George Takei just shared this wonderful video on Facebook. It tells a story told by Ronald E. McNair’s brother about an incident that happened in their childhood. Ronald E, McNair later became a physicist and astronaut. He was selected for the astronaut program in 1978 and later flew on the Challenger mission STS-41-B in February 1984. He was later selected for the ill-fated Challenger mission STS-51-L of January 1986 in which all crew died 73 seconds after liftoff.
The video is made by a group called ‘Storycorps’.
2.25 billion light years away lies Galaxy Cluster Abell 1689, a region of the universe thick with dark matter. Each dot and swirl you see in this image is not a star, but a galaxy, 100 billion stars each.
What is so special about this far away cluster is the amount of globular clusters surrounding these galaxies. Globular clusters are old stars that orbit outside the main region of a galaxy and are thought to be leftovers from galaxy formation. The Milky Way is thought to have about 150 of these regions, but Abell is thought to have 160,000. Why is a good question and it seems to be linked to dark matter. According to NASA:
“The research team found that the globular clusters are intimately intertwined with dark matter. “In our study of Abell 1689, we show how the relationship between globular clusters and dark matter depends on the distance from the galaxy cluster’s center,” explained team member Karla Alamo-Martinez of the Center for Radio Astronomy and Astrophysics of the National Autonomous University of Mexico in Morelia. “In other words, if you know how many globular clusters are within a certain distance, we can give you an estimate of the amount of dark matter.”
From Hubblesite and io9
So yet again comes the news that Voyager has left the Solar System. But this time it’s a bit more reassuring as it comes from NASA itself.
But you could not be faulted for believing over the last couple of years that:
- Voyager is lost and too masculine to ask for directions.
- The edge of the solar system consists of a series of alternating stripes of Solar System and Non-Solar System.
- Spacetime is curved.to a massive degree.
- No one has any fucking idea where the Solar System starts and when it ends.
The last one is the closest. It seems that there are differing definitions upon what should constitute the edge of the solar system and these guesses end up being not so easy to be defined and measured.
I guess it’s kind of like saying “Today a certain molecule of water passed from the Indian Ocean to the Atlantic Ocean”. Sure these oceans have their own currents, differing salinity levels, temperatures, etc so how would you define an edge between them both? Say there was a major difference in salinities, where would you define the boundary? The average value of salinity content between the two? Sounds like a great idea but this will not give one definite line (an isosaline?) between Africa and Antarctica.
Back to space and we start defining regions by the density of ions, plasmas and the presence of magnetic fields. The main area around the Solar System is defined as the heliosphere, where the Sun’s magnetic influence is strong and the area is streamed with charged ions from the sun.
Beyond the heliosphere is interstellar space, where the suns magnetic and ion influence drops almost altogether, and a high concentration of interstellar plasma takes over. The transition happens over a wide concentration gradient called the heliopause.
Looking back upon readings from August, NASA confirms a change in magnetic influence on the craft and a much greater concentration of plasma in the surroundings. I guess that NASA has made the calling that Voyager is in the latter of the heliopause if not in interstellar space. It just goes to show, definitions are hard to make.