Star Mergers

[Lancewen]

I was watching a program on the History channel "The Universe" and they brought up the topic of two stars merging. I don't believe there have been any direct observations of two stars merging. At least I could find nothing about it on any searches I did. However there is a great deal about neutron star mergers. Not being able to find any information on a subject is a bit disconcerting.

 

The evidence that was mentioned to support star mergers is the discovery of what they referred to as blue stragglers in old star clusters that are primarily made of old small red stars. The way they explained the younger large blue star was that two old red stars merged and changed the characteristics of the newly merged star.

 

I am still very curious about this possibility, because until this program I always assumed two stars coming together would cause a supernova. So if anybody on this forum can help with this topic, please do, and thank you.

[maddog]

I was watching a program on the History channel "The Universe" and they brought up the topic of two stars merging. I don't believe there have been any direct observations of two stars merging. At least I could find nothing about it on any searches I did. However there is a great deal about neutron star mergers. Not being able to find any information on a subject is a bit disconcerting.

 

The evidence that was mentioned to support star mergers is the discovery of what they referred to as blue stragglers in old star clusters that are primarily made of old small red stars. The way they explained the younger large blue star was that two old red stars merged and changed the characteristics of the newly merged star.

 

I am still very curious about this possibility, because until this program I always assumed two stars coming together would cause a supernova. So if anybody on this forum can help with this topic, please do, and thank you.

Star mergers has been theorized and/or speculated since the 19th century. Partly due to all the double star data of that era. When binaries were close to each other, the larger star would suck the stuff from its neighbor. The evolution of either star goes according to its mass. I don't know if full on merged stars was ever considered before the notion of black holes. This concept though has been around awhile.

 

maddog

[Lancewen]

Star mergers has been theorized and/or speculated since the 19th century. Partly due to all the double star data of that era. When binaries were close to each other, the larger star would suck the stuff from its neighbor. The evolution of either star goes according to its mass. I don't know if full on merged stars was ever considered before the notion of black holes. This concept though has been around awhile.

 

maddog

 

Thanks maddog, once again I'm somewhat guilty of letting my SF reading past influence my thinking on star mergers. For anybody that has read E.E. Doc Smith's The Skylark Series will know what I am talking about. That is, it is not very hard to believe that two stars coming together would destabilize into a super nova. The idea that such a thing would only produce a bigger hotter star never really crossed my mind. Do we know if there is any current research on this issue? I still find it hard to believe there is not much of anything documented on this subject. After all I picked up on this subject on a popular TV program.

[Cyberia]

Two stars drift within the gravitational field of each other, if close enough they go into a declining orbit and the collision will depend on what they are. Obviously the denser a star is, the more advantage it would have in such a case. Unless the total mass passes a certain point, I don't necessarily see a nova/supernova happening though there could be a lot of ejected material.

[Lancewen]

Two stars drift within the gravitational field of each other, if close enough they go into a declining orbit and the collision will depend on what they are. Obviously the denser a star is, the more advantage it would have in such a case. Unless the total mass passes a certain point, I don't necessarily see a nova/supernova happening though there could be a lot of ejected material.

 

With so little data available on this subject, it's kind of hard to even talk about it. The example being used is two small very old red stars merging to become a larger young hotter blue star. Anyway that's how they are explaining finding these stars where they are not expecting to find them, such as in a very old star cluster that has no capacity to create new stars.

[Cyberia]

With so little data available on this subject, it's kind of hard to even talk about it. The example being used is two small very old red stars merging to become a larger young hotter blue star. Anyway that's how they are explaining finding these stars where they are not expecting to find them, such as in a very old star cluster that has no capacity to create new stars.

 

Over time, stars build up a crust of heavy elements on their surfaces so smother or violently blow the crust off. However with two stars merging, the heavy elements would either be slung off into space because they have greater impetus than lighter elements or sink into the inside of the new star so making it look young again.

 

Think of stirring up a bowl of custard where a skin has formed on the top of it.

[Lancewen]

Over time, stars build up a crust of heavy elements on their surfaces so smother or violently blow the crust off. However with two stars merging, the heavy elements would either be slung off into space because they have greater impetus than lighter elements or sink into the inside of the new star so making it look young again.

 

Think of stirring up a bowl of custard where a skin has formed on the top of it.

 

Yes I think two stars coming together would stir things up a bit. I would sure like to see an observation of such an event happening, rather than speculating why there is a young blue star where none should be.

[maddog]

Thanks maddog, once again I'm somewhat guilty of letting my SF reading past influence my thinking on star mergers. For anybody that has read E.E. Doc Smith's The Skylark Series will know what I am talking about. That is, it is not very hard to believe that two stars coming together would destabilize into a super nova. The idea that such a thing would only produce a bigger hotter star never really crossed my mind. Do we know if there is any current research on this issue? I still find it hard to believe there is not much of anything documented on this subject. After all I picked up on this subject on a popular TV program.

I for one being an avid SF Reader, have not read Doc E.E. Smith's series Skylark of Space series (even though I have it). However, I have read (with fond regard of my youth) his Lensmen series. :lol: It is not likely that two stars in and of themselves "merging" would generate supernova/nova type explosion. That is with one exception. This would be where on star (assume both to be about same mass) is moving at much higher velocity than the other. They both smack each other nearly spot on (bulk of moment of inertia near the center of mass). This would definitely create a spectacular show. This is definitely not likely for binaries (which are already in stable orbits). This however, could theoretically happen in a large globular cluster. The larger the higher probability. What defines the temperature of a star is more to do with where they start on the main sequence. For instance Sirius is a type A0 which is pretty hot. Our star is a G2 and Tau Ceti is G0 which is slightly hotter than ours.

 

If you were to have two stars as a binary system with a very fast period for both (couple of days). You would have a lot of accretion of the smaller onto the larger. As this material accretes, the star does not change type on the main sequence. An A star stays an A star and does not become an O star. The star Eta Carinae is an O hypergiant star (over 100 solar masses).

 

maddog

Edited May 7, 2012 by maddog

[maddog]

With so little data available on this subject, it's kind of hard to even talk about it. The example being used is two small very old red stars merging to become a larger young hotter blue star. Anyway that's how they are explaining finding these stars where they are not expecting to find them, such as in a very old star cluster that has no capacity to create new stars.

Doc E.E. Smith his books in the 30's as I remember. So I thought this was known by then (though by Astronomers). Yes, red giant stars are definitely old, while hotter stars often newer. Merging as an event does not renew a star (it's not like a face lift). This is because a red giant star got big because it ran out Hydrogen for fuel. As it imploded, enough pressure built up in the core to allow the nucleosynthesis of Helium into heavier elements. As it does, it balloons out in size. Antares is a good example red giant. It's size is about the orbit of Mars (just inside).

 

There also is a thing about which Population a star is (kinda' what Sexton may have alluding to). I will have to go look up which is which as I don't wish make a goof on mislabeling. The newer stars have some heavier elements from the remnants of previous stars. This will change some of the parameters temperature, etc. While older start were just Hydrogen and Helium.

 

I hope that clarifies.

 

maddog

[Lancewen]

Doc E.E. Smith his books in the 30's as I remember. So I thought this was known by then (though by Astronomers). Yes, red giant stars are definitely old, while hotter stars often newer. Merging as an event does not renew a star (it's not like a face lift). This is because a red giant star got big because it ran out Hydrogen for fuel. As it imploded, enough pressure built up in the core to allow the nucleosynthesis of Helium into heavier elements. As it does, it balloons out in size. Antares is a good example red giant. It's size is about the orbit of Mars (just inside).

 

There also is a thing about which Population a star is (kinda' what Sexton may have alluding to). I will have to go look up which is which as I don't wish make a goof on mislabeling. The newer stars have some heavier elements from the remnants of previous stars. This will change some of the parameters temperature, etc. While older start were just Hydrogen and Helium.

 

I hope that clarifies.

 

maddog

 

If you liked the Lensmen series, you will like the Skylark series. The part about two stars coming together is at the end of book 4 of the series. The main characters gained enough knowledge and power that they were able to take stars from one galaxy and instantly transport them to a second galaxy and place them next to stars in systems with some really bad news chlorine breathing aliens. Also EE Doc Smith has been dead for several years now and I had to search used book sites to find complete copies of his series's. I think the Skylark series was published before the Lensmen series, but not sure without looking it up.

 

About the red giants, yes you are right, but I was not talking about red giants but red dwarfs that haven't even used up a quarter of the Hydrogen fuel yet. I believe red dwarfs have the longest life spans of any stars, so if they merge into a bigger hotter star they will actually shorten the life span of the new star. There must be something about regular star mergers that makes them hard to detect, or they are a very rare event.

[maddog]

... red dwarfs that haven't even used up a quarter of the Hydrogen fuel yet. I believe red dwarfs have the longest life spans of any stars, so if they merge into a bigger hotter star they will actually shorten the life span of the new star. There must be something about regular star mergers that makes them hard to detect, or they are a very rare event.

Once I get my books (Library) in order, I will have to pull them out and read the series.

 

Yes, it is true that definitely dwarfs burn slower than other main sequence start. The thing I am talking about though is the classification which is linked to temperature. A typical dwarf is say a K or an M type. Yet if two M's were to merge would not make a K or an F type. A leopard does not change his spots as they say. Whatever characteristic of a star (class) is that for the life of the star. The red giant phase is what happens after Hydrogen runs out. What you would get is a larger M dwarf (or regular sized M star). Now if a direct collision and high enough impact, maybe some more exotic candidates. Typical binaries are often to dissimilar star types.

 

maddog

[Lancewen]

Once I get my books (Library) in order, I will have to pull them out and read the series.

 

Yes, it is true that definitely dwarfs burn slower than other main sequence start. The thing I am talking about though is the classification which is linked to temperature. A typical dwarf is say a K or an M type. Yet if two M's were to merge would not make a K or an F type. A leopard does not change his spots as they say. Whatever characteristic of a star (class) is that for the life of the star. The red giant phase is what happens after Hydrogen runs out. What you would get is a larger M dwarf (or regular sized M star). Now if a direct collision and high enough impact, maybe some more exotic candidates. Typical binaries are often to dissimilar star types.

 

maddog

 

What your saying does make sense to me. I was just quoting what I heard on the Universe program. Two small stars merging will only make a larger small star. Probably not enough to change the color to blue. That being the case how would you explain the presence of a new large blue star in a very old star cluster with no capacity to make a new star?

[CarlNGraham]

Merging two white dwarf stars is one possible cause of Type 1a supernovas.

Wikipedia

Another model for the formation of a Type Ia explosion involves the merger of two white dwarf stars, with the combined mass momentarily exceeding the Chandrasekhar limit.[53] A white dwarf could also accrete matter from other types of companions, including a main sequence star (if the orbit is sufficiently close).

[Lancewen]

Merging two white dwarf stars is one possible cause of Type 1a supernovas.

Wikipedia

 

 

My knowledge of Type 1A supernova is that they happen when a white dwarf is paired with a normal star and slowly steals mass from it as described in the link below.

 

 

In the case of the type Ia supernova, a white dwarf in a slowly-rotating binary system (composed of two stars) can get more mass from its pair. Because of this, the limit is never achieved. The core of the star is left with increased temperature and pressure. When the star has approached to 1% of the limit, nuclear reactions occur that is not regulated by this kind of white dwarf unlike in other stars.

 

The core of the star becomes unstable and within seconds, the temperature peaks to billions of degrees, causing its particles to gain enough energy to dismantle the star resulting into a Type Ia supernova. When explosion occurs, it can be so bright that it can outshine other galaxies near it.

 

http://planetfacts.org/type-1a-supernova/

 

What you are describing would most likely cause a collapse into a neutron star as it would put the total mass over the Chandrasekhar limit. (also from the same link)

 

White dwarfs are the end of most of stars. They are then supported by electron pressure because of their intense density. However, there is a certain limit, known as the Chandrasekhar limit, to which the electron pressure can support the electrons. When the Chandrasekhar limit is achieved, the white dwarf becomes a neutron star.

 

There are many observations to support the theory on Type 1A supernovas. However, I haven't been able to locate one single observation of two normal stars merging.

[maddog]

What your saying does make sense to me. I was just quoting what I heard on the Universe program. Two small stars merging will only make a larger small star. Probably not enough to change the color to blue. That being the case how would you explain the presence of a new large blue star in a very old star cluster with no capacity to make a new star?

Without know more about the cluster (or where it is wrt to the galaxy it is near), I don't know I would be able to definitively say. If a typical O or B star (large blue - i.e. T = 50k K) and this cluster was in the galaxy's halo, I would guess it might be a rogue star from somewhere else - say the disk. This is because the halo cluster are often old. Some hot bluish big star (O or B) is going to be "very young" primarily because these critters don't last long -- say 100-150 MYrs or so. Eta Carinae is such an example (extreme though it is). If forget who, it was in the news in last two years or so - that an astronomer gave an estimate on this star to have a lifetime of 19 MYrs +/- a few. This is a Very short lifespan. It is consuming at a way faster rate than any star so discovered. What could make a star like this end up in the wrong place might be strange. The simplest answer might be its normal orbit where it was in the galaxy it was in encountered the proximity of some large gravitational object (BH) that shot it off on a hyperbolic orbit up out of the plane of the galaxy into the halo where your globular cluster was. Maybe.

 

As for your merger idea of two M dwarfs making just a larger M dwarf, I would think be about right.

 

maddog

Edited May 9, 2012 by maddog

[CarlNGraham]

My knowledge of Type 1A supernova is that they happen when a white dwarf is paired with a normal star and slowly steals mass from it as described in the link below.

 

 

What you are describing would most likely cause a collapse into a neutron star as it would put the total mass over the Chandrasekhar limit. (also from the same link)

 

 

 

There are many observations to support the theory on Type 1A supernovas. However, I haven't been able to locate one single observation of two normal stars merging.

 

I was under the impression that white dwarf collisions were now the main candidate for Type 1a, because observations do not show a large companion star.

A shocked red giant remnant coated in heavy elements should be easy to detect.

 

The only suspect companion I know of found so far is a star Tycho G in the vicinity of SN 1572.

However, that is a Type G like the sun and thought to be on the wrong trajectory.

[Lancewen]

I was under the impression that white dwarf collisions were now the main candidate for Type 1a, because observations do not show a large companion star.

A shocked red giant remnant coated in heavy elements should be easy to detect.

 

The only suspect companion I know of found so far is a star Tycho G in the vicinity of SN 1572.

However, that is a Type G like the sun and thought to be on the wrong trajectory.

 

Well the link below and the Wikipedia both agree that this is still a very much debated subject. I still didn't see where mainstream is leaning towards two white dwarfs merging though.

 

Type Ia. These result from some binary star systems in which a carbon-oxygen white dwarf is accreting matter from a companion. (What kind of companion star is best suited to produce Type Ia supernovae is hotly debated.) In a popular scenario, so much mass piles up on the white dwarf that its core reaches a critical density of 2 x 10⁹ g/cm³. This is enough to result in an uncontrolled fusion of carbon and oxygen, thus detonating the star.

 

http://imagine.gsfc.nasa.gov/docs/science/know_l2/supernovae.html