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Hubble finds Mass of White Dwarf
Chris Bradshaw writes "The mass of the nearest white dwarf star to Earth has been measured accurately for the first time. from the article: 'Sirius B is just 12,000 km (7,500 miles) in diameter, similar to Earth, but its mass is 98% that of the Sun. Studying Sirius B has been difficult because of the bright light coming from its neighbour Sirius A, the "Dog Star." The results, published in the Monthly Notices of the Royal Astronomical Society, come from astronomers using the Hubble Space Telescope.'"
additionally, more can be found on the white dwarfs in general Here.
I'm not fat, just big boned...
Mass of RED Dwarf
http://washingtontimes.com/upi-breaking/20050420-1 25927-9641r.htm
To bad they are going to plough it into earths atmosphere.
http://en.wikipedia.org/wiki/Karma_whoring
Although NASA (or the US goverment, it is all politics) does not want to fund Hubble anymore, the telescope proves that it is valuable every time again. Astronomers just need more time with the equipment to take more readings of an object so that they can catch the details. Is it an idea that a commercial company adopts the Hubble telescope and rents the time on the telescope out again to different agencies around the globe? The price for the adoption could be the operational cost of keeping Hubble in orbit in working order.
My wife's sketchblog Blob[p]: Gastrono-me
Actually, I may have spoken too soon:
Many white dwarfs are approximately the size of the Earth, typically 100 times smaller than the Sun. They may have the same mass as the Sun and so are very compact.
Do they really vary in density that much?
not mentioned in the article, at http://columbia.thefreedictionary.com/Sirius
Selected excerpt:
"Sirius A is about twice the size of the sun and about 20 times as luminous. It is also one of the nearest stars, lying at a distance of 8.7 light-years, so that it has been studied extensively. From an analysis of its motions, F. W. Bessel concluded (1844) that it had an unseen companion, which was later (1862) confirmed by observation. The companion, Sirius B, is a white-dwarf star and has also been the object of considerable study because it is the first white dwarf whose spectrum was found to exhibit a gravitational red shift, as predicted by the General Theory of Relativity."
Not necessarily. Is Sirius B a -typical- white dwarf or is it half the typical white dwarf size?
Does anyone know?
Anagram("United States of America") == "Dine out, taste a Mac, fries"
The upper limit, known as the Chandrasekhar limit, for a white dwarf is 1.4 solar masses (more or less).
http://en.wikipedia.org/wiki/Anonymous_Coward
Perhaps the Mod thought the parent post was suggesting that "the advanced Siriusian aliens were planning to hit the Earth with Sirius B. Obviously the Siriusians are an advanced corporate culture, and are intent on "downsizing" their system, cutting their aging former stars loose, in an attempt to get lean and (very) mean, and to eliminate possible future competition from other evolving corporatized systems."
Do they really vary in density that much?
Yes. White dwarfs vary in density a whole lot; degenerate gases behave quite oddly. If you add matter to a white dwarf, it actually gets a little smaller. The limit is about 1.4 solar masses, at which point the white dwarf collapses to form a neutron star.
Real Daleks don't climb stairs - they level the building.
Just to expand that a bit, if the mass of a white dwarf goes over 1.4 solar masses, the gravitational collapse is strong enough to trigger a supernova explosion. In other words, at masses greater than the Chandrasekhar limit, the (inward) gravitational pressure overcomes the (outward) thermal/fusion pressure, thus causing a collapse and the ignition of most of the remainder of the stars fuel, thus the supernova explosion.
No folly is more costly than the folly of intolerant idealism. - Winston Churchill
I still keep thinking the HST isn't really needed anymore
You just got troll'd!
Right idea, wrong mechanism.
A white dwarf is not supported by thermal pressure, or by nuclear fusion; it is supported by degeneracy pressure between electrons, a consequence of the exclusion principle in quantum mechanics that forbids two electrons from occupying the same quantum state.
1.4 solar masses is correctly given as the critical point at which gravity prevails over the internal pressure; at this point, the star switches from degeneracy pressure between electrons to degeneracy pressure between neutrons, in the process dropping considerably more than the weight of the Sun from the size of the Earth to something more like the size of Belgium, through an enormously strong gravitational field. This releases an awful lot of energy, and is the main power source for such a supernova.
There's another type of supernova which is driven by fusion, but that's more typical of accretion systems in which the infalling matter has heated the white dwarf sufficiently to reignite fusion processes; then the fusion reaction is an uncontrolled runaway and can wholly disrupt the star.
Real Daleks don't climb stairs - they level the building.
The BBC article cited in the main post has no mention of the redshift associated with this whitedrawf. It just says "The mass calculations are based on how the star's light is distorted by its neighbour's intense gravitational field." This New Scientist article reporting on the same news does mention redshift - I like redshift: http://www.newscientist.com/article.ns?id=dn8460&f eedId=space_rss20
Other info on redshit can be found here: http://en.wikipedia.org/wiki/Redshift
I don't think the Chandrasekhar limit has anything to do with gravity overcoming the forces of thermal energy. According to the wikipedia article, it's the amount of mass required to overcome electron degeneracy pressure, producing a neutron star or a black hole.
Mea navis aericumbens anguillis abundat
Perhaps this is some cleverly disguised viral marketing to promote Howard Stern's move to satellite radio?
they are decommissioning Hubble. It hasn't ammounted to anything anyway.
- what is the definition of simultanagnosia?! I've been meaning to look it up!
White Dwarf needs food badly.
Cheesy Movie Night
I think Neutron stars are around 20km diameter (size of a small city), quite a bit smaller than Belgium. Plus, they often spin very quickly due to the conservation of angular momentum (think of the ice skaters spinning with arms stretched compared to closed thing).
Or "Caucasian vertically challenged person"
What you are referring to is a nova. Not a supernova. White dwarfs can in fact go through several nova events, as long as their total mass remains below the limit. A nova explosion is usually fueled by nuclear reactions in the outer portion of the star, in the accretted material. As the material acretes recurring nova can happen almost periodicaly. However, a Type I supernova is a different beast entirely, and results from the amount of acreted material raising the density and pressure in the core of the white dwarf enough to reinitiate nuclear fusion in the core. When this happens, the reaction is catastrophic and blows the star apart.
Shop Smart, Shop S-mart!
Detectig and studying non-luminous objects like Buffy is a lot harder than luminous ones like Sirius B.
Actually "caucasian" has gone out of vouge. "White" is now the accepted term.
Free as in speech, free as in beer, or free as in lunch?
This releases an awful lot of energy, and is the main power source for such a supernova.
What type of supernova? Simply collapsing to a neutron star doesn't *cause* a supernova, although a neutron star can be a supernova remnant.
It sounds like you're saying that if you have a white dwarf sitting there, and it accretes mass from some other source, like a binary companion, when its mass grows to be greater than the C-limit, it collapses into a neutron star, and that the energy released in the collapse generates a supernova.
That's not the case. If you have a white dwarf sitting there, and it accretes enough mass to go over that limit, then basically what happens is that carbon begins to fuse. It happens everywhere, throughout the star, and you wind up with a carbon detonation supernova, a Type 1a supernova. It's not the energy of gravitational collapse which blows the star apart, it's the new fusion reactions.
Sorry , Funny. Now Please mod us all down some more because on of the Official Slashdot Mods (OSM) originally zinged the parent before he had his coffee. Oh, BTW, cooperate with the DIA, much? Not so much? Much too much!
how do they know it was measured 'accurately'?
always mosh clockwise
Detectig and studying non-luminous objects like Buffy is a lot harder than luminous ones like Sirius B.
What about detecting and studying Lumines itself? And, if you value Freedom, what about Luminesweeper?
Their paper.
Sirius B is pretty typical, though there is still a lot of variation. If I remember correctly, their masses can range from about half solar to 1.4 solar with a radius similar to Earth's.
Shouldn't the aliens from Sirius be called the Nommos
...dark elfs?
Well, I don't think it's a typical scenario for a white dwarf star to collapse into a neutron star due to mass accretion; that usually leads to a Type Ia supernova. Neutron stars form from the core of their progenitor star directly, do they not, skipping the white dwarf stage?
Don't just stand there, get that other dog!
The Nommo are ancestral spirits (sometimes referred to as deities) worshipped by the Dogon tribe of Mali, Africa. The word Nommos is derived from a Dogon word meaning, "to make one drink"
Considering how the slashdot mods tapped into this thread and harvested 2-3 Karma pints^^^^^points from every contributor, yes, it does seem appropriate
The Dogon reportedly related to Griaule and Dieterlen a belief that the Nommos were inhabitants of a world circling the star Sirius
Oh, yeah and that too.
Something doesn't add up for me with that description of a 1a supernova. There's a hell of a lot of gravitational potential held in a white dwarf -- something like 10^44 joules. This is also incidentially approximately the same as the energy released in the fusion process, assuming 0.1% of rest mass is converted to energy. So either I'm missing something, or about half the energy of a 1a supernova comes from fusion, and the other half from gravitational collapse. It's not clear to me that one would dominate, in the way you describe.
No, white dwarfs do become fusion-powered supernovae, not gravity-powered. IAAA (I am an astrophysicist.)
A white dwarf becomes a Type Ia supernova when, at around 1.4 solar masses, the pressure at the center reaches the point where it can burn by fusion the carbon-nitrogen-oxygen left over from previous rounds of burning. This leads to a fusion-driven explosion that gets no net energy from gravitational collapse, leading to an expanding gas cloud that is largely hot iron-group elements.
There is another class of supernova that is gravitationally driven. Core collapse supernovae are produced when a massive star (>8 solar masses, last I heard) has burned 1.4 solar masses at its center to iron. (The 1.4 solar mass value is semi-coincidental with that in the previous paragraph, based on similar but not identical physics.) This is a gravity-powered supernova that blows the outer parts of the core away, leaving a neutron star or black hole where the core was.
There is no way for a white dwarf to become a core collapse supernova, the fusion kicks in and blows it apart before that happens.
The Dogon, a tribe in West Africa, are believed to be of Egyptian descent. After living in Libya for a time, they settled in Mali, West Africa, bringing with them astronomy legends dating from before 3200 BCE. In the late 1940s, four of their priests told two French anthropologists of a secret Dogon myths about the star Sirius (8.6 light years from the earth). The priests said that Sirius had a companion star that was invisible to the human eye. They also stated that the star moved in a 50-year elliptical orbit around Sirius, that it was small and incredibly heavy, and that it rotated on its axis.
All these things happen to be true. But what makes this so remarkable is that the companion star of Sirius, called Sirius B, was first photographed in 1970. While people began to suspect its existence around 1844, it was not seen through a telescope until 1862 -- and even then its great density was not known or understood until the early decades of the twentieth century. The Dogon beliefs, on the other hand, were supposedly thousands of years old.
http://www.dreamscape.com/morgana/thalass2.htm
Health Insurance Quotes
You are right that the gravitational binding energy of a white dwarf is comparable to the fusion energy of its combustion from carbon to iron. However, comparable doesn't mean equal and if you work it out, the fusion energy dominates. The gravitational energy is negative, so it reduces the amount of available energy for the supernova (i.e. the ejecta are moving more slowly because it has to climb out of its own gravity well), but it is still energetically favorable to go from a dense chunk of carbon to an expanding diffuse cloud of iron.
They went to a comic/magazine collector and asked them how much that issue weighed.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
According to the MSNBC article, white dwarfs are the result of "Type Ia supernovas".
Is that really true?
It seems like an event like that only 8 light years away would have fried our little pitiful planet in a away that would be very noticeble today, or more likely exterminate all life.
Anyone know?
Excellent article on this topic.
I knew my wife did something my collection. Who would've thought game magazines would do so well in space?
"It is a miracle that curiosity survives formal education." -Albert Einstein
The gravitational energy is negative, so it reduces the amount of available energy for the supernova
No, that's not right. If the dwarf collapses to, say, a neutron star, energy will be liberated when the radius of the star decreases. The change in gravitational potential is negative, so that extra energy has to go somewhere. This fuels Type 2 supernovas. I'm just not sure where that energy fits into the Type 1a.
I've heard that it might be that no neutron star is formed in 1a supernovas (the star is just blown apart), so there is no liberation of gravitational potential. That's probably the answer.
We'll figure out how to put people back in space just as soon as China does it. Coincidence? Hardly.
There is no way in holy Hell that the Hulk can ever stand up even to the weakest, post-John Byrne incarnation.
Very recently, Superman was able to easily support 200 quintillion tons with one arm, no straining. This is roughly 1/30,000th of the mass of the Earth itself. (Hence he could, with effort, actually move the earth, and without taking eons to slowly accelerate it.) Yes, he was over-amped on sun juice, and may be "dying", but his strength was only up by 3x over its normal level according to the poindexter examining him.
Meanwhile, the Hulk's greatest feat, lifting a 150 billion ton mountain, was not even that great. The Secret Wars issue involved clearly states inside he was merely supporting a tiny section of it, under a hollow created by Iron Man after the Molecule Man dropped the mountain range on the heroes.
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
Just a terminology thing: Gravitational potential energy is measured relative to the system dispersed out to infinity. A white dwarf has negative potential energy, and so combined with the positive energy release by fusion will diminish the energy of this Type Ia supernova, relative to what you would get if you jcoudl just ignore gravity.
The iron core of a core-collapse supernova progenitor (similar to a white dwarf in size and mass, but made of un-fusable iron) has negative gravitational energy. The 12-km radius neutron star it becomes as it collapses has a much much more negative gravitational energy, by of order -1e46 Joules (-1e53 ergs). As you'd expect, this means that there's about 1e46J of positive energy suddenly liberated. 99% of that comes out in neutrinos, which have almost no effect once they get out of the star. The remaining 1e44 ergs comes in the form of supernova light and kinetic energy of the exploding ejecta.
The non-neutrino portion of the energy of a core collapse supernova is comparable to the total energy of a Type Ia supernova (which does not produce much in the way of neutrinos).