Salyut space station has been launched by Russia in 1971.
Salyut space station has been divided into three sections.
It had three working compartments: a small-diameter working area, a large-diameter working area, and an airlock transfer and docking component. The two working areas provided room and equipment for dining, recreation, control stations, food and water storage, hygiene, exercise, and science experiments. A round opening on top of the large working area had sensors for studying micrometeoroids in the Earth's vicinity.
Saturday, May 2, 2009
Evolution of Universe
The three main theories put forward to explain the origin and evolution of the universe are:
The Big Bang Theory
The Steady State Theory
The Pulsating Theory
1. The Big Bang Theory: Le Maitre and Gammow proposed this theory. According to this theory, at the beginning of the universe, the whole matter of the universe was once concentrated in an extremely dense and hot (~10 12K) fireball. Then about 20 billion years ago a vast explosion (big bang) occurred. The matter was broken into pieces, which were thrown out with high speed in all directions forming stars and galaxies; which are still moving way from one another. According to Hubble's law, the velocity of recession of a galaxy becomes equal to the velocity of light at a distance equal of 20 billing light years. It means, the light rays from stars and galaxies, which are situated at a distance of 20 billion light years or more, can never reach us. Thus this distance becomes the boundary of observable universe. On account of continuous recession, more and more galaxies will go beyond this boundary and the will be lost. As a result of this, the number of galaxies per unit volume will go on decreasing and ultimately a time may come when we may have empty universe.
2. Steady State Theory: Bondi, Gold and Fred Hoyle developed this theory. According to this theory, the number of galaxies in the observable universe is constant and new galaxies are continuously being created out of empty space, which fill up the gaps caused by those galaxies, which have crossed the boundary of the observable universe. As a result of it, the overall size of mass of the observable universe remains constant. Thus a steady state of the universe is not disturbed at all.
3. Pulsating Theory: According to this theory, the universe is supposed to be expanding and contracting alternately i.e. pulsating. At present, the universe is expanding. According to pulsating theory, it is possible that at a certain time, the expansion of the universe may be stopped by the gravitational pull and the may contract again. After it has been contracted to a certain size, explosion again occurs and the universe will start expanding. The alternate expansion and contraction of the universe give rise to pulsating universe.
The Big Bang Theory
The Steady State Theory
The Pulsating Theory
1. The Big Bang Theory: Le Maitre and Gammow proposed this theory. According to this theory, at the beginning of the universe, the whole matter of the universe was once concentrated in an extremely dense and hot (~10 12K) fireball. Then about 20 billion years ago a vast explosion (big bang) occurred. The matter was broken into pieces, which were thrown out with high speed in all directions forming stars and galaxies; which are still moving way from one another. According to Hubble's law, the velocity of recession of a galaxy becomes equal to the velocity of light at a distance equal of 20 billing light years. It means, the light rays from stars and galaxies, which are situated at a distance of 20 billion light years or more, can never reach us. Thus this distance becomes the boundary of observable universe. On account of continuous recession, more and more galaxies will go beyond this boundary and the will be lost. As a result of this, the number of galaxies per unit volume will go on decreasing and ultimately a time may come when we may have empty universe.
2. Steady State Theory: Bondi, Gold and Fred Hoyle developed this theory. According to this theory, the number of galaxies in the observable universe is constant and new galaxies are continuously being created out of empty space, which fill up the gaps caused by those galaxies, which have crossed the boundary of the observable universe. As a result of it, the overall size of mass of the observable universe remains constant. Thus a steady state of the universe is not disturbed at all.
3. Pulsating Theory: According to this theory, the universe is supposed to be expanding and contracting alternately i.e. pulsating. At present, the universe is expanding. According to pulsating theory, it is possible that at a certain time, the expansion of the universe may be stopped by the gravitational pull and the may contract again. After it has been contracted to a certain size, explosion again occurs and the universe will start expanding. The alternate expansion and contraction of the universe give rise to pulsating universe.
Do Dreams Really Mean Anything?
No doubt even the earliest humans were perplexed and fascinated by dreams that can sometimes seem as real as the world around us. Do they really mean anything? Scholars tended to dismiss them as little more than mental fireworks until the latter part of the 19th century. But when Sigmund Freud published "The Interpretation of Dreams" in 1899, he introduced science to the complex and bizarre world hidden in the human mind.
Freud called dreams the "royal road to the unconscious," and for more than a century now, researchers have tried to travel down that road. We know now that dreams do mean something, and they are universal. The most common dream, according to some studies, occurs in all cultures, and it's virtually certain that anyone reading this article has experienced the same dream. Someone, or something, is in hot pursuit, and if the dreamer can't escape, the consequences will be deadly.
That universal dream usually means the person feels threatened, or under attack, or is recalling a time when an attack was real.
Freud called dreams the "royal road to the unconscious," and for more than a century now, researchers have tried to travel down that road. We know now that dreams do mean something, and they are universal. The most common dream, according to some studies, occurs in all cultures, and it's virtually certain that anyone reading this article has experienced the same dream. Someone, or something, is in hot pursuit, and if the dreamer can't escape, the consequences will be deadly.
That universal dream usually means the person feels threatened, or under attack, or is recalling a time when an attack was real.
10 Ways to Fail in Life, Almost Guaranteed
Avoid these and you'll automatically be on the right track (provided you want to be successful)…
1. Mixing With Losers
It's a guaranteed way to fail in life with this. Whatever you like to do, losers will just tell you it won't work and after some time, you will also become a loser. High five, welcome to the losers' club. Something about losers you should know: they like to recruit new people and are very comfortable in their shoes. They don't welcome change. So when you see someone with either of these two characteristics, you know what you should do.
2. Don't Know What You Want
The most common goal I hear all of the time is, "I want to be rich". I mean it's fine with that generic goal but the problem is, how rich do you want to be? Or how rich is rich? Put it this way - the methods used to make a million and $3,000 are different. No wonder some people couldn't experience breakthroughs in life because they are playing small for big goals. If you want to make a million, you better put in that level of commitment, bucko.
3. You Want Everything
It's nice to have a lot of things but if you go chasing everything, you get nothing. Let me tell you why - you only have 24 hours a day and you've got to focus on your priorities. I know, I know, you can hire others and so on but the fact is, you've got to want 'something' first to lead to another 'something', then to everything. Make sense?
4. Watching "The Secret" Way Too Much
I'm not here to criticize Law Of Attractions (LOA) and don't want to receive hate emails. As a matter of fact, I do believe in it and have friends who appeared in the Secrets. But it's a surefire way to fail if you keep on watching "The Secret" and doing ‘attraction' by sitting down on your floor manifesting 3 hours a day. In my point of view, scientifically, Law of Attraction runs on the concept of 'believing'. When you believe you can achieve your goal, you will take actions to actually achieve it but if you don't understand this basic element and think LOA is some sort of miracle remedy, oh boy, you're in for a big surprise for failure.
5. You Don't Truly Know Why You Want Success
Wanting everything is bad enough - but it gets even worse if you don't even know the reason why you're trying to achieve your goal. What's the deal? Without a solid reason, a compelling reason, where are you going to find the motivation and encouragement for you to overcome obstacles? You think it's going to be fun ride to success? Then you haven't been traveling - it's a rocky road, my friend. Most people failed to achieve their goals because they never complete the journey– they give up half way (or at the beginning) because they cannot see the worth of accomplishments.
6. You Don't Remember Your Roots
The thing I get most irritated about is people who achieved success and never felt gratitude towards those who have helped them. Is it so hard to say thank you? The law of reciprocity is simple – you return favors to those who helped you in the past. And maybe, they'll help you again in the future. Remember this - it takes more than just you to achieve success, so don't be a jerk.
7. You Think You're Smart
The day you stop learning is the day you stop improving yourself. If you don't want to fail in life, make you sure you stop acting as though you already know everything. The fact is, all successful people are people who continuously learn to be even more successful. They don't stop. Let me put it in this perspective - you don't know what you don't know, you know?
8. You Listen To The Wrong People
I watched this funny movie called, "He Is Just Not That Into You" and it just reaffirmed what I'm about to tell you. At the beginning of the movie, it shows a clip of a boy pushing a girl in the playground because he somehow doesn't like her. He thinks she smells like dog pooh. She cried and asked her mum why did the boy do that to her. And her mum replied, "It's because boys do that to girls when they like you." Do yourself a favor, don't get wrong advice. It'll stick in your brain and lead you to make stupid interpretations in life.
9. You Think Short Term
You'll hear this happening often in many 'successful' people's stories – make a lot of money to lose it all. This probably because they became too comfortable and the other thing is, once you achieve success, you should ride on the wave when the momentum is there. When you think short term, you're only going after the instant pleasure. You must learn to master ‘delay gratification' so that you can enjoy your today's labor.
10. You're Blind To What Is Important In Life
I believe there are only two things that are important in your life – control of time and experiencing happiness. Money, love, big cars, diamonds, etc are the things that contribute to these two benchmarks of successes. For instance, if you have money, you don't need to work so that you can have more time to do the things you like. It's not the money that you're trying to get but what the money CAN DO FOR YOU. I know this topic is bigger than one sentence explanation but I guess you get the point.
So now you know the 10 ways to fail in life. Question is, are you doing any of these? I'll be BS'ng you if I said I don't. I'm human, flesh and blood - I do mistakes too.
But I was fortunate to experience my fair share of success today because I learn powerful lessons from other successful people…
"It's okay to fail and you should fail as many times as you can. That is how you learn but more importantly, you should never give up – each time you get kick dirt in your face, wash your face and ‘fight' back. Don't go crying like a sissy because Mum's not going to come cleaning your face."
Are you ready? Go get your goals.
1. Mixing With Losers
It's a guaranteed way to fail in life with this. Whatever you like to do, losers will just tell you it won't work and after some time, you will also become a loser. High five, welcome to the losers' club. Something about losers you should know: they like to recruit new people and are very comfortable in their shoes. They don't welcome change. So when you see someone with either of these two characteristics, you know what you should do.
2. Don't Know What You Want
The most common goal I hear all of the time is, "I want to be rich". I mean it's fine with that generic goal but the problem is, how rich do you want to be? Or how rich is rich? Put it this way - the methods used to make a million and $3,000 are different. No wonder some people couldn't experience breakthroughs in life because they are playing small for big goals. If you want to make a million, you better put in that level of commitment, bucko.
3. You Want Everything
It's nice to have a lot of things but if you go chasing everything, you get nothing. Let me tell you why - you only have 24 hours a day and you've got to focus on your priorities. I know, I know, you can hire others and so on but the fact is, you've got to want 'something' first to lead to another 'something', then to everything. Make sense?
4. Watching "The Secret" Way Too Much
I'm not here to criticize Law Of Attractions (LOA) and don't want to receive hate emails. As a matter of fact, I do believe in it and have friends who appeared in the Secrets. But it's a surefire way to fail if you keep on watching "The Secret" and doing ‘attraction' by sitting down on your floor manifesting 3 hours a day. In my point of view, scientifically, Law of Attraction runs on the concept of 'believing'. When you believe you can achieve your goal, you will take actions to actually achieve it but if you don't understand this basic element and think LOA is some sort of miracle remedy, oh boy, you're in for a big surprise for failure.
5. You Don't Truly Know Why You Want Success
Wanting everything is bad enough - but it gets even worse if you don't even know the reason why you're trying to achieve your goal. What's the deal? Without a solid reason, a compelling reason, where are you going to find the motivation and encouragement for you to overcome obstacles? You think it's going to be fun ride to success? Then you haven't been traveling - it's a rocky road, my friend. Most people failed to achieve their goals because they never complete the journey– they give up half way (or at the beginning) because they cannot see the worth of accomplishments.
6. You Don't Remember Your Roots
The thing I get most irritated about is people who achieved success and never felt gratitude towards those who have helped them. Is it so hard to say thank you? The law of reciprocity is simple – you return favors to those who helped you in the past. And maybe, they'll help you again in the future. Remember this - it takes more than just you to achieve success, so don't be a jerk.
7. You Think You're Smart
The day you stop learning is the day you stop improving yourself. If you don't want to fail in life, make you sure you stop acting as though you already know everything. The fact is, all successful people are people who continuously learn to be even more successful. They don't stop. Let me put it in this perspective - you don't know what you don't know, you know?
8. You Listen To The Wrong People
I watched this funny movie called, "He Is Just Not That Into You" and it just reaffirmed what I'm about to tell you. At the beginning of the movie, it shows a clip of a boy pushing a girl in the playground because he somehow doesn't like her. He thinks she smells like dog pooh. She cried and asked her mum why did the boy do that to her. And her mum replied, "It's because boys do that to girls when they like you." Do yourself a favor, don't get wrong advice. It'll stick in your brain and lead you to make stupid interpretations in life.
9. You Think Short Term
You'll hear this happening often in many 'successful' people's stories – make a lot of money to lose it all. This probably because they became too comfortable and the other thing is, once you achieve success, you should ride on the wave when the momentum is there. When you think short term, you're only going after the instant pleasure. You must learn to master ‘delay gratification' so that you can enjoy your today's labor.
10. You're Blind To What Is Important In Life
I believe there are only two things that are important in your life – control of time and experiencing happiness. Money, love, big cars, diamonds, etc are the things that contribute to these two benchmarks of successes. For instance, if you have money, you don't need to work so that you can have more time to do the things you like. It's not the money that you're trying to get but what the money CAN DO FOR YOU. I know this topic is bigger than one sentence explanation but I guess you get the point.
So now you know the 10 ways to fail in life. Question is, are you doing any of these? I'll be BS'ng you if I said I don't. I'm human, flesh and blood - I do mistakes too.
But I was fortunate to experience my fair share of success today because I learn powerful lessons from other successful people…
"It's okay to fail and you should fail as many times as you can. That is how you learn but more importantly, you should never give up – each time you get kick dirt in your face, wash your face and ‘fight' back. Don't go crying like a sissy because Mum's not going to come cleaning your face."
Are you ready? Go get your goals.
Saturday, April 25, 2009
Simplified approach for Data Recovery : ASR
The ASR is one of the aspects in Windows Vista that has been evolved with the introduction of Vista Service Pack-1. A Windows application programming interface, ASR is designed to keep track of and record the configuration of disks and volumes on a system. It will also manage disks in accordance with Critical and non-Critical labels, depending on whether they do or do not contain system state or operating system components.
With Windows Vista SP1, Microsoft has introduced supports for the Extensible Firmware Interface (EFI). As such the ASR in both Vista SP1 and Windows Server 2008 was tweaked in order to be capable of recovering EFI system partitions in a bare metal recovery.
IBM
IBM-Tivoli is ASR in static IP environments using Tivoli Storage Manager was introduced in November last year.
The IBM Tivoli Storage Manager Automated System Recovery Process supports Networks that are DHCP enabled. In networks that do not support DHCP and uses Static IP's, the local backup sets are used to recover these systems in case of a crash or total failure.
ASR is used to recover Microsoft Windows Server system in the event of a catastrophic system or hardware failure. The goal of ASR process is to return the operating system to the point of last backup. It is a two-phase process.
* Microsoft Windows installs a temporary operating system image using the original operating system media.
* Windows invokes TSM to restore the system volume and system state information.
IBM Tivoli Storage Manager (TSM) interfaces with Microsoft Windows to provide system recovery.
Hewlett Packard
HP Blade PC Automated System Recovery Utility 2.00 Rev. E description was introduced earlier this year.
This package contains the Automated System Recovery (ASR-2) Service for the supported desktop models and operating systems. The ASR-2 service causes an HP Blade PC that has stopped responding (locked up), or that has experienced a "blue-screen" error, to restart (reboot), bringing it back online and making it available for network users.
Development includes the modification of the installation script to add support for 64-bit Microsoft Windows Operating Systems (Microsoft Windows XP and Microsoft Windows Vista).
Conclusion
ASR does not backup user's files or other data, it should be used only as a last resort because in preparation for a restore ASR will format the system and boot volumes of the hard-drive, making other, less drastic recovery methods impossible.
With Windows Vista SP1, Microsoft has introduced supports for the Extensible Firmware Interface (EFI). As such the ASR in both Vista SP1 and Windows Server 2008 was tweaked in order to be capable of recovering EFI system partitions in a bare metal recovery.
IBM
IBM-Tivoli is ASR in static IP environments using Tivoli Storage Manager was introduced in November last year.
The IBM Tivoli Storage Manager Automated System Recovery Process supports Networks that are DHCP enabled. In networks that do not support DHCP and uses Static IP's, the local backup sets are used to recover these systems in case of a crash or total failure.
ASR is used to recover Microsoft Windows Server system in the event of a catastrophic system or hardware failure. The goal of ASR process is to return the operating system to the point of last backup. It is a two-phase process.
* Microsoft Windows installs a temporary operating system image using the original operating system media.
* Windows invokes TSM to restore the system volume and system state information.
IBM Tivoli Storage Manager (TSM) interfaces with Microsoft Windows to provide system recovery.
Hewlett Packard
HP Blade PC Automated System Recovery Utility 2.00 Rev. E description was introduced earlier this year.
This package contains the Automated System Recovery (ASR-2) Service for the supported desktop models and operating systems. The ASR-2 service causes an HP Blade PC that has stopped responding (locked up), or that has experienced a "blue-screen" error, to restart (reboot), bringing it back online and making it available for network users.
Development includes the modification of the installation script to add support for 64-bit Microsoft Windows Operating Systems (Microsoft Windows XP and Microsoft Windows Vista).
Conclusion
ASR does not backup user's files or other data, it should be used only as a last resort because in preparation for a restore ASR will format the system and boot volumes of the hard-drive, making other, less drastic recovery methods impossible.
Mars Rover Spirit is Rolling Again After Memory Problems
It’s been a worrying month for the health of Mars Expedition Rover Spirit. Two weeks ago, the embattled robot failed to wake up after three successive communication sessions, and then over the Easter weekend (April 12th and 13th), mission HQ noticed the rover had rebooted its systems at least twice during use of the high-gain antenna. The same thing happened on April 18th. In addition to this, Spirit has been suffering bouts of what seems to be an ‘electronic amnesia’, where the onboard computers have failed to record data onto their flash memory.
Today however, it would appear Spirit is still operational after over two weeks of remaining planted in the same position. It managed to enact commands sent from NASA to start driving once more, trundling 1.7 metres over the Martian regolith. She hasn’t given up the good fight quite yet…
Since when have electronics on Earth ever lasted more than five years? I always seem to hit a two-year wall with my laptops when something nasty happens to the hardrive and/or motherboard (usually a day or two after the warranty runs out). But when we talk about the computers on board the Mars Expedition Rovers (MER), these electronics aren’t in the snug safety of my office; they are on the surface of an alien planet, dealing with extremes in temperature, high energy particles and copious amounts of dust. What’s more, the rovers were only designed to operate for a few months and yet they are still going strong, five years later. It’s the NASA mission that just keeps on giving.
I think this is what makes the MER mission so impressive for me. Not only are Spirit and Opportunity still operational, they are operating 20 times longer than their designated lifetime and they are notching up a very healthy odometer count. Their cumulative distance travelled is not measured in metres, or kilometres; it’s measured in tens of kilometres. They are giving us an unprecedented insight to the Martian surface, information that will shape our understanding of planetary science for generations to come.
But like any planetary mission, times can be tough, and both rovers have been tested to their engineered limits. Unfortunately, Spirit has been hit by a few more setbacks than Opportunity, but NASA has been able to find workarounds for each problem. The Mars Science Laboratory has a lot to live up to, I wonder if the MER mission will still be operational when the MSL finally touches down? Perhaps the next generation rover will have a robotic welcoming party!
The most recent issue for Spirit has been the flash memory problem. Flash memory helps the rovers store data even when they are powered down, but when the little rover forgets to actually store the data on the flash memory, something is obviously awry. In an attempt to make sure the rover can still take commands and to see if the computer problems persist, NASA ordered Spirit to travel 1.7 metres toward a target 150 metres away. All seems to be going well so far.
“We expect we will see more of the amnesia events, and we want to learn more about them when we do,” said JPL’s Sharon Laubach, chief of the rover sequencing team, which develops and checks each day’s set of commands.
“We decided not to wait until finishing the investigations before trying to drive again. Given Spirit’s limited power and the desire to make progress toward destinations to the south, there would be risks associated with not driving.”
Hopefully keeping the rover mobile will help NASA troubleshoot the recent computer problems, but so far, she’s still rolling over the Martian dirt…
Today however, it would appear Spirit is still operational after over two weeks of remaining planted in the same position. It managed to enact commands sent from NASA to start driving once more, trundling 1.7 metres over the Martian regolith. She hasn’t given up the good fight quite yet…
Since when have electronics on Earth ever lasted more than five years? I always seem to hit a two-year wall with my laptops when something nasty happens to the hardrive and/or motherboard (usually a day or two after the warranty runs out). But when we talk about the computers on board the Mars Expedition Rovers (MER), these electronics aren’t in the snug safety of my office; they are on the surface of an alien planet, dealing with extremes in temperature, high energy particles and copious amounts of dust. What’s more, the rovers were only designed to operate for a few months and yet they are still going strong, five years later. It’s the NASA mission that just keeps on giving.
I think this is what makes the MER mission so impressive for me. Not only are Spirit and Opportunity still operational, they are operating 20 times longer than their designated lifetime and they are notching up a very healthy odometer count. Their cumulative distance travelled is not measured in metres, or kilometres; it’s measured in tens of kilometres. They are giving us an unprecedented insight to the Martian surface, information that will shape our understanding of planetary science for generations to come.
But like any planetary mission, times can be tough, and both rovers have been tested to their engineered limits. Unfortunately, Spirit has been hit by a few more setbacks than Opportunity, but NASA has been able to find workarounds for each problem. The Mars Science Laboratory has a lot to live up to, I wonder if the MER mission will still be operational when the MSL finally touches down? Perhaps the next generation rover will have a robotic welcoming party!
The most recent issue for Spirit has been the flash memory problem. Flash memory helps the rovers store data even when they are powered down, but when the little rover forgets to actually store the data on the flash memory, something is obviously awry. In an attempt to make sure the rover can still take commands and to see if the computer problems persist, NASA ordered Spirit to travel 1.7 metres toward a target 150 metres away. All seems to be going well so far.
“We expect we will see more of the amnesia events, and we want to learn more about them when we do,” said JPL’s Sharon Laubach, chief of the rover sequencing team, which develops and checks each day’s set of commands.
“We decided not to wait until finishing the investigations before trying to drive again. Given Spirit’s limited power and the desire to make progress toward destinations to the south, there would be risks associated with not driving.”
Hopefully keeping the rover mobile will help NASA troubleshoot the recent computer problems, but so far, she’s still rolling over the Martian dirt…
Hubble Discovers a Strange Collection of White Dwarf… Dwarfs
A collection of very odd white dwarfs have been discovered in a local globular cluster. Twenty-four white dwarfs (18 of them are new discoveries) have been spotted. Although these degenerate stars aren’t exactly an uncommon (they are the small sparkling remnants left over after star death), this particular set are unique; they are made from helium, rather than the “standard” carbon and oxygen. And they are small, even smaller than the smallest dwarfs.
How did this dense cluster of old stars evolve? It turns out their stellar material is being stolen, stifling their development…
“Helium-core white dwarfs have only about half the mass of typical white dwarfs, but they are found concentrated in the center of the cluster,” said Prof. Adrienne Cool, from San Francisco State University, in a paper to be published in the Astrophysical Journal in July. “With such low masses, the helium-core white dwarfs ought to be floating all around the cluster, according to theory. The fact that we find them only in the central regions suggests that they have heavy companions — partner stars that anchor them to the cluster center.”
Cool and co-author Rachel R. Strickler believe they are seeing a case of stellar plasma theft by companion binary stars in the NGC 6397 cluster, approximately 7,200 light years away. These binary partners not only anchor these strange-looking white dwarfs in the centre of the cluster, they also have a huge role to play during the dwarfs evolution.
Before a white dwarf emerges from a planetary nebula, the parent star will have gone through the red giant phase (a phase our Sun is expected to go through in 4-5 billion years time). If this red giant has a binary partner (which seems to be the case of the 24 white dwarfs in this study), the outer layers of the puffed-up giant will be stripped away by the partner, stifling the red giant’s evolution. As mass is lost, the giant never gets the chance to burn helium and then progressively heavier elements such as carbon and oxygen in and around its core. Helium then becomes the key component of these smaller-than-usual white dwarfs.
“This is the first time that helium-core white dwarf stars have been discovered in partnerships with other white dwarfs in a globular cluster,” Cool said. “This large sample allows us to answer questions about the mass and nature of the partner stars, and the prevalence of these kinds of binaries in the globular cluster.”
Binary stars are known to affect their partners fairly radically, they are even known to slow or even stop the development of black holes, stripping the outer layers of the dying star, stifling black hole development by removing mass from the parent star. However, not all questions have been answered.
From Cool’s calculations, 5% of the stars found in NGC 6397 should end their lives as dim helium-core white dwarf stars, but after studying Hubble data, many of these tiny dwarfs are missing. “It’s possible that these helium-core white dwarfs cool so slowly that they haven’t had time to get very faint yet,” Cool said.
There remains the possibility that the oldest binaries containing helium-core white dwarfs have actually been destroyed by interactions with other stars in the cluster. Regardless, this is a fascinating area of study. To understand how these ancient stars evolve will not only aid the development of globular cluster models, but it will provide an invaluable insight to how binary stars influence their partners.
How did this dense cluster of old stars evolve? It turns out their stellar material is being stolen, stifling their development…
“Helium-core white dwarfs have only about half the mass of typical white dwarfs, but they are found concentrated in the center of the cluster,” said Prof. Adrienne Cool, from San Francisco State University, in a paper to be published in the Astrophysical Journal in July. “With such low masses, the helium-core white dwarfs ought to be floating all around the cluster, according to theory. The fact that we find them only in the central regions suggests that they have heavy companions — partner stars that anchor them to the cluster center.”
Cool and co-author Rachel R. Strickler believe they are seeing a case of stellar plasma theft by companion binary stars in the NGC 6397 cluster, approximately 7,200 light years away. These binary partners not only anchor these strange-looking white dwarfs in the centre of the cluster, they also have a huge role to play during the dwarfs evolution.
Before a white dwarf emerges from a planetary nebula, the parent star will have gone through the red giant phase (a phase our Sun is expected to go through in 4-5 billion years time). If this red giant has a binary partner (which seems to be the case of the 24 white dwarfs in this study), the outer layers of the puffed-up giant will be stripped away by the partner, stifling the red giant’s evolution. As mass is lost, the giant never gets the chance to burn helium and then progressively heavier elements such as carbon and oxygen in and around its core. Helium then becomes the key component of these smaller-than-usual white dwarfs.
“This is the first time that helium-core white dwarf stars have been discovered in partnerships with other white dwarfs in a globular cluster,” Cool said. “This large sample allows us to answer questions about the mass and nature of the partner stars, and the prevalence of these kinds of binaries in the globular cluster.”
Binary stars are known to affect their partners fairly radically, they are even known to slow or even stop the development of black holes, stripping the outer layers of the dying star, stifling black hole development by removing mass from the parent star. However, not all questions have been answered.
From Cool’s calculations, 5% of the stars found in NGC 6397 should end their lives as dim helium-core white dwarf stars, but after studying Hubble data, many of these tiny dwarfs are missing. “It’s possible that these helium-core white dwarfs cool so slowly that they haven’t had time to get very faint yet,” Cool said.
There remains the possibility that the oldest binaries containing helium-core white dwarfs have actually been destroyed by interactions with other stars in the cluster. Regardless, this is a fascinating area of study. To understand how these ancient stars evolve will not only aid the development of globular cluster models, but it will provide an invaluable insight to how binary stars influence their partners.
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