A Stellar Comet

Well, a star producing a comet-like tail. Not because it is losing material from being too close to a star like a comet does, but because of powerful winds at its surface. Read about it here and here.

The Curious Case of the Fading Star

I never knew this, but apparently one of the brighter stars in the sky, Epsilon Aurigae, had a peculiar habit of fading for a short period of time every 27 years. While changes in a star's brightness are normal, regular 27 year variations are peculiar. Go here to read how, using Spitzer observations, astronomers might have just been able to figure out what is going on. Enjoy!

Twinkle, twinkle older star...

... maybe your brightness variations will tell me what you are?

Go here to read about some interesting, year-long brightness variations observed from stars believed to be similar to what the Sun will turn into once it exhausts all of the Hydrogen in its core. So far, no models seems to explain this data - making it a very interesting problem indeed.

Description of October 29th Radio Show: Evolution of Low Mass Stars

Long available here, below is a detailed description of the October 29th edition of this radio show. On this program I talked about:

• Opening Song: Why Are Stars of Different Colors? by Tom Glazer & Dottie Evans
• News: Phoenix Mars Lander survives a dust storm that lowered its solar power intake (link), HiRISE camera on Mars Reconnaissance Orbiter sees evidence for a crater underneath the polar ice caps on Mars (link) and the Compact Reconnaissance Imaging Spectrometer sees evidence for opal on Martian surface - evidence for the presence of liquid water at some point in the past; detection of plumes of methane erupting on Martian surface may change landing location for future Mars Science Laboratory rover; both NASA and ESA having major cost overruns on next generation Mars missions; images of Mars's moon Phobos by Mars Express satellite suggests it is a rubble pile of many smaller asteroids stuck together; Cassini successfully sweeps into geysers on Saturn's moon Enceladus; radio observations of the nucleus of the Comet Tuttle suggests it consists of two objects orbiting each other very closely; new comet discovered by Rob Cardinal at University of Calgary (link); University of Western Ontario automated cameras video another meteor crashing down on Earth (link, videos); NASA launches IBEX spacecraft to study particles accelerated at the boundary of our Solar System (link); India launches its first spacecraft to the Moon, Chandrayaan-1 (link) - contains instruments built by NASA and ESA; NASA's next Lunar spacecraft, Lunar Reconnaissance Orbiter, begins testing before launch; congrats to Armadillo Aerospace for winning prizes at NASA's recent Lunar Landing Challenge; ESA hosts university challenge for Lunar Rovers; NASA tests its own future lunar rovers in Arizona and Hawaii (link); NASA and Challenger Center for Space Education host naming contest for astronaut housing prototype in Antarctica (link); waterless concrete developed to built structure on the Moon using only the lunar surface (link); ESA develops "replicators" to build future structure on Mars (link); backup computer on Hubble Space Telescope has glitch, causing spacecraft to go into safe mode (since resolved); ESA lost contact with XMM-Newton temporarily, since restored; Fermi Gamma Space Telescope (born GLAST) discovers first gamma-ray only pulsar (link); letter in Science about funding GLAST and Advanced Technology Solar Telescope; ESA satellite GOCE delayed due to rocket malfunction, cause identified; continued fighting over AMS experiment to Space Station; NASA reinstalls mirror on SOFIA observatory, scientists selected to do projects with this observatory; congrats to Kenneth Ford for becoming chairman of NASA Advisory Council Service and to Expedition 17 to the International Space Station for safe return home; Great World Wide Star Count begins.
• Wednesday Morning Astronomer (a response to this and this ESPN column): eta Carinae's bright flash not a supernova but something else, sci-fi explanations not science, I agree that launch of Chandrayaan-1 does not represent a decline in US capabilities at all.
• Calendar of upcoming Astronomy and science events in the greater Poughkeepsie and New York City area.
• Evolution of Low-Mass Stars: The definition here of low mass stars are stars born with a mass less than eight times that of the Sun, because these stars do NOT end their life in a core-collapse supernova. When these stars fuse all of their hydrogen to helium, fusion stops and they contract. As they contract, the stars core will get hot enough and dense enough to fuse helium to heavier elements. Helium fusion releases more energy than Hydrogen fusion, causing star to expand again and possibly blowing off outer layer. This results in structures called planetary nebula, and this mass loss process is poorly understood but important in understanding effect of stars on their surroundings. New observing techniques (link) being developed to better study this. Images of planetary nebula, like Cat's Eye Nebula and NGC 2371 (link) suggest process extremely complicated and variable. When Helium fusion stops, star's core begins to collapse again. In doesn't get dense or hot enough to fuse these heavier elements, but electrons in the core get close enough that their repulsion supports the core from gravity (this is called "electron degeneracy pressure"). Such an object is called a white dwarf. The internal structure of white dwarfs is poorly understood, and the best way to study it is by looking a pulsations from them. "Starquakes" in a white dwarf will change the brightness, and by studying these pulsations can learn about their structure. A new campaign to do this by the Whole Earth Telescope has begun (link). These pulsations also depend on the chemical composition of the white dwarf, and for the first time were detected from a Carbon white dwarf (link). Young white dwarfs produce a lot of ultraviolet light, which ionizes and illuminates the planetary nebula produced by the progenitor star - though in one case the white dwarf response for this has yet to be detected (link). If a white dwarf is close to another star, matter from that star will flow onto the surface of the white dwarf. This matter, as it accumulates will heat up until it is hot and dense enough to star fusion, releasing a flash of light called a "nova". XMM-Newton serendipitously observed X-ray from such a nova produced by a previously unknown white dwarf. Mass flowing from one object to another often produces radio jets - radio emission from fast moving material flowing AWAY from the central source. These jets had not been observed from a type of white dwarf system, until now. These nova explosions also believed to produce dust - the fusion creates heavier elements which, as they cool, condense to dust grains. Recent observations of a nova in 2006 suggests this might not be the case (link) for this one, though dust production has been observed in other novae (for example, this one.). If a white dwarf accumulates so much material that electron degeneracy pressure can no longer support it against gravity, it explodes in an event called a Type Ia supernova. How it explodes is currently unknown, and being simulated on lots of super-computers at the University of Chicago (link) - among other places. Additionally, it has been theorized that a white dwarf which passes to close to a black hole might be ripped apart and explode (link).
• Closing Song: Wolf 359 by The Chromatics

Thank you very much for listening. As always, any questions, comments, or concerns are deeply appreciated.

November 5th Radio Show online: Evolution of High-Mass Stars

I'm really sorry for taking so long to post this, but here is the November 5th episode of this radio show where, in addition to the usual Astronomy news and notes, I discuss the evolution of massive stars before they go supernova. Hope you enjoy!

And yes, I do owe you a detailed description of the October 29th radio show as well.

October 29th Radio Show: Evolution of Low Mass Stars

Available here (finally) is the October 29th edition of this radio show. On this program, in addition to the latest Astronomy news and calendar, I discuss the evolution of low mass stars like the Sun, from Sun-like stars to red giants and then to white dwarfs. Hope you enjoy! As always, any and all feedback is appreciated. Thanks a lot for listening.

August 27th radio show online: Stars, stars, stars

Available here is the August 27th edition of this radio show, where - in addition to the latest Astronomy news - I discuss recent research on stars of all masses, and how they evolve. A more detailed description will come later, but in the meantime, hope you enjoy!