Planck sees the Crab

September 29, 2009 by

[cross-posted from Planck UK site]

Last week, the Planck satellite observed the Crab Nebula, also known as M1 from Messier’s catalogue, and Tau A to radio astronomers. The Crab Nebula is one of the brightest objects in the sky at radio and sub-mm wavelengths, and is used by many astronomers to calibrate their instruments. It is the remnants of a star which underwent a violent and catastrophic explosion at the end of its life, an event known as a supernova. The Crab Nebula is associated with one of the few supernovae which was observed, as it was seen by Chinese and Arab astronomers in 1054.

Hubble image of the Crab Nabula
Hubble Space Telescope image of the Crab Nebula, showing the colourful nebula and filaments. Image credit: NASA/ESA

After the supernova, the outer layers of the star were scattered widely into a huge cloud of gas, which we now see as a nebula, and is frequently observed by amateur and professional astronomers. The core of the star ended up as a pulsar, a rapidly rotating, magnetised neutron star. However, it is the surrounding nebula that Planck is interested in. The nebula is around 13 lightyears across, which is around 10,000 times larger than our solar system (depending on where you define the edge). It is also relatively close in astonomical terms, at about 6 lightyears distance, and so is also relatively large in terms of astronomical objects see from Earth. It is around 7 arcminutes across, which is 7/60th of a degree, or about 1/4 the diameter of the full moon as seen from Earth. The smallest of Planck’s beams on the sky is 5 arcminutes and the largest 30 arcminutes, so to the majority of Planck’s detectors the Crab Nebula will have appeared as a “point source” – a single blip in the data. However, it is so bright that it would still be very obvious.

SCUBA measurements of the Crab nebula
SCUBA image of the Crab Nebula at 350GHz. The colour shows the brightness (blue/black=dark, red/white=bright), and the length og the black lines shows the relative amount of polarisation. Image credit: J.S. Greaves, W.S. Holland & T. Jenness (Joint Astronomy Centre)

Because the central pulsar is magnetised, the Crab Nebula is permeated by a magnetic field. This causes any electrons in the nebula, of which there are many, to spiral around the magnetic field lines and emit radiation known as synchrotron radiation. This radiation, which is brightest at radio wavelengths, but still very strong at Planck frequencies, is polarised, which makes the Crab an ideal object for calibrating the polarisation-sensitive detectors on Planck. Many experiments have observed its polarised radiation, including the SCUBA instrument on the JCMT on Hawaii, which observed it at 350GHz (a wavelength of 850 microns). One of the properties of synchrotron radiation is that it varies in a fairly predictable way with frequency, so it is possible to tell from an observation at one frequency what it will look like at another.

The data will take time to analyse, but will be ingested into the Planck database and used to help calibrate its instruments. The Crab Nebula is not the only calibration source, but is the best single source in the sky for calibrating the polarisation angles.  Other non-polarised sources include the planets in our own solar system, particularly Jupiter, which are very bright at Planck’s frequencies as well as to the naked eye.


In the News

September 18, 2009 by

Various news outlets have picked up on the Planck press release. These include:

The Telegraph who even quote me!

The Times

AFP via Google



And I’m sure there will be more. Anybody who spots something please add to the list via a comment!

Number one!

September 17, 2009 by

Thanks to all the slashdotters for making this blog the Number 1 Fastest Growing Blog on WordPress today!

I am seriously impressed!

ETA: And here’s the proof!

First Results from Planck Released!

September 17, 2009 by

ESA has just announced the first results form the Planck satellite. The ESA release can be found here and some more images and information (if you can read French) can be found here, and similar extra details are also on the UK Planck site here. My colleague Andrew Jaffe also has his take on things here.

These first images of strips of the sky look great, and are visibly better than those from WMAP, the previous NASA CMB satellite. We have a lot more work to do to cover the entire sky. Only then can we start to look at the details of the microwave background and the Big Bang physics that this allows us to probe. But this is a great start to things!

The Planck First Light Survey

Press Release Imminent!

September 17, 2009 by

There should be a Planck press release later today, showing images from the first look survey.

Watch this space for more news and links to the images once ESA has released them. All I can say for the moment is that things are looking good!

Great Debates

September 13, 2009 by

Imperial College Astrophysics is hosting the next in its series of Great Debates on Tuesday 15th September. The topic is: “Do Other Universes Exist”.

More details and registration available here.

Start of the Normal Operations!

August 29, 2009 by

The results of a two week mini-survey finished on 27th August. All went well, so the all sky surveys, due to last 15 months, have now begun!

More information available from ESA.

Results from the mini-survey are being analyzed but we’re not allowed to say anything about them until something official is released.

Visit to Dorchester

August 23, 2009 by

I will be doing a reading, a signing and also answering questions with fellow Footprints author Kate Kelly at the Dorchester Waterstone’s, 45-46 South Street, Dorchester, this Thursday 27 August, starting at 7:30pm. Refreshments will be served, and questions about Herschel and Planck will be most welcome.

This will be the publisher’s first event at a UK bookshop. If we do well hopefully there’ll be more!

“Far into the future, intelligent beings from the stars discover the footprints and relics left behind by the inhabitants of earth on the Moon. As non-human archaeologists, they try to speculate what the long-since vanished humans were like.”

45-46 South Street
Thursday, 27th August, 7.30pm.
Tel 01305 257123

Minisurvey and First Results!

August 15, 2009 by

This weekend Planck should be moving from performance verification phase and into observations that are closer to full scale operations with the start of a minisurvey that will be very similar to (indeed, if all goes well, part of) the main all sky survey.

Meanwhile, the very first results from Planck have been presented at the International Astronomical Union General Assembly in Rio. These show a few scans around the sky and demonstrate Planck’s ability to detect the CMB ‘dipole’, which is due to Planck’s motion relative to the CMB frame of reference (this motion is due to the motion of Planck around the sun, the sun around the galaxy and of the galaxy relative to the background).

Sadly I don’t have any pictures of this yet as none have been released, but hopefully we will get something we can show you before long.

Planck moves from commissioning to PV phase

July 28, 2009 by

Latest news from ESA:

’24 July: The In-Orbit Commissioning Review finalised successfully on 21 July. We are now officially in Calibration and Performance Verification (CPV) Phase ! The activities planned in the CPV plan in fact started already in June, interleaved with commissioning activities. So far everything is behaving nominally, and the CPV activities are being carried out largely according to plan, which explains why there has been little to report in this page. A few anomalies in the first two weeks of July – all now under control – have induced some slip in the schedule. It is now expected to start the First Light Survey around the 8th of August. The First Light Survey is a two-week period which makes the transition from CPV Phase into Routine Phase. So routine surveying of the sky should start in the last week of August.’

This means the instruments are working properly, that we’ve moved into calibration observations and that, by the end of August, the all sky surveys should be underway.

This is a major and very positive step forward!