By Nola Wilkinson
Ever wondered what there is between the stars? Dr Naomi McClure-Griffiths not only wonders about it, she’s on a mission to find out.
Naomi is fascinated with the life of stars, the behaviour of interstellar gas, and how gas and stars interact. “As an astronomer, I’d like to understand how the galaxy formed and how it’s living its life,” she says.
“The galaxy is much more frothy and bubbly than we ever thought. It looks like the head on a glass of beer.”
Very large stars, 8-20 times the size of our sun, experience dramatic supernova explosions that push gas out of the galaxy via solar winds travelling at up to 1000 kilometres a second.
It is these solar winds that blow bubbles in the gas between the stars, creating a frothy, foamy appearance.
Watch this video to find out more about Naomi and her amazing work:
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, 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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Galaxies may look pretty and delicate, with their swirls of stars of many colours – but don’t be fooled. At the heart of every galaxy lies a supermassive black hole, including in our own Milky Way.
Black holes in some nearby galaxies contain ten billion times the mass of our sun in a volume a few times the size of our solar system. That’s a lot of mass in a very small space – not even light travels fast enough to escape a black hole’s gravity.
So how did they get that big? In the journal Science, we tested a commonly-held view that black holes become supermassive by merging with other black holes – and found the answer is not quite that simple.
Searching for gravitational waves
The answer may lie in a related question: when two galaxies collide to form a new galaxy, what happens to their black holes?
When galaxies collide, they form a new, bigger galaxy. The colliding galaxies’ black holes sink to the centre of this new galaxy and orbit each other, eventually combining to form a new, bigger black hole.
Black holes, as the name suggests, are very hard to observe. But orbiting black holes are the strongest emitters in the universe of an exotic form of energy called gravitational waves.
Gravitational waves are a prediction of Einstein’s General Theory of Relativity and are produced by very massive, compact objects changing speed or direction. This, in turn, causes the measured distances between objects to change.
For example, a gravitational wave passing through your computer screen will cause it to first stretch in one direction, then in a perpendicular direction, over and over again.
Fortunately for your laptop, but unfortunately for astronomers, gravitational waves are very weak. Gravitational waves from a pair of black holes in a nearby galaxy causes your screen size to change by one atomic nucleus over ten years.
While they’re not quite as extreme as black holes, pulsars are massive and compact enough to crush atoms into a sea of nuclei and electrons. They compress up to twice the mass of our sun into a volume the size of a large city.
So how do pulsars help? First, they rotate very quickly – some of them up to 700 times per second – and very predictably. They emit intense lighthouse-like beams of radio waves, which, when they sweep by the Earth, appear as regular “ticks” – see the video below.
So here’s the punchline: gravitational waves from pairs of black holes throughout the universe will disrupt the otherwise extremely regular ticks from pulsars in a way we can measure.
Our pulsar measurements
We found that the theory that black holes grew mainly by absorbing other black holes is not consistent with our data.
If the theory was right, gravitational waves would exist at a level that would cause the ticks to appear less regularly than our measurements. This means that black holes must have grown by other means, such as by consuming vast swathes of gas churned up during galaxy mergers.
The measurements span over ten years, and are some of the most precise in existence.
These data are being collected to eventually directly observe gravitational waves. In our work, however, we compared the data with gravitational wave predictions from various theories for how black holes grew.
Our work gives us great encouragement for the prospects for using pulsars to detect gravitational waves from black holes.
We are confident that gravitational waves are out there – galaxies, after all, do collide – and we have shown that we can measure pulsar ticks with sufficient accuracy to be able to detect gravitational waves in the near future.
In the meantime, we can even use the absence of gravitational waves to study elusive super-massive black holes.
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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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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