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Astronomy Without A Telescope – Special Relativity From First Principles

December 17, 2011 Uncategorized

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There’s hope for us all if a mild-mannered patent office clerk can become Person Of The 20th Century.

Einstein’s explanation of special relativity, delivered in his 1905 paper On the Electrodynamics of Moving Bodies focuses on demolishing the idea of ‘absolute rest’, exemplified by the theoretical luminiferous aether. He achieved this very successfully, but many hearing that argument today are left puzzled as to why everything seems to depend upon the speed of light in a vacuum.

Since few people in the 21st century need convincing that the luminiferous aether does not exist, it is possible to come at the concept of special relativity in a different way and just through an exercise of logic deduce that the universe must have an absolute speed – and from there deduce special relativity as a logical consequence.(…)
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Astronomy Without A Telescope – Could Dark Matter Not Matter?

December 3, 2011 Uncategorized

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Rotation curves of the Andromeda Galaxy. Actual rotational velocities of the outer stars are the white line, while velocities that would be expected from the estimated mass of the visible matter in the galaxy are the red line. Hence, we conclude that over 80% of the galaxy’s mass must be dark matter. (Credit Queens Uni.).

You probably want to put on your skeptical goggles and set them to maximum for this one. An Italian mathematician has come up with some complex formulae that can, with remarkable similarity, mimic the rotation curves of spiral galaxies without the need for dark matter.

Currently, these galactic rotation curves represent key evidence for the existence of dark matter – since the outer stars of spinning galaxies often move around a galactic disk so fast that they should fly off into intergalactic space – unless there is an additional ‘invisible’ mass present in the galaxy to gravitationally hold them in their orbits.(…)
Read the rest of Astronomy Without A Telescope – Could Dark Matter Not Matter? (732 words)

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Astronomy Without A Telescope – The Progenitor Problem

November 27, 2011 Uncategorized

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DEM L71 – a Type 1a supernova remnant. Analysis of the outer shockwave and inner ejecta indicate the remnant material does not greatly exceed 1 solar mass – and it contains a high iron to silicon/oxygen ratio. This all suggests that the progenitor star was a compact white dwarf. But, apart from that, the steps that led up to the explosion are a mystery (Credit: NASA/Chandra).

With so much of our current understanding of the universe based on Type 1a supernovae data, a good deal of current research is focused upon just how standard these supposed standard candles are. To date, the weight of analysis seems reassuring – apart from a few outliers, the supernovae do all seem very standard and predictable.

However, some researchers have come at this issue from a different perspective by considering the characteristics of the progenitor stars that produce Type 1a supernovae. We know very little about these stars. Sure, they are white dwarfs that explode after accumulating extra mass – but just how this outcome is reached remains a mystery.(…)
Read the rest of Astronomy Without A Telescope – The Progenitor Problem (520 words)

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Astronomy Without A Telescope – Mass Is Energy

November 20, 2011 Uncategorized

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The USS Enterprise in 1964 (pre Zefram Cochrane era), during Operation Sea Orbit when it sailed around the world in 65 days without refuelling – demonstrating the capability of nuclear-powered ships. Credit: US Navy.

Some say that the reason you can’t travel faster than light is that your mass will increase as your speed approaches light speed – so, regardless of how much energy your star drive can generate, you reach a point where no amount of energy can further accelerate your spacecraft because its mass is approaching infinite.

This line of thinking is at best an incomplete description of what’s really going on and is not a particularly effective way of explaining why you can’t move faster than light (even though you can’t). However, the story does offer some useful insight into why mass is equivalent to energy, in accordance with the relationship e=mc².(…)
Read the rest of Astronomy Without A Telescope – Mass Is Energy (740 words)

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Astronomy Without A Telescope – Flat Universe

October 16, 2011 Uncategorized

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Various universe evolution scenarios. A universe with too much density collapses in on itself, a critical density universe stays static, while a universe with not enough density keeps expanding at a steady (coasting) rate. However, today’s cosmology puts emphasis upon the cosmological constant, which gives an accelerating expansion. Does this mean that density is irrelevant? Credit: NASA.

A remarkable finding of the early 21st century, that kind of sits alongside the Nobel prize winning discovery of the universe’s accelerating expansion, is the finding that the universe is geometrically flat. This is a remarkable and unexpected feature of a universe that is expanding – let alone one that is expanding at an accelerated rate – and like the accelerating expansion, it is a key feature of our current standard model of the universe.

It may be that the flatness is just a consequence of the accelerating expansion – but to date this cannot be stated conclusively.(…)
Read the rest of Astronomy Without A Telescope – Flat Universe (687 words)

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Astronomy Without A Telescope – Light Speed

October 9, 2011 Uncategorized

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You could cross the universe in a matter of hours without ever 'breaking light speed' – it is not the speed limit that it seems to be.

The recent news of neutrinos moving faster than light might have got everyone thinking about warp drive and all that, but really there is no need to imagine something that can move faster than 300,000 kilometres a second. Indeed, the whole idea is illogical.

Light speed, or 300,000 kilometres a second, might seem like a speed limit, but this is just an example of 3 + 1 thinking – where we still haven’t got our heads around the concept of four dimensional space-time and hence we think in terms of space having three dimensions and think of time as something different.(…)
Read the rest of Astronomy Without A Telescope – Light Speed (671 words)

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Astronomy Without A Telescope – New Physics?

September 11, 2011 Uncategorized

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The Sun can affect a lot of things on Earth – but the rate of radioactive decay isn’t normally considered to be one of those things. Credit: NASA.

Radioactive decay – a random process right? Well, according to some – maybe not. For several years now a team of physicists from Purdue and Stanford have reviewed isotope decay data across a range of different isotopes and detectors – seeing a non-random pattern and searching for a reason. And now, after eliminating all other causes – the team are ready to declare that the cause is… extraterrestrial.

OK, so it’s suggested to just be the Sun – but cool finding, huh? Well… maybe it’s best to first put on your skeptical goggles before reading through anyone’s claim of discovering new physics.(…)
Read the rest of Astronomy Without A Telescope – New Physics? (561 words)

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Astronomy Without A Telescope – Cosmic Coincidence

September 4, 2011 Uncategorized

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The standard model of the universe has it that the energy density of its contents and the ‘dark energy’ of its expansion are, just now, of the same order of magnitude. Coincidence? Credit: NASA.

Cosmologists tend not to get all that excited about the universe being 74% dark energy and 26% conventional energy and matter (albeit most of the matter is dark and mysterious as well). Instead they get excited about the fact that the density of dark energy is of the same order of magnitude as that more conventional remainder.

After all, it is quite conceivable that the density of dark energy might be ten, one hundred or even one thousand times more (or less) than the remainder. But nope, it seems it’s about three times as much – which is less than ten and more than one, meaning that the two parts are of the same order of magnitude. And given the various uncertainties and error bars involved, you might even say the density of dark energy and of the more conventional remainder are roughly equivalent. This is what is known as the cosmic coincidence.(…)
Read the rest of Astronomy Without A Telescope – Cosmic Coincidence (556 words)

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Astronomy Without A Telescope – Why The LHC (Still) Won’t Destroy The Earth

August 28, 2011 Uncategorized

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Concerns about a 'big science machine' destroying the Earth have been around since the steam engine. The LHC is the latest target for such conspiracy theories. Credit: CERN.

Surprisingly, rumors still persist in some corners of the Internet that the Large Hadron Collider (LHC) is going to destroy the Earth – even though nearly three years have passed since it was first turned on. This may be because it is yet to be ramped up to full power in 2014 – although it seems more likely that this is just a case of moving the goal posts, since the same doomsayers were initially adamant that the Earth would be destroyed the moment the LHC was switched on, in September 2008.

The story goes that the very high energy collisions engineered by the LHC could jam colliding particles together with such force that their mass would be compressed into a volume less than the Schwarzschild radius required for that mass. In other words, a microscopic black hole would form and then grow in size as it sucked in more matter, until it eventually consumed the Earth.

Here’s a brief run-through of why this can’t happen.(…)
Read the rest of Astronomy Without A Telescope – Why The LHC (Still) Won’t Destroy The Earth (799 words)

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Astronomy Without A Telescope – Cubic Neutrons

August 21, 2011 Uncategorized

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The currently popular analogy to describe the density of matter within a neutron star is that it’s like compressing the entire human population into a sugar cube. And speaking of cubes… Credit: E. Galactica.

The nature of the highly compressed matter that makes up neutron stars has been the subject of much speculation. For example, it’s been suggested that under extreme gravitational compression the neutrons may collapse into quark matter composed of just strange quarks – which suggests that you should start calling a particularly massive neutron star, a strange star.

However, an alternate model suggests that within massive neutron stars - rather than the neutrons collapsing into more fundamental particles, they might just be packed more tightly together by adopting a cubic shape. This might allow such cubic neutrons to be packed into about 75% of the volume that spherical neutrons would normally occupy.(…)
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Astronomy Without A Telescope – Impact Mitigation

August 14, 2011 Uncategorized

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The Don Quijote mission, which may launch by 2015. The Sancho spacecraft will orbit an asteroid, collecting data as another spacecraft Hidalgo collides with that asteroid, in an attempt to alter its trajectory. Credit: ESA.

The save-the-Earth rehearsal mission Don Quijote, commissioned by the European Space Agency, is planned to test the potential of a real life-or-death mission to deflect a mass-extinction-inducing asteroid from a collision course with Earth.

Currently at ‘concept’ stage, the Don Quijote Near Earth Asteroid Impact Mitigation Mission – has been modelled on a proposed flight to either 2002 AT4 or 1989 ML, both being near-Earth asteroids, though neither represent an obvious collision risk. However, subsequent studies have proposed that Amor 2003 SM84 or even 99942 Apophis may be more suitable targets. After all, 99942 Apophis does carry a marginal (1 in 250,000) risk of an Earth impact in 2036.(…)
Read the rest of Astronomy Without A Telescope – Impact Mitigation (727 words)

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Astronomy Without A Telescope – A Photon’s Point Of View

August 7, 2011 Uncategorized

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The way Hollywood envisions moving at light speed doesn't really work – since it still implies that you move a certain distance over a certain time period. As far as a photon is concerned, it does neither. Source: zidbits.

From a photon’s point of view, it is emitted and then instantaneously reabsorbed. This is true for a photon emitted in the core of the Sun, which might be reabsorbed after crossing a fraction of a millimetre’s distance. And it is equally true for a photon that, from our point of view, has travelled for over 13 billion years after being emitted from the surface of one of the universe’s first stars.

So it seems that not only does a photon not experience the passage of time, it does not experience the passage of distance either. But since you can’t move a massless consciousness at the speed of light in a vacuum, the real point of this thought experiment is to indicate that time and distance are just two apparently different aspects of the same thing. (…)
Read the rest of Astronomy Without A Telescope – A Photon’s Point Of View (474 words)

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Astronomy Without A Telescope – Gravitational Waves

July 17, 2011 Uncategorized

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An artist's impression of gravitational waves. In reality, a single uniform massive object does not generate gravitational waves. However, a massive binary system in orbital motion, could generate dynamic pulses of gravitational energy that might be detected from Earth. Credit: NASA.

Gravitational waves have some similar properties to light. They move at the same speed in a vacuum – and with a certain frequency and amplitude. Where they differ from light is that they are not scattered or absorbed by matter, in the way that light is.

Thus, it’s likely that primordial gravitational waves, that are speculated to have been produced by the Big Bang, are still out there waiting to be detected and analyzed.(…)
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Astronomy Without A Telescope – Granularity

July 10, 2011 Uncategorized

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A gamma ray burst is an opportunity to assess the nature of the apparent 'empty space' vacuum that exists between you and it. In GRB 041219A's case, that's 300 million light years of vacuum. Credit: ESA.

The very small wavelength of gamma ray light offers the potential to gain high resolution data about very fine detail – perhaps even detail about the quantum substructure of a vacuum – or in other words, the granularity of empty space.

Quantum physics suggests that a vacuum is anything but empty, with virtual particles regularly popping in and out of existence within Planck instants of time. The proposed particle nature of gravity also requires graviton particles to mediate gravitational interactions. So, to support a theory of quantum gravity we should expect to find evidence of a degree of granularity in the substructure of space-time.(…)
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Astronomy Without A Telescope – Big Rips And Little Rips

July 3, 2011 Uncategorized

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The concept of accelerating expansion does get you wondering just how fast the universe can end up expanding by. Theorists think that the rate of expansion might become so extreme as to produce a Big Rip. Or, after fiddling with the math a bit, maybe just a Little Rip? Credit: NASA.

One of a number of seemingly implausible features of dark energy is that its density is assumed to be constant over time. So, even though the universe expands over time, dark energy does not become diluted, unlike the rest of the contents of the universe.

As the universe expands, it seems that more dark energy appears out of nowhere to sustain the constant dark energy density of the universe. So, as times goes by, dark energy will become an increasingly dominant proportion of the observable universe – remembering that it is already estimated as being 73% of it.(…)
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Astronomy Without A Telescope – Star Seeds

June 19, 2011 Uncategorized

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The Rho Ophiuchi cloud complex – within which the cloud L1688 is the most active star-forming location. Although hidden by dust, it is possible to study star formation by sub-millimetre astronomy. Credit NASA.

Molecular clouds are called so because they have sufficient density to support the formation of molecules, most commonly H₂ molecules. Their density also makes them ideal sites for new star formation – and if star formation is prevalent in a molecular cloud, we tend to give it the less formal title of stellar nursery.(…)
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Astronomy Without A Telescope – Oh-My-God Particles

June 12, 2011 Uncategorized

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Centaurus A – one of the closest galaxies with an active galactic nucleus – although it is over 10 million light years away. If you are looking for a likely source of ultra-high-energy cosmic rays – you may not need to look further. Credit: ESO.

Cosmic rays are really sub-atomic particles, being mainly protons (hydrogen nuclei) and occasionally helium or heavier atomic nuclei and very occasionally electrons. Cosmic ray particles are very energetic as a result of them having a substantial velocity and hence a substantial momentum.

The Oh-My-God particle detected over Utah in 1991 was probably a proton traveling at 0.999 (and add another 20 x 9s after that) of the speed of light and it allegedly carried the same kinetic energy as a baseball traveling at 90 kilometers an hour.(…)
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Astronomy Without A Telescope – Holographic Dark Information Energy

May 29, 2011 Uncategorized

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The bubble nebula NGC 7635 – it doesn't have a lot to do with Holographic Dark Information Energy, but you have to start these articles with an image. Credit: Croman/an APOD for November 7 2005.

Holographic Dark Information Energy gets my vote for the best mix of arcane theoretical concepts expressed in the shortest number of words – and just to keep it interesting, it’s mostly about entropy.(…)
Read the rest of Astronomy Without A Telescope – Holographic Dark Information Energy (630 words)

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Astronomy Without A Telescope – Small Bangs

May 22, 2011 Uncategorized

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Gamma-ray bursts. We tend to think of them as big explosions – but it has been suggested that they might actually be Small Bangs. Credit: NASA.

Most gamma-ray bursts come in two flavors. Firstly, there are long duration bursts which form in dense star-forming regions and are associated with supernovae – which would understandably generate a sustained outburst of energy. The technical definition of a long duration gamma-ray burst is one that is more than two seconds in duration – but bursts lasting over a minute are not unusual.

Short duration gamma-ray bursts more often occur in regions of low star formation and are not associated with supernovae. Their duration is technically less than 2 seconds, but a duration of only a few milliseconds is not unusual. These are assumed to result from collisions between massive compact objects – perhaps neutron stars or black holes – producing a short, sharp outburst of energy.

But there are also rare instances of gamma-ray bursts that don’t really fill either category. (…)
Read the rest of Astronomy Without A Telescope – Small Bangs (589 words)

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Astronomy Without A Telescope – Planet Spotting

May 8, 2011 Uncategorized

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The current search area of the Kepler mission, monitoring 145,000 stars for signs of exoplanets – with a particular interest in those that may be in a star’s ‘habitable zone’. Credit: Lomberg/NASA.

The Extrasolar Planets Encyclopedia counted 548 confirmed extrasolar planets at 6 May 2011, while the NASA Star and Exoplanet Database (updated weekly) was today reporting 535. These are confirmed findings and the counts will significantly increase as more candidate exoplanets are assessed. For example, there were the 1,235 candidates announced by the Kepler mission in February, including 54 that may be in a habitable zone.

So what techniques are brought to bear to come up with these findings? (…)
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Astronomy Without A Telescope – Our Unlikely Solar System

April 10, 2011 Uncategorized

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A circumstellar disk of debris around a matured stellar system may indicate that Earth-like planets lie within – since such a disk results from the collisional grinding of rocky planetesimals. Credit: NASA.

Recent modeling of solar mass stars with planetary systems, found that a system with four rocky planets and four gas giants in stable orbits – and only a sparsely populated outer belt of planetesimals – has only a 15 to 25% likelihood of developing. While you might be skeptical about the validity of a model that puts our best known planetary system in the unlikely basket, there may be some truth in this finding.(…)
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Astronomy Without A Telescope – Our Inferred Universe

April 3, 2011 Uncategorized

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A galaxy far, far away and long. long ago. UDFy-38135539 – about the most distant observed object, where UDF stands for (Hubble) Ultra-Deep Field. Credit: HST – NASA/ESA.

The universe is a big place – and getting bigger all the time – so at a large scale all unbound structures are all moving away from each other. So when we look out at distant objects, we need to remind ourselves that not only are we seeing them as they appeared in the past, when the light that hits our eyes first left them, but also that they are no longer in that location where they appear to be.(…)
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Astronomy Without A Telescope – Dark Statistics

March 27, 2011 Uncategorized

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The dark flow hypothesis. A region of the observable universe is being influenced by a mysterious something outside the observable universe (which we can’t observe). Source: universe-review.ca

The hypothetical dark flow seen in the movement of galaxy clusters requires that we can reliably identify a clear statistical correlation in the motion of distant objects which are, in any case, flowing outwards with the expansion of the universe and may also have their own individual (or peculiar) motion arising from gravitational interactions. (…)
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Astronomy Without A Telescope – Doubly Special Relativity

March 20, 2011 Uncategorized

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The Large Hadron Collider – destined to deliver fabulous science data, but it remains uncertain if these will include an evidence basis for quantum gravity theories. Credit: CERN.

General relativity, Einstein’s theory of gravity, gives us a useful basis for mathematically modeling the large scale universe – while quantum theory gives us a useful basis for modeling sub-atomic particle physics and the likely small-scale, high-energy-density physics of the early universe – nanoseconds after the Big Bang – which general relativity just models as a singularity and has nothing else to say on the matter.

Quantum gravity theories may have more to say. By extending general relativity into a quantized structure for space-time, maybe we can bridge the gap between small and large scale physics. For example, there’s doubly special relativity. (…)
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Astronomy Without A Telescope – Black Hole Entropy

March 13, 2011 Uncategorized

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Black holes – throw something in them and that’s the end of the story, right? Well, apparently some physicists just can’t seem to leave it there.

An easy way to think about the entropy of black holes is to consider that entropy represents the loss of free energy – that is, energy that is available to do work – from a system. Needless to say, anything you throw into a black hole is no longer available to do any work in the wider universe.(…)
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Astronomy Without A Telescope – Unreasonable Effectiveness

March 5, 2011 Uncategorized

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Some indication of the complex math involved in modeling a close massive binary system of compact objects – be they neutron stars or black holes. Surely, you couldn’t possibly just guess the outcome here – at least you wouldn’t think that you possibly could. Credit: NASA.

Gravitational waves are apparently devilishly difficult things to model with Einstein field equations, since they are highly dynamic and non-symmetric. Traditionally, the only way to get close to predicting the likely effects of gravity waves was to estimate the Einstein equation parameters by assuming the objects causing the gravity waves do not generate strong gravity fields themselves – and nor do they move at velocities anywhere close to the speed of light.

Trouble is, the mostly likely candidate objects that might generate detectable gravity waves – close binary neutron stars and merging black holes – have exactly those properties. They are highly compact, very massive bodies that often move at relativistic (i.e. close to the speed of light) velocities. (…)
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Astronomy Without A Telescope – Knots In Space

February 28, 2011 Uncategorized

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A rare double Einstein ring (SDSSJ0946+1006). Either two distant galaxies are lined up directly behind a closer massive galactic cluster (which is gravitationally-lensing their light into a double ring) – or of course it could be a donut-shaped portal to an alternate universe. You decide. Credit: NASA/ESA HST.

So finally you possess that most valuable of commodities, a traversable wormhole – and somehow or other you grab one end of it and accelerate it to a very rapid velocity. (…)
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Astronomy Without A Telescope – Plausibility Check

February 12, 2011 Uncategorized

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OK, this looks nice – but let’s think it through. You’ve got two binary stars with angular diameters and spectral properties roughly analogous to our Sun – shining through an atmosphere containing semi-precipitous water vapor (also known as clouds). Plausible? Credit: NASA.

So we all know the story. Uncle Owen has just emotionally blackmailed you into putting off your application to the academy for another year – and even after you just got those two new droids, darn it. So you stare mournfully at the setting binary suns and…

Hang on, they look a lot like G type stars – and if so, their roughly 0.5 degree angular diameters in the sky suggest they are both only around 1 astronomical unit away. I mean OK, you could plausibly have a close red dwarf and a distant blue giant having identical apparent diameters, but surely they would look substantially different, both in color and brightness. (…)
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Astronomy Without A Telescope – Situation Cloudy

February 7, 2011 Uncategorized

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The Magellanic Stream trails behind the Large and Small Magellanic Clouds – two bright shapes visible below the Milky Way’s galactic disk, to the right. The stuff ahead of the Clouds is called the Leading Arm. The pink is false color – the Stream and Arm are only visible in radio wavelengths. Credit: Nidever et al.

Most people agree that the Magellanic Clouds are in orbit around the Milky Way. What’s not clear is whether it is a bound orbit or just a temporary ‘ships passing in the night’ arrangement. Something which could clarify the relationship is the Magellanic Stream, a 600,000 light year long string of gas dragged through and beyond the Small and Large Magellanic Clouds. (…)
Read the rest of Astronomy Without A Telescope – Situation Cloudy (700 words)

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Astronomy Without A Telescope – Gravity Probe B

January 30, 2011 Uncategorized

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Gravity Probe B – testing the null hypothesis that the spin axis of a gyroscope will stay aligned with a distant reference point when it’s in a free fall orbit. General relativity says it won’t.

There’s a line out of an early episode of The Big Bang Theory series, where Gravity Probe B is described as having seen ‘glimpses’ of Einstein’s predicted frame-dragging effect. In reality, it is not entirely clear that the experiment was able to definitively distinguish a frame-dragging effect from a background noise created by some exceedingly minor aberrations in its detection system.

Whether or not this counts as a glimpse – frame-dragging (the alleged last untested prediction of general relativity) and Gravity Probe B have become linked in the public consciousness. So here’s a quick primer on what Gravity Probe B may or may not have glimpsed.(…)
Read the rest of Astronomy Without A Telescope – Gravity Probe B (703 words)

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Astronomy Without A Telescope – Time Freeze

January 23, 2011 Uncategorized

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Is it ever possible to find yourself in a situation where you see the hands of a clock freeze? Nnnnnnnnnn….

There is a story told about traveling at the speed of light in which you are asked to imagine that you begin by standing in front of a big clock – like Big Ben. You realize that your current perception of time is being informed by light reflected off the face of the clock – which is telling you it’s 12:00. So if you then shoot away at the same speed as that light – all you will continue to see is that clock fixed at 12:00, since you are moving at the same speed that this information is moving. And so you discover that at the speed of light, time essentially stands still.

While there are a number of things wrong with this story – as it happens, one correct thing is that if you were able to travel at the speed of light you would experience no passage of time – although there are several reasons why this is probably an impossible situation to find yourself in.(…)
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Astronomy Without A Telescope – Why Carbon?

January 16, 2011 Uncategorized

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Although we consider life on Earth to be carbon-based, the ATGC coding components of DNA are nucleotides – with a carbon content of zero. Credit: NASA (adapted image).

Last week’s AWAT Why Water? took the approach of acknowledging that while numerous solvents are available to support alien biochemistries, water is very likely to be the most common biological solvent out there – just on the basis of its sheer abundance. It also has useful chemical features that would be advantageous to alien biochemistries – particularly where its liquid phase occurs in a warmer temperature zone than any other solvent. (…)
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Astronomy Without A Telescope – Why Water?

January 9, 2011 Uncategorized

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Mono Lake – no alien biochemistry here, but makes for a nice photo all the same. Credit: NASA.

The assumption that alien biochemistries probably require liquid water may seem a little Earth-centric. But given the chemical possibilities available from the most abundant elements in the universe, even an alien scientist with a different biochemistry would probably agree that a water-solvent-based biochemistry is quite likely to occur elsewhere in the universe – and might well be the most likely foundation for a complex ecosystem in which intelligent life could develop.(…)
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Astronomy Without A Telescope – Secular Evolution

December 25, 2010 Uncategorized

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M51 – the Whirlpool Galaxy. Like most spiral galaxies, the spiral arms are really density waves. Drag forces produced by these density waves could drive the ‘secular’ evolution of galaxies. Credit: NASA-HST.

A traditional galaxy evolution model has it that you start with spiral galaxies – which might grow in size through digesting smaller dwarf galaxies – but otherwise retain their spiral form relatively undisturbed. It is only when these galaxies collide with another of similar size that you first get an irregular ‘train-wreck’ form, which eventually settles into a featureless elliptical form – full of stars following random orbital paths rather than moving in the same narrow orbital plane that we see in the flattened galactic disk of a spiral galaxy.

The concept of secular galaxy evolution challenges this notion – where ‘secular’ means separate or isolated. Theories of secular evolution propose that galaxies naturally evolve along the Hubble sequence (from spiral to elliptical), without merging or collisions necessarily driving changes in their form. (…)
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Astronomy Without A Telescope – The Edge of Greatness

December 19, 2010 Uncategorized

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The foamy-looking cosmic web – at this scale we run out of superlatives to describe the large scale structure of the universe. Credit: NASA.

The so-called End of Greatness is where you give up trying to find more superlatives to describe large scale objects in the universe. Currently the Sloan Great Wall – a roughly organised collection of galactic superclusters partitioning one great void from another great void – is about where most cosmologists draw the line.

Beyond the End of Greatness, it’s best just to consider the universe as a holistic entity – and at this scale we consider it isotropic and homogenous, which we need to do to make our current cosmology math work. But at the very edge of greatness, we find the cosmic web. (…)
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Astronomy Without A Telescope – Forbidden Planets

December 13, 2010 Uncategorized

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The theorized evolution of the circumbinary planet PSR B1620-26 b. Credit: NASA.

Binary star systems can have planets – although these are generally assumed to be circumbinary (where the orbit encircles both stars). As well as the fictional examples of Tatooine and Gallifrey, there are real examples of PSR B1620-26 b and HW Virginis b and c – thought to be cool gas giants with several times the mass of Jupiter, orbiting several astronomical units out from their binary suns.

Planets in circumstellar orbits around a single star within a binary system are traditionally considered to be unlikely due to the mathematical implausibility of maintaining a stable orbit through the ‘forbidden’ zones – which result from gravitational resonances generated by the motion of the binary stars. The orbital dynamics involved should either fling a planet out of the system or send it crashing to its doom into one or other of the stars. However, there may be a number of windows of opportunity available for ‘next generation’ planets to form at later stages in the evolving life of a binary system. (…)
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Astronomy Without A Telescope – Through A Lens Darkly

December 5, 2010 Uncategorized

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Gravitational lensing in action – faint hints of an ‘Einstein ring’ forming about light sources which have been ‘lensed’ by the warping of space-time. If the galactic cluster causing the warping was orientated in a plane that was face-on directly at Earth – the Einstein ring would be much more apparent. Credit: HST, NASA.

Massive galactic clusters – which are roughly orientated in a plane that is roughly face-on to Earth – can generate strong gravitational lensing. However, several surveys of such clusters have reached the conclusion that these clusters have a tendency towards lensing too much – at least more than is predicted based on their expected mass.

Known (to some researchers working in the area) as the ‘over-concentration problem’, it does seem to be a prima facie case of missing mass. But rather than just playing the dark matter card, researchers are pursuing more detailed observations – if only to eliminate other possible causes. (…)
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Astronomy Without A Telescope – Black Hole Evolution

November 28, 2010 Uncategorized

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The idea that every galaxy of significant size has a supermassive black hole at its centre keeps gaining momentum. So… coincidence? Or are these SMBHs somehow fundamental to the process of galaxy formation? Credit: NASA.

While only observable by inference, the existence of supermassive black holes (SMBHs) at the centre of most – if not all – galaxies remains a compelling theory supported by a range of indirect observational methods. Within these data sources, there exists a strong correlation between the mass of the galactic bulge of a galaxy and the mass of its central SMBH – meaning that smaller galaxies have smaller SMBHs and bigger galaxies have bigger SMBHs.

Linked to this finding is the notion that SMBHs may play an intrinsic role in galaxy formation and evolution – and might have even been the first step in the formation of the earliest galaxies in the universe, including the proto-Milky Way.
(…)
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Astronomy Without A Telescope – Necropanspermia

November 14, 2010 Uncategorized

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Could an alien spore really travel light years between different star systems? Well, as long as your theory doesn’t require it to be alive when it arrives – sure it can.

The idea that a tiny organism could hitchhike aboard a mote of space dust to cross vast stretches of space and time until it landed and took up residence on the early Earth does seem a bit implausible. More likely any such organisms would have been long dead by the time they reached Earth. But… might those long dead alien carcasses still have provided the genomic template that kick started life on Earth? Welcome to necropanspermia.
(…)
Read the rest of Astronomy Without A Telescope – Necropanspermia (560 words)

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Astronomy Without A Telescope – Indigenous Australian Astronomy

November 8, 2010 Uncategorized

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The Homunculus Nebula arising from the Eta Carinae star system – thought to be stellar material blown off by this massive star system during a ‘supernova impostor’ event that occurred around 1840.

Eta Carinae is a massive binary system – of which the dominant member is an eruptive luminous blue variable star. The system’s last significant eruption – also known as the ‘great outburst’ – made Eta Carinae briefly the second brightest star system in the night sky after Sirius over the period of 1837 to 1845, after which it faded again. The great outburst left behind the Homunculus Nebula – and also left an impression on the indigenous Aboriginal people of Australia who observed it at that time.
(…)
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© Steve Nerlich for Universe Today, 2010. | Permalink | 5 comments | Add to del.icio.us
Post tags: Archaeoastronomy

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Astronomy Without A Telescope – Warp Drive On Paper

October 31, 2010 Uncategorized

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It’s sixteen years since Miguel Alcubierre suggested that faster-than-light travel might be achieved by generating a warp bubble that contracts space-time ahead of the spaceship and expands it behind. Now a metamaterial test laboratory is available to see if this idea really could work. Image sourced from: andersoninstitute.com

The Alcubierre drive is one of the better known warp drive on paper models – where a possible method of warp drive seems to work mathematically as long as you don’t get too hung up on real world physics and some pesky boundary issues.

Recently the Alcubierre drive concept has been tested within mathematically modeled metamaterial – which can provide a rough analogy of space-time. Interestingly, in turns out that under these conditions the Alcubierre drive is unable to break the light barrier – but quite capable of doing 25% of light speed, which is not what you would call slow.
(…)
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Post tags: Alcubierre metric, metamaterial

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