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Skywatching

Searching for the Milky Way's Black Hole

Milky Way's Black Hole

When we look into the southern sky close to the horizon on summer evenings, we are looking towards the centre of our galaxy, the Milky Way.

It is lurking around 30,000 light years behind the stars making up the constellation of Sagittarius, "The Archer". However, thanks to our location in the disc of our galaxy, our view is blocked by huge clouds of stars, gas and dust.

Our first images of the centre of the Milky Way were obtained by means of radio telescopes, which show us what the universe would look like if we could see radio waves rather than light. They revealed a strange, bright and unusually small radio source.

Measurements of the speeds stars orbit the centre of our galaxy indicate that at the same position as the bright radio source lies something very massive, very small and active. The best candidate to explain this is a black hole.

Radio waves have power to penetrate clouds and dust, which is why radar is so useful for navigation, detecting threats and avoiding hazards at night or in bad weather. However, radio waves have this greater penetration power because they are much longer than light waves. This means that to see detail when observing at radio wavelengths we need to use huge antennas.

To have the same ability to discern detail as the human eye, a radio telescope tuned to the wavelength of emissions from cosmic hydrogen (21cm) the antenna would need to be about a kilometre in diameter. Moreover, black holes are small by cosmic standards and at great distances, so to discern any details the radio telescope would need an antenna the size of the Earth.

This sounds impossible, but there is a solution, a technique called "Very Long Baseline Interferometry".

In the 1960s, Canada was the first country to succeed in combining radio telescopes thousands of kilometres apart so that they would have the detail discerning ability of a radio telescope thousands of kilometres in diameter.

This procedure has made possible a powerful, new astronomical instrument, the Event Horizon Telescope (EHT).

Several radio telescopes, thousands of kilometres apart operate in collaboration to observe the centre of the Milky Way at the same time. One of them is the Atacama Large Millimetre Array, located in Chile, in which Canada is a partner. In addition, scientists at several Canadian universities are involved.

The collaboration is named after the boundary that forms around black holes, called the event horizon. This is a one-way boundary in space-time—stuff can fall in but nothing, not even light, gets out. This is why they are called black holes.

However, even if we cannot see the black holes directly, we can certainly see the disc of material swirling around the black holes as it gets sucked in. This stuff gets very hot, and has intense magnetic fields trapped in it, so the black hole announces itself with radio emissions and X-rays from that disc.

The first target for the Event Horizon Telescope was the galaxy M87, located some 55 million light years away. It had long been suspected that a very energetic black hole lies at its centre, a big one, around 5 billion times the mass of the Sun. The EHT gave us our first image of that black hole.

Then the EHT radio telescopes were turned on the centre of our galaxy, and got our first image of our black hole. Luckily for us, it is much less massive and active than the one at the centre of M87. At four million times the mass of the Sun, it is relatively tiny.

We believe most spiral galaxies have big black holes in their cores. It is not clear whether galaxies get them when they form or they appear later. However, learning about their roles in galaxies should tell us more about how galaxies form and evolve to the point where they develop stars and planets, and because we live in one, it would be nice to know.

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• Venus, Jupiter, Mars and Saturn are still lined up in the dawn glow, in order of decreasing brightness.

• The Moon will be new on May 30.

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



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Looking at where we came from

Origins of life

Where did we come from?

The main science-based ideas propose life on Earth began in shallow, sunlit water, or around hydrothermal vents in the deep ocean.

The latter idea is intriguing because it means that we can look for life in the oceans under the ice on Europa and other moons in the outer Solar System.

Another idea that has been discussed for years is "panspermia", which proposes space is filled with the seeds of life, and these thrive, multiply and diversify in any environment to which they can adapt. If the "basic stuff of life" came from out there in space, how did it arrive here safely?

Every night we see meteors (shooting stars), which are little pieces of grit coming into our atmosphere at many kilometres a second. The short-lived, glowing streak we see in the sky is that piece of grit being heated to thousands of degrees by friction, and then vaporized. While being burned away it is decelerating at tens or hundreds of times the force of gravity.

This does not sound like a good way for prebiotic materials—the building blocks of life—to safely arrive on a new world. It does not take much heat to break down the carbon-based molecules on which earthly life is based. However, scientists looking at meteorites, chunks of cosmic material that reach the ground without being completely burned away, see a more optimistic situation than we might expect.

A typical meteorite is usually a lump of rock or iron that has been heated and melted by its passage from space to the ground. However, when something is moving tens of kilometres a second, it does not take long to get down to the ground. Basically, although the heat of its passage through the atmosphere might be intense, that heat may not have time to penetrate deeply into the meteorite. If the lump of cosmic material is big enough, the heat might not reach its centre at all.

The deceleration stresses would certainly kill any animal, but things of molecular sizes embedded in the body of the meteorite would be quite happy. This is why a lot of effort is going into searching for prebiotic materials inside meteorites.

DNA, a fundamental ingredient in life as we know it is a double spiral comprising an enormous sequence of combinations of four chemicals known as bases, rather like a long story written with an alphabet of four letters.

Ten years ago, scientists found two of those bases in meteorites. Now, meteorites have yielded the remaining bases. Moreover, there is evidence a meteorite that hit our planet several billion years ago contained at least some of these bases. This was while the Solar System was still forming and the Sun had not yet been born.

If this is the case, it seems that there is a supply of prebiotic material available whenever new stars and planets are forming. It looks as though the seeds of life could have come from outside. If this happened to Earth, then those same ingredients must have found their way to almost all other worlds, orbiting other stars as well as ours. It is true that conditions on many worlds could have been too hostile for life to take root. However, it is hard to imagine that our world is the only one on which it succeeded.

There have been suggestions chemicals that can act as the seeds of life can be blasted off a planet by an impact, and subsequently find their way to new worlds. However, at the moment it seems likely they are formed in space, and then incorporated into rocks that end up as meteorites.

There is a very big distance between having the four ingredients of DNA and having that complicated molecule itself. However, it happened here, so it is likely to have happened elsewhere. Interestingly, it does seem as though the universal standard life form is likely to be carbon-based, just like life on Earth.

That does not however mean it has to look anything like us, or like any of the diverse life forms sharing our world.

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• Venus, Jupiter, Mars and Saturn are lined up in the dawn glow, in order of increasing brightness.

• The Moon will reach it last quarter on May 22.

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



Looking at how our universe will come to an end

How might it all end?

Almost 14 billion years ago, the universe began, in an event often referred to as the "Big Bang".

At some point in the remote future, we think the universe will end. It cannot last forever because of two things: it is finite, and it is subject to "the second law of thermodynamics".

So what could the end of the universe be like? Is it likely to be the end of absolutely everything?

As the incredibly hot and dense newly born universe expanded and cooled, it eventually became cool enough for the hardiest atoms to form. These are hydrogen, and helium, which is a little less hardy.

The result was, about 380,000 years after beginning, the universe was filled with clouds of hydrogen with some helium and basically not much else. By the time the primordial stuff would have cooled enough for other atoms to form, it had all been used up making hydrogen and helium. It is from this original mixture that the first stars were born.

They lit and warmed the universe by fusing hydrogen and helium into heavier elements, such as oxygen, nitrogen, sulphur, carbon, phosphorus and so on. All the energy sources we use today, such as fossil fuels, hydroelectric and nuclear fission, are all basically reformatted energy supplied originally by stars.

Fossil fuels are solar energy trapped millions of years ago by living things. Hydroelectric power is driven by the water cycle, which in turn is powered by the Sun. Nuclear energy involves splitting heavy atoms forged in the death throes of dying stars.

Basically, this means when all the hydrogen is used up, shortly afterward, all other energy sources will fade out and the universe will become cold and dark.

Every process in the universe that involves work requires taking in concentrated, high quality energy and converting it into lower quality energy. For example, we take in high quality, concentrated energy in our food and convert it to low quality energy, basically heat.

When all concentrations of higher-quality energy are dissipated, and the universe is at a constant temperature, everything will come to a stop. This is often referred to as the "heat death" of the universe.

Is it possible to avoid this by concentrating energy so that it can be used over again? This is where the second law of thermodynamics comes in. Basically the law says that unless helped, heat won't flow from colder objects to warmer ones, or waste products turn themselves back into fuel.

You can make this happen, but it takes more energy than you are saving. No matter what we do, we are on an inexorable slide downhill to a future with no stars, with frigid dust clouds and cold, lifeless planets and being swallowed by black holes, in the dark.

If the universe had a definite beginning, and will have a sort of cold, dark, fading out end, what happened before the beginning, and what will be going on after it's all finished? One might argue that these questions are more religious than scientific, in that they take us to the boundaries of what we think we know, or even beyond them.

The issue is made more complicated by almost all our astronomical knowledge coming from the study of only 4% of the stuff making up the universe. Dark energy and dark matter make up the other 96%. These concepts were originally concocted to make calculations agree with observations. As yet we don't know what either of these things are, or even have independent proof of their existence.

A comforting concept receiving a lot of scientific attention these days is the "multiiverse".

In this idea, what we understand as universes form like bubbles in a multidimensional cosmic foam, expanding and then dissipating and being replaced by others. Researchers have suggested that if our bubble universe is touching another, the area of contact should be detectable.

Do multiverses have beginnings and endings? Are we just finding ways to push back the hard questions?

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• Jupiter, Venus, Mars and Saturn are lined up low in the dawn glow, in order of increasing brightness.

• The Moon will be full on May 16.

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



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Venus: From steamy jungle to super hot furnace

Second rock from the Sun

One of the demonstrations done for public tours of the (National Research Council's Dominion Radio Astrophysical) observatory (in Penticton) involves a small radio telescope.

This can be pointed at visitors to demonstrate that everything in the universe with a temperature, including people, gives off radio waves. We can use these radio emissions to measure the temperature of a distant object, such as the Moon, or Mars.

One thing that makes these radio measurements of temperature really useful is that they are unaffected by clouds. This made it possible for radio telescopes to produce a final answer to a question that had puzzled radio astronomers for a long time; how hot is Venus?

The sight of the bright spark of Venus against that magical blue we get in the sky after sunset or before sunrise is one of the most beautiful sights in nature.

This is even more so when Venus shares the sky with a crescent moon. It is probably the beauty of the planet in the sky that led to it being named after the goddess of love, and of course called the "Morning Star", when it rises before the Sun and the "Evening Star", when it sets afterwards.

Venus is the second planet out from the Sun (we live on the third), which means as Venus moves around the Sun we see it successively left or right of the Sun: Evening Star and Morning Star respectively.

Despite Venus being an easy target for even small telescopes, it is a frustrating one, because its surface is always covered by a thick layer of cloud. It is this cloud that is responsible for the brightness of the planet in our skies, because it reflects about 65% of the sunlight hitting it. Compare that with our Earth's 37% or the Moon's mere 12%.

The amount of sunlight reflected by Venus is another reason why looking at the planet is difficult. The glare of the bright planet when viewed against a dark sky is very hard to deal with. Experienced observers do it against a twilit sky or even during daylight, making sure the telescope does not get pointed at the Sun. However, even under the best conditions one only sees subtle changes in the colours of the cloud layer: not ever a glimpse of the surface.

This led the imaginations of astronomers and science fiction writers to run riot. Some scientists concluded the clouds were water vapour and that they concealed a surface covered in steamy, swampy jungle, like the Earth some 300 to 350 million years ago, during the Carboniferous Period.

Edgar Rice Burroughs, along with other science fiction writers, populated that world with swashbuckling heroes and beautiful princesses, or nasty, aggressive aliens. Then the radio telescope came along to shatter all those illusions.

By the middle 1950s radio telescopes had become highly developed and in 1956, astronomers at the Naval Research Laboratory in Washington pointed their new 50-foot dish at Venus, to penetrate down through the clouds to measure the temperature of the planet's surface.

The result was a shock. The surface was hot enough to melt lead and tin. There were no prospects of steamy jungles, warriors or princesses or nasty aliens. This was a surprise.

If we assumed Venus's atmosphere was like Earth’s, then the increased amount of reflected sunlight would to some extent balance the planet being closer to the Sun, which is where the steamy jungle idea came from.

We learned more when the first spacecraft landed on Venus's surface and sent back a few minutes' worth of data before it fried. The planet has a thick, dense atmosphere. The pressure on the surface is about ninety times the pressure on our planet's surface, and that atmosphere is rich in carbon dioxide and other greenhouse gases.

The result is a candidate for most unpleasant planet in the Solar System.

It is not clear if we will ever bother to try walking on the surface of the "planet of love" any time soon, considering that nothing we landed there has lasted more than a few minutes.

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• Jupiter, Venus, Mars and Saturn are lined up low in the dawn glow, in order of increasing brightness.

• The Moon will reach it first quarter on May 8.

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



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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



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The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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