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Afraid of the dark

I've never been afraid of the dark.  When it's all you've ever known, it seems a rather silly notion.  But now... well, this seems different somehow.  Now we're all frightened.

It wasn't always like this.  We all grew up with the stories about the old times, when there were colonies every few parsecs, all set on planets (artificial or otherwise) around healthy stars, and supply stations strung along the major trade routes likes beads of water on an invisible web.  The galaxy thrived back then, or so the stories go.  Civilisation reaching ever outwards, colonising, trading, cooperating, and fighting, naturally.  There was rarely ever total peace, not in our nature say the historians.  But it's all long gone now.

Slowly, imperceptibly at first, night began to fall across the universe.  Complete and total darkness, the end of all things.  Our own star (we knew it as Suryan) faded from glory long before I was born.  I've never known real daylight, never felt the warmth of the midday sunlight on my skin.  Growing up, we were all told the stories and legends of the light times, when Suryan made the sky glow from horizon to horizon and stars filled the sky when Suryan herself slipped below the edge of the world.

But all that has faded with the generations.  Long ago our star melted away into the darkness and we were left clinging to this rock, digging ever deeper into its crust just to reach the feeble warmth of the planet's ancient cooling core.  At least we had that, other colonies were not so lucky.  Those who had settled on artificial planets didn't last long when their stars faded, their power systems were never designed to cope with such extreme cold.  The cold metal constructions lost their heat quickly and their inhabitants (those unlucky enough not to make an escape on whatever ships they might have had) froze in a matter of months.  There are those who say that was a better way to go.

Suryan isn't completely dead of course, that takes billions of years.  When she ran out of material to fuse, her outer atmosphere expanded, reaching almost as far as our colony here on the fourth planet.  Protected under the colony's thick-walled domes, the inhabitants watched from safety as the star put on its last and greatest show.  While the core began to shrink, those burnt-orange layers continued to expand, becoming a fading wisp-like shell centred on the dying remains of what had once been a giant nuclear fusion reactor.  That remnant core still sits at the centre of this system like the last dying ember of a fire.  It still produces light and heat of course but not enough to be useful, not by a long way.

It's been some decades now since the last ship left this system.  When Suryan burnt its last, up there in the sky, there was widespread panic.  People were desperate to leave, to go somewhere else with a star that was still viable.  But there wasn't anywhere to go.  Slowly but surely, the stars were dying everywhere and there was no more gas left to create new ones.  These are the last days of the Universe, but people refused to believe it.  Somewhere there's another star, they said, somewhere.  The ships left, heading out towards whatever points of light they could see in the sky, and those who stayed behind attempted to carry on as normal.  We've known what was coming for generations but there was nothing we could do.  You either accept it and get on with life as best you can, or panic and most likely hasten your demise.  While we have no ships any more, nor the capabilities to construct any, we can still communicate with other colonies although that happens rarely these days.  There isn't anything left to communicate, and it uses power we can little afford to waste.

I often wonder what happened to those ships that left.  The records show that they kept in communication with the colony for some time after they set out, promising to return for survivors when they found a new home in the sunlight.  But then the logs stop.  When I was younger I assumed they just stopped transmitting, that they were saving energy or something.  But now, well, I've heard the stories from other colonies of madness and chaos and I wonder if the same fate befell those ships we dispersed into the night like seeds.

That's the problem with space flight of course.  It takes time.  Those ships leaving Suryan would each have headed towards a distant glimmer of light, some far-off star that hadn't yet reached the end of its days.  But in the mean time, the light from those little balls would have been travelling for centuries before it reached our system, if not longer.  What would happen to the crew if, after using all of the fuel they could spare to send them rushing onwards towards some distant star, keeping just enough to slow down again at their intended destination, they suddenly saw that their promised Eden was disappearing, fading away before their very eyes?  By that point there would be nothing they could do, no way of changing course without using up the precious fuel they would need in order to slow down once they reached somewhere habitable.  Game over.  What then?

I ask myself: what would I do in that situation?  It would be tempting to open an airlock, destroy the safety interlocks and just let everything be pulled out into the vacuum.  Not a pleasant way to go, certainly, but quicker than most options available on a tug.  We were never an exploration colony, merely a mining outpost, and those craft had never been designed for long-term use.  Your options were starvation (water was recycled, even on the tugs, so no problem there), carbon dioxide poisoning (the filters worked pretty well, but were usually replaced every couple of years), or some manner of your own choosing.  Most colonists would rather chose their way out rather than go slowly - we'd all seen it happen, read the case studies.  It was part of basic schooling on these outposts.  Harsh, may be, but the sooner you realised the realities of colony life the better.

So, here lies the remains of a once busy and reasonably prosperous colony.  Mirroring the downfall of the empire, it withered with the dying of the light.  There were those who refused to believe it would happen, others who proclaimed it as the ultimate test of faith in whatever deity they served, still others who maintained that we'd find a way out somehow.  But the truth was that we'd known for generations that this was coming.  Ways of restarting stars were proposed, but they all required more energy than the empire could spare, just for a single star.  Society crumbled, the trade routes grew silent, colonies began shutting off their contact with the outside world.  Where colonies were close enough, wars broke out.

The stars didn't all go out at once.  It takes time for a star to use up its fuel, and that depends on many things, but larger stars burn up faster.  Despite the dangers, the empire loved placing colonies around massive stars because they were the most profitable.  You could have several large artificial colonies around a massive star where they could harvest huge amounts of energy, and stellar mechanics was developed enough that the onset of a catastrophic supernova explosion, so characteristic of these massive stars, could be predicted to an accuracy of a few months.  Smaller stars like our Suryan were far more sedate.  Not massive enough to go supernova, they took many billions of years to use up their fuel.  While our colony was never rich, we lasted longer then many others simply because our star was a comparative weakling.

But even by the time this colony was founded, the universe was old.  Really, it was a wonder our species had lasted as long as it had without destroying itself from within.  Galaxies formed new stars at the rate of a few per standard solar year, but they have to come from something, you need gas to create them.  No more gas, no more stars.  We knew, as a species, that this was what would happen someday but, like countless cultures before us had done throughout history, we always assumed it would be far enough in the future that it would be someone else's problem.  For the most part that was right, but now we are that someone else, and we are scared.

Most of the colony, those who didn't leave in the tugs, have chosen to carry on as normal.  Each year we just dig a bit deeper towards the dying heart of the planet to keep the thermal plants supplied with enough energy from our world's cooling interior.  None of us alive now really knew Suryan as anything other than the dying ember that hangs in the sky today, so to us the sight is normal.  I once saw a holograph of an Earthscape - its open spaces and vivid blue sky were nauseating.  There were no stars in that picture either, apart from Sol of course, now long gone.

That's the difference.  Their sky was bright and harsh.  Ours is black and cold, as if oblivion had been given form.  I look out every day at that sky and my eyes wander, searching for the last faint pinpricks of light - something I know I'll never see again, now.  Last night, the last star in our sky faded forever.  We knew it had to happen sometime, but it was still something of a shock when it finally came.  None of us can claim to be astronomers, but we all knew the movements of that last star.  We watched it grow fainter and fainter, occasional bursts of light giving unwarranted hope of a reprieve.  Every one of those upward-gazing eyes knew what those fits meant, but still the soul hopes.... may be.

The last star.  The final vestiges of warmth are gone from the sky.  Those photons will continue on, travelling out into the darkness long after this little colony has gone.  For all we know, we may be the last, interstellar communication is a luxury that we can no longer afford.  But what's left now?  There will be no more stars, no more colonies, just endless darkness and cold like the long-dead surface of this planet.

There's still time for a walk before lights out.  I've never been outside the dome before, may be the air isn't as poisonous as they say.... I'm not afraid of the dark.

This is really going to happen, eventually. Galaxies only form stars from their own gas reservoirs, supplemented by the gas which falls onto them from their own halos, the surrounding intergalactic medium, or from galactic cannibalism where a merging galaxy provides a fresh injection of gas (often triggering a massive burst of star formation). Eventually though, this gas will run out and stars will stop forming, but not for billions of years. Stars will only shine while they have sufficient fuel in their cores for nuclear fusion to proceed; when that fuel runs out, the star dies. The ultimate fate of a star is determined by its mass, but they all stop shining eventually. The story above is based on the following paper by Braun et al. What Braun et al do in this paper is study a sample of particularly luminous galaxies known as ULIRGs, Ultra-Luminous InfraRed Galaxies, investigating their molecular gass mass. Studies of these galaxies can tell us about the evolution of molecular gass mass over time which can help in our understanding of the evolution of star formation rate density, both past and future. This particular sample is interesting because they sample a particular redshift range (0.2<z<0.5) where data is currently sparse. Coincidentally, I spotted the associated this press release from CSIRO a week after I wrote this story. You can find the paper here:

Braun, R., Popping, A., Brooks, K., & Combes, F. (2011). Molecular gas in intermediate-redshift ultraluminous infrared galaxies Monthly Notices of the Royal Astronomical Society, 416 (4), 2600-2606 DOI: 10.1111/j.1365-2966.2011.19212.x

Posted by Megan on Friday 23rd Sep 2011 (07:43 UTC) | Add a comment | Permalink

In the news this month: and finally, Allen telescope revived

The Allan Telescope Array
The Allen Telescope Array at Hat Creek Radio Observatory CREDIT: The SETI Institute

In 2007 the Allen Telescope Array began operations.  Designed and constructed to participate in both conventional radio astronomy studies and the Search for Extra-Terrestrial Intelligence, the array is jointly operated by the SETI Institute and the University of California.  One of the goals is to observe planetary systems detected by the Kepler mission, searching for possible signals.  However, in April 2011, funding shortfalls for operations of the Hat Creek Radio Observatory (HCRO) where the ATA is located resulted in the Allen Telescope Array being put into hibernation.  After launching the SETIstars campaign in June, an appeal to supporters to help raise the 200,000 dollars needed to get the telescope back online, thousands of people from around the world made donations and operations are due to restart in September.

This blog post is a news story from the Jodcast, aired in the September 2011 edition.

Posted by Megan on Wednesday 07th Sep 2011 (18:38 UTC) | Add a comment | Permalink

In the news this month: a planet darker than coal

Artists impression of the planet.
The distant exoplanet TrES-2b, shown here in an artists conception, is darker than the blackest coal. This Jupiter-sized world reflects less than one percent of the light that falls on it, making it blacker than any planet or moon in our solar system. Astronomers arent sure what vapors in the planets superheated atmosphere cloak it so effectively. CREDIT: David A. Aguilar (CfA)

Stars are bright because they generate heat and light through nuclear fusion processes in their cores, planets are visible because they reflect some of that light.  The percentage of light that is reflected, a quantity known as a planet's albedo, varies depending on the nature of the planet's surface and its atmosphere.  Jupiter, with its thick bands of highly reflective cloud, has an albedo of 52%, while the Earth's is somewhat lower, only reflecting around 37% of the sunlight which falls on the surface.  But now, a duo of astronomers have discovered a planet with an exceptionally low albedo, reflecting just 1% of its host star's light, making it less reflective than coal.

The planet, discovered by the Trans-Atlantic Exoplanet Survey, is known as TrES-2b and lies about 750 light years away in the constellation of Draco.  David Kipping (of the Harvard-Smithsonian Center for Astrophysics) and David Spiegel (of Princeton University) used data from the Kepler space telescope to investigate the planet's nature.  To calculate its albedo, the astronomers measured its brightness at two different points in its orbit around the host star, once when it was located directly between us and the star, and again when it was on the far side, just before it went into eclipse.  The difference between the two measurements is therefore the difference in brightness between the day and night sides of the planet, and tells us how much of the star's light is reflected by the surface of TrES-2b.

The planet orbits its star at a distance of just five million kilometres, far closer than Mercury is to the Sun.  Mercury is a dense rocky planet with a large iron core and a rocky, silicate surface which has an albedo of 12%.  Surface temperatures on the closest planet to the Sun range between 90 and 700 degrees Kelvin.  In contrast, TrES-2b, an exoplanet in the category of "hot-Jupiters" shows brightness variations of just 6.5 parts per million, corresponding to an albedo of less than 1%.  But, this assumes that the only cause of the brightness variations is due to the geometry of the planet.  The authors calculate that there is significant emission coming from the day side of the planet.  Its proximity to its host star means that its surface temperature is likely to be around 1000 degrees and any atmosphere it has will likely be composed of chemicals such as vaporised sodium and potassium, or gaseous titanium oxide.  Such a hot temperature also means that the planet actually emits some of its own light, possibly glowing dimly red like an electric bar heater.

The Kepler satellite is designed to search for planets using the transit technique, observing one densely-packed star field for its entire operational lifetime, searching for the tiny fluctuations in brightness of a star due to a transiting planet. The exceptional sensitivity of Kepler's instruments has led to this particular discovery in just four months of data acquisition.  In their paper, accepted for publication in the Monthly Notices of the Royal Astronomical Society, the researchers suggest that, over six years of continuous observation, the telescope may be capable of detecting planets with albedos as low as 0.1%.

This blog post is a news story from the Jodcast, aired in the September 2011 edition.

David M. Kipping, & David S. Spiegel (2011). Detection of visible light from the darkest world Monthly Notices of the Royal Astronomical Society arXiv: 1108.2297v2

Posted by Megan on Wednesday 07th Sep 2011 (18:21 UTC) | Add a comment | Permalink

In the news this month: discovery of antimatter in the Earth's Van Allen belts

Simulated Van Allen belts.
Simulated Van Allen Belts generated by plasma thruster in 1966 in tank #5 Electric Propulsion Laboratory at the Lewis Research Center, Cleveland Ohio, now John H. Glenn Research Center at Lewis Field. CREDIT: NASA-HQ-GRIN
Antimatter is often thought of as something that is only created in particle accelerators (or that only exists in science fiction movies), but it is actually present in small quantities throughout the universe.  Now, a team of researchers have detected the presence of naturally occurring antimatter right here in the neighbourhood of the Earth.  This population of antiparticles originates from cosmic ray interactions in the Earth's upper atmosphere where they are subsequently trapped in the planet's magnetosphere.

Anti-protons can be produced in a number of ways, through cosmic rays interacting with the interstellar medium, the natural decay processes of some types of particles from our own atmosphere, or in cosmic ray air showers from high energy particles impacting on the atmosphere, although most of the antiparticles would annihilate with their normal counterparts fairly quickly, especially at lower altitudes where the density of the atmosphere is higher.

The existence of anti-protons around the Earth was predicted many years ago, but predictions differ, and experiments on board both Salyut-7 and the Mir Space Station only succeeded in placing upper limits on their abundance.  The anti-protons found by the PAMELA satellite (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) are located in the Earth's Van Allen belts, doughnut-shaped regions defined by the magnetic field of the Earth.  The magnetic fields trap charged particles, resulting in regions with a relatively high density of positively charged protons, and others with a high density of anti-protons.

Launched from the Baikonur Cosmodrome in 2006, PAMELA is designed to detect cosmic particles with energies between tens of mega electron Volts and hundreds of giga electron Volts. PAMELA's orbit takes it through the area known as the South Atlantic Anomaly, the region where the Van Allen belts pass closest to the Earth's surface.  Since it began operations in 2006, PAMELA has detected anti-protons at a rate more than 1000 times higher than that expected from Galactic sources.  The researchers say that this implies a belt of anti-protons located between two belts of ordinary matter in the Earth's Van Allen belts.

The signal detected by PAMELA is ten thousand times times stronger inside the South Atlantic Anomaly than it is outside the Earth's radiation belts, and thousands of times stronger than that expected from Galactic cosmic rays.  The likely explanation, say the researchers, is that the Earth's Van Allen belts are acting in the same way as they trap protons, trapping the anti-protons in a layer around the Earth (at least until they encounter a particle of normal matter and annihilate).

Although antimatter is pretty destructive stuff if it comes into contact with ordinary matter, luckily for orbiting spacecraft there isn't that much of it.  In 850 days of data acquisition, PAMELA's detectors collected just 28 anti-protons in the previously unknown antimatter region of the inner Van Allen belts.

This blog post is a news story from the Jodcast, aired in the September 2011 edition.

O. Adriani, G. C. Barbarino, G. A. Bazilevskaya, R. Bellotti, M. Boezio, E. A. Bogomolov, M. Bongi, V. Bonvicini, S. Borisov, S. Bottai, A. Bruno, F. Cafagna, D. Campana, R. Carbone, P. Carlson, M. Casolino, G. Castellini, L. Consiglio, M. P. De Pascale, C. De Santis, N. De Simone, V. Di Felice, A. M. Galper, W. Gillard, L. Grishantseva, G. Jerse, A. V. Karelin, M. D. Kheymits, S. V. Koldashov, S. Y. Krutkov, A. N. Kvashnin, A. Leonov, V. Malakhov, L. Marcelli, A. G. Mayorov, W. Menn, V. V. Mikhailov, E. Mocchiutti, A. Monaco, N. Mori, N. Nikonov, G. Osteria, F. Palma, P. Papini, M. Pearce, P. Picozza, C. Pizzolotto, M. Ricci, S. B. Ricciarini, L. Rossetto, R. Sarkar, M. Simon, R. Sparvoli, P. Spillantini, Y. I. Stozhkov, A. Vacchi, E. Vannuccini, G. Vasilyev, S. A. Voronov, Y. T. Yurkin, J. Wu, G. Zampa, N. Zampa, & V. G. Zverev (2011). The discovery of geomagnetically trapped cosmic ray antiprotons ApJ, 737, L29, 2011 arXiv: 1107.4882v1

Posted by Megan on Wednesday 07th Sep 2011 (17:58 UTC) | Add a comment | Permalink

In the news this month: supernova spotted in the Pinwheel galaxy

The first three nights of observing the supernova show how it brightens very rapidly.
Supernova PTF11kly in M101: the first three nights of observing the supernova show how it brightens very rapidly. CREDIT: Peter Nugent and the PTF collaboration

August 24th saw the discovery of one of the closest supernovae of its kind in recent years.  Located in the nearby spiral galaxy M101, the explosion was reported by the Palomar Transient Factory (PTF), a survey of the sky which aims to detect and catalogue transients using two telescopes at the Palomar Observatory in California.  Catalogued by the PTF collaboration as PTF11kly, the position of the supernova was distributed rapidly through the Astronomers Telegrams, allowing follow-up by other astronomers using a variety of telescopes across the electromagnetic spectrum.

With transient events like supernovae, such rapid follow-up with other telescopes is extremely useful in trying to understand the physics of what happens in the explosion.  Comparatively little is known about the first few hours to days of supernova evolution since they are often discovered days (and sometimes weeks) after the initial explosion.

In the case of PTF11kly, also catalogued as SN2011fe, the event was spotted very early in its evolution, as the brightness was still increasing, and spectroscopic observations by the Liverpool Telescope in the Canary Islands quickly showed that this particular event was of the class known as type Ia supernovae.  This kind of event is thought to be caused by a thermonuclear explosion on the surface of a white dwarf star in a binary system, although there are variations in the theoretical models which detailed observations could help to resolve.  This particular supernova is the closest example of a type Ia event in almost forty years.  This is significant because it is this type of supernova which is used to measure the expansion of the universe, so having a good understanding of the underlying physics of these explosions is essential for cosmological studies.

Since it was discovered so early in its evolution, PTF11kly should continue to brighten over the next few days before it begins to fade.  At discovery, the object had a magnitude of 17 but was brightening rapidly.  Located in M101, the Pinwheel galaxy in Ursa Major, it is estimated that the supernova could become bright enough to spot with binoculars or a small telescope.  In contrast, observations carried out with the Very Large Array, a collection of 27 radio telescopes located in New Mexico, show no radio emission from this supernova.  This is not surprising, as so far no type Ia supernova has ever been spotted by radio telescopes, despite numerous searches.

Telescopes of various types will continue to monitor this supernova as it evolves over the following months, and astronomers will use the data collected to test various aspects of the physics and chemistry of supernova models.

This blog post is a news story from the Jodcast, aired in the September 2011 edition.

Posted by Megan on Wednesday 07th Sep 2011 (17:34 UTC) | Add a comment | Permalink

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