Tag Archives: astrophysics

You too can be an astrophysicist with your new telescope

The Conversation

File 20171116 15412 1f7ob2l.jpg?ixlib=rb 1.1
Look up … some things to do with your new telescope. Flickr/Grand Canyon National Park, CC BY

Michael J. I. Brown, Monash University

A telescope can reveal the beauty of the universe, such as the Moon’s craters, Saturn’s rings, and the glowing gas of the Orion nebula. But a telescope isn’t just for sightseeing – it is also a scientific instrument.

If you’ve just received a telescope as a present then it’s probably better than any used by the Italian scientist Galileo Galilei (1564-1642). A small telescope with a modern camera can be more capable than professional telescopes from just a century ago.

An illustration of Galileo Galilei with a telescope. Iryna/Shutterstock

You can use your telescope to see astrophysics in action, such as the planets travelling around the Sun, see how stars have different colours and even detect worlds orbiting distant stars.

Read more: What to look for when buying a telescope

At the eyepiece

Look through the eyepiece of your telescope and you can retrace the beginnings of astrophysics.

Galileo only had a tiny telescope with a lens just a few centimetres across. Yet he mapped the Moon, saw Saturn’s rings, and discovered Jupiter’s four largest moons – Io, Europa, Ganymede and Callisto – now known as the Galilean moons.

Galileo was also persecuted for advocating the theory that the planets (including Earth) orbit around the Sun, at a time when the popular belief was that Earth was the centre of the universe.

His observation of the phases of Venus are among his most compelling pieces of evidence that Earth and the other planets of our Solar System orbit the Sun.

Galileo charted the apparent size and phases of Venus with his small telescope. NASA

If the planets travel around the Sun, as Galileo believed, then sometimes the Sun will be (almost) between us and Venus, so we can view most of the daytime side of Venus. At other times, Venus will be between us and the Sun, and will appear as larger (since it’s closer) crescent.

Venus is never too far from the Sun in the sky (indeed it’s lost in the Sun’s glare during January 2018), and is only visible near sunrise or sunset. The phases of Venus, which resemble those of the Moon, can be seen with even a small telescope.

There are plenty of guides on how to find Venus (and other planets, stars, constellations, galaxies and so on) including Sky and Telescope, apps for Android and Apple devices and the free Stellarium computer software.

Use any of these to find Venus, and then use your telescope to see the phases of the planet as Galileo did four centuries ago.

The lives of stars

Understanding the lives of stars was the biggest puzzle for astrophysicists during the early 20th century. One of the first clues is the fact that different stars have different colours, which tells us they have different temperatures.

Even without a telescope, you can see the red star Betelgeuse and the blue star Rigel in the constellation of Orion. Betelgeuse has a surface temperature of 3,000℃, while Rigel’s surface is at 12,000℃.

Why do different stars have different temperatures? Measuring the luminosities of stars with different colours provides a critical clue. Look at open star clusters such as Pleiades and you will see that (with some exceptions) the brightest stars are blue.

The most luminous stars in the Pleiades star cluster are blue. Flickr/Joel Tonyan, CC BY-NC-ND

Blue stars are often the most luminous (and most massive), and their high temperatures result from the rapid fusion of hydrogen into helium. Some blue stars are 100 times as bright as the Sun.

These stars live for just millions of years, as they are using their hydrogen fuel so rapidly. In contrast, some dull red stars may live for tens of billions of years.

What about the exceptions – the very luminous stars that are red, such as Betelgeuse? Some stars have run out of hydrogen in their cores, and instead fuse hydrogen in shells and/or fuse helium in their cores.

These stars can become enormous in size but have (relatively) cool surface temperatures. These red giants are also approaching the end of their lives.

Strange new worlds

So far your telescope has been used for simple observations of stars and planets. With the addition of some more equipment you can use your telescope to detect planets around distant stars.

To do this you need a good digital camera, the ability to track a star for a few hours, and some free software for your computer.

The first planets orbiting other stars were detected in the 1990s and now thousands of such worlds are known. Some of these planets orbit stars that are 100 times fainter than the unaided eye can see, and such stars are easily seen with small telescopes.

Read more: Google’s artificial intelligence finds two new exoplanets missed by human eyes

But what about the planets? Well, at predictable times planets pass between us and their stars, making the stars dim by about 1%. You can’t see that tiny change in brightness with your eye, but you can record it digitally.

The ConversationIf you can take digital images of a star with a planet and several neighbouring stars, then you can use computer programs (such as OSCAAR) to measure how the star dims relative to its neighbours. You can thus see the passage of a distant world around its star.

You don’t need a big telescope to detect a planet orbiting a distant star, and a bit of DIY can help.

Michael J. I. Brown, Associate professor, Monash University

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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Black holes are even stranger than you can imagine

The Conversation

Alister Graham, Swinburne University of Technology

Our love of black holes continues to grow as our knowledge of these celestial bodies expands. The latest news is the discovery of a rare “middleweight” black hole, a relative newcomer to the black hole family.

We already knew that some black holes are just a few times the mass of our Sun, while others are more than a billion times as massive. But others with intermediate masses, such as the one 2,200 times the mass of our Sun recently discovered in the star cluster 47 Tucanae, are surprisingly elusive.

So what is it about black holes, these gravitational prisons that trap anything that gets too close to them, that captures the imagination of people of all ages and professions?

‘Dark stars’

As far back as 1783, within the framework of Newtonian dynamics, the concept of “dark stars” with sufficiently high density that not even light can escape their gravitational pull had been advanced by the English philosopher and mathematician John Michell.

Almost immediately after Albert Einstein presented his theory of general relativity in 1915, which supplanted Newton’s description of our Universe and revealed how space and time are intimately linked, fellow German Karl Schwarzschild and Dutchman Johannes Droste independently derived the new equations for a spherical or point mass.

Although at the time the issue was still something of a mathematical curiosity, over the ensuing quarter of a century nuclear physicists realised that sufficiently massive stars would collapse under their own weight to become these previously theorised black holes.

Their existence was eventually confirmed by astronomers using powerful telescopes, and more recently colliding black holes were the source of the gravitational waves detected with the LIGO instrumentation in the United States.

A dense object

The densities of such objects is mind-boggling. If our Sun were to become a black hole, it would need to collapse from its current size of 1.4 million km across to a radius of less than 3km (6km across). Its average density within this “Schwarzschild radius” would be nearly 20 billion tonnes per cubic centimetre.

The increasing strength and pull of gravity as you get closer to a black hole can be dramatic.

On Earth, the strength of the gravitational pull holding you to its surface is roughly the same at your feet as it is at your head, which is a little bit farther away from the planet.

But near some black holes, the difference in gravitational pull from head to toe is so great that you would be pulled apart and stretched out on an atomic level, in a process referred to as spaghettification.

In 1958, the American physicist David Finkelstein was the first to realise the true nature of what has come to be called the “event horizon” of a black hole. He described this boundary around a black hole as the perfect unidirectional membrane.

It’s an intangible surface encapsulating a sphere of no return. Once inside this sphere, the gravitational pull of the black hole is too great to escape – even for light.

In 1963, the New Zealand mathematician Roy Kerr solved the equations for the more realistic rotating black holes. These yielded closed time-like curves that permitted movement backwards through time.

While such strange solutions to the equations of general relativity first appeared in the 1949 work of Austrian-American logician Kurt Gödel, it is commonly thought that they must be a mathematical artefact yet to be explained away.

A video simulation of two black holes merging.

Black and white holes

In 1964, two Americans, the writer Ann Ewing and the theoretical physicist John Wheeler, introduced the term “black hole”. Subsequently, in 1965, the Russian theoretical astrophysicist Igor Novikov introduced the term “white hole” to describe the hypothetical opposite of a black hole.

The argument was that if matter falls into a black hole, then perhaps it is spewed out into our universe from a white hole.

This idea is partly rooted in the mathematical concept known as an Einstein-Rosen bridge. Discovered (mathematically) in 1916 by the Austrian physicist Ludwig Flamm, and re-introduced in 1935 by Einstein and the American-Israeli physicist Nathan Rosen, it was later termed a “wormhole” by Wheeler.

In 1962, Wheeler and the American physicist Robert Fuller explained why such wormholes would be unstable for transporting even a single photon across the same universe.

Fact and fiction

Not surprisingly, the idea of entering a (black hole) portal and re-emerging somewhere else in the universe – in space and/or time – has spawned countless science fiction stories, including Doctor Who, Stargate, Fringe, Farscape and Disney’s Black Hole.

Ongoing productions can simply claim that their characters are travelling to a different or a parallel universe to our own. While it appears to be mathematically feasible, there is of course no physical evidence to support the existences of such universes.

But this is not to say that time travel, at least in a limited sense, is not real. When travelling at great speed, or perhaps falling into a black hole, the passage of time does slow down relative to that experienced by stationary observers.

Clocks flown quickly around the world have demonstrated this, displaying time lags in accordance with Einstein’s theory of special relativity.

The 2014 movie Interstellar played on this effect around a black hole, thereby creating a sense of travelling forward in time for astronaut Cooper (played by Matthew McConaughey).

Despite the strangely endearing name, the phrase “black hole” is perhaps somewhat misleading. It implies a hole in space-time through which matter will fall, as opposed to matter falling onto an incredibly dense object.

What actually exists within a black hole’s event horizon is hotly debated. Attempts to understand this include the “fuzzball” picture from string theory, or descriptions of black holes in quantum gravity theories known as “spin foam networks” or “loop quantum gravity”.

One thing that does seem certain is that black holes will continue to intrigue and fascinate us for some time yet.

The ConversationAlister Graham, Professor of Astronomy, Swinburne University of Technology

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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Why is Einstein’s general relativity such a popular target for cranks?

The Conversation

Michael J. I. Brown, Monash University

Scientists maybe celebrating the 100th anniversary of Albert Einstein’s general theory of relativity, but there was also a death in 1915. It was one of the many deaths of simple and intuitive physics that has happened over the past four centuries.

Today the concepts and mathematics of physics are often removed from everyday experience. Consequently, cutting edge physics is largely the domain of professional physicists, with years of university education.

But there are people who hanker for a simpler physics, toiling away on their own cosmologies. Rightly or wrongly, these people are often labelled cranks, but their endeavours tell us much misconceptions about science, its history and what it should be.

I regularly browse open access website arxiv.org to look for the latest astrophysics research. Real astrophysics, that is. But if I want to take a look at what pseudoscientists are up to, I can browse vixra.org. That’s right, “arxiv” backwards. The vixra.org website was founded by “scientists who find they are unable to submit their articles to arXiv.org” because that website’s owners filter material they “consider inappropriate”.

There are more than 1,800 articles on vixra.org discussing relativity and cosmology, and many don’t like relativity at all. Perhaps one reason why cranks particularly dislike relativity is because it is so unlike our everyday experiences.

Einstein predicted that the passage of time is not absolute, and can slow for speeding objects and near very massive bodies such as planets, stars and black holes. Over the past century, this bizarre predication has been measured with planes, satellites, and speeding muons.

But the varying passage of time is nothing like our everyday experience, which isn’t surprising as we don’t swing by black holes on our way to the shops. Everyday experience is often central to cranky ideas, with the most extreme example being flat earthers.

Thus many crank theories postulate that time is absolute, because that matches everyday experience. Of course, these crank theories are overlooking experimental data, or at least most of it.

History and linearity

One of the most curious aspects of pseudoscience is an oddly linear approach to science. To be fair, this can result from an overly literal approach to popular histories of science, which emphasise pioneering work over replication.

A pivotal moment in relativity’s history is Albert Michelson and Edward Morley’s demonstration that the speed of light didn’t depend on its direction of travel nor the motion of the Earth.

Of course, since 1887 the Michelson-Morley experiment has been confirmed many times. Modern measurements have a precision orders of magnitude better than the original 1887 Michelson-Morley experiment, but these don’t feature prominently in popular histories of science.

Interestingly many pseudoscientists are fixated on the original Michelson-Morley experiment, and how it could be in error. This fixation assumes science is so linear that the downfall a 19th century experiment will rewrite 21st century physics. This overlooks how key theories are tested (and retested) with a myriad of experiments with greater precision and different methodologies.

Another consequence of the pseudoscientific approach to history is that debunked results from decades past are often used by buttress pseudoscientific ideas. For example, many pseudoscientists claim Dayton Miller detected “aether drift” in the 1930s. But Miller probably underestimated his errors, as far more precise studies in subsequent decades did not confirm his findings.

Unfortunately this linear and selective approach to science isn’t limited to relativity. It turns up in cranky theories ranging from evolution to climate.

Climate scientist Michael E Mann is still dealing with cranky accusations about his seminal 1998 paper on the Earth’s temperature history, despite the fact it has been superseded by more recent studies that achieve comparable results. Indeed, it devoured so much of Mann’s time he has literally written a book about his experience.

What about the maths?

During the birth of physics, one could gain insights with relatively simple (and beautiful) mathematics. My favourite example is Johannes Kepler’s charting of the orbit of Mars via triangulation.

In the 17th century, Johannes Kepler used elegantly simple mathematics to chart the motion of Mars. Johannes Kepler / University of Sydney

Over subsequent centuries, the mathematics required for new physical insights has become more complex, as illustrated by Newton’s use of calculus and Einstein’s use of tensors. This level of mathematics is rarely in the domain of the enthusiastic but untrained amateur? So what do they do?

One option is to hark back to an earlier era. For example, trying to disprove general relativity by using the assumptions of special relativity or even Newtonian physics (again, despite the experiments to the contrary). Occasionally even numerology makes an appearance.

Another option is arguments by analogy. Analogies are useful when explaining science to a broad audience, but they aren’t the be-all and end-all of science.

In pseudoscience, the analogy is taken to the point of absurdity, with sprawling articles (or blog posts) weighed down with laboured analogies rather than meaningful analyses.

Desiring simplicity but getting complexity

Perhaps the most fascinating aspect of pseudoscientific theories is they hark for simplicity, but really just displace complexity.

A desire for naively simple science can produce bizarrely complex conclusions, like the moon landing hoax conspiracy theories. NASA/flickr

Ardents of the most simplistic pseudoscientific theories often project complexity onto the motives of professional scientists. How else can one explain scientists ignoring their brilliant theories? Claims of hoaxes and scams are commonplace. Although, to be honest, even I laughed out loud the first time I saw someone describe dark matter was a “modelling scam”.

Again, this isn’t limited to those who don’t believe in relativity. Simple misunderstandings about photography, lighting and perspective are the launch pad for moon landing conspiracy theories. Naively simple approaches to science can lead to complex conspiracy theories.

Changing intuition

Some have suggested that pseudoscience is becoming more popular and the internet certainly aids the transmission of nonsense. But when I look at history I wonder if pseudoscience will decay.

In the 19th century, Samuel Rowbotham promoted Flat Earthism to large audiences via lectures that combined wit and fierce debating skills. Perhaps in the 19th century a spherical world orbiting a sun millions of kilometres away didn’t seem intuitive.

But today we can fly around the globe, navigate with GPS and Skype friends in different timezones. Today, a spherical Earth is far more intuitive than it once was, and Flat Earthism is the exemplar of absurd beliefs.

Could history repeat with relativity? Already GPS utilises general relativity to achieve its amazing precision. A key plot device in the movie Interstellar was relativistic time dilation.

Perhaps with time, a greater exposure to general relativity will make it more intuitive. And if this happens, a key motivation of crank theories will be diminished.

Will general relativity become more widely understood via popular media, such as the movie Interstellar?

Michael will be on hand for an Author Q&A between 4 and 5pm AEDT on Tuesday, November 24, 2015. Post your questions in the comments section below.

The ConversationMichael J. I. Brown, Associate professor, Monash University

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.


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The sun won’t die for 5 billion years, so why do humans have only 1 billion years left on Earth?

The Conversation

By Jillian Scudder, University of Sussex

In a few billion years, the sun will become a red giant so large that it will engulf our planet. But the Earth will become uninhabitable much sooner than that. After about a billion years the sun will become hot enough to boil our oceans.

The sun is currently classified as a “main sequence” star. This means that it is in the most stable part of its life, converting the hydrogen present in its core into helium. For a star the size of ours, this phase lasts a little over 8 billion years. Our solar system is just over 4.5 billion years old, so the sun is slightly more than halfway through its stable lifetime.

Even stars die

After 8 billion years of happily burning hydrogen into helium are over, the sun’s life gets a little more interesting. Things change because the sun will have run out of hydrogen in its core – all that’s left is the helium. The trouble is that the sun’s core is not hot or dense enough to burn helium.

In a star, gravitational force pulls all the gases towards the centre. When the star has hydrogen to burn, the creation of helium produces enough outward pressure to balance out the gravitational pull. But when the star has nothing left in the core to burn, gravitational forces take over.

Eventually that force compresses the centre of the star to such a degree that it will start burning hydrogen in a small shell around the dead core, which is still full of helium. As soon as the sun begins to burn more hydrogen, it would be considered a “red giant”.

The process of compression in the centre allows the outer regions of the star to expand outwards. The burning hydrogen in the shell around the core significantly increases the brightness of the sun. Because the size of the star has expanded, the surface cools down and goes from white-hot to red-hot. Because the star is brighter, redder and physically larger than before, we dub these stars “red giants”.

Earth’s fiery demise

It is widely understood that the Earth as a planet will not survive the sun’s expansion into a full-blown red giant star. The surface of the sun will probably reach the current orbit of Mars – and, while the Earth’s orbit may also have expanded outwards slightly, it won’t be enough to save it from being dragged into the surface of the sun, whereupon our planet will rapidly disintegrate.

Life on the planet will run into trouble well before the planet itself disintegrates. Even before the sun finishes burning hydrogen, it will have changed from its present state. The sun has been increasing its brightness by about 10% every billion years it spends burning hydrogen. Increased brightness means an increase in the amount of heat our planet receives. As the planet heats up, the water on the surface of our planet will begin to evaporate.

An increase of the sun’s luminosity by 10% over the current level doesn’t sound like a whole lot, but this small change in our star’s brightness will be pretty catastrophic for our planet. This change is a sufficient increase in energy to change the location of the habitable zone around our star. The habitable zone is defined as the range of distances away from any given star where liquid water can be stable on the surface of a planet.

Magnificent coronal mass eruption. Source: NASA, CC BY

With a 10% increase of brightness from our star, the Earth will no longer be within the habitable zone. This will mark the beginning of the evaporation of our oceans. By the time the sun stops burning hydrogen in its core, Mars will be in the habitable zone, and the Earth will be much too hot to maintain water on its surface.

Uncertain models

This 10% increase in the sun’s brightness, triggering the evaporation of our oceans, will occur over the next billion years or so. Predictions of exactly how rapidly this process will unfold depend on who you talk to. Most models suggest that as the oceans evaporate, more and more water will be present in the atmosphere instead of on the surface. This will act as a greenhouse gas, trapping even more heat and causing more and more of the oceans to evaporate, until the ground is mostly dry and the atmosphere holds the water, but at an extremely high temperature.

As the atmosphere saturates with water, the water held in the highest parts of our atmosphere will be bombarded by high energy light from the sun, which will split apart the molecules and allow the water to escape as hydrogen and oxygen, eventually bleeding the Earth dry of water.

Where the models differ is on the speed with which the earth reaches this point of no return. Some suggest that the Earth will become inhospitable before the 1 billion year mark, since the interactions between the heating planet and the rocks, oceans, and plate tectonics will dry out the planet even faster. Others suggest that life may be able to hold on a little longer than 1 billion years, due to the different requirements of different life forms and periodic releases of critical chemicals by plate tectonics.

The Earth is a complex system – and no model is perfect. However, it seems likely that we have no more than a billion years left for life to thrive on our planet.

The ConversationThis article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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