ATLANTIC SKIES: Did you know there are zombie stars in our universe?

Pa 30, initially catalogued IRAS 00500+6713, is a unique and rare nebula discovered in 2013 by American amateur astronomer Dana Patchick.

This was Patchick’s 30th nebula discovery, thus the label Pa 30. The nebula itself was created by a supernova explosion in the constellation of Cassiopeia – the Queen and was first observed, according to astronomical records, by Chinese, Japanese, and Arabic astronomers in 1181.

Located approximately 7,500 light-years from Earth, this supernova was first observed between Aug. 4-6, 1181, and recorded in eight separate texts.

A unique feature of Pa 30 is its central star, designated WDJ005311, a supermassive, magnetic white dwarf believed to be the result of a merger of two lower-mass white dwarf stars.

Now a stellar remnant, such stars are informally referred to as “zombie stars” by astronomers, as they have survived a supernova explosion that would typically have blasted them apart.

Optical spectroscopy of the central star showed it to be a very hot star, with temperatures near 200,000 Kelvin, making it one of the hottest known stars, and having intense stellar winds.

Follow-up X-ray spectroscopy of Pa 30 demonstrated it was a supernova remnant which, in addition to being very hot, contains carbon-burning ashes, neon, magnesium, sulfur, and silicon.

Collectively, the nebula and the central star are the remnants of a rare class of supernovae referred to as “sub-luminous Type 1ax” — a rare form of thermonuclear explosion involving white dwarf stars, capable, in some instances, of leaving part of the original progenitor star intact.

A 2021 study measured the nebula’s outward expansion rate at approximately 3,600,00 kilometres per hour, which, when combined with the nebula’s angular size, confirmed its age of nearly 1,000 years.

The nebula’s expansion velocity and the inferred absolute brightness for the 1181 supernova event are consistent with a Type 1ax supernova.

Supernova explosions are rarely perfectly symmetrical; material thrown out during the explosion is subject to the conservation of momentum, accelerating the stellar ejecta in opposite directions, a motion often referred to as a “kick.”

If a supernova explosion is perfectly symmetrical, the path of the ejecta would also be symmetrical, with the result that the surviving star would not be subject to a substantial kick.

Findings concerning the geometry of the 1181 event appear to indicate that, as Pa 30’s central star has remained nearly stationary, the supernova blast distributed its momentum more evenly than expected. This, combined with the knot structure of the event filaments, is helping astronomers determine what may have happened during the original thermonuclear event itself, and how the ejecta subsequently evolved.

Observations in 2024 with the Keck Cosmic Web Imager spectroscope constrained the actual date of the initial supernova event to 1152. These observations, in conjunction with the 2021 study, reinforced the theory that Pa 30 is the most likely candidate for the supernova observations recorded in 1181. The 1181 supernova event remained visible for months (185 days), and is only one of a handful of pre-telescope era supernova explosions documented in surviving historical records.

Recent observations of Pa 30 reveal fine filamentary structures within the nebula consisting of chains of uniform gas knots radiating outward from the surviving stellar core.

The expanding debris field from the supernova gives Pa 30 a somewhat “dandelion-like” appearance. However, what makes these filaments unique is the fact that many of them, instead of forming continuous strands, are made up of compact clumps arranged in measured sequences, similar to pearls on a necklace.

These knots or pearls are, in fact, extremely large emissions from ionized sulfur in the red portion of visible light, along with doubly-ionized oxygen visible in the blue-green wavelengths.

Higher resolution imagery of the dense, similarly-sized, sequenced emission knots suggests the filament material may have fragmented as a result of repeated physical processes rather than random turbulence.

The filamentary knots in Pa 30 are extremely large; our entire planetary system (Mercury to Neptune) of our solar system could fit 10 times within each knot, and still have room to spare.

Pa 30 is the only known supernova remnant of its kind in the Milky Way Galaxy.

For centuries, astronomers have lacked a convincing modern remnant associated with the 1181 supernova event.

Supernova remnants can persist for tens of thousands of years, making their age notoriously difficult to determine. Fortunately, in the case of Pa 30, written observations in historical records provide an independent timeline reference point.

Pa 30’s radial filaments, chemical emissions, central star, and unique knot morphology now provide astronomers with a distinct set of observational signatures against which they can compare other large survey databases.

Utilizing these signatures, astronomers may be able to identify those celestial objects that, resembling Pa 30, will enable them to estimate how frequently Type 1ax supernovae occur in the Milky Way Galaxy.

Mercury (magnitude -0.1, in Libra – the Scales) is not observable this coming week, as it sits right on the western horizon (0 degrees) at dusk.

Venus (mag. -4.3, in Virgo – the Maiden), soon to pass in front of the sun (inferior solar conjunction) on Oct. 24, is likewise not observable this week, as it is eight degrees below the western horizon at dusk. Venus reaches inferior solar conjunction (passing between the Earth and the sun) on Oct. 24 at 12:39 a.m. ADT.

Mars (mag. +1.0, in Cancer – the Crab) rises around 12:50 a.m. ADT, reaching 56 degrees above the southeast horizon before fading from view by about 6:50 a.m. ADT.

Jupiter (mag. -1.9, in Leo – the Lion), now visible in the dawn sky, rises around 1:50 a.m. ADT, reaching 51 degrees above the southeast horizon before fading from view in the brightening dawn around 7:15 a.m. ADT.

Saturn (mag. +0.3, in Cetus – the Sea Monster) becomes accessible 10 degrees above the eastern horizon by about 7 p.m. ADT, before reaching its highest point in the sky 45 degrees above the southern horizon around midnight ADT, and then becoming inaccessible shortly after 5 a.m. ADT, when it sinks below 10 degrees above the western horizon.

On Oct. 24, Saturn and the 14-day-old, waxing gibbous moon will be in conjunction (share the same right ascension) with one another at 2:41 p.m. ADT. At around the same time, they will make an appulse (close approach) to one another.

Uranus (mag. +5.76 in Taurus – the Bull) becomes accessible 21 degrees above the eastern horizon around 10:10 p.m. ADT, reaching its highest point in the sky 64 degrees above the southern horizon around 3:30 a.m. ADT, where it will be lost to the dawn twilight 47 degrees above the western horizon by about 6:20 a.m. ADT.

Neptune (mag. +7.8, in Pisces – the Fish) becomes accessible when it reaches 21 degrees above the southeast horizon around 7:40 p.m. ADT, and reaches its highest point in the sky 43 degrees above the southern horizon around 11:30 p.m. ADT, before becoming inaccessible around 3:15 a.m. ADT, when it sinks below 21 degrees above the southwest horizon.

Active between Sept. 22 and Nov. 22, the Orionid meteor shower has a broad, plateau-like maximum, lasting several nights, centered around Oct. 21.

The shower’s radiant (apparent point of origin in the sky) lies in the constellation of Orion – the Hunter, near his upraised club.

Best viewed once the radiant clears the eastern horizon in late evening until dawn brightens the sky, the Orionids are debris from the famous comet 1P/Halley, and hit Earth’s upper atmosphere at speeds of more than 236,000 km/hr.

Unfortunately, this year, those watching the Orionids will have to contend with a bright, waxing moon, up most of the night as it heads towards full moon on the overnight period of Oct. 25-26. However, under a dark sky away from city lights, the pre-dawn hours should see approximately 10 to 20 bright meteors per hour.

The weak meteor shower Leonis Minorid, active through Nov. 3, will peak on the evening of Oct. 24. There will only be a brief window to see any of these meteors, from dusk until about 7:30 p.m., when the shower radiant in Leo Minor – the Little Lion drops below the western horizon.

The Leonis Minorids are debris from cometC/1739 K1, discovered in 1739 by Italian astronomer Eustachio Zanotti (1709 – 1782). Although considered a minor shower, producing only about two to three bright meteors per hour, the Leonis Minorids have, on occasion, surprised their observers with tens of meteors per hour.

Correction: In paragraph four of last week’s article (Oct. 12 – 18), it should have read “…4.1 million solar masses”. My apologies for the error.

Until next week, clear skies.

Events:
Oct. 21 – Orionids meteor shower peak (see above)
Oct. 23 – Moon at aphelion (farthest point from the Sun); 9:15 a.m. ADT; 148,353,699 km or 0.9970 AU
Oct. 24 – Venus at inferior solar conjunction at 12:39 a.m. ADT; close approach of moon and Saturn; conjunction of moon and Saturn at 2:41 p.m. ADT; Leonis Minorid meteor shower peak (see above)