December 17, 2018

Astro Event: An Interesting Equatorial Galaxy.

Many northern hemisphere observers many not realize the wealth of galaxies that exist in the late fall sky. This week, we look at an interesting galaxy that transits to the south right around 9 PM local time; M77. Also known as NGC 1068, this large extended galaxy sports a bright nucleus shining a magnitude of about +10. Under moderate magnifications with a good-sized aperture telescope perhaps three distinct spiral arms can be seen.

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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”?

18.04.10- Zeroing in on Nearby Exoplanets.

It’s hard to believe that a little less than two decades ago, no extra-solar planets were known. Now, the count climbs daily, and platforms like the Kepler Space Telescope threaten to launch the tally into the thousands. Recently, an international team of astronomers made six new discoveries in two nearby star systems that may eventually lead towards the cosmic Holy Grail; an exoplanet resembling Earth. The team was led by prolific planet hunter Paul Butler and Steve Vogt, who discovered the super-Earths by combining radial velocity data gathered from the Anglo-Australian telescope and the Keck observatory. First up is 61 Virginis, a Sun-like star 28 light years away. This system has always been of interest to astronomers because it is a near twin to our own Sun and is on the short list for NASA’s Terrestrial Planet Finder. The team discovered three worlds ranging in mass from 5 Earths to 25. In addition, follow-up studies with the Spitzer Space telescope find evidence for a dust ring around 61 Virginis about twice Pluto’s distance from our own Sun. The second discovery is one 7.5 Earth mass planet and a possible two more found around the star HD 1461 in the constellation Cetus about 76 light years distant. Again, HD 1461 could pass for our Sun in terms of age, size, and mass. Both stars would be visible to the naked eye under reasonably dark skies. It remains to be seen if these worlds are rocky terrestrial planets or Uranus-like slush balls. Evidence is mounting, however, that planets may be common around nearby Sun-like stars. The innermost planetary detection for 61 Virginis also represents the smallest amplitude discovery ever made by astronomers. These discoveries were backed up by brightness measurements made by robotic telescopes based in Arizona and operated by Tennessee University’s George Henry. This ruled out the possibility that the amplitude variations seen were due to variability or “starspots”. The Lick-Carnegie Exoplanet Survey Team will also soon have a new weapon in its arsenal; the recently completed Automated Planet Finder (APF) Telescope atop Mount Hamilton. All that’s needed now is for the Discovery Channel to fund a new hit series; The Exoplanet Hunters!