Monday, October 4, 2021

3294 - NEUTRON STARS - have more to tell us?

  -  3294   -  NEUTRON  STARS  -  have more to tell us?  How many white dwarfs were the result of massive stars experiencing a supernova, and how many were the result of binary companions merging near the end of their lives? What is the rate of white dwarf mergers in the galaxy, and is it enough to explain the number of type 1a supernovae?  How is a magnetic field generated in these powerful events, and why is there such diversity in magnetic field strengths among white dwarfs? 


---------------------  3294  -  NEUTRON  STARS  -  have more to tell us?

-  The universe is full of colliding objects: stars, blackholes and ultradense objects called neutron stars.  And when neutron stars collide, the collisions release a flood of elements necessary for life.

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-  Just about everything has collided at one point or another in the history of the universe.   Neutron stars, which are the superdense objects left behind after the explosive deaths of large stars that smashed together.

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-  A neutron star collision would go out with a flash. It wouldn't be as bright as a typical supernova, which happens when large stars explode.  An explosion generated from a neutron star collision would be roughly a thousand times brighter than a typical nova,  a “kilo nova“.

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-  When you put a bunch of neutrons in a high-energy environment, they start to combine, transform, splinter off and do all sorts of other wild nuclear reactions.  With all the neutrons flying around and combining with each other, and all the energy needed to power the nuclear reactions, kilonovas are responsible for producing enormous amounts of heavy elements, including gold, silver and xenon. 

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-  Supernovas and kilonovas fill out the periodic table and generate all the elements necessary to make rocky planets ready to host living organisms.  You too are made of star dust. 

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-  In 2017, astronomers witnessed their first kilonova. The event occurred about 140 million light-years from Earth and was first heralded by the appearance of a certain pattern of gravitational waves, or ripples in space-time, washing over Earth. 

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-  These gravitational waves were detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo observatory, which immediately notified the astronomical community that they had seen the distinct ripple in space-time that could only mean that two neutron stars had collided. Less than 2 seconds later, the Fermi Gamma-ray Space Telescope detected a gamma-ray burst, a brief, bright flash of gamma-rays.

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-  Astronomers around the world trained their telescopes, antennas and orbiting observatories at the kilonova event, scanning it in every wavelength of the electromagnetic spectrum. One-third of the entire astronomical community around the globe participated in the effort. It was perhaps the most widely described astronomical event in human history, with over 100 papers on the subject appearing within the first two months.

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-  Kilonovas had long been predicted, but with an occurrence rate of 1 every 100,000 years per galaxy, astronomers weren't really expecting to see one so soon.  In comparison, supernovas occur once every few decades in each galaxy.

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-  The addition of gravitational wave signals provided an unprecedented glimpse inside the event itself. Between gravitational waves and traditional electromagnetic observations, astronomers got a complete picture from the moment the merger began.

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-  That kilonova alone produced more than 100 Earths' worth of pure, solid precious metals, confirming that these explosions are fantastic at creating heavy elements.  The gold in your jewelry was forged from two neutron stars that collided long before the birth of our solar system.

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-  Albert Einstein's theory of general relativity predicted that gravitational waves travel at the speed of light. But astronomers have long been trying to develop extensions and modifications to general relativity, and the vast majority of those extensions and modifications predicted different speeds for gravitational waves.

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-   The gravitational wave signal and the gamma-ray burst signal from the kilonova arrived within 1.7 seconds of each other. But that was after traveling over 140 million miles. To arrive at Earth that close to each other over such a long journey, the gravitational waves and electromagnetic waves would have had to travel at the same speed to one part in a million billion.

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-  About 97% of all stars in our Universe are destined to end their lives as white dwarf stars, which represents the final stage in their evolution. Like neutron stars, white dwarfs form after stars have exhausted their nuclear fuel and undergo gravitational collapse, shedding their outer layers to become super-compact stellar remnants.

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- This will be the fate of our Sun billions of years from now, which will swell up to become a “red giant star” before losing its outer layers.  Unlike neutron stars, which result from more massive stars, white dwarfs were once about eight times the mass of our Sun or lighter. 

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-  The density and gravitational force of these objects is an opportunity to study the laws of physics under some of the most extreme conditions imaginable.   One such object has been found that is both the smallest and most massive white dwarf ever seen.

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-  This white dwarf is located about 130 light-years from Earth and is estimated to be 1.35 times as massive as our Sun.   This white dwarf has a stellar radius of about 1,125 miles,  slightly larger than the Moon which is 1,080 miles.   This makes it the smallest and most massive white dwarf ever observed. 

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-   It may seem counterintuitive, but smaller white dwarfs happen to be more massive. This is due to the fact that white dwarfs lack the nuclear burning that keep up normal stars against their own self gravity, and their size is instead are regulated by quantum mechanics.

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-  This white dwarf also has an extreme magnetic field, ranging from 600 to 900 MegaGauss over its entire surface, or roughly 1 billion times stronger than our Sun’s magnetic field. 

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-  This magnetic field has one of the fastest rotational periods ever observed in an isolated white dwarf, whipping around the star’s axis once every 6.94 minutes.

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-  Spectra obtained by Keck’s Low-Resolution Imaging Spectrometer (LRIS) revealed signatures of a powerful magnetic field, ultraviolet data from Swift helped constrain the size and mass of the white dwarf.

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-  Between its strong magnetic field and seven-minute rotational speed.  This was the result of two smaller white dwarfs coalescing into one. Roughly 50% of the stars in the observable Universe are binary systems, consisting of two stellar companions that orbit one other. If these stars are less than eight solar masses each, they will evolve into white dwarfs that eventually merge to form a more massive star.

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-  This process boosts the magnetic field of the resulting white dwarf and speeds up its rotation compared to that of its progenitors. It explains how this star manages to concentrate such a considerable mass into a volume slightly more than that of the Moon. 

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-    This white dwarf is massive enough to further collapse into a neutron star. It is so massive and dense that, in its core, electrons are being captured by protons in nuclei to form neutrons. Because the pressure from electrons pushes against the force of gravity, keeping the star intact, the core collapses when a large enough number of electrons are removed.

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-  If their hypothesis is correct, it may mean that a significant portion of other neutron stars in our galaxy did not start their lives as massive stars, but instead evolved from smaller binary stars. 

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- The newfound object’s close proximity to Earth, 130 light-years,  and the fact that it is relatively young, 100 million years old, are indications that similar objects could be common in our galaxy.

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-  There is always more to learn.

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-  October 4, 2021       NEUTRON  STARS  -  have more to tell us?    3294                                                                                                                                                   

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--------------------- ---  Monday, October 4, 2021  ---------------------------






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