November 19, 2017

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.

16.03.10:Relativity Triumphant over Bizarre Binary.

The unique dance of DI Herculis. (Credit: Simon Albrect/MIT).

The unique dance of DI Herculis. (Credit: Simon Albrect/MIT).

 

   For years, a unique binary system has plagued Einsteinian physics. DI Herculis (DI Her) is a seemingly innocuous binary star about 2,000 light years distant. Type B stars each about five times the mass of our Sun, these stars are in a mutual orbital embrace about 0.2 A.U. apart. Visually, the system is at magnitude +8.5, and the orbit is inclined along our line of sight so that mutual eclipses occur every 10.55 days. First recorded in 1900, this feature allows the systems’ mass, luminosity and orbital characteristics to be known to a high degree of precession. For the past several decades, however, astronomer Ed Guinan at Villanova University couldn’t shake an odd effect; namely, periastron of the two stars is advancing at a rate of only ¼ what’s predicted by Einstein’s theory of general relativity. Is an unseen companion lurking in the DI Her system, or is it Albert himself who was wrong? Prediction of such anomalies as the precession of the perihelion of Mercury is one of the great cornerstones of relativity.  In a massive system such as DI Her, this effect should be even more pronounced. Like the Pioneer anomaly, several would-be theorists have pointed to this discrepancy as a potential chink in the relativistic armor…

 Enter Simon Albrecht of MIT. Using a 1.93-meter telescope to obtain a high-resolution spectrograph of the two suns, a bizarre fact has become apparent; both stars are tipped on their rotational axes, giving them an orbital “kick” at their closest approach. This configuration adequately accounts for the relativistic anomaly. Apparently, DI Her underwent a close passage of another star or massive object sometime in its history. Guinan is relieved, but will no doubt continue to receive a flood of email from alternate-gravity theorists!

LIGO: A Quest for Gravity Waves.

LIGO, Livingston. (All Photos by Author).
LIGO, Livingston. (All Photos by Author).

We had to go there… last month’s NASA Tweetup at the Johnson Spaceflight Center saw us undertake the great American road trip from Astroguyz HQ north of Tampa, Florida, to Houston on the other side of the Gulf of Mexico and back. Ever the opportunists, we scoured the route for any astronomical pilgrimages of note. Then, like a bolt from the sky, a lone commenter drew our attention to a recent news piece we did on LIGO, the Laser Interferometer Gravitational-Wave Observatory[Read more...]

Astro-Challenge: Groombridge 34; a Nearby Red Dwarf Pair!

Sure, everyone’s heard of Alpha Centauri, but have you ever heard of… Groombridge 34? We came across this little known binary red dwarf pair while perusing Burnham’s Celestial Handbook last month during our write up for M31. Also in the constellation Andromeda, Groombridge 34 is a unique system; a pair of red dwarf flare stars relatively close to our own solar system. At 11.62 light years, its the 16th closest stellar system to our own. The separation of the two stars are about 147 Astronomical units (A. U.s) (for reference, Pluto is about 50 A.U.s from the sun!) in a estimated 2,600 year orbit.

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06.11.09:A New Type of Supernova?

Astronomers at  the University of California at Berkley may have added a new type of supernova to the list. Typical type I supernovae consist of a carbon-oxygen white dwarf accreting matter from a companion star until a runaway reaction occurs, while type II supernovae involve a collapse of a star perhaps nine times as massive as our Sun. Recently, astronomers uncovered evidence that an extragalactic supernova previously classified as a type II may in fact deserve a class of its own. Named SN 2002bj, this exploding star exhibited the characteristics of a garden variety nova, such as the brief flare up of in-falling hydrogen, but created an explosion 1,000 times more massive. In the case of SN 2002bj, however, the flash also had a conspicuous absence of hydrogen, with instead a strong helium flash and the presence of vanadium in its spectra, a first for a supernova. Theoretical models suggest that this may have been a binary white dwarf pair, with one feeding the other a steady flow of helium until it reached the collapse limit and burst. Also, unlike typical type Ia supernovae, the white dwarf involved survived the explosion. Another unusual signature to this supernova was the way it rapidly faded from sight in about 20 days, about four times faster than usual. SN 2002bj is located in the galaxy NGC 1821 and was spotted in February 2002. Does the classification of supernovae need tweaking?

AstroEvent of the Week: January 19th-25th, 2009: Will EE Cephei Fade?

Variable star observing stands as a key area that amateur astronomers can still make a significant contribution. Either via imaging or visual observation, its fun to know that you are doing some of the grunt work of science and not just taking pretty pictures. This week’s event will require a telescope of at least 4″ aperture; it’s a rare dimming of the eclipsing variable EE Cephei.

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