This week, a number of scientists have gathered in Madrid to discuss the first science results from the Herschel Space Telescope. Herschel is the largest astronomical telescope ever put in space (the mirror is 3.5m wide!) and observes light at infrared to submillimetre wavelengths (50 - 550 microns), around 500 times larger than the wavelength of visible light. Astronomers built this telescope to observe cold objects (shining at 10K or -260C) in the Universe, since these sources radiate at this wavelength. Herschel will detect hidden star formation, cold gas, molecules and atoms, planets, Solar-System objects and invisible stardust - the building blocks of planets and even life. Stardust is very important in galaxies, it only makes up a tiny fraction of their mass (about 1%), but profoundly affects its view. Half of all the light shone by stars in galaxies is absorbed by stardust, hidden from our optical telescopes and re-radiated at infrared-submillimetre wavelengths. If we use only optical telescopes alone, we are missing half the light! Telescopes like Herschel allow us to directly see the stardust shining and therefore observe sources which are invisible to our optical telescopes.
Since Herschel was launched on May 14th this year, astronomers across the globe have been working hard to test the instrument and find out if it's working correctly. Herschel has given us an amazing glimpse of its power during these Performance Verification and Science Demonstration phases, and these show that Herschel is doing better than expected with some beautiful images of the far-infrared sky. This week, however, is the first time we get a chance to learn about some scientific results based on the observations taken so far. All I can say is, "wow". Here's an update on the latest results.
Now for a truly astonishing image. Here we see Herschel's view of the Aquila star forming region, located about 1000 light years away in our Galaxy. The image shows the combination of 50, 150 and 500 microns and the bright regions are areas where large newborn stars are heating up hydrogen gas. Aquila is a stellar nursery completely invisible to optical telescopes (in fact, this is the first time its been seen in the infrared) and the image shows some pretty neat stuff. Firstly, in this image alone, astronomers have detected 700 candidates for stellar embryoes (stars which are about to be born). 100 of these candidates are in the protostar phase and are just waiting for the final step to start before they become a fully-fledged star - all they need is for nuclear fusion to ignite in the core and they are ready. The rest are likely to be in the stage before this. Secondly, we can clearly see that stars form in clumps along larger filaments of dust and gas (much like pearls on a necklace); these filaments are probably following magentic fields in the region. More details on this result can be found here.
Space is wispy
The next image shows that space is filled with wisps and filaments of dust, these filaments could hold embryonic stars if they accumulate enough mass. This image, combined with all the data from Herschel will help us understand what the dust is made from and how efficiently it shines (which also tells us how much stardust is there).
Dusty spiral arms
Next we see the spiral galaxy M81 with Herschel. The spiral arms are really clear in this image, and this is astounding since we have never had the resolution or sensitivity to see this kind of structure before at these wavelengths. After 400 years of using visible telescopes and seeing spiral arms a million times before, it may seem a little strange that I am so excited about seeing spiral arms with Herschel. There are some hints that dust may be being pulled out from the galaxy as in the M86 system above (see the diffuse light in the north), and astronomers have long been looking for evidence for vast amounts of dust being stripped from a galaxy due to the gravitational pull from its close neighbours. However, these two galaxies are in a region of sky where there happens to be a lot of dust from our own Galaxy in front. This means that we are also looking through the debris in our own Galaxy, and as you can see from the "wispy" image above, there are places where space is filled with lots of dusty filaments. The material in the north may actually be in our own Galaxy and not associated with M81 so this needs further checking to be sure.
We can also use Herschel to look deep into space and see distant galaxies which were around when the Universe was very young, when the Universe was about a third to a tenth of its present day age. In this image we are literally detecting thousands of galaxies. One of the really surprising things we've learnt with Herschel, is that we see so many sources like this in the background of our images, far more than we expected. The colours in this image give an idea how distant the galaxies are.
Herschel has not just been busy taking images, it has also used its numerous spectrographs to search for molecules and atoms in galaxies, stars and comets. One example is the spectra of the famous galaxy Arp220 shown here, which is the result of two giant galaxies merging together. Arp 220 is around 250 million light years away and is undergoing a renewed (and active) period of star formation as a result of the merger which has comrpessed and heated the gas. Arp 220 is an important "laboratory" for astronomers to test theories on what the first few generations of galaxies would look like. What we see in this spectrum are emission and absorption features of water and carbon monoxide. Herschel is the first instrument to allow us to look at spectra in the submillimetre wavebands and the wealth of information it tells us is outstanding. Not only can we detect water (seen for the first time in emission here), but we can figure out what its temperature and density is. The latest spectra of the massive giant star VY Majoris shows evidence for hot steam, which is cooling the star in the same way we use steam to cool nuclear reactors in power stations!
Dusty evidence of galaxy-scale interactions
At Cardiff,we have been working hard this week on some data we have of a giantelliptical galaxy in the Virgo cluster, the nearest group of galaxiesto us. Ellipticals, so called due to their elliptical-like appearancein visible light, are often described as "red and dead" galaxies,where stars are no longer forming and all the dust has been used up. The elliptical galaxies we see today, are thought to be the descendantsof the massively dusty, active star forming galaxies seen in the veryearly Universe; these galaxies are forming stars thousands of timesfaster than our own and are likely harbouring an active galacticnucleus at their centre. Astronomers are not really sure how thesemassive systems form, particularly whether or not they are formed bymerging galaxies together from collisions. An important question toaddress is whether or not environment affects the formation andevolution of these systems. Other questions we want to ask is "areellipticals really devoid of dust?" and, "what can we learn about theirhistory using any dusty features we can see?". Well it turns out alot!
Take a look at the optical image of the galaxies in theVirgo cluster. The brightest galaxy in this image is the giantelliptical M86 (bottom right). We can also see the spiral galaxyNGC4438 on the left, with a smaller galaxy nearby. In the Herschelsubmillimetre image however, the elliptical galaxy is now the faintestgalaxy (this is because it must have used all its dust up in formingstars). We also see something quite unusual, the dust is offset fromthe centre of the galaxy and appears to be distributed in a verydifferent way to the stars. If we now compare the dust to hot hydrogengas (which shows gas being pulled out of the galaxy due to theinteraction with the galaxy in the top right) we see a pretty goodmatch. The dust appears to be following the ionised hydrogen trailingout of M86 and is being pulled towards the galaxy in the top left. This is really strong evidence that environment significantly affectsdust and metals in galaxies, the data points to more than a millionSun's worth of dust being stripped from this source.
So that's a small introduction into some of the results from Herschel, but there are many more to come, and plenty of work left to do! Keep up with the latest news here.
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