JamesSavik

There are two types of supernova: Type I and Type II. Then there are numerous sub-species which are spectroscopic variations on those two themes. Type I supernova are always white dwarf stars that have grown beyond the Chandrasekhar limit- the maximum mass possible for a white dwarf. When a white dwarf accumulates mass in excess of between 1.2 to 1.4 solar masses[there is some debate on this exact number]. Matter in the state of a white dwarf at that density and pressure becomes unstable and explodes. Type II supernova are very different. This event marks the end point of a massive stars evolution. Giant stars operate like huge reactors. Because of their size and mass, the gravitational pressure of the star on it's core is huge. Under these conditions, the fusion reactions proceed at a furious rate. Such stars are very short-lived. It only takes 10-40 Myrs for one of these giants to burn through their core fuel. First hydrogen is fused into helium, and in successive phases the stars core fuel will be built up- oxygen, nitrogen then carbon. When the core has become Iron, that's when trouble begins. The energy of an Iron fusion reaction is insufficient to keep the star in hydrostatic equilibrium and the star's core collapses. The explosion part of a type II is the rebound from its core. Type II SN are quite rare and are usually seen at extra-galactic distances. In 1987, a SN occurred in the LMC, some 150,000 lyrs away, which is a mere drop in the bucket by cosmic standards. It gave us our first opportunity to study one of these events relatively "close up" with modern instruments. Supernovas play a very important role in stellar evolution. They are the furnace in which all elements heavier than iron are formed. They enrich the interstellar medium with important elements like Nitrogen, Oxygen, Carbon, Silicon, etc. Their massive shock waves are known to trigger star formation by compressing nebular gas which leads gas clouds to collapse under their own gravity. I've studied SN 1987A since it occurred and continue to follow its progress. It created a millisecond pulsar and its ejected shell continues to expand. I have some 80 books and hundreds of papers on the topic. The LMC and SMC are important objects of study: as small galaxies interacting with one another and the Milky Way, as a stellar nursery and laboratory to study the life cycle of stars. They are only observable by ground based observers in the southern hemisphere. My idea of heaven would to be to retire to Australia and study the Magellanic Clouds. This is the Tarantula Nebula in the Large Magellanic Cloud. It is a region of prolific star formation and is quite beautiful. Notice the hot, young blue and white stars in contrast it with the older red giant.

Stellar explosion revealed in unique detail David Shiga for NewScientist.com news service July 19, 2006 Source Link The material collected from the red giant leads to a nuclear explosion on the surface of its companion, a white dwarf star (Artist's impression: David A Hardy/PPARC) ____________________________________________________________________ An unprecedented glimpse of the blast wave from an erupting star has been seen by astronomers. The new view suggests the binary system observed could be responsible for some of the universe's most powerful explosions, called Type Ia supernovae. These are very important to astronomers as they are used as "standard candles" to measure distances, but their source has been a major mystery in astronomy. The explosion occurred in a binary star system called RS Ophiuchi. It consists of a red giant star orbited by the dense core of a burned-out star, called a white dwarf. The outbursts occur because the white dwarf slowly collects gas shed by the red giant. When enough gas piles up on the white dwarf, the mounting pressure triggers a tremendous nuclear explosion. RS Ophiuchi explodes this way every few decades, but not with a regular schedule. Before the latest outburst, it had not exploded since 1985. Astronomers were therefore excited to discover a new explosion in progress on 12 February 2006. They were able to track the blast wave's progress sooner after its onset and in more detail than ever before. "We really saw much, much more this time," says Jennifer Sokoloski of the Harvard-Smithsonian Center for Astrophysics, in Cambridge, US. Sokoloski led a team that observed the event with the Rossi X-ray Timing Explorer (RXTE), starting the day after the initial detection of the outburst. Flickering candles The researchers found evidence that the system was on its way to producing a Type Ia supernova. Although these are used as standard candles, there are in fact slight differences in their brightness. This adds uncertainty to distance measurements. Part of the problem is that astronomers do not know for sure what causes the supernovae. Evidence strongly suggests that they occur when a white dwarf collects too much mass, triggering a nuclear explosion that completely destroys the white dwarf. Although astronomers have seen many systems where a white dwarf is collecting matter, none seemed to have the right conditions to lead to a Type Ia supernova. For example, some white dwarfs are collecting matter at too low a rate to get to the critical mass in the universe's lifetime. The properties of the shock wave observed around RS Ophiuchi allowed Sokoloski's team to calculate the mass of the white dwarf that produced it. They determined it is very close to the critical mass that would trigger a supernova. That led them to suggest that systems like RS Ophiuchi, called recurrent novae, account for at least some of the Type Ia supernovae. If true, this would help solve the mystery of their origin and could help refine the distance scale they underpin. "It would be very nice to explain why there is this slight variation in supernova brightness," Sokoloski told New Scientist. Lack of hydrogen But there is a problem with this idea, argues Sumner Starrfield of Arizona State University in Tempe, US, who is also studying RS Ophiuchi's recent outburst. Type Ia supernovae are distinguished by a lack of hydrogen in their blast waves, he says, and the red giant in the RS Ophiuchi system has shed a lot of hydrogen into the surrounding area. "I think it will explode as a supernova but it's not going to be a Type Ia," Sumner told New Scientist. Sokoloski argues that the white dwarf's recurrent outbursts have probably removed the hydrogen from the immediate vicinity, so that it would not appear in a future Type Ia blast wave. A second study released on Wednesday shows that the material from the explosion seen in February was probably spewed out in jets rather than equally in all directions. Tim O'Brien of the Jodrell Bank Observatory in Macclesfield, UK, led the study. It was based on radio data from the UK's Multi-Element Radio Linked Interferometer Network (MERLIN) and the European VLBI Network (EVN). "It's a jet-like explosion, probably shaped by the geometry of the binary-star system at the centre," says O'Brien. "This suggests that there is much more going on than we believed," says Sumner. He added that it will probably take years to figure all out the implications of the new information. Journal reference: Nature (vol 442, p 276, 279) __________________________________________________________________ Mystery of Explosive Star Solved Ken Thar for space.com July 19, 2006 Source Link In February, a faint star a few thousand light-years away flared suddenly, beaming so brightly that for a few days it was visible to the naked eye. The star is a stellar corpse the size of Earth, known as a white dwarf, and it is paired in a binary system with a red giant, a dying, bloated star that once resembled our Sun. The red giant has been dumping gas onto the surface of the white dwarf, and every few years, enough matter accumulates to set off a giant thermonuclear explosion. It was one of these explosions, called a "nova," that astronomers and stargazers detected earlier this year. The two-star system, called RS Ophiuchi, is known as a recurrent nova because five similar eruptions have been detected before. The first observation occurred in 1898; the last eruption prior to this latest one happened in 1985. The new observations, made using advanced radio and X-ray telescopes not available during the last outburst, reveal the explosion to be more complex than was previously assumed. Standard computer models had predicted a spherical explosion with matter ejected in all directions equally. The latest observations instead showed that the explosion evolved into two lobes, confirming suspicions that the nova outburst produces twin jets of stellar material that spews out from the white dwarf in opposite directions. "The radio images represent the first time we've ever seen the birth of a jet in a white dwarf system. We literally see the jet 'turn on,'" said Michael Rupen, an astronomer at the National Radio Astronomy Observatory who studied RS Ophiuchi using the Very Long Baseline Array (VLBA). As impressive as the nova are, they might just be precursors for a more violent supernova explosion that will occur in the future, scientists say. Like the Sun, Only More Powerful The white dwarf's thermonuclear blasts are similar to those that occur on the surface of the sun, but they can be over 100,000 times more powerful. During each outburst, an amount of gas equal to the mass of the Earth is flung into space. Some of this ejected matter slams into the extended atmosphere of the inflated red giant, creating blast waves that accelerate electrons to nearly the speed of light. As the electrons travel through the stars' magnetic fields, they emit radio waves that can be detected by telescopes on Earth. The blast waves move at over four million miles (about 6.4 million km) per hour. For a few weeks during each outburst, the white dwarf becomes a red giant. "After the [thermonuclear explosion], the white dwarf will puff up into a red giant for a few weeks as the hydrogen that has been blasted into space fuses into helium," explains Richard Barry of the NASA Goddard Space Flight Center in Maryland. All eyes on Ophiuchi Japanese astronomers first detected signs of RS Ophiuchi's latest nova on the night of Feb. 12. Follow-up observations by radio telescopes revealed an expanding blast wave whose diameter was already the size of Saturn's orbit around the Sun. In the weeks following, several radio and X-ray telescopes around the world tracked RS Ophiuchi closely, including the MERLIN array in the UK, the European EVN array, the Very Long Baseline Array (VLBA) and Very Large Array (VLA) in the United States, and NASA's Swift and Rossi X-ray Timing Explorer satellites. Findings from the Rossi X-ray Timing Explorer and the VLBA/EVN observations are detailed in two separate studies published in the July 20 issue of the journal Nature. The red giant and white dwarf stars making up RS Ophiuchi are separated by about 1.5 astronomical units, or one and a half times the distance the Earth is from the sun. The binary star system is located in the constellation Ophiuchus, about 5,000 light-years away

any volunteers?

Kevin You've been a ray of sunshine here. You are always upbeat and have something positive to say. Your presence here has enriched us all. JS

OK. Two cats. Check. I'm liking you better already. Now for your boy friend: is the teasing friendly and good natured or malicious and demeaning? Either way it seems to be bothering you. Talk to him about it. Unless he is a jerk that is being intentionally mean, he will be considerate of your feelings and stop. Now- if he is being intentionally mean, kick the *&^%% to the curb! Don't stay with someone who is mean to you! This is how abusive relationships happens. MANY people stay with someone who is bad for them because of low self-esteem and insecurity. Worse, they stay with an abusive partner because they don't think that they can do better or don't deserve any better. You can do better and you deserve better! Soooo... he's not a jerk and you're keeping him? It sounds like the two of you need to develop some common interests. Take a class. Volunteer- something that the two of you can do together. This will help your relationship in a number of ways and add new dimensions to it. Boredom often masks other problems. What some people call boredom is really anxeity, worry or depression. Is something else on your mind?

Eric is legal now!!!! Woo-hoo! :king:

May your 17th year be your best yet!

Xander is lucky to have you! You pay attention to him, walk him and play with him. Way too many people just put their dogs in the back yard and don't give them enough attention. Then when they act up, they say stupid dog when it's really a stupid owner.

Hi Vance! Glad to hear that your blood pressure is under control. My doctor always seems disappointed when my blood pressure is so normal since I could lose 20 pounds and smoke camels. Blood pressure can be greatly effected by nerves. If you were stressed out when they took it, it could have skewed the reading toward the high side. You're way too young for high blood pressure. You are supposed to be over forty, 20+ pounds overweight and smoke camels to have high blood pressure. You could get in trouble with our Union! JS

In my old age I don't have that distraction problem. I'm real nearsighted and with my glasses, I can only see directly in front. It's kinda like wearing blinders like they put on plow mules. Downside is that if I look at someone, I look directly at them. None of those coy out-of-the-corner of my eye looks for me. I don't recommend it- becoming very near sighted that is.

Beautiful Skin was hot but the subject matter creeped me out. :wacko: If he is gay, then w00t!- welcome to the family Joey!!!

I hate to rain on the Parade but Lance bass doesn't strike me as being smart enough to be gay. There is an IQ requirement you know. In that picture, he looks like a doofus.

get a cat. you'll never be bored again.

I couldn't decide which of the two pups in the video was the cutest.

Thanks for all of your comments and votes in the poll! Keep them coming and tell us about any technical issues you may have. I would also like to hear from some of our dial-up users: how does the site perform at low speeds?

I've been dieting and I hate it. Why is it that everything in the Southern diet has too much cholesterol, fat or sugar? Maybe it would help if we didn't roll everything in flour and lemon-pepper and fry it. Salad and pasta and fruit oh my! Salad and pasta and fruit oh my! I'm sorry but I'm a carnivore. Nothing made of meat is safe near me at the moment. I'm liable to kill it and fry it. I'm hoping that my cat will bring me a squirrel carcass. Awe- screw it. I'm going to Wendy's. I'm going to have the triple bypass special: a triple bacon-cheese burger with chili and jalape

Luc- Anniversaries suck. They remind you of loss and reopen old wounds. I have the same problem every February 22nd. The love of my life died that day in 1996. Every year it rolls around, every year it stings a little less- but it still stings. It was 10 years ago this past February. This year was worse than most because- well hell, it has been 10 years. I feel like I should be over it but I'm not because I'm weak or a dumb ass or something. No- the scars don't go away. Every year they pop out like an unwelcome visitor and torment us for a while until we figure out how to put them back into the little box we keep them in. I don't have an answer for you. I don't have a magic formula to make it any better. Just know that you aren't alone. There are dates on my calender too that make me cringe every time they come up. JS

Ummm- post a link so we can find them! I'm always looking to discover new stories.

DSL is typically associated with phone companies like Bellsouth or PacBell. Cable modem service is provided by CTV providers on the same coax cable that your cable TV comes in on. It's usually a little faster than DSL.

My apologies to the Mac legions. I didn't mean to leave you guys out. From the feedback that I've gotten, all "other" entries appear to be Macintosh.

NO changes. It never has acted right.

It gives out Main Page a Break. It was getting entirely too crowded. I think that it gives the author forums better coverage, not less.

Welcome! What remarkably good taste you must have to have ended up here.

I'm never scared by horror movies. [except for maybe the Hills Have Eyes] It takes a dentist to make my hair stand on end.

Did I mention that the MSN messenger hates me? I'm not sure what I did to piss it off so bad. Every time I try to use MSN, it connects,might work for a short time (or might not) and then it locks up my internet connection. GRRRR. I missed the GAC meeting tonight because it wouldn't work. That bums me out because I hate to let down the team. I even uninstalled it and tried to reload it, then cold booted the entire system. Same crap. How embarrassing. The International Brotherhood of Geekdom is going to demand that I return my pocket protector. Sorry guys.