Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Friday, February 3, 2023

A rare firecracker

A layperson might be excused if looking up at the night sky, (s)he concluded that other than slight variations in color and brightness, one star is pretty much like another.

I can't deny they look that way.  Even with the best telescope available to amateur astronomers, stars are featureless points of light.  About all we earthbound amateurs could discern that might clue us in to stars' wide variety of features, compositions, and behaviors is that some (many of them, in fact) are in binary or multiple star systems, and that a few fluctuate in brightness at regular intervals.  (Variable stars, in fact, were known to the ancients, and because in general our ancestors felt that the heavens should be eternal and changeless, they were viewed with great suspicion; one of the best-known, in fact, is Algol, which comes from the Arabic words for "the ghoul's head.")

First with the Hubble Space Telescope, and now with the James Webb Space Telescope, we've finally gotten the first direct photographs of stars showing any kind of detail (and the first direct photographs of exoplanetary systems).  But astrophysical data collection, often in regions of the electromagnetic spectrum the eye can't see, has given us more information about the wild variety of stars out there -- many of which are only now beginning to be understood.

Take for example the binary star system with the euphonious name CPD-29-2176, located a bit over eleven thousand light years away.  This pair is so strange that its characteristics are thought to match only one in every ten billion star systems, meaning there are probably only ten or so of them in the entire Milky Way.  (Fortunate, then, that one is close enough to study.)  First discovered from its x-ray signature by NASA's Neil Gehrels Swift Observatory and later studied by the SMARTS 1.5-meter Telescope, CPD-29-2176 is a kilonova progenitor system -- a pair of stars in which one is destined to blow up.

Artist's impression of CPD-29-2176  [Image courtesy of CTIO/NOIRLab/NSF/AURA/J. da Silva]

The mechanism is a little like a type 1a supernova, in which a white dwarf is in a close orbit with a larger main-sequence star.  The white dwarf, a dense, hot stellar nucleus of a moribund star, slowly draws off material from it partner through its intense gravitational pull, creating a whirlpool of accreting matter.  This, however, can only go on so long; once the white dwarf exceeds the Chandrasekhar limit, about 1.4 solar masses, it suddenly collapses.  The temperature skyrockets, and the former white dwarf becomes a supernova intense enough to blow the companion right out of orbit.

Here, though, the dynamics are a bit different.  If a supernova is a "holy shit!" event, a kilonova is more of a "meh."  What apparently is happening is the two stars are already so close that one is losing material to the other at a colossal rate.  The result: once the losing star burns through its fuel, at which point it should undergo the collapse/explosion cycle, there won't be enough fuel left to spike its temperature much.  It will trigger a kilonova (also called an ultra-stripped supernova), which is to an actual supernova what a wet firecracker is to a nuclear bomb.

What's even more interesting is that the same fate is predicted for the companion star; ultimately, what will be left is two neutron stars whirling around a common center of gravity, eventually falling inward and coalescing.  The release of gravitational potential energy by the merger will tear the stars apart -- stunning this could happen to objects so dense -- and the resulting debris, highly enriched in heavy elements, will be dispersed to the cosmos.

As astonishing as it sounds, all of the heavy elements -- the gold and silver in our jewelry, the mercury in our thermometers (well, old ones, at least), the uranium in our nuclear power plants, the rare earth elements in our computers -- were created in the cores of dying stars.  (If you want to learn more about this astonishing process, I did a piece here at Skeptophilia about it a couple of years ago.)

While a kilonova isn't going to be anything spectacular to watch from here on Earth, it's a rara avis indeed in the galactic zoo.  

Every time I read about some new astronomical discovery, it highlights for me how much more complex the universe is than the ancients dreamed.  Their point sources of light on crystal spheres, driven by deities and heavenly powers, miss the true intricacy of the cosmic clockwork by light years.  How delighted Galileo and Copernicus and Eratosthenes would be to know what we know -- to get a glimpse of a universe so vast, and so diverse, that it far surpasses the famous quote by Shakespeare -- "There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."


No comments:

Post a Comment