about 2000 Full moon’s all side by side.
By observing in the far-infrared, Herschel sees material that cannot be seen at visible wavelengths so we see a different view of the galaxies out there. In the Herschel maps the thousands of galaxies look like tiny pin-pricks of colour. The colour is actually pretty useful, as it can signify that the galaxy is much further away. Some of the galaxies in these images are tens of billions of light years away –
that means light from these objects has taken 10 billion years before they hit Herschel’s mirror.
Right. Because Herschel is so sensitive and produces sharper images than we’ve had before, we can start to count these galaxies individually and look at how they change over cosmic history. It turns out, they change quite a lot more than we realised. To put the leap in technology we have with Herschel’s in perspective, some of these faint galaxies are around ten thousand times fainter than say Uranus. That’s how powerful Herschel is.
ok, so what else do we know now we have all these galaxies
One thing astronomers have done is to look and see if these galaxies are clustered together more than would be expected compared to them all being randomly distributed on the sky.
Are they?
Well it looks like the massive galaxies in the early universe (the ones which are forming lots of stars quickly) are clustered together. It looks like they are crashing or merging, and possibly settling down at centres of large superclusters
How does that compare to the Milky Way?
Good question, ok. We know that the MW (our galaxy) is on the suburbs of a large supercluster of galaxies. The nearest neighbouring supercluster of galaxies to us is about 300 million light years away.
But galaxies Herschel see (remember these are from the early universe), were only about 20 million light years apart (on average). This is really close in comparison to the MW and it’s nearest cluster. So we figure that in the early Universe we would expect many of these galaxies will eventually collide with one another since they are so close.
No 2: Would you like to make water near the surface of a star? Well just add a dash of starlight.
In 2001, astronomers discovered an unexpected cloud of water vapour around the old star CW Leonis which we’re going to call CW Leo and they immediately began searching for the source of this water. Water is known to be present around several types of stars, but CW Leo is a “carbon rich star” and so it really shouldn’t be able to produce water.
Why does being a carbon star have anything to do with whether it has water in its atmosphere?
Because all the oxygen in the star has been swept up by all the carbon going around so all the oxygen should be locked up in carbon monoxide.
And then you have no oxygen free to make water?
Yes. And since carbon monoxide is pretty hard to break up, astronomers initially suspected that the water they only tentatively discovered in 2001 was coming from icy-comets orbiting CW Leo, and the ice on these comets evaporates as they come close to the central star. Now they had no other information to go by so that was that.
Until Herschel.
Until Herschel. So Herschel used two of it’s instruments PACS and SPIRE to image CW Leo producing sharper images of the star and all the material billowing out of the surface. They also split the light up using a spectrometer and looked for the tell-tale fingerprints of water. Using this data, they realised that the water vapour seen before is being formed much closer to the star than previously thought, and that the water is pretty hot – at temperatures approaching 1000oC!
Ok, but what does this mean?
Two things really: first the water vapour must be created by some chemical process which we didn’t realise was happening and that process goes a little like this:
hot ultraviolet radiation from interstellar space is interacting with the molecules billowing out from the surface of CW Leo and this radiation breaks up the stable carbon monoxide.
And this then releases the oxygen atoms from the carbon monoxide which can pair up with their hydrogen neighbours to create water before another carbon comes along?
Exactly. But the Herschel results also tells us something else: Ultraviolet light from the surroundings shouldn’t be able to penetrate the material flowing out from the star as it’s thought to be pretty dense. So for this chemical process to happen in the first place, the Herschel results tell us that some regions around the star must have no outflowing material. It’s in these empty regions, that ultraviolet light is able to reach the deepest layers of the star’s atmosphere and initiate the chemical reactions that produce the water.
Nice.
No 1: exquisite map of stars forming in nearest neighbour
Ok, so the top news story is about the Andromeda galaxy. Andromeda (some of you may know it as M31) is our nearest large spiral galaxy and it’s pretty close by (well, relatively) at a distance of 2.5 million light years. It’s very similar in size to the Milky Way, and has been observed with lots of different telescopes as it’s so close to us, because of this it provides a way to study how stars form and where dust comes from on galaxy-wide scales in exquisite detail.
Yes, we can do this because Andromeda appears very large in the sky, as wide as almost 6 full moons, and on a dark night the bright central core can sometimes even be seen with the naked eye. In visible light, the stars are seen in the spiral arm structure, separated by dark dusty lanes.
At Christmas, Herschel took images of Andromeda and could trace out where all the dust is. In the Herschel images, we see cool and cold dust that shines because it is heated by massive young stars that are forming within the dust clouds.
What’s particularly interesting about Andromeda is that, unlike other bright galaxies, it shows a large ring of dust about 75,000 light years across around the centre. Some astronomers think that this dust ring may have been formed in a recent collision with another galaxy. The Herschel image reveals even more intricate details with several rings of dust seen, all hiding baby stars being born. This is work in progress of course, but the images will allow us to study the star formation in a galaxy remarkably similar to our own, but from the outside!
These images were actually shown on the BBC Stargazing Live programme in January as well!
Ok, that ends this podcast, hope you’ve enjoyed hearing more about the latest Herschel news. For more results, check out www.herscheltelescope.org.uk. Thanks to Chris North who writes the news stories which we’ve based this podcast on. Goodbye.
End of podcast:
365 Days of Astronomy
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