I’ve really missed podcasting since the demise of Living Space’s previous incarnation, and the odd interview just isn’t the same. I’m delighted to say that I’ve managed to cajole the very busy and very knowledgeable Douglas Pierce-Price from ESO, the European Southern Observatory to join me. You can listen to our first show here :
or download it by right clicking here. We’ll have a web site up to go with this shortly, but in the meantime here’s this episode’s show notes.
In today’s show, Chris and Douglas talked about the how the planet Mars has turned out to be colder than expected, how the youngest supernova remnant in our Galaxy has just been discovered, and how astronomers have used a distant quasar and galaxy to take the temperature of the early Universe.
NASA’s Mars Reconnaissance Orbiter finds that Mars is colder than previously thought
Observations made with the Shallow Radar instrument (SHARAD) on the Mars Reconnaissance Orbiter (MRO) have shown that the outer shell of Mars is colder and more rigid that previously thought. SHARAD, which was built for the spacecraft by the Italian Space Agency, uses shallow subsurface radar to search for liquid or frozen water to a depth of about a kilometre in Mars’ crust. By looking through the layer of ice, sand and dust in the Martian north polar cap, the researchers could see through to the surface of the rocky crust underneath. It turns out that the planet’s surface is not sagging under the weight of the icy polar cap (as would happen on Earth), meaning that Mars’ outer shell must be very thick and cold. This result has implications for the search for liquid water hidden beneath the surface (and therefore also possible sites for life on Mars), as any underground aquifers would have to be deeper than previously thought in order for temperatures to be high enough.
Youngest Supernova Remnant in our Galaxy discovered
When a massive enough star reaches the end of its life, it can explode as a supernova. Theoretical models suggest that roughly two or three supernovae should happen in our Galaxy every century, but astronomers do not see as many as they would expect. The most recent observation of a supernova in our Galaxy was in 1604, of what is known as “Kepler’s Supernova”, and the youngest known “supernova remnant” – the shell of expanding material following the explosion – had until recently been Cassiopeia A. Observations of Cassiopeia A suggest that its parent supernova would have been observed on the Earth around 1680, but there are no definite historical records of it. Now, astronomers have found a supernova remnant in our Galaxy which has been caught at the new record youngest age of 140 years. The object, called G1.9+0.3, was first identified as a supernova remnant in 1985 by astronomers led by Dave Green from the University of Cambridge, using the Very Large Array (VLA) radio telescope in New Mexico. Then, in 2007, a team led by Stephen Reynolds of North Carolina State University observed the same object with the Chandra X-ray Observatory, and found that it was 16% larger than in 1985. The shell must be expanding very quickly to have grown so much in 22 years, which tells us that it must be very young. Follow-up observations at the VLA confirmed this result, and by looking at the expansion rate the astronomers were able to calculate the record-breaking age of the young supernova remnant. The supernova itself could not have been seen 140 years ago because of obscuring dust towards the centre of the Galaxy, but thanks to radio and X-ray observatories which can penetrate the dust, today’s team were able to find this example of the “missing population” of young supernova remnants.
Using a quasar and a galaxy to take the temperature of the early Universe
Astronomers have used a distant galaxy, and an even more distant quasar, to take the temperature of the early Universe. For the first time, they were able to detect a tell-tale absorption of light by carbon monoxide (CO) molecules in a galaxy so far away that its light has taken 11 billion years to reach us. The observations, made with ESO’s Very Large Telescope (VLT) in Chile, used the light from an even more distant quasar – a galaxy which emits intense radiation powered by a black hole in its core – as a ‘flashlight’ to study the galaxies between the quasar and the Earth. When the quasar’s light passes through each intervening galaxy, molecules in the galaxies absorb specific wavelengths of that light. Due to the expansion of the Universe and of the light itself over these billions of years, each galaxy leaves a fingerprint in the quasar’s light at different wavelengths. In this particular very distant galaxy, the astronomers observed the fingerprint of CO molecules, where the precise levels of absorption depend on their temperature, so the molecules act like a cosmic ‘thermometer’. Today, the Universe is filled with Cosmic Microwave Background radiation at a temperature of 2.725 K (about -270 Celsius). However, according to the Big Bang theory, the Universe was hotter in the past. The theory predicts that the temperature 11 billion years ago would be about 9.3 Kelvin, and the observations of the CO molecules gave a temperature of 9.15 Kelvin, plus or minus 0.7. This is an excellent match with theory, and an exciting new result which shows how interstellar chemistry in the early Universe can be used to tackle big cosmological questions.