Our Galaxy takes its food in pills

Vanessa Hill:

Where does our Galaxy get the fuel to keep forming stars? The answer may lie in thousands of gas clouds flying around the outskirts of our Galaxy.

Originally posted on Universe @ CSIRO:

“Food pills” were a staple of science fiction for decades. For our Galaxy, they may be real.

The Galaxy has been making stars for the last 8 billion years. What’s kept it going all that time?

When old stars die, some of their gas goes back into the galactic “soup” for star making. But in the long run a lot of it gets locked up in long-lived dwarf stars.

So the Galaxy needs fresh supplies of gas.

Astronomer think that gas rains in from intergalactic space, probably in the form of “clouds”, and that this fuels the star-making.

But there’s a problem.

If a regular gas cloud were to hit the warm outer parts of the Galaxy — the halo — the gas would dissipate, and not reach the Galaxy’s starry disk where the party is going on.

Something must hold the gas clouds together on their way to the…

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The question of astrobiology

Vanessa Hill:

The Square Kilometre Array radio telescope will give astronomers an unprecedented view of the magnificent invisible universe. What are the chances of it finding life outside the Earth?

Originally posted on Universe @ CSIRO:

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.

So when I was invited to give a talk about the Square Kilometre Array at the Australian Astrobiology Conference, held at the University of New South Wales last week, I was interested but a bit perplexed. What is astrobiology?

A quick trip to Google will tell you that astrobiology is the study of the origin, evolution, distribution, and future of life in the universe, including life on Earth.  My talk addressed the…

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Cataclysms in the distant Universe

Vanessa Hill:

Some exciting news from ‘The Dish’ today.

Originally posted on Universe @ CSIRO:

In the journal Science today, astronomers using our Parkes telescope have revealed signs of cataclysms in the distant Universe.

They’ve found four ‘bursts’ or ‘flashes’ of radio waves, the furthest one coming from about 11 billion light-years away. And, they say, if you had ‘radio eyes’ — eyes that could detect radio waves — you’d see one of these ‘bursts’ going off somewhere in the sky every ten seconds. It would be like a continuous show of distant fireworks.

What is a ‘burst’? It’s a spike in the radio energy the telescope receives. Here, from the Science paper, is what the astronomers found. (‘Flux density’ means signal strength.)


‘FRB’ stands for Fast Radio Burst. Because they really are very fast, lasting for only a couple of milliseconds.

The speed of the bursts, their strength, and other characteristics of the radio signal, all help to show what the bursts…

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Make me a star!

Originally posted on Universe @ CSIRO:

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.

Using a variety of tools, astronomers can spot signs of star-formation in very distant galaxies. Because light takes time to travel, those galaxies are not merely far away in space — they are far away in time. That is, they existed early in the Universe’s history.

For how long did those ancient galaxies keep making stars? And how many stars did they make? If we can answer those questions, we can determine what those distant galaxies evolved into — what the relationship is between those galaxies and the galaxies we…

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Taking the temperature of the Universe

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.

temperature picture

Radio waves from a distant quasar pass through another galaxy on their way to Earth. Changes in the radio waves indicate the temperature of the gas. (Image: Onsala Space Observatory)

“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).

CSIRO's Australia Telescope Compact Array. (Photo: David Smyth)

CSIRO’s Australia Telescope Compact Array. (Photo: David Smyth)

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

MEDIA: Helen Sim Ph: +61 2 9372 4251 E: helen.sim@csiro.au


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