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THE DAILY ASTRONOMER
Tuesday, October 25, 2022
A Strange Star?


Wow!
Double Wow!
Treble Wow!
....and, Hmmm....

Astronomers Victor Doroshenko, Valery Suleimanov, Gerd Puhlhofer and Andrea
Santangelo just published a paper in Nature Astronomy pertaining to the
Supernova remnant HESS* J1731-347.   Located within Scorpius the Scorpion
at a distance of  3,200 parsecs (10,432 light years), this remnant is most
likely the least massive neutron star ever discovered.  In fact, with a
calculated mass of 0.77 solar masses (77% as massive as the Sun), this
city-sized sphere of super high density falls well below 1.17 solar masses,
defined as the theoretical lower limit for any neutron star.       In fact,
perhaps this remnant is not a neutron star at all, but, instead, could be a
strange star:  one composed of strange quarks.   If so, it will be the
first strange star ever discovered.

Let's review some of the science.

When a Type II supernova explodes, a highly massive star's innermost layers
collapse in on themselves with such an overwhelming force as to create one
of two possible by-products: a neutron star or a black hole.    Spanning
the width no greater than that of a large city, a neutron star consists
-naturally- of neutrons.  When the star collapses, the constituent protons
and electrons are literally compressed together to create neutrons,
particles without any charge.        Neutron degeneracy pressure, a quantum
effect by which the neutrons, themselves, resist any further compression,
sustains the neutron star's shape despite the fiercely powerful
gravitational contraction.      According to theoretical models, neutron
stars cannot be heavier than 1.44 solar masses, known as the *Chandrasekhar
limit.** *  The neutron degeneracy pressure could not resist the
gravitational compression of anything heavier.    Conversely, the lower
limit for a neutron star is about 1.17 solar masses.  Anything lighter
would be a white dwarf, the remnant of a solar mass star.

[image: NeutronStar (1).jpg]
Formed by a Type II supernova, a neutron star's mass range is quite narrow
1.17 - 1.44 solar masses.  However, the remnant associated with HESS
J1731-347 is calculated to only be 0.77 solar masses.   Instead of a
neutron star, could it be a *strange star*?

How can an object produced by a Type II supernova weigh so little?

Well, now, the situation becomes a bit tricky.       It is theoretically
possible that the compression force within a neutron star could become so
intense that the neutrons themselves are transmuted into quarks, the
elementary particle comprising subatomic particles. Quarks come in many
"flavors," a wholly inappropriate term used in reference to these
particles:   Up, Down, Top, Charmed and Strange.        A proton***
contains two up quarks and one down quark and a neutron is comprised of one
up quark and two down quarks.

As a quark star would also contain "strange quarks," such an object would
classify as a "strange star." Such a star could be less massive than a
neutron star, perhaps even as light  as 0.77 solar masses.      Have they
found the first strange star?    Perhaps.       As is so often the case,
further observations are necessary.




*High Energy Spectroscopic System

**Named for Subrahmanyan Chandrasekhar (1910-1995), the Indian-American
astrophysicist who determined this limit.  He shared the 1983 Nobel Prize
in physics for this discovery.

***Someday, when we're feeling irrationally ambitious, we will delve into
the unfathomably complex Universe of the proton.    To suggest that it is a
simple little sphere encapsulating quarks is so absurd as to be comical.
 Each proton is a bustling, thriving, dynamic, unquiet realm of exotic
particles darting in and out of existence like mad thoughts in a disturbed
mind.      If you persist in the belief that reality is not as
fantastically weird as a hundred cyperpunk graphic novels, just wait until
we explore the proton.


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