February 24, 2018

19.06.10: A New Breed of Supernova?



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”?

Astro-Event of the Week-Redder than Red: V Hydrae.

This week, we here at Astroguyz are going to introduce you to a star that isn’t on the top 10 star party faves, but perhaps should be; V Hydrae. [Read more...]

21.04.10-The Puzzle of Blue Stragglers.

Astronomers may have recently solved a half a century long mystery of stellar evolution. Since the 1950’s a type of star known as  a blue straggler has stubbornly refused to fit the Hertzsprung-Russell diagram mold. These older stars should be approaching seniority, but instead burn brightly and spin energetically as if they had somehow gained mass. Most exist in globular or open clusters, and were first identified in the M3 globular cluster. The most well studied example of this stellar sub-class exist in NGC 188, a star cluster about 6,000 light years distant where 21 have been identified. Now, astronomers Robert Mathieu and Aaron Geller of the University of Wisconsin Madison have gained insight into the formation of these elusive beasties and come up with three leading hypotheses;

  1. Matter is accreted from an aging red giant star onto a main sequence companion similar to the process seen in a type IA supernova, but not as massive, causing the star to re-energize;
  2. Two lower mass stars collide, an improbable but not impossible scenario in a densely packed globular cluster;
  3. A third stellar companion perturbs the orbit of a tightly knit binary pair, causing them to merge.

These possibilities were advanced after Mathieu and Geller used observing time on the 3.5-meter WIYN telescope on Kitt Peak spanning the past decade. Studies involved NGC 188, the original “blue straggler” cluster. “These aren’t just normal stars that are straggling behind in their evolution,” stated Mathieu.” There is something unusual going on with their companions.” Computer models would suggest that door number #3 is the most likely candidate; the most logical proof that astronomers would like to have in hand would be to catch a merger in progress.  Interestingly, two known blue stragglers with white dwarf companions lie in the field of the Kepler space telescope, a plus for the accretionary camp. Will we soon have definitive evidence for the origins of these bizarre stars? Or is it perhaps a hybrid of the three models? Stay tuned…

15.04.10- Do We Know the Future of our Sun?

Our modern understanding of stellar evolution states that our Sun is a middle-aged main sequence star, destined to bellow up into a Red Giant in a few billion years and eventually wind up as a degenerate white dwarf embedded in a shroud of a planetary nebula. Looking out at the stars in various stages of evolution in our galaxy, we see systems that have done just that. These Red Giants often exhibit a rhythmic oscillation as their atmospheres swell and contract, but about one third also display a longer five year variation that scientists do not completely understand. Now, a study conducted by the European Southern Observatories’ Very Large Telescope (VLT) is looking into this mystery by studying 58 sun-like stars towards their elderly Red Giant stage located in the Large Magellanic Cloud. Known since the 1930’s, this mystery has baffled astronomers. “Astronomers are left in the dark, and for once, we do not enjoy it,” stated Christine Nicholls of Australia’s Mount Stromlo Observatory. Some of the long term pulsations could be explained by the presence of an unseen binary companion, but not all. This phenomenon is of special interest to astrophysicists because our own Sun may one day throw similar temper tantrums. Could stellar evolution be in need of tweaking?

08.04.10-Epsilon Aurigae Update.

   We couldn’t resist shooting this one out there today, as it contains some fairly mind-blowing imagery. Late last year, we put a shout-out to observe the eclipsing binary star Epsilon Aurigae, a bright naked eye star that undergoes periodic diming once every 27 years. For over 190 years, this star has stubbornly not only refused to match stellar evolutionary models, but sometimes threatened to overthrow them, to boot. Now, scientists have solved the case of the disappearing star, and it’s a strange one, indeed. The variation in brightness appears to be the result of three factors; a bright type F supergiant, orbited by a hot type B star about 1,000 times dimmer shrouded in a massive dust disk. The entire system passes along our line of sight and obscures the host for an 18 month period. The grouping is about 2,000 light years distant. In fact, if Epsilon Aurigae were tipped away even 10 degrees more from our line of sight, we wouldn’t see anything unusual at all! This model of the systems’ total luminous output matches the observed brightness curve from the recent dimming. (see above) [Read more...]

Astro-Challenge:Spy a White Dwarf!

This week, I’m going to introduce you to a unique but fascinating multiple star system, and one that’s definitely worth seeking out as it’s a good study in comparative stellar evolution; Omicron Eridani. This one will require a telescope of about 4′ aperture or greater, a go-to scope or a good finder chart, and patience. But the quarry is worth it; for Omicron Eridanus B is a white dwarf, the most easily observable in the sky, paired with C, a red dwarf star! Omicron Eridani is a triple star system, about 16.5 light years distant. The primary star, a K type main sequence star, is visible to the naked eye at a magnitude of about +4.5. Known to the Arabs as Al Keid (“the Egg”),

[Read more...]