It was a pleasant Summer's night. It was mild and clear, with enough Moonlight to see my hill field's dry-stone walls. But, that made it a Hunters' Night.

I huddled under my cape in the stock enclosure's guard niche. Behind me, the llamas, sheep and small cattle huddled together. I kept flexing my grip on my staff lest I cramp.

I'd seen 'Big Puss', one of our barn cats, patrol the field wall's line about an hour earlier. An inky swirl of motion, a bitten off yelp suggested Puss and her weaned kitties would eat well tonight. A minor predator, she was safely gone before any Heavies could arrive.

First up was the wicked wedge of a male Great Fox. His red eyes scanned my field from the wall's stile notch. He focussed on this enclosure. Surely he could not see me, but the wind blew that way.

Great Uncle Tam had taught that foxes were clever, but only took the lame, lambs and carrion. This, though, was a Fall Beast. No calf or young sheep was safe until yearling. And, even then, a Great Fox was so clever...

That canny stare reckoned me too great a threat for now. With a swirl, he was gone. Too swiftly, perhaps ?

Yes, the new spread of eyes, the size of head warned of a 'Lone Wolf'. Tam called this grim Fall Beast a 'Dire Wolf'. At least, as yet, they ran alone. And, after tallying the odds, this male followed the Great Fox into the night.

The Moon and its bee-swarm of Fall Rocks moved a quarter hour-- I could almost hear Tam's sigh, see his head shake. Yes, yes, our round Earth turned beneath the slower Moon, whose pace set Neaps and Springs in the harbour...

More eyes at the stile ? Two big ? Four small ? Green ? Slits ? These were the local Mountain Leopard and her yearling cubs. Though not Fall Beasts, perhaps even kin to our big barn cats, their like had thrived in the Fall Time. Their keen noses tested the stile for its visitors, decided this place was not for them.

The Moon angle gradually shifted. The greatest of those circling Fall Rocks passed across the freshly scarred Face. Then, the small noises of the night fell quiet. Suddenly, the top of the field wall bore humps, humps with eyes. The wolf on the stile was big, very big. I counted six or seven looking over the wall. There would be as many juniors or whelps in the wall's lee.

I gulped. Our small Clan would have to track this big pack, smoke and wall their den. Of course, I must first live to bear witness.

I took a slow, deep breath as that 'death tide' flowed over the wall. They knew I was here. They knew I was alone. They knew there was an 'all you can eat' feast to be had. I rose from my niche, crouched in the enclosure's entrance and, pointing my staff towards the wolves, set its shod heel against the front face of the threshold slab. Behind me, this field's live-stock bunched up. If I failed, there would be terrible slaughter. Yes, a few junior wolves, even a lower male or female might be trampled or gored, but my morning relief would find only bloody bones.

It had happened before, it would happen again.

The pack halted half way from the wall. That was but a few swift heart-beats should they attack. Their next step was simple, cruel. Starting with the Alpha Male, they focussed on me, tried to stare me down. Any wolf was frightening, a dozen by Moonlight froze my marrow. Yet, there was more, perhaps gained during the terrible Fall Time. Shepherds had been found, unmarked, their minds broken to babes. Such slowly taught that the simple, weak-minded or ignorant among us must not stand guard on a Hunter's Night.

I could Scribe. I could Tally. I could recount the terrible Fall Time tales and our small Clan's short, proud line. Thus, I endured.

When their combined stares failed, the Alpha Male took a step forwards. I twice rapped my staff's shod heel against the  threshold slab.

Snick-snick ? A long shape aimed ? A doubled metal sound ?

Did I have a Gun ? I'd given the Alpha Male a pretty problem.

Wounded, he would have to fight upstarts while weakened. He might lose his Pack status. He might lose his life. On a long chase, others could take the lead by turn. Here, he must lead. For better or worse, he must 'Stick or Twist'.

For long, long seconds, the Alpha Male re-tallied his counters. My respite could not last. Nor did it, for the wind shifted. Perhaps he smelled the animals behind me afresh ?  Perhaps he smelled their fear ? Perhaps he was too hungry to delay further ?

He launched.

When no Gun fired on his first stride, he surely thought himself safe. He was not far wrong. I had one chance. Just one. I placed my right foot on top of my staff's heel, tallied the distance.

Three strides.

Two strides.

Now ! I rose from my crouch, guided the staff's shank tip into the great wolf's upper chest.

The shock would have thrown me down but for the planted heel. As it was, my stout staff bowed, bowed. If it broke, I died.

The staff straightened, dumped the wolf in a heap. I let go of the staff, dived forwards, drawing the curved 'wolfbane' knife from my cross-belt. The heavy blade was not great metal, but it was crafted for this task. It bore a keen, keen edge. My strong slash across the Alpha Male's exposed throat sprayed hot blood everywhere.

As I clambered to my feet, the other wolves stood uncertainly. I'd killed their Alpha Male, and that changed everything. Their Pack order lay in ruins. The Alpha Female must defend her pups against her rivals, then against the new Alpha Male when he emerged from tonight's ruck. Already there was shifting, growling and snarling in the ranks.

I eased the hand-span spike from the dead wolf, repositioned my staff, again twice rapped the heel on the threshold slab.

Snick-snick !

Who's next ?

The stink of spilled wolf blood surely drowned the smell of our livestock. If the Alpha Male had a Lieutenant, this was his time to strike. But, no. Un-nerved, the Alpha Female turned away. The humbled pack filed back over the stile, faded into the night.

I allowed myself the smallest, blood-spattered grin. Hunting, only the Alpha Male would scent mark, and only on special places. Slinking home, their Pack order broken, every contender would mark everywhere. Our Clan's hunting dogs would track them with ease. Their lair destroyed, survivors driven into the hills, we would have peace until the boundaries settled.

Tonight, with the reek of hot wolf blood on me, no other Night Hunter would dare approach. This carcass was mine, mine, mine. I'd give skull and paws to the Clan Tally-man, who'd trade them to the coast for fish, plus more 'rebar' to arm our shepherds' staffs. I'd thread the lumpy spine bones as babies' rattles. I'd throw the big bones to the Clan's dogs. I'd give the smaller bones as play-things to our Bairns and our barn cats.

Best of all, this Winter, I would have a wolf-skin coat beneath my much-patched cape...

A close call of 0.8 light years

17 February 2015

This is an artist's conception of Scholz's star and its brown dwarf companion (foreground) during its flyby of the solar system 70,000 years ago. The Sun (left, background) would have appeared as a brilliant star. The pair is now about 20 light years away. Credit: Michael Osadciw/University of Rochester

A group of astronomers from the US, Europe, Chile and South Africa have determined that 70,000 years ago a recently discovered dim star is likely to have passed through the solar system's distant cloud of comets, the Oort Cloud. No other star is known to have ever approached our solar system this close - five times closer than the current closest star, Proxima Centauri.

In a paper published in Astrophysical Journal Letters, lead author Eric Mamajek from the University of Rochester and his collaborators analyzed the velocity and trajectory of a low-mass star system nicknamed "Scholz's star."

The star's trajectory suggests that 70,000 years ago it passed roughly 52,000 astronomical units away (or about 0.8 light years, which equals 8 trillion kilometers, or 5 trillion miles). This is astronomically close; our closest neighbor star Proxima Centauri is 4.2 light years distant. In fact, the astronomers explain in the paper that they are 98% certain that it went through what is known as the "outer Oort Cloud" - a region at the edge of the
solar system filled with trillions of comets a mile or more across that are thought to give rise to long term comets orbiting the Sun after their orbits are perturbed.

The star originally caught Mamajek's attention during a discussion with co-author Valentin D. Ivanov, from the European Southern Observatory. Scholz's star had an unusual mix of characteristics: despite being fairly close ("only" 20 light years away), it showed very slow tangential motion, that is, motion across the sky. The radial velocity measurements taken by Ivanov and collaborators, however, showed the star moving almost directly away from the solar system at considerable speed.

"Most stars this nearby show much larger tangential motion," says Mamajek, associate professor of physics and astronomy at the University of Rochester. "The small tangential motion and proximity initially indicated that the star was most likely either moving towards a future close encounter with the solar system, or it had 'recently' come close to the solar system and was moving away. Sure enough, the radial velocity measurements were consistent with it running away from the Sun's vicinity - and we realized it must have had a close flyby in the past."

To work out its trajectory the astronomers needed both pieces of data, the tangential velocity and the radial velocity. Ivanov and collaborators had characterized the recently discovered star through measuring its spectrum and radial velocity via Doppler shift. These measurements were carried out using spectrographs on large telescopes in both South Africa and Chile: the Southern African Large Telescope (SALT) and the Magellan telescope at Las Campanas Observatory, respectively.

Once the researchers pieced together all the information they figured out that Scholz's star was moving away from our solar system and traced it back in time to its position 70,000 years ago, when their models indicated it came closest to our Sun.

 1 / 3
 Until now, the top candidate for the closest known flyby of a star to the solar system was the so-called "rogue star" HIP 85605, which was predicted to come close to our solar system in 240,000 to 470,000 years from now. However, Mamajek and his collaborators have also demonstrated that the original distance to HIP 85605 was likely underestimated by a factor of ten. At its more likely distance - about 200 light years - HIP 85605's newly calculated trajectory would not bring it within the Oort Cloud.

Mamajek worked with former University of Rochester undergraduate Scott Barenfeld (now a graduate student at Caltech) to simulate 10,000 orbits for the star, taking into account the star's position, distance, and velocity, the Milky Way galaxy's gravitational field, and the statistical uncertainties in all of these measurements. Of those 10,000 simulations, 98% of the simulations showed the star passing through the outer Oort cloud, but fortunately only one of the simulations brought the star within the inner Oort cloud, which could trigger so-called "comet showers."

While the close flyby of Scholz's star likely had little impact on the Oort Cloud, Mamajek points out that "other dynamically important Oort Cloud perturbers may be lurking among nearby stars." The recently launched European Space Agency Gaia satellite is expected to map out the distances and measure the velocities of a billion stars. With the Gaia data, astronomers will be able to tell which other stars may have had a close encounter with us in the past or will in the distant future.

Currently, Scholz's star is a small, dim red dwarf in the constellation of Monoceros, about 20 light years away. However, at the closest point in its flyby of the solar system, Scholz's star would have been a 10th magnitude star - about 50 times fainter than can normally be seen with the naked eye at night. It is magnetically active, however, which can cause stars to "flare" and briefly become thousands of times brighter. So it is possible that Scholz's star may have been visible to the naked eye by our ancestors 70,000 years ago for minutes or hours at a time during rare flaring events. The star is part of a binary star system: a low-mass red dwarf star (with mass about 8% that of the Sun) and a "brown dwarf" companion (with mass about 6% that of the Sun). Brown dwarfs are considered "failed stars;" their masses are too low to fuse hydrogen in their cores like a "star," but they are still much more massive than gas giant planets like Jupiter.

The formal designation of the star is "WISE J072003.20-084651.2," however it has been nicknamed "Scholz's star" to honor its discoverer astronomer Ralf-Dieter Scholz of the Leibniz-Institut für Astrophysik Potsdam (AIP) in Germany - who first reported the discovery of the dim nearby star in late 2013. The "WISE" part of the designation refers to NASA's Wide-field Infrared Survey Explorer (WISE) mission, which mapped the entire sky in infrared light in 2010 and 2011, and the "Jnumber" part of the designation refers to the star's celestial coordinates.

 More information: Astrophysical Journal Letters, iopscience.iop.org/2041-8205/800/1/L17
Provided by University of Rochester

 2 / 3
APA citation: A close call of 0.8 light years (2015, February 17) retrieved 30 April 2015 from
http://phys.org/news/2015-02-years.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.