[Karen W. (OP)]

I was wondering Is there such a thing as a twin star..

One that is identical to another which was born at

the same time?

I know that sounds silly but is there?

[Soul Surfer]

This very often happens, in fact most stars form in binary and multiple star systems as a way of getting rid of excess angular momentum as the clouds that form the stars collapse stars that for on their own almost certainly have planetary systems for exactly the same reason.

Stars are generally formed in open clusters in a large galaxy but these are not usually gravitationally bound.

It is the realisation that star clusters were probably formed together that allowed astronomers to deduce and then model so precisely the complex life of an individual star.

The life of any star depends mostly on the mass of material in it with a small dependence on its "metalicity" that is the amount of heavier elements than hydrogen and helium in it.

[Karen W. (OP)]

It seems we have lost a couple posts!

Thank you Ian for the information as I have often wondered about that.

Do you know what kind of ratio it is with Helium and hydrogen verses metallic properties in a average size Star?

[chris]

Yes, I believe that roughly 60-80% of the stars in the sky are in fact binary systems whereby two stars twirl around each other. In some cases one star steals material from the other, producing a bright flare up known as a nova (not to be confused with a supernova which is at least 10000 times brighter and associated with a dying star blowing itself to pieces).

Space scientist Shri Kulkarni published a paper in Nature last year when he and his colleagues discovered a strange glow in the sky; it was too bright to be a nova yet too dim to be a supernova. Their conclusion? It was the merger of two stars in a binary system:

Here's a transcript of the interview I did with him:

"First this week a story of special significance to anyone who is a Virgo because that is the part of the sky where Shri Kulkarni recently spotted something very unusual. It was a very short-lived red glow. It was too dim to be an exploding star or supernova and it was too bright to be a nova, which is when a star obtains some fresh fuel and transiently flares up. So, what could it be? Well, it might be the first glimpse that astronomers have ever had of two stars merging together. Nature 447, 458–460

Shrinivas Kulkarni: We reported a discovery of an entirely new type of explosion, which occurred in a nearby galaxy in the Virgo cluster. This explosion is distinctly different from the supernovae and novae family of explosions. Supernovae are explosions of stars when they are dying or about to die. The star basically shreds itself to pieces, sometimes leaving a black hole or a neutron star. Novae, on the other hand, are explosions which occur on the surface of a White Dwarf. So, these two types of explosions have been studied extensively since there were recognition of explosions in the sky over, let us say, about 100 years ago.

Chris Smith: So, how does that one that you have seen actually differ from these and how did you spot it in the first place?

Shrinivas Kulkarni: I hate to say this, but we found it entirely accidentally. Every night, there is a telescope near San Jose, California that is run by the University of California System and they scan the skies looking for supernovae and last year we found that one of the sources that looked very dim to be a supernovae and therefore it was rejected by the supernovae groups, but I thought this might be very interesting because it was very dim. It is a much more gentle explosion. Also the colour is quite different. Both novae and supernovae are quite blue to our eyes at their maximum light. In contrast, our explosion is red, perhaps infrared. Furthermore, this explosion, and this is the fun part, is about 100 times fainter than the faintest supernovae ever found. On the other hand, it is about 100 times brighter than the brightest novae ever found. So, this is a new type of beast in the heavens.

Chris Smith: Have you got any ideas as to what sorts of stellar convulsions could have actually triggered something like that?

Shrinivas Kulkarni: The current data are not good enough to absolutely and decisively say this is the particular model, although we do think that the best by explanation for this event is the merger of two stars. About half the stars in the sky, you may be surprised to know, are in fact binaries, i.e., they have a companion star. Over time, one of the stars evolves and usually gets larger, just like people do as they get old I suppose, and the material from that larger star spills onto the smaller star.

Chris Smith: For you to have thought, given, you are saying that half the stars in the sky are like this, you would have thought this kind of event would be very common and you would have seen this before and actually we have not so much have we? So how do you account for that?

Shrinivas Kulkarni: Yes, that is always a question one asks when you find something new and then it turns out they are common. As I mentioned, it is a supernova reject that became our prized finding. So, there may well be and I would in fact claim that there probably are a number of such objects in supernovae surveys that have been routinely ignored, but after this I am sure that people will be looking rather eagerly. The other thing you have to bear in mind is these events live for a rather short time. For example, this event lived only for a month and the chance of finding something which lasts only for a month is actually not that high. In any case, my prediction is that the weight of these objects is probably no different than that of supernovae and further searchers, especially if one is diligent, will start uncovering more of these sources.


Chris

[Soul Surfer]

Wikipedia gives the sun as being 1.6 percent by mass elements heavier than helium

http://en.wikipedia.org/wiki/Metallicity

It is usually quoted as the ratio of iron to hydrogen in the stellar spectrum measured by looking at the relative intensities of spectrum lines against that found in the sun which is considered to be a typical star.  Youngish stars like the sun and younger have higher metallicities.  Very old stars have very low metallicities but these are mostly small dim red stars because they are the only sort of stars that last that Long the oldest stars are often found in globular clusters which are probably the remains of small galaxies that have merged with our galaxy.

Even a tiny amount of elements heavier than hydrogen has a profound effect on how a star works because the elements carbon nitrogen and oxygen help to catalyse the reaction that converts hydrogen to helium much more efficiently than just bashing hydrogen atoms together

[Karen W. (OP)]

I know how much I love looking at the stars, but it amazes me to hear about their properties how they work and about all the different aspects of a star and how many different types etc. Amazing.. Thank you..

By the way does the younger stars having higher rates of metallicities  account for why they are so bright? Is it that that makes them burn brighter?

[Karen W. (OP)]

Yes, I believe that roughly 60-80% of the stars in the sky are in fact binary systems whereby two stars twirl around each other. In some cases one star steals material from the other, producing a bright flare up known as a nova (not to be confused with a supernova which is at least 10000 times brighter and associated with a dying star blowing itself to pieces).

Space scientist Shri Kulkarni published a paper in Nature last year when he and his colleagues discovered a strange glow in the sky; it was too bright to be a nova yet too dim to be a supernova. Their conclusion? It was the merger of two stars in a binary system:

Here's a transcript of the interview I did with him:

"First this week a story of special significance to anyone who is a Virgo because that is the part of the sky where Shri Kulkarni recently spotted something very unusual. It was a very short-lived red glow. It was too dim to be an exploding star or supernova and it was too bright to be a nova, which is when a star obtains some fresh fuel and transiently flares up. So, what could it be? Well, it might be the first glimpse that astronomers have ever had of two stars merging together. Nature 447, 458–460

Shrinivas Kulkarni: We reported a discovery of an entirely new type of explosion, which occurred in a nearby galaxy in the Virgo cluster. This explosion is distinctly different from the supernovae and novae family of explosions. Supernovae are explosions of stars when they are dying or about to die. The star basically shreds itself to pieces, sometimes leaving a black hole or a neutron star. Novae, on the other hand, are explosions which occur on the surface of a White Dwarf. So, these two types of explosions have been studied extensively since there were recognition of explosions in the sky over, let us say, about 100 years ago.

Chris Smith: So, how does that one that you have seen actually differ from these and how did you spot it in the first place?

Shrinivas Kulkarni: I hate to say this, but we found it entirely accidentally. Every night, there is a telescope near San Jose, California that is run by the University of California System and they scan the skies looking for supernovae and last year we found that one of the sources that looked very dim to be a supernovae and therefore it was rejected by the supernovae groups, but I thought this might be very interesting because it was very dim. It is a much more gentle explosion. Also the colour is quite different. Both novae and supernovae are quite blue to our eyes at their maximum light. In contrast, our explosion is red, perhaps infrared. Furthermore, this explosion, and this is the fun part, is about 100 times fainter than the faintest supernovae ever found. On the other hand, it is about 100 times brighter than the brightest novae ever found. So, this is a new type of beast in the heavens.

Chris Smith: Have you got any ideas as to what sorts of stellar convulsions could have actually triggered something like that?

Shrinivas Kulkarni: The current data are not good enough to absolutely and decisively say this is the particular model, although we do think that the best by explanation for this event is the merger of two stars. About half the stars in the sky, you may be surprised to know, are in fact binaries, i.e., they have a companion star. Over time, one of the stars evolves and usually gets larger, just like people do as they get old I suppose, and the material from that larger star spills onto the smaller star.

Chris Smith: For you to have thought, given, you are saying that half the stars in the sky are like this, you would have thought this kind of event would be very common and you would have seen this before and actually we have not so much have we? So how do you account for that?

Shrinivas Kulkarni: Yes, that is always a question one asks when you find something new and then it turns out they are common. As I mentioned, it is a supernova reject that became our prized finding. So, there may well be and I would in fact claim that there probably are a number of such objects in supernovae surveys that have been routinely ignored, but after this I am sure that people will be looking rather eagerly. The other thing you have to bear in mind is these events live for a rather short time. For example, this event lived only for a month and the chance of finding something which lasts only for a month is actually not that high. In any case, my prediction is that the weight of these objects is probably no different than that of supernovae and further searchers, especially if one is diligent, will start uncovering more of these sources.


Chris

Thank you Chris I do not believe I have ever read that. That is very interesting. I just happen to be a Virgo! LOL! I am wondering is, "Nature 447, 458–460" the stars that were noted during this discovery? If so have they now disappeared from the Virgo Cluster and burned completely out? I am assuming it is over since the paper was published last year and this phenomenon only lasts a year. Is this a correct assumption?

[chris]

No, that's the journal reference, which was included should you feel compelled to read the original paper!

Chris

[Soul Surfer]

No Karen the basic brightness of a star depends only on its mass in fact stars living their lives in isolation (as most do) are really very simple things.  They also have a relatively small range of masses most having from about one tenth the mass of the sun to ten times the mass of the sun

A star forming nebula contracts to form a star it is a bit brighter as it initially settles down on to its position on the main sequence and then burns with an almost constant brightness for most of its life on the main sequence before brightening up a lot in its final stages as it runs out of fuel.  Most stars a the end of their lives just fluff up and waft their outer layers away to leave what is known as a white dwarf behind.  This is the burnt out core of the star that consists mostly of helium and this just sits there for countless billions of years slowly cooling down. 

The smaller the star the longer it lives.  The very big stars (bigger than ten times the mass of the sun) get all the press attention because they have short lives (only a few million years, blow up spectacularly as supernovae and make neutron stars and black holes.

The metalicity has a bit of an effect as to precisely which track they follow and where they lie on the "main sequence" but all stars with the same mass rotation speed and metalicity are essentially identical and follow identical lives

[Karen W. (OP)]

No, that's the journal reference, which was included should you feel compelled to read the original paper!

Chris

Thanks Chris!

[Karen W. (OP)]

No Karen the basic brightness of a star depends only on its mass in fact stars living their lives in isolation (as most do) are really very simple things.  They also have a relatively small range of masses most having from about one tenth the mass of the sun to ten times the mass of the sun

A star forming nebula contracts to form a star it is a bit brighter as it initially settles down on to its position on the main sequence and then burns with an almost constant brightness for most of its life on the main sequence before brightening up a lot in its final stages as it runs out of fuel.  Most stars a the end of their lives just fluff up and waft their outer layers away to leave what is known as a white dwarf behind.  This is the burnt out core of the star that consists mostly of helium and this just sits there for countless billions of years slowly cooling down. 

The smaller the star the longer it lives.  The very big stars (bigger than ten times the mass of the sun) get all the press attention because they have short lives (only a few million years, blow up spectacularly as supernovae and make neutron stars and black holes.

The metalicity has a bit of an effect as to precisely which track they follow and where they lie on the "main sequence" but all stars with the same mass rotation speed and metalicity are essentially identical and follow identical lives

This really is new to me... I did not know there would be anything left of the star at all.. Thats very cool!! very cool....Thank you Ian... A star that will basically live forever at least billions of years even after it dyes down.. Thank you for that imformation.. It's just what I needed to hear today!