September 21, 2017

19.06.10: A New Breed of Supernova?

Discovery image of SN 2005E. (Credit: SDSS/Lick Observatory).

Discovery image of SN 2005E. (Credit: SDSS/Lick Observatory).

 

   Every student of Astrophysics 101 soon learns that there are two main types of supernovae; Type 1a, which occur when a white dwarf star accretes matter from a bloated companion, passes the Chandrasekhar Limit and explodes, and Type II, when a star 8 times the mass of our Sun or larger reaches the end of its fusion burning life and promptly explodes… but are these snapshots of the final phases of stellar evolution really that neat and tidy? Recently, evidence has been mounting that there may be other sub-branches to the supernova tale, and not just the two flavors and the sub-categories that we learned in school. The first round of evidence comes from a team at the Harvard-Smithsonian Center for Astrophysics and their study of supernova 2005E. This blast occurred in the galactic halo of the galaxy NGC 1032 in the constellation Cetus, not your typical supernova breeding territory. Supernovae are usually seen in rich star forming regions, not in metal poor outer galactic suburbs. This event was a fizzle, ejecting only 300 times the mass of Jupiter into its nearby environs.

The mystery deepened as a team from Hiroshima University released their results of a study of another supernova, 2005cz. Located in the elliptical galaxy NGC 4589, this eruption was also only 20% as bright as models predict, showing that while the initial mass may have been just above what was required for a Type II supernova, it beared none of the classic hallmarks of either species of events. Both of these supernovae, along with 6 others recorded, show a high concentration of calcium in their spectra, a hint that they may not be related to either of the previously known types.

So, what’s going on? Do we need to re-write all those old astrophysical texts? It’s unlikely that a progenitor star migrated all the way to a galactic halo region in its short life span simply to explode. A possible scenario could be a pair of binary white dwarfs (or do you say dwarves?) in a tight orbit, with one stealing the helium shell of another and bursting. Spectra taken of both events seem to support this scenario… this mystery may have a tie-in with the seeming lack of “Type 1A’s in waiting” mentioned in this space in an article on a recent survey of nearby galaxies… will this hybrid style of supernova become known as “Type III” or “Type 2.5”?

08.05.10: Does Type Ia Supernova Formation Need Revision?

(Credit: NASA).

(Credit: NASA).

An artist’s conception of a traditional Type Ia supernova in the making.

    A key measurement device used by modern astrophysicists may also hold an elusive mystery. It has been long known that a Type Ia supernova occurs when a white dwarf accretes in-falling material from a binary companion, grows past the Chandrasekhar limit of 1.4 solar masses, and promptly blows itself up in a thermonuclear chain reaction that can be seen across the universe. These brilliant displays rise in brightness and then fade in a predictable fashion, allowing them to serve as “standard candles” marking the intergalactic distances to their host galaxies. These accreting white dwarfs should give off copious amounts of X-rays leading up to their eventual ignition. If this is the case, where are these accreting white dwarf SN Ia’s in waiting? An interesting study was released earlier this year by Akos Bogdan and Marat Gilfanov of the Max Planck Institute. Analyzing five elliptical galaxies and the nearby Andromeda with NASA’s Chandra X-Ray observatory, they found X-Ray output to be up to 50 times less than expected if the seeds for Type Ia’s were indeed being sown. Several factors may account for this discrepancy;

  1. Perhaps energetic accretion is not a constant state in these binary systems;
  2. The types of galaxies surveyed (with the exception of Andromeda) are not known for their energetic star formation;
  3.  Type Ia’s may be more prevalent during certain epochs of star formation in the universe;
  4. Other mechanisms, such as merging white dwarf binaries, may produce Type Ia supernovae without accretion. But these populations would surely be lower throughout the universe than mixed systems; it isn’t even clear if a merging white dwarf pair would explode, or simply collapse into a neutron star. And white dwarfs are just plain tough to spot at galactic distances!

Whatever is the case, there still isn’t a consensus in the astronomical community as to where the Type Ia’s-in-waiting are hiding. It should be noted that this controversy does not center on the luminosity relationship;   naysayers look elsewhere for your chink in the frame-work of the Big Bang Theory! Instead, we suspect that “sub-breeds” Of Type Ia (Type IAa?) supernovae will come to light as new platforms such as James Webb Space Telescope come on line in the next decade.

Astro-Challenge:When will T Pyxidis Finally Pop?

T Pyxidis; a supernova in the making? (Credit: M. Shara & R. Williams STS, R. Gilmozzi ESO, & NASA)

T Pyxidis; a supernova in the making? (Credit: M. Shara & R. Williams STS, R. Gilmozzi ESO, & NASA)

 

   Earlier this year, the astronomical community was wowed by the eruption of the star U Scorpii. As reported last year in this space, U Sco is a recurrent nova, a flare star that undergoes outburst at irregular intervals. Less than 10 recurrent novae have been identified. The initial action was caught by two Florida based amateurs, and demonstrates that hands on, observational astronomy is still alive and well even in the modern age of astronomical automation. This week, as the waning gibbous moon slides out of the evening sky, I’d like to turn your attention to another of these rare beasts; T Pyxidis. Located in the constellation Pyxis, the Mariner’s Compass, this is one of those unimaginative southern hemisphere constellations thrust upon us in the 18th century. Visually unremarkable, it contains a handful of deep sky objects and clears the horizon sufficiently in the spring evenings for observers in the southern United States to perform routine observations. T Pyxidis itself is a binary system consisting of a white dwarf cannibalizing a sun-like star. When enough in falling matter accumulates, T Pyx flares up from its normal barely detectable magnitude +15.5 to +7.0, almost naked eye visibility. This has happened at roughly 20 year intervals in the years 1890, 1902, 1920, 1944, 1966…and then T Pyx fell silent. We are currently 44 years and counting for an outburst, and this is definitely a star worth continuous scrutiny. The light curve is that of a slow nova, rapidly brightening over a couple of nights, fluctuating at its peak brightness for about a month, and then fading out over proceeding months. T Pyx is a prime candidate for a galactic Type Ia supernova, and at a distance of 3260 light years, could put on quite a show. Of course, said final act could occur tonight, or 10 million years from now; but this current lull makes you think; there has to be a lot of material accreting up there! Its coordinates are;

R.A: 09h 04m 41.5s

Dec: -32 22m 47.5s   

And for an uber-cool finder chart that Sky & Telescope produced a few years back, follow this link… (hint: for use in the field, take the chart and  invert the colors in Paint or Photoshop!)

Good luck, and with a little patience, YOU could be the next amateur to catch T Pyx in the act!

The Astro-term for this week is Chandrasekhar Limit. This is the mass limit of a body in which electron degeneracy pressure can push outward against gravitational collapse. First calculated by Indian astrophysicist Subrahmanyan Chandrasekhar in 1930, this mass is usually given as 1.44 solar masses. Below this limit, a white dwarf and an accompanying planetary nebula will occur; above this mass limit, a core collapse supernova will occur, leaving behind a pulsar or a black hole. T Pyxidis has to be very near its very own Chandrasekhar Limit, with the amount of in-falling mass it is accumulating… will it pop in our lifetime?

Review: The Cosmic Connection by Jeff Kanipe

Out by Prometheus Books!

Out by Prometheus Books!

Cosmic catastrophe seems to be trending today, much unlike the currently pallid 11-year sunspot cycle. Without a doubt, the next killer asteroid will top your Tweetdeck, although whether it will bump #TGIF and Paris Hilton remains to be seen. The Cosmic Connection: How Astronomical Events Impact Life on Earth, by Jeff Kanipe and out by Prometheus Books comes as a sort of impromptu trilogy of reviews, as fans of this space will remember our recent review of Death from the Skies! And our forthcoming review of Heavens Touch, due out next month. Do not confuse this title with Sagan’s Cosmic Connection: An Extraterrestrial Perspective from 1973, which was complete with the trippy space age cover designed to pull in UFO buffs, but was Sagan all the way!

The Cosmic Connection shows how we are intimately related to the continual celestial goings-on all around us, and that we’re ultimately not immune to our stellar environs. I always like to point this out to the astrologically minded; the universe does indeed influence human affairs but not in the mundane way your newspaper horoscope might suggest. Instead, solar activity, supernovae, and even the evolving tilt of our own planet form a continuing ballet, and we’re all along for the ride!

The book opens with a deconstruction of our planet’s own complicated orbital behavior. Cycles such as the precession of the equinoxes the variation of the obliquity and fluctuation of our axial tilt all add up to a very complex affair, and that’s just for starters. Its hard to imagine that the “Goldilocks” epoch that we live in just happens to be stable and “just right” for us to thrive, and that this won’t always be so.

A flare sketched during the Total Solar eclipse of 1860. (Credit: F.A. Dom).

A flare sketched during the Total Solar eclipse of 1860. (Credit: F.A. Dom).

Even our own star, the Sun, is exposed for the notorious side it can sometimes exhibit. Its role in climate change is discussed; we thought that the “exorcism” of the Chamonix glacier, which was prone to advancing 100 acres per day in 1610, was an especially unique tale. The infamous solar season of 1859-1860 is also discussed; we have yet in modern technological times  to see a season quite as active as this one!

Chamonix Glacier Today. (Credit: Danny Sullivan).

Chamonix Glacier Today. (Credit: Danny Sullivan).

Think we know our own cosmic back yard? The Cosmic Connection will give you pause to think again. The chapter …At any time delves into the state and history of Near Earth Object (NEO) detection. For example, did you know that astronomers estimate that there remains perhaps 20,000 Near Earth Asteroids (NEAs) of the 140 meter or greater class to be discovered? In a timely fashion, the book makes mention of the October 5th 2008 impact in Sudan, the first time we’ve been able to spot an asteroid before impact. The author also lays out a template for increased funding and efforts towards detection. Of all the cosmic disaster death scenarios, killer space rocks are one of the few that we possess any means to do something about!

And as mentioned, I’ll bet that doomsday asteroid will trend on Twitter…

Even our place and epoch in the galactic scheme of things is addressed. True, a death dealing potential supernova candidate currently doesn’t lurk nearby in our local galactic neighborhood.The currently accepted “kill zone” is a radius of about 25 light years, and Spica and Betelgeuse, at distances of 260 and 425 light years, respectively are the nearest potential candidates. However, as we continue our 225 million year circuit about the galaxy, this will not always be the case. In addition, we bob up and down around the galactic plane, through largely unknown mediums of intergalactic dust. Our overall motion about the center of our galaxy is oblong, with our motion towards the solar apex in the constellation Hercules at about 12 miles per second. About 20 “Galactic Years” have passed since the formation of our solar system, and less than a hundredth of the past GY since the dawn of humanity. The author also points out that we may owe our placid existence to our current placement just outside of whats termed as the Local Bubble, an expanse of 300 light years across in the Orion Arm carved out by ancient supernovae.

Our home in the Local Bubble. (Credit: NASA/JPL)

Our home in the Local Bubble. (Credit: NASA/JPL)

All in all, its pretty remarkable to note the cosmic ingredients that go into an Earth as we know it; we live on a planet that orbits a relatively stable star, within its habitable zone, with a Moon to stabilize our tilt, in a supernovae free zone of our galaxy in just the right epoch. Of course, the Drake Equation has been given treatment, as it has here at Astroguyz… the sentiment echoes a recent controversial book, Rare Earth, which posits that our circumstances make life here unique. Of course, we are talking about life that know, as in carbon based, water-loving life…

In the end, the author presents a very convincing argument as to how our existence is intimately related to our evolving place in the cosmos. Consider it a sort of “volume two” in our cosmic review trilogy, Death From the Skies! being first and Heavens Touch to be forth coming. And next clear night, (we do our review reading on the cloudy ones!) be sure to check out the summer Milky Way (if you don’t suffer from light pollution) and thank your lucky stars that we’re here at all to appreciate our privileged place in space and time!

Thank goodness for...our Moon! (Photo by Author).

Hooray for...our Moon! (Photo by Author).

The Contributions of Amateur Astronomers to Modern Science

(Author’s note; the essay below was a paper submitted recently by yours truly as part of my quest for a bachelors degree in science teaching. I’ve posted it here pretty much intact. Some explanations on the graphs have been expanded; I thought it was a shame for all of my research on the subject to go to waste. The bibliography is also included.)

Today, the modern science of astronomy is growing like never before. New technologies are opening up unseen vistas scarcely imagined just twenty years ago. [Read more...]