StarNews — June 2024

Avoidance Behavior

On any clear summer night, we can look up and see a beautiful array of stars scattered across the sky. The heavens seem dense with cosmic matter. 

Astronomical study over the past decades has dramatically altered our view of space. We now realize that large parts of space consist mostly of …space: or as we now call it: “voids.” These voids are enormous, encompassing areas of space that are millions of light years across. Matter, as distributed in the form of galaxies and gases, is distributed around the edges of these voids. In a recent Scientific American article, scientists, such as Alice Pisani (Flatiron Institute, NY) and Benjamin Wandel (LaGrange Institute, Paris) present a view that space more vast than we ever could imagine. 

The older image of a homogeneous uniform distribution of matter, such as that projected by the Cosmic Microwave Background, (think “cream cheese”) has been replaced by an image of a largely nonhomogeneous distribution of matter, in the form of galactic strands surrounding vast volumes of “empty” space (think “swiss cheese”).

Getting these 3-dimensional perspectives requires mountains of data points. So it should not be surprising that the improved analyses of voids could only have occurred with the more recent advances in AI and machine learning. By contrast, Johannes Kepler worked 20 years with pen and paper just to realize that planetary orbits are elliptical, not circular.

Getting more accurate volume measures of these vast volumes is tricky. Specifically, line-of-sight redshift values of z give a distorted measure of the length of a void. Dopplering values of z are a distance benchmark for much of astronomy: the higher the z, the further the distance. But the universe is expanding at an accelerating rate. So comparing z values at the closest edge to z values at the farthest edge of the void distorts the measured length because the accelerations at both ends are different. 

How did the universe get to look like this? The most preferred theory is that dark energy is involved. It is thought that the higher density of matter in galaxy clusters shrouds the effect of dark energy. The vast volume of low-density space in voids allows the effects of dark energy to be more manifest: an energy that propels strands of galaxy clusters to accelerate farther and farther apart. 

The studies surrounding voids (their origins, effects, and future) are complex. This PBS video hosted by Matt O’Dowd (Lehman College) provides a useful overview of this topic.

Gummy Bears

As we all know, unprotected human exposure to space would be instantly fatal. Yet, there are, in fact, animals that can survive considerable time in space. They are called tardigrades.

Also known as “water bears” due to their resemblance to bears, the existence of tardigrades has been known for centuries. These 0.5-millimeter creatures are readily available for microscopic study. There are 1500 known species and they are ubiquitous around the world. Their ability to survive extreme conditions is what makes them so attractive for research in space studies. Reviews, such as this paper coming out of Poland, confirm the value of studying their biology. 

A recent study unravels part of the mystery of how these critters can survive such extreme environments. Tardigrades are experts at quickly entering what is known as a tun state: an extreme version of hibernation.

Smythers, et al., induced tun by subjecting tardigrades to metabolic toxins thereby leading to metabolic stasis (chemobiosis). What they discovered was a particular chemical reaction underlying this rapid process. 

In humans, free radicals, or what chemists call Reactive Oxygen Species, are considered dangerous and usually indicative of cancers or other dangerous diseases. In tardigrades, these radicals react chemically with the most unstable of the stable amino acids: cysteine. It appears that this highly reactive chemical process initiates rapid alteration of tardigrade metabolism. They shrink rapidly into small balls and maintain the barest of metabolic activity. Apparently, it is a reversible process. Once the extreme conditions are removed, tardigrades can recover and go on as if nothing had occurred. The process borders on science fiction, yet it is real and replicable. It offers a glimmer of possibilities of how humans can survive the rigors of space travel.

Ménage à Trois

In this Stormy Daniels-era of lurid misinformation concerning two bodies, it is a relief to know that there are lots of people focusing on even more intractable problems involving three bodies. This, of course, concerns the gravitational dynamics between three bodies: think the Earth, Jupiter, and the Sun. Each gravitationally affects the other two in ways that are too complex to unravel. 

The phrase, Three Body Problem, happens to also be the title of a series introduced by Netflix. The series is based on the science fiction trilogy written by Liu Cixin. Set against the backdrop of China’s Cultural Revolution, it is a tale of war in which our poor little Earth, so innocent, frail and peace loving (sic.), is threatened by an invading interstellar army. The actual problem, however, is more likely to induce a headache than aggression. 

Because the gravitational interactions between three moving objects is so complex it would seem that such a system was inherently unstable leading to chaos. But empirically we know that such systems remain stable. Centuries worth of mathematicians and astronomers have established that there is no closed set of equations that can solve this problem.

Finding solutions to this problem would be a great boon to astronomy, especially given the fact that most star systems are binary. Additionally, such solutions would improve navigation in space voyages, maximizing energy drawn from gravity, rather than fuel on board. 

Earlier mathematicians such as Laplace, Euler, Lagrange, and Poincare (paper and pencil efforts) grappled with these issues by restricting certain initial conditions: including adherence to basic principles of physics. But, from observing thousands of exoplanetary systems it is clear that these restrictions limit our ability to effectively analyze these systems.

Enter the supercomputer. Ivan Hristov, Radoslava Hristova, Veljko Dmitrašinović, Kiyotaka Tanikawa using such a supercomputer were able to generate 12,000 possible solutions to this conundrum. This number may appear too large for us to manage. But employing AI or machine learning may reduce that number to one that allows astronomers to find solutions that have the highest probability of being useful. As space travel becomes more prevalent it becomes imperative for navigators to apply the principle of least action (using the least energy to travel the furthest distance) This can only be accomplished once the best scenarios to the three-body problem have been identified. Whether this “finale” is more exciting than the Netflix series remains to be seen.