THE SOUTHWORTH PLANETARIUM
70 Falmouth Street Portland, Maine 04103
(207) 780-4249 usm.maine.edu/planet
43.6667° N 70.2667° W
Founded January 1970
2022-2023: XXIX
Sunrise: 7:08 a.m.
Sunset: 5:42 p.m.
Civil twilight ends: 6:11 p.m.
Sun's host constellation: Virgo the Maiden
Moon phase: New Moon
Moonrise: 7:12 a.m.
Moonset: 5:53 p.m.
Julian date: 2459878.21
"The world at night, for much of history, was a very dark place, indeed." Bill Bryson
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.
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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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