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Study sheds light on turbulence in astrophysical plasmas
(Theoretical analysis uncovers new mechanisms in plasma turbulence)
David L. Chandler | MIT News Office
Plasmas, gas-like collections of ions and electrons, make up an estimated 99 percent of the visible matter in the universe, including the sun, the stars, and the gaseous medium that permeates the space in between. Most of these plasmas, including the solar wind that constantly flows out from the sun and sweeps through the solar system, exist in a turbulent state.
How this turbulence works remains a mystery; it’s one of the most dynamic research areas in plasma physics.
Magnetic reconnection is a complicated phenomenon that Nuno Loureiro, an associate professor of nuclear science and engineering and of physics at MIT, has been studying in detail for more than a decade.
To explain the process, he gives a well-studied example: “If you watch a video of a solar flare” as it arches outward and then collapses back onto the sun’s surface, “that’s magnetic reconnection in action. It’s something that happens on the surface of the sun that leads to explosive releases of energy.”
Loureiro’s understanding of this process of magnetic reconnection has provided the basis for the new analysis that can now explain some aspects of turbulence in plasmas.
Read more at>>
http://news.mit.edu/2017/study-uncovers-new-mechanisms-astrophysical-plasma-turbulence-1201
#astronomy #astrophysics #science #space
(Theoretical analysis uncovers new mechanisms in plasma turbulence)
David L. Chandler | MIT News Office
Plasmas, gas-like collections of ions and electrons, make up an estimated 99 percent of the visible matter in the universe, including the sun, the stars, and the gaseous medium that permeates the space in between. Most of these plasmas, including the solar wind that constantly flows out from the sun and sweeps through the solar system, exist in a turbulent state.
How this turbulence works remains a mystery; it’s one of the most dynamic research areas in plasma physics.
Magnetic reconnection is a complicated phenomenon that Nuno Loureiro, an associate professor of nuclear science and engineering and of physics at MIT, has been studying in detail for more than a decade.
To explain the process, he gives a well-studied example: “If you watch a video of a solar flare” as it arches outward and then collapses back onto the sun’s surface, “that’s magnetic reconnection in action. It’s something that happens on the surface of the sun that leads to explosive releases of energy.”
Loureiro’s understanding of this process of magnetic reconnection has provided the basis for the new analysis that can now explain some aspects of turbulence in plasmas.
Read more at>>
http://news.mit.edu/2017/study-uncovers-new-mechanisms-astrophysical-plasma-turbulence-1201
#astronomy #astrophysics #science #space
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Space Station Transits the Moon
The International Space Station, with a crew of six onboard, is seen in silhouette as it transits the Moon at roughly five miles per second, Saturday, Dec. 2, 2017, in Manchester Township, York County, Pennsylvania.
Other astrophysics news here>>
https://youtu.be/jPrHDkyvs4U
Image Credit: NASA/Joel Kowsky
https://www.nasa.gov/image-feature/space-station-transits-the-moon
#astronomy #astrophysics #space #science
The International Space Station, with a crew of six onboard, is seen in silhouette as it transits the Moon at roughly five miles per second, Saturday, Dec. 2, 2017, in Manchester Township, York County, Pennsylvania.
Other astrophysics news here>>
https://youtu.be/jPrHDkyvs4U
Image Credit: NASA/Joel Kowsky
https://www.nasa.gov/image-feature/space-station-transits-the-moon
#astronomy #astrophysics #space #science
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# Annual Review of Astronomy and Astrophysics Figure 2: Percentage of articles in ArXiv astro-ph abstracts containing the terms (a) Bayesian and (b) MCMC. Computed using the code arxiv.py; courtesy of Dustin Lang.” Figure 3: Fitting a straight line to…
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Last, but certainly not least, StarTalk Radio’s “Cosmic Queries #Astrophysics Mashup”
With host Neil deGrasse Tyson and co-hosts Leighann Lord, Chuck Nice, Iliza Shlesinger, and Godfrey. Listen now at https://www.patreon.com/posts/cosmic-queries-15530289
Image credit: © Mark A. Garlick / space-art.co.uk.
With host Neil deGrasse Tyson and co-hosts Leighann Lord, Chuck Nice, Iliza Shlesinger, and Godfrey. Listen now at https://www.patreon.com/posts/cosmic-queries-15530289
Image credit: © Mark A. Garlick / space-art.co.uk.
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Blowing in the stellar wind: Scientists reduce the chances of life on exoplanets in so-called habitable zones
In two papers in The Astrophysical Journal Letters, the scientists develop models showing that the stellar wind—the constant outpouring of charged particles that sweep out into space—could severely deplete the atmosphere of exolanets over hundreds of millions of years, rendering them unable to host surface-based life as we know it.
Read more at>>
https://phys.org/news/2017-11-stellar-scientists-chances-life-exoplanets.html
#astronomy #astrophysics #space #science
In two papers in The Astrophysical Journal Letters, the scientists develop models showing that the stellar wind—the constant outpouring of charged particles that sweep out into space—could severely deplete the atmosphere of exolanets over hundreds of millions of years, rendering them unable to host surface-based life as we know it.
Read more at>>
https://phys.org/news/2017-11-stellar-scientists-chances-life-exoplanets.html
#astronomy #astrophysics #space #science
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Gravitational Waves Could Reveal Primordial Black Hole Mergers
What are primordial black holes (PBHs)?
They are a hypothetical type of black holes that could have formed in the very early Universe (less than one second after the Big-Bang), during the so-called radiation dominated era. The essential ingredient for a primordial black hole to form is a fluctuation in the density of the Universe, inducing its gravitational collapse. There are several mechanisms able to produce such inhomogeneities in the context of cosmic inflation (in hybrid inflation models, for example axion inflation, ...), reheating, or cosmological phase transitions.
In summary, some cosmological models suggest that— immediately after the Big Bang, some 13.82 billion years ago— the early quantum density fluctuations may have been dramatic enough to create black holes — known as primordial black holes — and these ancient Big Bang remnants may still exist to this day.
These theoretical models, however, are hard to test as observing the universe immediately after the Big Bang is very difficult. But recent discoveries of gravitational waves from black hole and neutron star mergers have ushered in a new era of astronomy, and astronomers have an observational tool at their disposal.
So, even if the standard theory predicts that black holes are born from supernovae, which implies that they couldn’t have formed any earlier than the first stars, in a new study published in Physical Review Letters, researchers have proposed that if we have the ability to detect gravitational waves produced before the first stars died, we may be able to carry out astronomical archaeological dig of sorts to possibly find evidence of these ancient black holes.
Savvas Koushiappas of Brown University, Rhode Island, and Abraham Loeb of Harvard University came up with a way to test this idea by calculating the earliest epoch in which baryonic black holes—those made of the matter we see in stars and planets—can form.
"The idea is very simple," Koushiappas said. "With future gravitational wave experiments, we'll be able to look back to a time before the formation of the first stars. So if we see black hole merger events before stars existed, then we'll know that those black holes are not of stellar origin."
Cosmologists measure how far back in time an event occurred using redshift -- the stretching of the wavelength of light associated with the expansion of the universe. Events further back in time are associated with larger redshifts. For this study, Koushiappas and Loeb calculated the redshift at which black hole mergers should no longer be detected assuming only stellar origin.
They find that beyond a redshift of about 40 —where observed objects were formed during the first 65 million years following the big bang—the rate of collisions should drop to less than one per year. This epoch should be within reach of the next generation of gravitational-wave observatories.
Finding evidence for primordial black holes could shed light on the nature of dark matter or on the origin of cosmic structure in the early Universe.
► Read the article from Brown University: "Gravitational waves could shed light on the origin of black holes">>
https://news.brown.edu/articles/2017/11/primordial
► The paper "Maximum Redshift of Gravitational Wave Merger Events", published in Physical Review Letters, 2017>>
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.221104
► Image: Black holes collide
Credit: Simulating eXtreme Spacetimes (SXS) Project (http://www.black-holes.org)
Further reading and references
► Gravitational Waves Could Reveal Black Hole Origins>>
https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.119.221104
► Gravitational Waves Might Reveal Primordial Black Hole Mergers Just After the Big Bang>>
https://astroengine.com/2017/11/30/gravitational-waves-might-reveal-primordial-black-hole-mergers-just-after-the-big-bang/
► Primordial black hole>> https://en.wikipedia.org/wiki/Primordial_black_hole
► NASA Scientist Suggests Possible Link Between Primordial Black Holes and Dark Matter>>
https://www.nasa.gov/feature/goddard/2016/nasa-scientist-suggests-possible-link-between-primordial-black-holes-and-dark-matter
#Astronomy, #PrimordialBlackHoles, #Cosmology, #DarkMatter, #GravitationalWaves, #Astrophysics, #Research
What are primordial black holes (PBHs)?
They are a hypothetical type of black holes that could have formed in the very early Universe (less than one second after the Big-Bang), during the so-called radiation dominated era. The essential ingredient for a primordial black hole to form is a fluctuation in the density of the Universe, inducing its gravitational collapse. There are several mechanisms able to produce such inhomogeneities in the context of cosmic inflation (in hybrid inflation models, for example axion inflation, ...), reheating, or cosmological phase transitions.
In summary, some cosmological models suggest that— immediately after the Big Bang, some 13.82 billion years ago— the early quantum density fluctuations may have been dramatic enough to create black holes — known as primordial black holes — and these ancient Big Bang remnants may still exist to this day.
These theoretical models, however, are hard to test as observing the universe immediately after the Big Bang is very difficult. But recent discoveries of gravitational waves from black hole and neutron star mergers have ushered in a new era of astronomy, and astronomers have an observational tool at their disposal.
So, even if the standard theory predicts that black holes are born from supernovae, which implies that they couldn’t have formed any earlier than the first stars, in a new study published in Physical Review Letters, researchers have proposed that if we have the ability to detect gravitational waves produced before the first stars died, we may be able to carry out astronomical archaeological dig of sorts to possibly find evidence of these ancient black holes.
Savvas Koushiappas of Brown University, Rhode Island, and Abraham Loeb of Harvard University came up with a way to test this idea by calculating the earliest epoch in which baryonic black holes—those made of the matter we see in stars and planets—can form.
"The idea is very simple," Koushiappas said. "With future gravitational wave experiments, we'll be able to look back to a time before the formation of the first stars. So if we see black hole merger events before stars existed, then we'll know that those black holes are not of stellar origin."
Cosmologists measure how far back in time an event occurred using redshift -- the stretching of the wavelength of light associated with the expansion of the universe. Events further back in time are associated with larger redshifts. For this study, Koushiappas and Loeb calculated the redshift at which black hole mergers should no longer be detected assuming only stellar origin.
They find that beyond a redshift of about 40 —where observed objects were formed during the first 65 million years following the big bang—the rate of collisions should drop to less than one per year. This epoch should be within reach of the next generation of gravitational-wave observatories.
Finding evidence for primordial black holes could shed light on the nature of dark matter or on the origin of cosmic structure in the early Universe.
► Read the article from Brown University: "Gravitational waves could shed light on the origin of black holes">>
https://news.brown.edu/articles/2017/11/primordial
► The paper "Maximum Redshift of Gravitational Wave Merger Events", published in Physical Review Letters, 2017>>
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.221104
► Image: Black holes collide
Credit: Simulating eXtreme Spacetimes (SXS) Project (http://www.black-holes.org)
Further reading and references
► Gravitational Waves Could Reveal Black Hole Origins>>
https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.119.221104
► Gravitational Waves Might Reveal Primordial Black Hole Mergers Just After the Big Bang>>
https://astroengine.com/2017/11/30/gravitational-waves-might-reveal-primordial-black-hole-mergers-just-after-the-big-bang/
► Primordial black hole>> https://en.wikipedia.org/wiki/Primordial_black_hole
► NASA Scientist Suggests Possible Link Between Primordial Black Holes and Dark Matter>>
https://www.nasa.gov/feature/goddard/2016/nasa-scientist-suggests-possible-link-between-primordial-black-holes-and-dark-matter
#Astronomy, #PrimordialBlackHoles, #Cosmology, #DarkMatter, #GravitationalWaves, #Astrophysics, #Research
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Achernar: the Flattest Star Known
The ten brightest stars in the nighttime sky in terms of apparent magnitude are, from brightest to least brightest: Sirius, Canopus, Alpha Centauri, Arcturus, Vega, Capella, Rigel, Procyon, Achernar and Betelgeuse.
So Achernar- lying at the southern tip of the constellation Eridanus (The River) at a distance of 139 ± 3 ly- is the 9th brightest star in the sky known!
But that star has other intriguing features: it is the flattest star ever seen and also the brightest Be star in the sky!
Be stars are massive dwarf or subgiant stars that present temporary emission lines in their spectrum, and particularly in the Halpha line. The mechanism triggering these Be episodes is currently unknown, but binarity could play an important role. Actually, based to some studies dating back to 2007 and 2008, Achernar is the primary component of the binary system designated Alpha Eridani. The two components are designated Alpha Eridani A and Alpha Eridani B (known informally as Achernar B).
The WGSN (Working Group on Star Names ) approved the name Achernar for Alpha Eridani A on 30 June 2016 and it is now so entered in the IAU Catalog of Star Names.
Be stars have too a fundamental property of rapid rotation. Theoretically, rotation has several consequences on the star structure. The most obvious is the geometrical deformation that results in a larger radius at the equator than
at the poles. This would obviously cause such stars to become flattened.
In the case of Achernar, its equatorial radius is more than 50% larger than the polar one (because of an unusually rapid rotational velocity), so the star appears oblate in shape.
In other words, this star is shaped very much like the well-known spinning-top toy, so popular among young children. The high degree of flattening measured for Achernar - a first in observational astrophysics - has posed an unprecedented challenge for theoretical astrophysics.
The presence of a circumstellar disk of ionized gas is a common feature of Be stars such as this. The disk is not stable and periodically decretes back into the star. The maximum polarization for Achernar's disk was observed in September 2014, and it is now decreasing.
Achernar is a hot blue main sequence star of spectral classification B6 with about seven times the mass of the Sun, but is roughly 3,150 times more luminous (than the Sun). Its companion star appears to be a blue-white main sequence star of spectral type A, with a stellar mass of about double that of the Sun. The separation of the two stars is roughly 12.3 AU and their orbital period is at least 14–15 years.
► Image: The position of Achernar (lower right).
Source>> https://en.wikipedia.org/wiki/Achernar#/media/File:Position_Alpha_Eri.png
Further reading and references
► H-alpha>> https://en.wikipedia.org/wiki/H-alpha
► The close-in companion of the fast rotating Be star Achernar>> https://arxiv.org/abs/0804.3465
► The spinning-top Be star Achernar from VLTI-VINCI>> https://www.aanda.org/articles/aa/pdf/2003/33/aafd053.pdf
► Flattest Star Ever Seen>> https://www.eso.org/public/unitedkingdom/news/eso0316/
► Achernar: Rapid Polarization Variability as Evidence of Photospheric and Circumstellar Activity>>
https://arxiv.org/abs/0710.4163
► On the Determination of the Rotational Oblateness of Achernar>>
https://arxiv.org/abs/0801.4901
► A-type main-sequence star>> https://en.wikipedia.org/wiki/A-type_main-sequence_star
► B-type main-sequence star>> https://en.wikipedia.org/wiki/B-type_main-sequence_star
► Circumstellar disk>> https://en.wikipedia.org/wiki/Circumstellar_disc
#Astrophysics, #Achernar, #BinarySystem, #Research, #MainSequenceStars, #ConstellationEridanus, #Universe
The ten brightest stars in the nighttime sky in terms of apparent magnitude are, from brightest to least brightest: Sirius, Canopus, Alpha Centauri, Arcturus, Vega, Capella, Rigel, Procyon, Achernar and Betelgeuse.
So Achernar- lying at the southern tip of the constellation Eridanus (The River) at a distance of 139 ± 3 ly- is the 9th brightest star in the sky known!
But that star has other intriguing features: it is the flattest star ever seen and also the brightest Be star in the sky!
Be stars are massive dwarf or subgiant stars that present temporary emission lines in their spectrum, and particularly in the Halpha line. The mechanism triggering these Be episodes is currently unknown, but binarity could play an important role. Actually, based to some studies dating back to 2007 and 2008, Achernar is the primary component of the binary system designated Alpha Eridani. The two components are designated Alpha Eridani A and Alpha Eridani B (known informally as Achernar B).
The WGSN (Working Group on Star Names ) approved the name Achernar for Alpha Eridani A on 30 June 2016 and it is now so entered in the IAU Catalog of Star Names.
Be stars have too a fundamental property of rapid rotation. Theoretically, rotation has several consequences on the star structure. The most obvious is the geometrical deformation that results in a larger radius at the equator than
at the poles. This would obviously cause such stars to become flattened.
In the case of Achernar, its equatorial radius is more than 50% larger than the polar one (because of an unusually rapid rotational velocity), so the star appears oblate in shape.
In other words, this star is shaped very much like the well-known spinning-top toy, so popular among young children. The high degree of flattening measured for Achernar - a first in observational astrophysics - has posed an unprecedented challenge for theoretical astrophysics.
The presence of a circumstellar disk of ionized gas is a common feature of Be stars such as this. The disk is not stable and periodically decretes back into the star. The maximum polarization for Achernar's disk was observed in September 2014, and it is now decreasing.
Achernar is a hot blue main sequence star of spectral classification B6 with about seven times the mass of the Sun, but is roughly 3,150 times more luminous (than the Sun). Its companion star appears to be a blue-white main sequence star of spectral type A, with a stellar mass of about double that of the Sun. The separation of the two stars is roughly 12.3 AU and their orbital period is at least 14–15 years.
► Image: The position of Achernar (lower right).
Source>> https://en.wikipedia.org/wiki/Achernar#/media/File:Position_Alpha_Eri.png
Further reading and references
► H-alpha>> https://en.wikipedia.org/wiki/H-alpha
► The close-in companion of the fast rotating Be star Achernar>> https://arxiv.org/abs/0804.3465
► The spinning-top Be star Achernar from VLTI-VINCI>> https://www.aanda.org/articles/aa/pdf/2003/33/aafd053.pdf
► Flattest Star Ever Seen>> https://www.eso.org/public/unitedkingdom/news/eso0316/
► Achernar: Rapid Polarization Variability as Evidence of Photospheric and Circumstellar Activity>>
https://arxiv.org/abs/0710.4163
► On the Determination of the Rotational Oblateness of Achernar>>
https://arxiv.org/abs/0801.4901
► A-type main-sequence star>> https://en.wikipedia.org/wiki/A-type_main-sequence_star
► B-type main-sequence star>> https://en.wikipedia.org/wiki/B-type_main-sequence_star
► Circumstellar disk>> https://en.wikipedia.org/wiki/Circumstellar_disc
#Astrophysics, #Achernar, #BinarySystem, #Research, #MainSequenceStars, #ConstellationEridanus, #Universe
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WASP-18b Has Smothering Stratosphere Without Water
A NASA-led team has found evidence that the oversized planet WASP-18b is wrapped in a smothering stratosphere loaded with carbon monoxide and devoid of water. The findings come from a new analysis of observations made by the Hubble and Spitzer space telescopes.
The formation of a stratosphere layer in a planet’s atmosphere is attributed to “sunscreen”-like molecules, which absorb UV and visible radiation coming from the star and then release that energy as heat.
The new study suggests that the “hot Jupiter” WASP-18b, a massive planet that orbits very close to its host star, has an unusual composition, and the formation of this world might have been quite different from that of Jupiter as well as gas giants in other planetary systems.
Read more at>>
https://www.nasa.gov/feature/goddard/2017/wasp-18b-has-smothering-stratosphere-without-water
Text Credit: NASA
#astronomy #astrophysics #space #science #wasp-18b #hotjupiter #exoplanet
A NASA-led team has found evidence that the oversized planet WASP-18b is wrapped in a smothering stratosphere loaded with carbon monoxide and devoid of water. The findings come from a new analysis of observations made by the Hubble and Spitzer space telescopes.
The formation of a stratosphere layer in a planet’s atmosphere is attributed to “sunscreen”-like molecules, which absorb UV and visible radiation coming from the star and then release that energy as heat.
The new study suggests that the “hot Jupiter” WASP-18b, a massive planet that orbits very close to its host star, has an unusual composition, and the formation of this world might have been quite different from that of Jupiter as well as gas giants in other planetary systems.
Read more at>>
https://www.nasa.gov/feature/goddard/2017/wasp-18b-has-smothering-stratosphere-without-water
Text Credit: NASA
#astronomy #astrophysics #space #science #wasp-18b #hotjupiter #exoplanet
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Voyager 1 Fires Up Thrusters After 37 Years
Voyager 1, NASA's farthest and fastest spacecraft, is the only human-made object in interstellar space, the environment between the stars. The spacecraft, which has been flying for 40 years, relies on small devices called thrusters to orient itself so it can communicate with Earth. These thrusters fire in tiny pulses, or "puffs," lasting mere milliseconds, to subtly rotate the spacecraft so that its antenna points at our planet. Now, the Voyager team is able to use a set of four backup thrusters, dormant since 1980.
Read more at>>
https://www.nasa.gov/feature/jpl/voyager-1-fires-up-thrusters-after-37
#astronomy #astrophysics #space #science #nasa
Voyager 1, NASA's farthest and fastest spacecraft, is the only human-made object in interstellar space, the environment between the stars. The spacecraft, which has been flying for 40 years, relies on small devices called thrusters to orient itself so it can communicate with Earth. These thrusters fire in tiny pulses, or "puffs," lasting mere milliseconds, to subtly rotate the spacecraft so that its antenna points at our planet. Now, the Voyager team is able to use a set of four backup thrusters, dormant since 1980.
Read more at>>
https://www.nasa.gov/feature/jpl/voyager-1-fires-up-thrusters-after-37
#astronomy #astrophysics #space #science #nasa
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