By Lisa Harvey-Smith
“So - what do you do?”
The question dreaded by astronomers seeking a quiet social evening. When I do fess up, quite often I get a grilling about alien life on other planets.
The truth is that most astronomers have little stake in finding life on other planets. Our work primarily focuses on studying a particular type of star or galaxy, or probing the physical or chemical processing that drive the evolution of our universe.
Like well-made tomato soup, the very early Universe was hot and (fairly) smooth. How did it evolve into the Universe that we have today — a Universe more like minestrone — a Universe that has galaxies, stars, planets and people?
One aspect of the process astronomers want to learn about is how galaxies assembled themselves and how they started forming stars.
Meet Giovanna Zanardo: a PhD student at the International Centre for Radio Astronomy Research who’s using our telescopes to study the remains of a star that exploded in 1987.
Called Supernova 1987A, the explosion made astronomers super excited, because it was the first naked-eye supernova to occur since optical telescopes were invented four centuries ago.
Giovanna has been using the Australia Telescope Compact Array - a set of six dishes near Narrabri, NSW – to study the aftermath of the exploded star. And this month she’s going to be using our iconic Parkes telescope to look at it again.
While at Parkes, Giovanna and fellow scientists will be looking to see if a pulsar – a compact spinning star packed with neutrons – has been created after the collapse of the star’s core, which drove the stellar explosion.
“My PhD in astronomy has been a fantastic journey. I’ve got a front row seat to watch the evolution of a truly amazing object and the chance to use all of Australia’s radio telescopes.”
Giovanna began her career as a structural engineer in Western Australia, but after hearing plans to build the Square Kilometre Array (SKA), she saw this as an opportunity to get into radio astronomy.
From the moment she had a glimpse at the early radio images of Supernova 1987A, Giovanna was hooked. And she’s never looked back.
“I became an engineer because I love structures – but I’ve always loved physics and astronomy. My work allows me to combine the two by investigating large structures in space and seeing how they impact and interact with the surrounding environment,” says Giovanna.
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Astronomers using a CSIRO radio telescope have taken the Universe’s temperature, and have found that it has cooled down just the way the Big Bang theory predicts.
Using the CSIRO Australia Telescope Compact Array near Narrabri, NSW, an international team from Sweden, France, Germany and Australia has measured how warm the Universe was when it was half its current age.
“This is the most precise measurement ever made of how the Universe has cooled down during its 13.77 billion year history,” said Dr Robert Braun, Chief Scientist at CSIRO Astronomy and Space Science.
Because light takes time to travel, when we look out into space we see the Universe as it was in the past — as it was when light left the galaxies we are looking at. So to look back half-way into the Universe’s history, we need to look half-way across the Universe.
How can we measure a temperature at such a great distance?
The astronomers studied gas in an unnamed galaxy 7.2 billion light-years away [a redshift of 0.89].
The only thing keeping this gas warm is the cosmic background radiation — the glow left over from the Big Bang.
By chance, there is another powerful galaxy, a quasar (called PKS 1830-211), lying behind the unnamed galaxy.
Radio waves from this quasar come through the gas of the foreground galaxy. As they do so, the gas molecules absorb some of the energy of the radio waves. This leaves a distinctive “fingerprint” on the radio waves.
From this “fingerprint” the astronomers calculated the gas’s temperature. They found it to be 5.08 Kelvin (-268.07 degrees Celsius): extremely cold, but still warmer than today’s Universe, which is at 2.73 Kelvin (-270.42 degrees Celsius).
According to the Big Bang theory, the temperature of the cosmic background radiation drops smoothly as the Universe expands. “That’s just what we see in our measurements. The Universe of a few billion years ago was a few degrees warmer than it is now, exactly as the Big Bang Theory predicts,” said research team leader Dr Sebastien Muller of Onsala Space Observatory at Chalmers University of Technology in Sweden.
“A precise and accurate determination of the cosmic microwave background temperature at z=0.89″, by S. Muller et al. Accepted for publication in the journal Astronomy & Astrophysics; online at http://arxiv.org/abs/1212.5456
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They’re big, powerful and fast. Top to bottom, they measure about half the Galaxy’s diameter. They contain as much energy as a million exploding stars. And they are roaring along at 1000 kilometres a second (yes, a second).
Revealed by our Parkes radio telescope (aka The Dish): they are giant geysers of charged particles shooting out from the centre of our Galaxy.
The finding is reported in today’s issue of Nature.
“These outflows contain an extraordinary amount of energy — about a million times the energy of an exploding star,” said the research team’s leader, CSIRO’s Dr Ettore Carretti.
But the outflows pose no danger to Earth or the Solar System.
The speed of the outflow is supersonic, about 1000 kilometres a second. “That’s fast, even for astronomers,” Dr Carretti said.
“They are not coming in our direction, but go up and down from the Galactic Plane. We are 30,000 light-years away from the Galactic Centre, in the Plane. They are no danger to us.”
From top to bottom the outflows extend 50,000 light-years [five hundred thousand million million kilometres] out of the Galactic Plane.
That’s equal to half the diameter of our Galaxy (which is 100,000 light-years — a million million million kilometres — across).
Seen from Earth, the outflows stretch about two-thirds across the sky from horizon to horizon.
So how could we have missed them before?
A couple of reasons. The particles are glowing with radio waves, rather than visible light, so seeing the geysers depends on having a telescope tuned to the right frequency (which happens to be 2.3 GHz). And the Galactic Centre is a messy, confusing place where a lot is going on.
VIDEO: Ettore Carretti talks about how the telescope makes maps of the sky.
Our Galaxy has a black hole at its centre, but it’s not that which is powering the geysers. Instead it’s star-power: “winds” from young stars, and massive stars exploding.
About half of all the star-formation that goes on in our Galaxy happens in and near the Galactic Centre. That’s a lot of stars, and a lot of energy.
VIDEO: The Parkes telescope observing as night falls and stars come out and the Milky Way appears overhead. Credit: Alex Cherney / terrastro.com
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