The Profane Dog

Palomar 5 Globular Cluster

Globular clusters are relatively dense groups of stars that are typically at least 12 billion years old. They formed with the Milky Way but often orbit not in the main plane of the galaxy, where the Sun and most other stars reside, but in a vast and sparsely populated halo that surrounds the entire galaxy.

The newly studied cluster, called Palomar 5, is now calculated by the researchers to be at the furthest point in its orbit, high above the plane of the galaxy and 75,000 light-years from Earth. Its streams span more than 13,000 light-years in space. On the sky as seen from Earth, the structure occupies the space of 20 full moons. In about 100 million years it will plunge down through the galactic plane.

Meanwhile, the cluster is being torn apart by a process similar to what generates ocean tides on Earth, Odenkirchen explained. The Moon pulls the Earth more on the near side than the far side, but centrifugal force creates a bulge in the oceans on both sides of the planet.

Stars from Palomar 5 undergo similar tidal forces, Odenkirchen said, due to the relatively tremendous mass that exists at the center of the Milky Way. Stars on the near side of the cluster are pulled slightly closer to the center of the galaxy. They then have slightly less far to go to make their orbit around the galactic center, so they move ahead of the rest of the cluster.

Stars on the far side of the cluster are pulled away from the galactic center. Forced to trace a longer orbit around the galaxy, they then lag other stars on the cluster, creating a trailing stream.

Odenkirchen said the patchy nature of the two star streams indicate that the tidal disruptions must have been episodic in the past, rather than continuous. He said the data, collected as part of the Sloan Digital Sky Survey, represents the first observational proof that globular clusters are in fact torn apart in this manner, as astronomers had suspected.

The Milky Way is also known to disrupt other galaxies, called dwarf galaxies, generating similar star streams as a smaller galaxy -- which originated somewhere else -- is swallowed whole.

Eventually, studies of Palomar 5 and other globular clusters being torn apart should help astronomers improve estimates of unseen "dark matter" that is known to make up a healthy percentage of the Milky Way's mass budget, the researchers said.

Source; Eva Grabel and Michael Odenkirchen, Max Planck Institute for Astronomy, in a report to the 200th Meeting of the American Astronomical Society, 03 June, 2002.

Noto bene: This record is from extremely ancient archives, some of the oldest in the Empire; their authenticity is dubious. Many of the oldest archives were lost or deliberately altered during the Time of Troubles. Be wary of arcane referrences; at no other point in the records is there any mention of the 'American Astronomical Society,' if indeed it existed at all.

The Space Ark Sleipnir

The Space Ark Sleipnir carried mostly evacuees from the Scandinavian nations of Denmark, Sweden, Norway, and Iceland; thus its name (Sleipnir was the eight-legged mount of Odin, the chief god of the ancient Norse pantheon). It carried a crew of 100, and a human cargo of 200,000 passengers, the last of whom entered their cold-sleep capsules in late 2104 A. D. (Old Reckoning; see conversion tables in the Appendices).

The Sleipnir's first destination upon departure from Earth was the double-star system of Procyon. The system has no planets, it was not the ship's ultimate destination. Procyon B, however, is a white dwarf, a dead star of extremely compact mass and high gravity. The ship was to pass within a few thousand kloms of Procyon B, in a gravity whip manuver that would increase its velocity dramatically with no comcomitant expenditure of fuel (always in short supply on the Arks). With careful use of directional thrusters, the Sleipnir would emerge from the manuver on a proper course for its destination of the Rigel system, moving at a signifigant fraction of lightspeed.

Astrogation, however, was in its infancy in those days; there was an unknown third companion in the Procyon system, a neutron star which travelled a wildly erratic orbit. For most of its orbit, it was further from its system than the Oort Cloud is from Old Sol. It was the Sleipnir's misfortune to arrive in-system when the neutron star was at perigee. Rather than the planned close approach to Procyon B, the ship encountered the fierce tidal pull of the neutron star. The crew, through prodigies of exertion and valor, managed to avoid impacting the neutron star, but the ship passed less than 10 kloms above its surface. Its trajectory was altered by only a few degrees of arc, but this was enough to send it hurtling at 30% of lightspeed above the galactic plane. They were gradually moving further and further off into intergalactic space.

After a period of despair, during which time almost a dozen crewmembers took their own lives, Assistant Astrogator Lars Herulfsson discovered the one chance they had to avoid becoming the fastest tomb ever launched by humanity; a small remnant of the Palomar 5 Globular Cluster (small by astronomical standards - upon arrival, they found that it contained more than 5000 stars), that over time had been drawn further in towards the ecliptic. It lay close enough to their computed trajectory to be reached by using their directional thrusters to alter their course enough to intersect the Cluster. It would require the expenditure of every last iota of their remaining fuel. After a long, fierce, and bitter debate, this plan was adopted.

The course-altering manuver was performed, and the crew settled down to routine maintenance tasks. At their present speed, they would reach the cluster remnant (hopefully renamed Yggdrasil, the great tree which contained all the worlds of ancient Norse mythology) in 150 years.

Time passed; the original crew aged and, one by one, retired to their cold-sleep capsules, replaced at their positions by their children. These too, grew old, and went to their frozen rest, while a third generation assumed the duties of maintaining the ship and its human cargo.

When the ship finally arrived at the outskirts of the Yggdrasil Cluster, frantic calculations were performed to determine the precise order of stars they must use in their gravitational braking manuver (their only hope of shedding their frightful velocity, and the exact opposite of the gravitational whip which had launched them on their journey). At last, they were able to calculate that by passing through the exosphere of a red giant star on the very borders of the Cluster, they would be able to scoop enough hydrogen from its outer layers to provide them with sufficient fuel for manuvering purposes. This was vital, as they could not be certain that they could alter their trajectory enough to achieve the series of stellar encounters they would need to finally come to rest, by the braking manuver alone.

Finally, after a series of nerve-wracking close stellar encounters, during which the crew suffered terribly from exhaustion, sleep deprivation, and mental fatigue, the Sleipnir lost all of her excess velocity. The crew were able to manuver her at normal speeds, and came to a unanimous decision to search for a habitable planet within the Cluster itself, rather than try to fulfill their original mission to reach the Rigel system.

Luckily, they found the Cluster abrim with planets; most of them were uninhabitable, requiring extensive terraforming to allow Earthlife to achieve a toehold, but they found enough gas giants to allow them to replenish their fuel as needed.

After a search of several years, they found a planet circling a G-type star at the limits of viability, with the basic requirement they needed; a reducing nitrogen-oxygen atmosphere. The planet was slightly larger than Earth, with approximately 75% of its surface area covered by ocean. There was one major landmass, extending southwards from the northern polar regions. Several small island chains dotted the equatorial seas, but the southern hemisphere, aside from the ice-covered polar region, was almost completely landless. The planet must have recently undergone a period of extensive, world-wide tectonic activity, for there were tall, sharp-peaked mountain ranges all through the northern continent, and even the island chains were mountainous.

The new world was generally somewhat colder than Earth, due to its orbit being somewhat larger than that of the Homeworld, and the sun (named Skinfaxi, after the bright horse that drew the chariot of Day) cooler and dimmer than Old Sol. Also the axial tilt was more extreme. Therefore, the seasons were longer, with winter starting earlier and lasting longer in the northern latitudes.

Due to the planets frigid, mountainous nature, and in keeping with their tradition of Norse mythological nomenclature, they named it Jotunheim.