Radojica
08-12-2009, 04:46 PM
The burning fuse
To astronomers there are two things immediately obvious about Eta Carinae: It is amazingly, almost impossibly bright, shining 4 million times brighter than our sun. It is also wildly unstable, being prone to huge flares, outbursts and dizzying swings in brightness that give the impression of something on the verge of self-destruction which it may well be.
What causes all this strange behavior in Eta Carinae is very simple: Its enormous, more than 100 times the mass of our sun. On Earth we tend to think of large things as being solid and stable, but in stars of this size the opposite is true. Their large size causes them to burn their nuclear fuel at an extremely rapid rate, blasting out so much heat, light and other energy that their outer layers are shredded, roiled and sometimes completely blown off in repeated violent outbursts.
The blast in the past
It was just such a violent outburst that first brought Eta Carinae to the attention of astronomers almost two centuries ago. It was first catalogued in 1677 as an unremarkable star, barely noticeable to the naked eye. But by 1730 observers noticed that Eta Carinae had grown much brighter, having become one of the most prominent stars in its constellation.
By 1782 it had dimmed to its former obscurity, but then in 1820 it again started growing and growing in brightness. By 1827 it had brightened more than tenfold, and by 1843 it was blazing as the second brightest star in the sky, outdone only by the star Sirius, which is 1,000 times closer to us.
At the time, no one understood what could possibly cause such strange behavior in a star, and it wasnt until 1994 that the Hubble Space Telescope first revealed what had happened 150 years before: Eta Carinae had blasted out an enormous two-lobed bubble of hot, glowing gas. Even today it can be seen racing outward at one and a half million miles per hour (2.4 million kilometers per hour). The amount of material blasted out was enough to make several of our suns, but for Eta Carinae it was just the latest outburst in its short and violent life.
The end of a short life
Eta Carinae is destined to die young. Most stars live for billions of years, but stars as massive and active as Eta Carinae burn through their fuel in an extremely short time -- as short as one million years or so, very quick for a star. They almost always end the same way: With a supernova explosion, a massive detonation that blows the star apart and scatters its remains for trillions of miles (kilometers) around.
Thats how most supermassive stars end, but Eta Carinae is such an extreme case that another possibility exists: It could end as a hypernova, a super-supernova that at its peak will outshine the entire galaxy.
The blazing violence of such an event is difficult to describe. Were it much closer it could even wipe out all life on Earth, eradicating our thin biosphere just like an ultraviolet lamp kills microbes. Fortunately its not that close, but at 7,500 light-years its still close enough to do some damage.
However, the likely damage is not to humans directly, but to satellites and the upper atmosphere. Thats because an explosion of this type generates huge amounts of high-energy radiation such as gamma rays. We on Earth are well shielded from gamma rays by our atmosphere, but satellites in space would be vulnerable and some of their electronics could be damaged by such an event.
Some have speculated that a huge blast of gamma rays could also affect the upper atmosphere, including the ozone layer. But that remains only speculation, and any such effect is likely to be very transient because the blast of gamma rays would be fairly brief.
The only humans who might suffer directly from Eta Carinaes violent demise would be astronauts in space. Outside of the Earths protective atmosphere they would be subject to the same powerful radiation as satellites, with conceivably lethal effect. While our own sun is also capable of lethal emissions, such as coronal mass ejections that could be harmful to astronauts, the difference is that our suns eruptions usually give us some warning, whereas Eta Carinae would not.
The star we've never seen
What makes the puzzle particularly difficult is that we have never actually seen Eta Carinae. When we look toward Eta Carinae or photograph it, what appears is not the star itself, but the huge shroud of glowing gas and dust it has thrown up around itself.
The glowing shroud around Eta Carinae has led some to speculate that behind the shroud lies not one star, but two or more massive stars combining to shine so brightly. But that still doesnt explain the burning question of the moment: What has happened to Eta Carinae in the last few months, and what will happen next?
No one really knows. Like geologists watching a trembling volcano, all we can do is watch and wait.
Eta Carinae could blow anytime, or it could continue rumbling and spewing gas until the day, perhaps tomorrow, perhaps thousands of years from now, when it will suddenly let go with the most phenomenal display of violence ever witnessed by humans and which will be possible to see even in the middle of the day shinning in the blue sky. It is now being watched almost around the clock, as much for the fascination as the science.
http://www.solstation.com/x-objects/eta-car2.jpg
http://www.solstation.com/x-objects/car2neb.jpg
http://www.solstation.com/x-objects/keyhole2.jpg
http://www.eso.org/gallery/d/80081-1/EtamosaicNM2_1.jpg
The Carina Nebula is a large bright nebula that surrounds several clusters of stars. It contains two of the most massive and luminous stars in our Milky Way galaxy, Eta Carinae and HD 93129A. Located 7500 light years away, the nebula itself spans some 260 light years across, about 7 times the size of the Orion Nebula, and is shown in all its glory in this mosaic. It is based on images collected with the 1.5-m Danish telescope at ESO''s La Silla Observatory. Eta Carinae (the brightest star in this image) is the most luminous star known in the Galaxy, and has most likely a mass over 100 times that of the Sun. It is the closest example of a luminous blue variable, the last phase in the life of a very massive star before it explodes in a fiery supernova. Eta Carinae is surrounded by an expanding bipolar cloud of dust and gas known as the Homunculus (''little man'' in Latin), which astronomers believe was expelled from the star during a great outburst seen in 1843.
To astronomers there are two things immediately obvious about Eta Carinae: It is amazingly, almost impossibly bright, shining 4 million times brighter than our sun. It is also wildly unstable, being prone to huge flares, outbursts and dizzying swings in brightness that give the impression of something on the verge of self-destruction which it may well be.
What causes all this strange behavior in Eta Carinae is very simple: Its enormous, more than 100 times the mass of our sun. On Earth we tend to think of large things as being solid and stable, but in stars of this size the opposite is true. Their large size causes them to burn their nuclear fuel at an extremely rapid rate, blasting out so much heat, light and other energy that their outer layers are shredded, roiled and sometimes completely blown off in repeated violent outbursts.
The blast in the past
It was just such a violent outburst that first brought Eta Carinae to the attention of astronomers almost two centuries ago. It was first catalogued in 1677 as an unremarkable star, barely noticeable to the naked eye. But by 1730 observers noticed that Eta Carinae had grown much brighter, having become one of the most prominent stars in its constellation.
By 1782 it had dimmed to its former obscurity, but then in 1820 it again started growing and growing in brightness. By 1827 it had brightened more than tenfold, and by 1843 it was blazing as the second brightest star in the sky, outdone only by the star Sirius, which is 1,000 times closer to us.
At the time, no one understood what could possibly cause such strange behavior in a star, and it wasnt until 1994 that the Hubble Space Telescope first revealed what had happened 150 years before: Eta Carinae had blasted out an enormous two-lobed bubble of hot, glowing gas. Even today it can be seen racing outward at one and a half million miles per hour (2.4 million kilometers per hour). The amount of material blasted out was enough to make several of our suns, but for Eta Carinae it was just the latest outburst in its short and violent life.
The end of a short life
Eta Carinae is destined to die young. Most stars live for billions of years, but stars as massive and active as Eta Carinae burn through their fuel in an extremely short time -- as short as one million years or so, very quick for a star. They almost always end the same way: With a supernova explosion, a massive detonation that blows the star apart and scatters its remains for trillions of miles (kilometers) around.
Thats how most supermassive stars end, but Eta Carinae is such an extreme case that another possibility exists: It could end as a hypernova, a super-supernova that at its peak will outshine the entire galaxy.
The blazing violence of such an event is difficult to describe. Were it much closer it could even wipe out all life on Earth, eradicating our thin biosphere just like an ultraviolet lamp kills microbes. Fortunately its not that close, but at 7,500 light-years its still close enough to do some damage.
However, the likely damage is not to humans directly, but to satellites and the upper atmosphere. Thats because an explosion of this type generates huge amounts of high-energy radiation such as gamma rays. We on Earth are well shielded from gamma rays by our atmosphere, but satellites in space would be vulnerable and some of their electronics could be damaged by such an event.
Some have speculated that a huge blast of gamma rays could also affect the upper atmosphere, including the ozone layer. But that remains only speculation, and any such effect is likely to be very transient because the blast of gamma rays would be fairly brief.
The only humans who might suffer directly from Eta Carinaes violent demise would be astronauts in space. Outside of the Earths protective atmosphere they would be subject to the same powerful radiation as satellites, with conceivably lethal effect. While our own sun is also capable of lethal emissions, such as coronal mass ejections that could be harmful to astronauts, the difference is that our suns eruptions usually give us some warning, whereas Eta Carinae would not.
The star we've never seen
What makes the puzzle particularly difficult is that we have never actually seen Eta Carinae. When we look toward Eta Carinae or photograph it, what appears is not the star itself, but the huge shroud of glowing gas and dust it has thrown up around itself.
The glowing shroud around Eta Carinae has led some to speculate that behind the shroud lies not one star, but two or more massive stars combining to shine so brightly. But that still doesnt explain the burning question of the moment: What has happened to Eta Carinae in the last few months, and what will happen next?
No one really knows. Like geologists watching a trembling volcano, all we can do is watch and wait.
Eta Carinae could blow anytime, or it could continue rumbling and spewing gas until the day, perhaps tomorrow, perhaps thousands of years from now, when it will suddenly let go with the most phenomenal display of violence ever witnessed by humans and which will be possible to see even in the middle of the day shinning in the blue sky. It is now being watched almost around the clock, as much for the fascination as the science.
http://www.solstation.com/x-objects/eta-car2.jpg
http://www.solstation.com/x-objects/car2neb.jpg
http://www.solstation.com/x-objects/keyhole2.jpg
http://www.eso.org/gallery/d/80081-1/EtamosaicNM2_1.jpg
The Carina Nebula is a large bright nebula that surrounds several clusters of stars. It contains two of the most massive and luminous stars in our Milky Way galaxy, Eta Carinae and HD 93129A. Located 7500 light years away, the nebula itself spans some 260 light years across, about 7 times the size of the Orion Nebula, and is shown in all its glory in this mosaic. It is based on images collected with the 1.5-m Danish telescope at ESO''s La Silla Observatory. Eta Carinae (the brightest star in this image) is the most luminous star known in the Galaxy, and has most likely a mass over 100 times that of the Sun. It is the closest example of a luminous blue variable, the last phase in the life of a very massive star before it explodes in a fiery supernova. Eta Carinae is surrounded by an expanding bipolar cloud of dust and gas known as the Homunculus (''little man'' in Latin), which astronomers believe was expelled from the star during a great outburst seen in 1843.