Measuring magnetic fields in space

Cosmic magnetism

Photo: Pixabay

Every week, the Dominion Radio Astrophysical Observatory (just south of Penticton) has a science meeting, where, after all the interesting admin updates are announced, progress in the various science activities are reported and discussed.

One of the main projects in progress at the moment is an international program to map the magnetic fields of our galaxy, the Milky Way.

Most of us don't think much about the incredibly weak magnetic fields pervading our and other galaxies. It is only recently that it has become possible to map them.

We cannot see the magnetic fields directly, but we can see the effects they have on the cosmic radio emissions passing through them. This has enabled researchers to make maps of those magnetic fields. The images show an amazing level of fine detail. In some of them, the magnetic fields and the material trapped in them resemble a fine, piled carpet, and in others, like long, carefully brushed hair.

A big cosmic cloud of just gas and dust has only one force acting on it, gravity. This will tend to pull the gas together into lumps. It won't produce any other kinds of fine structure. Because there are motions and flows of material in the cloud, these motions get concentrated in those collapsing lumps, leading to them becoming rotating discs. However, when we add the magnetic fields things become more complicated, and more interesting.

Magnetic fields with material trapped in them behave rather like rubber, forming loops, tubes and sheets. They can be stretched, twisted or compressed. Depending on how they are arranged, they can allow structures to combine, or keep them as separate objects. Those fibres and other fine structures we see in the cosmic clouds could not exist without embedded magnetic fields. In addition, depending on how they are arranged, magnetic fields can either inhibit or encourage the collapse of clouds to form new stars and planets. In addition, those collapsing clouds take their magnetic fields with them, embedding them into those new stars and planets.

Stars are often described as balls of hot gas with nuclear fusion reactors in the middle. However, images of the Sun show it to be a lot more than that. It has an identifiable surface layer, loaded with fine details, with sunspots and with great loops and streamers extending into space. These structures exist because of the magnetic fields.

When the Sun formed, it inherited magnetic fields from its birth clouds. With the flows of hot materials in the interior of the newly born star, they formed a dynamo, which generated electric currents, which in turn generated new and stronger magnetic fields. Because these magnetic structures can be bent, twisted and compressed, they can store energy, just like stretched elastic bands, providing the energy for solar storms and flares.

The situation is similar for earth-like planets. In this case the dynamos are formed by the interaction of the captured magnetic fields with the flow of hot, molten iron in their cores. The dynamo running inside the Earth gives rise to a magnetic envelope around the planet, keeping the solar wind away, stopping it from scrubbing away our atmosphere.

Gradually, the cores of planets cool off and solidify. At this point the dynamos shut down, the electric currents cease and the magnetic field protecting the planet vanishes. This has been the fate of Mars. It is smaller than our world, cooled off faster and lost its magnetic field long ago, allowing the solar wind to remove most of its atmosphere.

It might have seemed that cosmic magnetic fields would be something of academic interest only. That is definitely not the case. Without them, we and the other living things sharing this planet would not be here.

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• After sunset, Venus shines low in the southwest.

• Saturn lies in the south and Jupiter is rising in the northeast.

• Mars rises about three hours later. The Moon will reach first quarter on Dec. 8.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

Looking back to see how astronomers of the past worked

How do stars work?

Photo: Wikipedia

The Sun

Our ancestors had no problem with the idea that the sun would rise and set every day, providing light and warmth, forever.

Things in the sky things could be eternal, whereas at ground level they weren't. However, in the 18th and 19th centuries, advances in science started raising difficult questions. At that point it was believed the entire universe was obeying the same laws. Therefore, if the sun was providing light and heat to us and the other planets, where was it getting the energy?

The question became even more intriguing in the light of the discoveries made by geologists. They found more and more proof the earth was not thousands of years old, it had to be many millions of years old.

The oldest fossils known at the time were in rocks some 500 million years ago, from what became known as the Cambrian period. These rocks were first studied in Wales, which was called Cambria by the Romans.

For living things to have been swimming in the earth's oceans since then, the sun had to be providing a more or less steady level of heat and light over all that time. More recently, signs of living things have been found in rocks around four billion years old, only 500 million years after our planet, the other planets and the sun formed.

The 19th century was the "Age of Steam" and the heat to provide that steam was provided by burning coal. It is not clear whether that was a serious calculation or something done for fun, but someone calculated if the sun were a ball of coal, it would have completely burned away in 10,000 years or so. Of course, that is, assuming oxygen was available to make combustion possible, which, of course, there was not.

Another, more serious calculation was based on the heat generated when a cloud of gas and dust collapses to form a star. The energy released by the collapse and compression of the material would release a lot of heat. However, as in the case of the "coal sun", the heat would not last long enough. The problem 19th and early 20th century physicists faced was they knew little about atomic processes and their capacity for energy production, which is where the solution lay.

Last Christmas, my stocking contained a lovely old science book, titled "The Story of Creation", about the appearance and evolution of life on Earth since the Cambrian era, 500 million years ago. The book was published in 1902. The author realized the importance of a stable sun and discussed the difficulty in explaining where it was getting its energy. He mentioned new knowledge about radioactive elements such as radium, which have large, unstable atoms, which break into smaller ones, releasing energy. He did point out that the sun is made of mostly hydrogen and helium, not radium, but raised the idea the solution lies at the atomic level.

Finally, around 1920, Arthur Eddington proposed that stars obtain energy through nuclear fusion, the merging of light atoms such as hydrogen to form larger ones. The question was how to find out if this idea is correct.

Fortunately, there were two pieces of evidence to be searched for. High-energy nuclear fusion reactions produce ghostly particles called neutrinos. These pass through almost anything, so escaping from the sun was not an issue. Similarly, they pass through the Earth too. A neutrino detector, a big tank of dry-cleaning fluid, was set up deep in a mine, and neutrinos were detected.

The second item of proof is the relative proportions of various elements in the dust between stars and in the stars themselves. These elements are the waste products of energy production in stars now dead.

If our fusion ideas are correct, we can calculate those relative proportions and then compare them with observations. They matched. However, we still have a lot to learn about energy production in stars, but we know the essentials.

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• After sunset, Venus shines brightly low in the southwest.

• Saturn lies in the south and Jupiter is rising in the northeast. Mars rises about three hours later. • The Moon will be new on Nov. 30.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

When it comes to galaxies, it's a case of eat or be eaten

History of the Milky Way

Photo: Pixabay

The Milky Way in the night sky.

Looking at the summer Milky Way on a clear, dark night from the shore of a lake is a wonderful experience.

It all looks so beautiful and peaceful. The images of other galaxies, such as the Andromeda Galaxy convey a similar feeling. However, these impressions are incorrect. Out there among the galaxies, the prime directive is to eat or be eaten, sometimes at the same time.

Our galaxy, the Milky Way, grew in this way, and at the moment it is busy feasting on its smaller neighbours. This new knowledge is the result of a recent big change in the way we do astronomy.

In the past we pointed telescopes at objects of interest, one at a time. However, we are now making telescopes that can observe huge areas of sky, collecting enormous amounts of data from everything they can "see". After a pause to let those who put the projects together get a first go at the data, it is made available to all researchers at sites in various countries around the world, like our Canadian Astronomy data centre.

One major instrument is Gaia, a space telescope system parked 1.5 million kilometres away in space. It has so far catalogued the motions and other properties of two billion objects in our galaxy.

Stars can tell us a lot. How they are moving tells us where they were in the past and possibly where they came from. Their surface layers are made up of the stuff from which they formed, unaffected by their own energy production.

Stars formed early in the history of the universe were composed of only hydrogen and helium. Later generations formed from clouds containing the remains of previous generations: elements other than hydrogen and helium. This tells us something about the age of the star and where it was born. The ability to sort through large numbers of observations seeking commonalities and finding out where stars were in the past is yielding some fascinating results.

Stars are often born in clusters or groups, sharing the same birth cloud. Then, when the newly born stars have burned their birth cloud away, they disperse. It has been possible to find siblings and track them back to their birth location. However, the biggest surprise was locating streams of stars and star clusters that came from the assimilation of other galaxies.

At the moment, the Milky Way is swallowing a small galaxy, which has an orbit oriented at almost right angles to the disc of our galaxy. It is also snacking on material from several small galaxies, including the Large and Small Magellanic Clouds. There is evidence of previous galaxies becoming part of ours.

Now we believe, this is how galaxies form and grow—small ones combine into bigger ones, which then gorge themselves on the neighbours.

We believe the Milky Way was born shortly after the Big Bang, as a concentration of material, which pulled in more and more. It has been suggested that a big growth spurt happened some 11 billion years ago, when the young Milky Way merged with another large galaxy, which has been referred to as the Kraken.

It might be surprising, but any inhabitants of planets orbiting stars in colliding galaxies are unlikely to be affected. Stars lie far apart and the chances of collisions are small. What those inhabitants would see is over time the appearance of their equivalent of the Milky Way in the sky might change, and the birth of lots of new stars will take place as the cosmic gas clouds collide.

The small chance of anything nasty happening is reassuring, as we are heading for a head-on collision with the Andromeda Galaxy, which is a bit larger than the Milky Way. We are heading for each other at more than 100 km/s and will collide in about 4.3 billion years. Mark your diaries.

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• Venus is very low is the southwest after sunset and Saturn in the southeast.

• Jupiter rises about an hour after and then Mars a couple of hours later.

• The Moon will reach last quarter on Nov. 22.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

The massive power when black holes merge in space

Colliding black holes

Photo: Wikipedia

Direct radio image of a supermassive black hole at the core of Messier 87 galaxy.

Black holes are good candidates for being the weirdest things in nature.

There are lots of them out there, some are the remains of giant stars, others, with millions or even billions of times the mass of the Sun, sit at the centres of galaxies. There is one at the centre of ours.

Black holes colliding could the topic of a disaster movie.

Albert Einstein predicted their existence back in 1915, when he formulated his General Theory of Relativity, which is basically an explanation of the force of gravity. He suggested gravity is a distortion of the fabric of space-time by massive objects.

His theory states that if a body is massive and/or compressed enough, its gravitational pull could become so strong it closes off the fabric of space-time around the body so nothing, not even light, can get out.

This boundary is known as the "event horizon.” However, that strong gravity reaches out beyond the event horizon and can pull things in, on a one-way trip, which led to these objects becoming known as “black holes".

Forming black holes requires very special circumstances. Our Sun, the Earth and other planets in the Solar System are highly unlikely to become black holes. However, there are cosmic situations where those extreme conditions occur.

If we compress the matter in a star or planet enough, either by piling more stuff on top or applying high-energy shock waves, we reach a point where the gravitational force becomes irresistible.

According to our current understanding of physics, the body will then shrink indefinitely, into a body of infinite density and gravitational attraction. That is almost certainly not the case. It is likely that as the conditions become more extreme, some new force we don't know about comes into action. Even so, the density and gravitational attraction can become high enough to fold the fabric of space-time around itself, closing it off, as Einstein predicted, forming a black hole.

This is a one-way door for incoming traffic, marked "No Exit". We have found lots of these bizarre objects scattered around in space. Most of them have star-like masses and are the remnants of collapsed supergiant stars. Others, having masses millions of times the mass of the Sun, sit at the centres of galaxies. Our galaxy has a big one.

Black holes can grow in two ways. They can pull in nearby gas clouds, stars and planets, pulling them apart into a hot disc of material slowly spiralling in, across the event horizon. Our infrared and radio telescopes show our black hole to be feasting on nearby stars and gas clouds. There are almost certainly planets being eaten too. The other way they can grow is by assimilating other black holes.

One black hole merging with another is a very different thing from gorging on nearby stars. The gravitational attraction between them as they spiral into one another is so intense it makes ripples in space-time, like the ripples we get on a pond if we move our fingers in circles. These waves, called gravitational waves, take away huge amounts of energy, allowing the black holes to spiral in closer and closer.

As they get closer, the energy radiated as gravitational waves gets higher, accelerating the inward spiral. At some point they start moving through each other's disc of star debris, which dissipates more energy. Finally, the two event horizons merge and those tiny balls of incredibly dense material sitting in their centres combine, forming a single, more massive black hole.

Almost any event in space-time generates gravitational waves. However, only big events such as black hole mergers produce gravitational waves strong enough for us to detect at our huge (and safe) distance, and we have now detected some.

As the black holes spiral in closer and closer, orbiting faster and faster, the pitch of the gravity waves increases, until they suddenly stop.

•••

• Venus is very low and hard to see in the sunset glow.

• In the late evening, Saturn lies low in the south-west. Brilliant Jupiter is high in the south and Mars, dimmer but distinctly reddish, high in the east.

• The Moon will be full Nov. 15.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.