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.

Monday, April 15, 2024

Stellar wind, the BOAT, and the Dragon's Egg

Since the news down here on Earth is not looking so good, today we're going to escape to my happy place, which is outer space.

We've got three new studies of fascinating astronomical phenomena to look at, the first of which comes out of the University of Vienna.  A team led by astrophysicist Kristina Kislyakova has, for the first time, directly detected stellar wind from three nearby Sun-like stars -- something which may effect the stability of the atmospheres of any planets orbiting them, and thus, their potential habitability.

Stellar wind -- which until now, we only knew about from studies of our own solar wind -- is a stream of particles given off by the upper atmosphere of stars, mainly composed of electrons, protons, and alpha particles with a kinetic energy of under 10 keV.  The solar wind is why comet tails always point away from the Sun (not, as many people erroneously think, simply the opposite of their direction of motion, like the wake of a boat).  Kislyakova's team looked for x-rays of specific frequencies coming from the three stars they studied (70 Ophiuchi, Epsilon Eridani, and 61 Cygni), because the stellar wind is expected also to contain small amounts of ionized oxygen, nitrogen, and carbon; as those ions are blown from the surface of the stars and ultimately slow down, they capture electrons, which drop into the atom's ground state and emit electromagnetic energy in the form of x-rays at particular frequencies.  From the amount of x-rays detected, they estimated the mass loss rate of the stars.

All three have much stronger stellar winds than the Sun does -- around 66, 16, and 10 (respectively) times the rate of mass loss from solar wind that the Sun experiences, which is itself considerable (estimated at 1.5 million metric tons per second).  The reason for the higher mass loss from the three stars studied is unknown -- but the Sun's calmer behavior is a good thing, because a strong stellar wind can peel away the atmosphere of exoplanets.  Any planets around 70 Ophiuchi, for example, are likely not to have much in the way of an atmosphere.

The second study is out of Northwestern University, and looked at something that has been nicknamed the BOAT (brightest of all time) -- a gamma-ray burst picked up in October of 2022 that saturated every gamma-ray detector on Earth.  It came from a source about 2.4 billion light years away in the constellation of Sagitta, and lasted for a few hundred seconds before starting to fade.  During that time it outshone the next-brightest observed gamma-ray burst by a factor of ten.

A team led by astrophysicist Peter Blanchard found that the BOAT was caused by a supernova -- but one acting very strangely.  The gamma-ray burst was so powerful that it took scientists some time to figure out that there even had been a supernova (imagine something so bright that it hides the light coming from a supernova!).  "The GRB was so bright that it obscured any potential supernova signature in the first weeks and months after the burst," Blanchard said.  "At these times, the so-called afterglow of the GRB was like the headlights of a car coming straight at you, preventing you from seeing the car itself.  So, we had to wait for it to fade significantly to give us a chance of seeing the supernova."

So why would an ordinary (if you can use that word) supernova cause such an enormous gamma-ray burst?  One possibility is that we might just be at the right place at the right time.  Models indicate that a rapidly-spinning massive star, when it reaches the end of its life, collapses into a black hole that gives off a a narrow jet of gamma rays aligned with the axis of its rotation.  It's possible that we just happened to be perfectly lined up with the black hole's axis -- looking right down the gun barrel, as it were.  But the fact is, they're still trying to figure that out, so we'll have to wait to see what more they learn.

The third study, led by astrophysicist Abigail Frost of the European Southern Observatory in Chile, looked at a strange and beautiful object nicknamed the "Dragon's Egg," in the southern constellation of Norma.

[Image credit: European Southern Observatory's Paranal Observatory in Cerro Paranal, Chile. ESO/VPHAS+/CASU/]

The curious thing about the pair of stars in the middle of the Dragon's Egg is that one of them has a magnetic field and the other doesn't.  Frost and her team believe that the same process that created the nebula surrounding them is what created the magnetic field in one of the stars.

It seems to be a case of stellar fratricide.  The more massive star in the binary pair is the one with the magnetic field, and the theory is that it used to be a triple star system -- but two of the stars underwent a merger.  The violence of that collision blew material out into space (the origin of the glowing dust cloud surrounding the remaining two stars) -- and the result dramatically increased the spin rate of the combined star, a bit like water speeding up as it goes down a drain.  Electrically-charged particles, such as those in stellar atmospheres, traveling in circles generate a magnetic field as per Maxwell's Laws, and that's why the more massive member of the surviving binary has such a powerful field.

So that's today's exploration of astronomical news.  Always makes me feel a bit tiny, when I consider phenomena out there in the depths of outer space.  Nothing wrong with that, of course -- humility is good.  And all in all, I'd rather be looking up than looking down in any case.


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