Post by Andrei Tchentchik on Sept 3, 2020 15:19:54 GMT 2
(.#505).- 2 white dwarfs merge into one, without exploding into a supernova.
Two white dwarfs would have merged into one without exploding into a supernova.
Laurent Sacco, Journalist
Posted on March 6, 2020.
WDJ0551 + 4135 is an atypical white dwarf from the Milky Way. Everything seems to indicate that it results from the fusion of two white dwarfs but, usually, this produces a SN Ia type supernova which leaves no more stars.
WDJ0551 + 4135 is a white dwarf from the Milky Way distant about 150 light years from the Sun who was identified in the astrometric data of the Gaia mission. A priori, this star is in no way as spectacular as Betelgeuse and yet an international team led by astronomers from the University of Warwick has just devoted a substantial article to it in the journal Nature Astronomy.
Its mass is not surprising, about 1.14 solar mass, almost double the average mass of white dwarfs, most of which are relatively light, about 0.6 times the mass of our Sun, but it is still below the famous limit mass - discovered for these stars by the great Indian astrophysicist Subrahmanyan Chandrasekhar around 1930 when he was only 20 years old - which is around 1.44 solar mass.
Beyond, these white dwarfs must collapse on themselves. So, when matter is added to a white dwarf and makes it exceed the mass of 1.44 solar mass, it contracts again and thermonuclear reactions are triggered, leading to an explosion blowing the white dwarf: a supernova SN Ia.
VIDEO :
Vie et mort des étoiles ordinaires, par Jean-Pierre Luminet…
Jean-Pierre Luminet talks about the evolution of solar-type stars, their transformation into red giants, then into white dwarfs. © ECP Productions
These stars are the corpses of stars initially containing less than 8 solar masses and which left the main sequence when their nuclear fuel has run out, after having synthesized helium, carbon and oxygen especially for the most massive.
They then contract to have a size comparable to that of the Earth and are in equilibrium with their own gravitational attraction force only thanks to the pressure called degeneration of the electrons of their plasma; the latter behave according to the famous Fermi-Dirac statistics as demonstrated in 1926 by British astronomer and physicist Ralph H. Fowler using the new quantum statistics, describing an electron gas, discovered by his former doctoral student Paul Dirac .
But, let's go back to WDJ0551 + 4135. What troubled astrophysicists was the composition of its atmosphere when they determined it with the instruments fitted to the William Herschel or WHT (William Herschel Telescope) found on La Palma, one of the Canary Islands. It is a mixture of hydrogen and carbon while the theory of nucleosynthesis and stellar structure tells us that we should see an outer layer of hydrogen, sometimes mixed with helium, or just a mixture helium and carbon.
VIDEO :
Artist’s impression of two white dwarf stars...
This artist's video shows the central part of the Henize 2-428 planetary nebula. The core of this unique object is made up of two white dwarf stars, each with a mass slightly less than that of the Sun. They are expected to slowly approach each other and merge in approximately 700 million years. This event will create a dazzling Type Ia supernova and destroy the two stars. © European Southern Observatory (ESO)
There is only one way to solve the puzzle for researchers, it is to admit that we are in the presence of a white dwarf resulting from the fusion of two white dwarfs of comparable mass. This is theoretically possible, in particular because two white dwarfs in a binary system will lose energy in the form of gravitational waves, which will decrease the size of their orbit to make them collide but we also know examples of this ongoing process as shown in the previous article below.
Another observation pleads for this scenario. We know that older stars gravitate around the Milky Way faster than younger ones, but the age deduced from the orbital speed of WDJ0551 + 4135 is higher than that deduced from its temperature which allows us to estimate an age at because of the cooling rate of a white dwarf of given mass. There again, the enigma is solved by a fusion of two white dwarfs.
However, generally, collisions of white dwarfs are made with stars which lead to a higher final mass than that of Chandrasekhar and therefore to a supernova. We already knew some similar cases but it is interesting to continue to estimate how many couples of white dwarfs will give by fusion a new white dwarf and not a SN Ia. Recall that the SN Ia are used to study the accelerated expansion of the observable cosmos and therefore the dark energy.
WHAT YOU MUST REMEMBER
• White dwarfs are stars of masses comparable to the Sun but the size of the Earth.
• WDJ0551 + 4135 is an atypical white dwarf from the Milky Way.
• Everything seems to indicate that it results from the fusion of two white dwarfs but usually, this produces a SN Ia type supernova which leaves no more stars.
• The two white dwarfs, which were to form a binary system, probably got closer to the fusion by losing energy in the form of gravitational waves.
Archives :
ESO article published on 02/13/2015
Two white dwarfs are about to merge into a supernova
For the first time, we were able to observe the coming together of stars that will one day merge into a supernova. Observed in the planetary nebula Henize 2-428, these surprisingly massive white dwarfs spiral around each other and, in 700 million years, will explode together, becoming a type Ia supernova.
The team of astronomers led by Miguel Santander-García (from the National Astronomical Observatory in Alcalá de Henares, Spain and the Institute of Materials Science in Madrid) discovered a couple of neighboring white dwarf stars one from the other and whose total mass is around 1.8 times that of the Sun. It is about the most massive pair of stars discovered to date (the maximum mass being determined by the Chandrasekar limit), whose next fusion will result in an uncontrolled thermonuclear explosion, manifesting in type Ia supernova .
The team behind this discovery was trying to solve a very different puzzle. She was indeed trying to understand the process of creation, by old stars, of planetary nebulae with strange and asymmetrical shapes like Henize 2-428, their research subject.
"When we observed the central star of this object by means of the Very Large Telescope (VLT) of Eso, we discovered not one, but two stars in the heart of this strangely asymmetrical luminous cloud", says Henri Boffin ( Eso), one of the authors of the article published in the journal Nature.
This discovery supports the hypothesis that the existence of a central system of double stars is at the origin of the strange shapes that some of these celestial objects display. However, a much more interesting result awaited the researchers.
The two white dwarfs will merge into a supernova Ia
"Other observations, made using telescopes installed in the Canary Islands, have enabled us to determine the orbits of the two stars, says Romano Corradi, another author of the study and researcher at the Institute of Astrophysics of the Canaries (Tenerife , IAC), and deduce their respective masses and the distance between them. And there, big surprise! "
It appeared to them that each of the two stars has a mass slightly less than that of the Sun and that their orbital period is around four hours. They are so close to each other that by virtue of Einstein's theory of general relativity, they will continue to get closer, spiraling under the effect of the emission of gravitational waves and then merge into one single entity within some 700 million years.
The resulting star will be so massive that nothing can oppose its gravitational collapse nor, subsequently, its explosion, in the form of a supernova. "Until now, the formation of a type Ia supernova following the fusion of two white dwarfs has been a purely theoretical scenario, explains David Jones, co-author of research and scholarship holder of the Eso when obtaining these data . The pair of stars located in the heart of Henize 2-428 is indeed a reality! "
"This system is enigmatic to say the least," concludes Santander. Its discovery will have important repercussions on the study of type Ia supernovae, widely used for the measurement of astronomical distances, and intimately linked to the discovery of the acceleration of the expansion of the Universe under the effect of dark energy. "
F I N .
Two white dwarfs would have merged into one without exploding into a supernova.
Laurent Sacco, Journalist
Posted on March 6, 2020.
WDJ0551 + 4135 is an atypical white dwarf from the Milky Way. Everything seems to indicate that it results from the fusion of two white dwarfs but, usually, this produces a SN Ia type supernova which leaves no more stars.
WDJ0551 + 4135 is a white dwarf from the Milky Way distant about 150 light years from the Sun who was identified in the astrometric data of the Gaia mission. A priori, this star is in no way as spectacular as Betelgeuse and yet an international team led by astronomers from the University of Warwick has just devoted a substantial article to it in the journal Nature Astronomy.
Its mass is not surprising, about 1.14 solar mass, almost double the average mass of white dwarfs, most of which are relatively light, about 0.6 times the mass of our Sun, but it is still below the famous limit mass - discovered for these stars by the great Indian astrophysicist Subrahmanyan Chandrasekhar around 1930 when he was only 20 years old - which is around 1.44 solar mass.
Beyond, these white dwarfs must collapse on themselves. So, when matter is added to a white dwarf and makes it exceed the mass of 1.44 solar mass, it contracts again and thermonuclear reactions are triggered, leading to an explosion blowing the white dwarf: a supernova SN Ia.
VIDEO :
Vie et mort des étoiles ordinaires, par Jean-Pierre Luminet…
Jean-Pierre Luminet talks about the evolution of solar-type stars, their transformation into red giants, then into white dwarfs. © ECP Productions
These stars are the corpses of stars initially containing less than 8 solar masses and which left the main sequence when their nuclear fuel has run out, after having synthesized helium, carbon and oxygen especially for the most massive.
They then contract to have a size comparable to that of the Earth and are in equilibrium with their own gravitational attraction force only thanks to the pressure called degeneration of the electrons of their plasma; the latter behave according to the famous Fermi-Dirac statistics as demonstrated in 1926 by British astronomer and physicist Ralph H. Fowler using the new quantum statistics, describing an electron gas, discovered by his former doctoral student Paul Dirac .
But, let's go back to WDJ0551 + 4135. What troubled astrophysicists was the composition of its atmosphere when they determined it with the instruments fitted to the William Herschel or WHT (William Herschel Telescope) found on La Palma, one of the Canary Islands. It is a mixture of hydrogen and carbon while the theory of nucleosynthesis and stellar structure tells us that we should see an outer layer of hydrogen, sometimes mixed with helium, or just a mixture helium and carbon.
VIDEO :
Artist’s impression of two white dwarf stars...
This artist's video shows the central part of the Henize 2-428 planetary nebula. The core of this unique object is made up of two white dwarf stars, each with a mass slightly less than that of the Sun. They are expected to slowly approach each other and merge in approximately 700 million years. This event will create a dazzling Type Ia supernova and destroy the two stars. © European Southern Observatory (ESO)
There is only one way to solve the puzzle for researchers, it is to admit that we are in the presence of a white dwarf resulting from the fusion of two white dwarfs of comparable mass. This is theoretically possible, in particular because two white dwarfs in a binary system will lose energy in the form of gravitational waves, which will decrease the size of their orbit to make them collide but we also know examples of this ongoing process as shown in the previous article below.
Another observation pleads for this scenario. We know that older stars gravitate around the Milky Way faster than younger ones, but the age deduced from the orbital speed of WDJ0551 + 4135 is higher than that deduced from its temperature which allows us to estimate an age at because of the cooling rate of a white dwarf of given mass. There again, the enigma is solved by a fusion of two white dwarfs.
However, generally, collisions of white dwarfs are made with stars which lead to a higher final mass than that of Chandrasekhar and therefore to a supernova. We already knew some similar cases but it is interesting to continue to estimate how many couples of white dwarfs will give by fusion a new white dwarf and not a SN Ia. Recall that the SN Ia are used to study the accelerated expansion of the observable cosmos and therefore the dark energy.
WHAT YOU MUST REMEMBER
• White dwarfs are stars of masses comparable to the Sun but the size of the Earth.
• WDJ0551 + 4135 is an atypical white dwarf from the Milky Way.
• Everything seems to indicate that it results from the fusion of two white dwarfs but usually, this produces a SN Ia type supernova which leaves no more stars.
• The two white dwarfs, which were to form a binary system, probably got closer to the fusion by losing energy in the form of gravitational waves.
Archives :
ESO article published on 02/13/2015
Two white dwarfs are about to merge into a supernova
For the first time, we were able to observe the coming together of stars that will one day merge into a supernova. Observed in the planetary nebula Henize 2-428, these surprisingly massive white dwarfs spiral around each other and, in 700 million years, will explode together, becoming a type Ia supernova.
The team of astronomers led by Miguel Santander-García (from the National Astronomical Observatory in Alcalá de Henares, Spain and the Institute of Materials Science in Madrid) discovered a couple of neighboring white dwarf stars one from the other and whose total mass is around 1.8 times that of the Sun. It is about the most massive pair of stars discovered to date (the maximum mass being determined by the Chandrasekar limit), whose next fusion will result in an uncontrolled thermonuclear explosion, manifesting in type Ia supernova .
The team behind this discovery was trying to solve a very different puzzle. She was indeed trying to understand the process of creation, by old stars, of planetary nebulae with strange and asymmetrical shapes like Henize 2-428, their research subject.
"When we observed the central star of this object by means of the Very Large Telescope (VLT) of Eso, we discovered not one, but two stars in the heart of this strangely asymmetrical luminous cloud", says Henri Boffin ( Eso), one of the authors of the article published in the journal Nature.
This discovery supports the hypothesis that the existence of a central system of double stars is at the origin of the strange shapes that some of these celestial objects display. However, a much more interesting result awaited the researchers.
The two white dwarfs will merge into a supernova Ia
"Other observations, made using telescopes installed in the Canary Islands, have enabled us to determine the orbits of the two stars, says Romano Corradi, another author of the study and researcher at the Institute of Astrophysics of the Canaries (Tenerife , IAC), and deduce their respective masses and the distance between them. And there, big surprise! "
It appeared to them that each of the two stars has a mass slightly less than that of the Sun and that their orbital period is around four hours. They are so close to each other that by virtue of Einstein's theory of general relativity, they will continue to get closer, spiraling under the effect of the emission of gravitational waves and then merge into one single entity within some 700 million years.
The resulting star will be so massive that nothing can oppose its gravitational collapse nor, subsequently, its explosion, in the form of a supernova. "Until now, the formation of a type Ia supernova following the fusion of two white dwarfs has been a purely theoretical scenario, explains David Jones, co-author of research and scholarship holder of the Eso when obtaining these data . The pair of stars located in the heart of Henize 2-428 is indeed a reality! "
"This system is enigmatic to say the least," concludes Santander. Its discovery will have important repercussions on the study of type Ia supernovae, widely used for the measurement of astronomical distances, and intimately linked to the discovery of the acceleration of the expansion of the Universe under the effect of dark energy. "
F I N .
