Author Topic: Astronomy Thread  (Read 95991 times)

Offline Star One

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Re: Astronomy Thread
« Reply #460 on: 06/13/2018 07:52 PM »
ALMA Discovers Trio of Infant Planets around Newborn Star

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Two independent teams of astronomers have used ALMA to uncover convincing evidence that three young planets are in orbit around the infant star HD 163296. Using a novel planet-finding technique, the astronomers identified three disturbances in the gas-filled disc around the young star: the strongest evidence yet that newly formed planets are in orbit there. These are considered the first planets to be discovered with ALMA.

http://www.eso.org/public/news/eso1818/

Offline Star One

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Re: Astronomy Thread
« Reply #461 on: 06/14/2018 07:53 PM »
New Constraints on the Abundance and Composition of Organic Matter on Ceres

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Near‐infrared reflectance spectra from the Dawn mission at Ceres were recently found to exhibit a 3.4 μm absorption indicative of the presence of aliphatic organic compounds. Constraints on abundance and composition of these organics are necessary to inform discussions of their origin. We model reflectance spectra of organic‐bearing regions on Ceres using laboratory spectra of insoluble organics of known composition extracted from terrestrial sedimentary rocks (i.e., kerogens) and carbonaceous chondrite meteorites (i.e., insoluble organic matter, IOM). The 3.4 μm aliphatic organic absorptions observed in Dawn near‐infrared data are stronger than those observed in lab spectra of carbonaceous chondrites, and modeling requires 45% to 65% spectral fraction of IOM to fit spectra from Ceres. The spectral fraction of kerogen necessary to fit the same Ceres spectra ranges from 5% to 15% depending on the hydrogen to carbon ratio of the kerogen. Any proposed mechanism of organic delivery or formation on Ceres should explain the presence of highly concentrated IOM or why the composition is distinct from meteorite‐derived IOM if lower organic abundances are considered more plausible.

Plain Language Summary
Organics were recently detected on the dwarf planet Ceres with infrared spectroscopy. The origin of these organics is, as yet, unknown. Using laboratory spectra of terrestrial and extraterrestrial (meteorite‐derived) organic materials with known composition, we reanalyze the Ceres spectra to constrain composition and abundance of those organics. Such constraints could help us discern whether these organics formed on Ceres or were delivered by an impactor.

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL077913

Offline Star One

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Re: Astronomy Thread
« Reply #462 on: 06/14/2018 09:25 PM »

Offline Star One

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Re: Astronomy Thread
« Reply #463 on: 06/15/2018 06:41 AM »
A dust-enshrouded tidal disruption event with a resolved radio jet in a galaxy merger

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Tidal disruption events (TDEs) are transient flares produced when a star is ripped apart by the gravitational field of a supermassive black hole (SMBH). We have observed a transient source in the western nucleus of the merging galaxy pair Arp 299 that radiated >1.5 × 1052 erg in the infrared and radio but was not luminous at optical or x-ray wavelengths. We interpret this as a TDE with much of its emission reradiated at infrared wavelengths by dust. Efficient reprocessing by dense gas and dust may explain the difference between theoretical predictions and observed luminosities of TDEs. The radio observations resolve an expanding and decelerating jet, probing the jet formation and evolution around a SMBH.

http://science.sciencemag.org/content/early/2018/06/13/science.aao4669

Offline Star One

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Re: Astronomy Thread
« Reply #464 on: 06/15/2018 08:02 PM »
Long suspected theory about the Moon holds water

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A team of Japanese scientists led by Masahiro Kayama of Tohoku University's Frontier Research Institute for Interdisciplinary Sciences, has discovered a mineral known as moganite in a lunar meteorite found in a hot desert in northwest Africa.

This is significant because moganite is a mineral that requires water to form, reinforcing the belief that water exists on the Moon.

"Moganite is a crystal of silicon dioxide and is similar to quartz. It forms on Earth as a precipitate when alkaline water including SiO2 is evaporated under high pressure conditions," says Kayama. "The existence of moganite strongly implies that there is water activity on the Moon."

https://www.tohoku.ac.jp/en/press/moon_holds_water.html

Offline Star One

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Re: Astronomy Thread
« Reply #465 on: 06/18/2018 08:36 PM »
EXPLOSIVE VOLCANOES SPAWNED MYSTERIOUS MARTIAN ROCK FORMATION

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Explosive volcanic eruptions that shot jets of hot ash, rock and gas skyward are the likely source of a mysterious Martian rock formation, a new study finds. The new finding could add to scientists’ understanding of Mars’s interior and its past potential for habitability, according to the study’s authors.

The Medusae Fossae Formation is a massive, unusual deposit of soft rock near Mars’s equator, with undulating hills and abrupt mesas. Scientists first observed the Medusae Fossae with NASA’s Mariner spacecraft in the 1960s but were perplexed as to how it formed.

https://news.agu.org/press-release/explosive-volcanoes-spawned-mysterious-martian-rock-formation/

Offline Star One

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Re: Astronomy Thread
« Reply #466 on: 06/20/2018 08:00 PM »
A possible explanation for varying measurements of Venus's rotation rate

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A trio of researchers with the University of California and Sorbonne Universités has found a possible explanation for why Venus probes have found different day lengths for the planet. In their paper published in the journal Nature Geoscience, T. Navarro, G. Schubert and S. Lebonnois describe a theory they have developed based on observational data.

https://phys.org/news/2018-06-explanation-varying-venus-rotation.amp?

Offline redliox

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Re: Astronomy Thread
« Reply #467 on: 06/20/2018 11:50 PM »
A possible explanation for varying measurements of Venus's rotation rate

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A trio of researchers with the University of California and Sorbonne Universités has found a possible explanation for why Venus probes have found different day lengths for the planet. In their paper published in the journal Nature Geoscience, T. Navarro, G. Schubert and S. Lebonnois describe a theory they have developed based on observational data.

https://phys.org/news/2018-06-explanation-varying-venus-rotation.amp?

So Venus' own winds might have slowed and warped its rotation?
"Let the trails lead where they may, I will follow."
-Tigatron

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Re: Astronomy Thread
« Reply #468 on: 06/22/2018 01:41 AM »
A possible explanation for varying measurements of Venus's rotation rate

Quote
A trio of researchers with the University of California and Sorbonne Universités has found a possible explanation for why Venus probes have found different day lengths for the planet. In their paper published in the journal Nature Geoscience, T. Navarro, G. Schubert and S. Lebonnois describe a theory they have developed based on observational data.

https://phys.org/news/2018-06-explanation-varying-venus-rotation.amp?

So Venus' own winds might have slowed and warped its rotation?

As the planet and its atmosphere are for this purpose a closed system, angular momentum is conserved. The mass of the atmosphere will carry proportionally more angular momentum than the mass of the planet because it is further from the axis of rotation and has a higher angular velocity (it goes around the planet up to 60 times faster than the planet itself rotates). So, as average wind speeds in the direction of rotation pick up the planet will slow down and as the winds die down the planet will speed up. The only question is how big is the effect.

Online jebbo

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Re: Astronomy Thread
« Reply #469 on: 06/22/2018 08:03 AM »
A very interesting discovery from Gaia:

A Gap in the Lower Main Sequence Revealed by Gaia Data Release 2

We present the discovery of a gap near MG≈10 in the main sequence on the Hertzsprung-Russell Diagram (HRD) based on measurements presented in Gaia Data Release 2 (DR2). Using an observational form of the HRD with MG representing luminosity and GBP−GRP representing temperature, the gap presents a diagonal feature that dips toward lower luminosities at redder colors. The gap is seen in samples extracted from DR2 with various distances, and is not unique to the {\it Gaia} photometry --- it also appears when using near-IR photometry (J−Ks vs MKs). The gap is very narrow (∼0.05 mag) and is near the luminosity-temperature regime where M dwarf stars transition from partially to fully convective, i.e., near spectral type M3.0V. This gap provides a new feature in the H-R Diagram that hints at an underlying astrophysical cause and we propose that it is linked to the onset of full convection in M dwarfs.

https://arxiv.org/abs/1806.07792

Offline Star One

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Re: Astronomy Thread
« Reply #470 on: 06/22/2018 08:30 AM »
A very interesting discovery from Gaia:

A Gap in the Lower Main Sequence Revealed by Gaia Data Release 2

We present the discovery of a gap near MG≈10 in the main sequence on the Hertzsprung-Russell Diagram (HRD) based on measurements presented in Gaia Data Release 2 (DR2). Using an observational form of the HRD with MG representing luminosity and GBP−GRP representing temperature, the gap presents a diagonal feature that dips toward lower luminosities at redder colors. The gap is seen in samples extracted from DR2 with various distances, and is not unique to the {\it Gaia} photometry --- it also appears when using near-IR photometry (J−Ks vs MKs). The gap is very narrow (∼0.05 mag) and is near the luminosity-temperature regime where M dwarf stars transition from partially to fully convective, i.e., near spectral type M3.0V. This gap provides a new feature in the H-R Diagram that hints at an underlying astrophysical cause and we propose that it is linked to the onset of full convection in M dwarfs.

https://arxiv.org/abs/1806.07792

The significance of this being?

Offline zubenelgenubi

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Re: Astronomy Thread
« Reply #471 on: 06/22/2018 12:13 PM »
A very interesting discovery from Gaia:

A Gap in the Lower Main Sequence Revealed by Gaia Data Release 2

We present the discovery of a gap near MG≈10 in the main sequence on the Hertzsprung-Russell Diagram (HRD) based on measurements presented in Gaia Data Release 2 (DR2). Using an observational form of the HRD with MG representing luminosity and GBP−GRP representing temperature, the gap presents a diagonal feature that dips toward lower luminosities at redder colors. The gap is seen in samples extracted from DR2 with various distances, and is not unique to the {\it Gaia} photometry --- it also appears when using near-IR photometry (J−Ks vs MKs). The gap is very narrow (∼0.05 mag) and is near the luminosity-temperature regime where M dwarf stars transition from partially to fully convective, i.e., near spectral type M3.0V. This gap provides a new feature in the H-R Diagram that hints at an underlying astrophysical cause and we propose that it is linked to the onset of full convection in M dwarfs.

https://arxiv.org/abs/1806.07792

The significance of this being?

Observational confirmation of stellar modelling, I presume.  Astrophysicists never had the data to confirm the stellar modelling of this transition before because the necessary spectroscopy didn't exist--finding red dwarfs that faint, in a sufficient quantity to be statistically significant, and then obtaining detailed spectrographs from such faint sources.  (Greater detail than that necessary to derive a spectral type.)

It appears that the photometry in multiple spectral bands is substituting for detailed spectrography.

If I remember correctly, the fuller the convection is within a star, the more of its total mass is available for fusion at the core.  Red dwarfs "process" at a very slow rate, so they are modelled to live on the main sequence--fusing hydrogen to helium--for an incredible length of time--tens to hundreds of billions of years.

Full convection means the entire star's mass is available, stretching the main sequence lifetime even more.  (I don't recall how much more.)
« Last Edit: 08/15/2018 10:45 PM by zubenelgenubi »
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Offline Star One

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Re: Astronomy Thread
« Reply #472 on: 06/23/2018 08:25 PM »
The Solar Twin Planet Search: The age - chromospheric activity relation

It is well known that the magnetic activity of solar type stars decreases with age, but it is widely debated in the literature whether there is a smooth decline or if there is an early sharp drop until 1-2 Gyr followed by a relatively inactive constant phase. We revisited the activity-age relation using time-series observations of a large sample of solar twins whose precise isochronal ages and other important physical parameters have been determined. We measured the Ca II H and K activity indices using 9000 HARPS spectra of 82 solar twins. We measured an average solar activity of  SMW  = 0.1712 ± 0.0017 during solar magnetic cycles 23−24 covered by HARPS observations and we also inferred an average of SMW = 0.1694 ± 0.0025 for cycles 10−24, anchored on a S index vs. sunspot number correlation. Also, a simple relation between the average and dispersion of the activity levels of solar twins was found. This enabled us to predict the stellar variability effects on the age-activity diagram and, consequently, estimate the chromospheric age uncertainties due to the same phenomena. The age-activity relation is still statistically significant up to ages around 6−7 Gyr, in agreement with previous works using open clusters and field stars with precise ages. Our research confirms that Ca II H \& K lines remain a useful chromospheric evolution tracer until stars reach ages of at least 6−7 Gyr. We found an evidence that, for the most homogeneous set of old stars, the chromospheric activity indices seem to continue decreasing after the solar age towards the end of the main-sequence. Our results indicate that a significant part of the scatter observed in the age-activity relation of solar twins can be attributed to stellar cycle modulations effects. The Sun seems to have a normal activity level and variability for its age.

https://arxiv.org/abs/1806.08014

Offline Star One

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Astronomy Thread
« Reply #473 on: 06/23/2018 08:35 PM »
New experiment to probe dark matter interactions

https://astronomynow.com/2018/06/17/new-experiment-to-probe-dark-matter-interactions/

Where does Titan Sand Come From: Insight from Mechanical Properties of Titan Sand Candidates

Extensive equatorial linear dunes exist on Titan, but the origin of the sand, which appears to be organic, is unknown. We used nanoindentation to study the mechanical properties of a few Titan sand candidates, several natural sands on Earth, and common materials used in the Titan Wind Tunnel, to understand the mobility of Titan sand. We measured the elastic modulus (E), hardness (H), and fracture toughness (Kc) of these materials. Tholin's elastic modulus (10.4+/-0.5 GPa) and hardness (0.53+/-0.03 GPa) are both an order of magnitude smaller than silicate sand, and is also smaller than the mechanically weak white gypsum sand. With a magnitude smaller fracture toughness (Kc=0.036+/-0.007 MPa-m^(1/2)), tholin is also much more brittle than silicate sand. This indicates that Titan sand should be derived close to the equatorial regions where the current dunes are located, because tholin is too soft and brittle to be transported for long distances.

https://arxiv.org/abs/1806.08056
« Last Edit: 06/23/2018 08:41 PM by Star One »

Offline theinternetftw

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Re: Astronomy Thread
« Reply #474 on: 06/24/2018 02:40 AM »
Awesome.  A little more on the Titan Wind Tunnel (w/ picture):
https://www.hou.usra.edu/meetings/lpsc2016/pdf/2356.pdf

And planetary wind tunnels in general:
https://www.nasa.gov/ames/planetary-aeolian-laboratory

The Planetary Society also has a great article on tholins:
http://www.planetary.org/blogs/guest-blogs/2015/0722-what-in-the-worlds-are-tholins.html

Offline Star One

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Re: Astronomy Thread
« Reply #475 on: 06/26/2018 07:54 PM »
New SPHERE view of Vesta

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Vesta was recently observed by the SPHERE/ZIMPOL instrument on ESO’s Very Large Telescope (VLT) — the SPHERE image is shown on the left, produced using the MISTRAL algorithm, with a synthetic view derived from space-based data shown on the right for comparison. SPHERE, the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument, is a powerful planet-finding and direct imaging instrument. ZIMPOL is one of its subsystems: a specialised camera perfectly suited to taking very sharp images of small objects — like Vesta.

http://www.eso.org/public/images/potw1826a/

Offline Star One

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Re: Astronomy Thread
« Reply #476 on: 06/27/2018 05:16 PM »
Apparently space is full of enough grease for 40 trillion trillion trillon packs of butter.

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It looks cold, dark and empty, but astronomers have revealed that interstellar space is permeated with a fine mist of grease-like molecules.
The study provides the most precise estimate yet of the amount of “space grease” in the Milky Way, by recreating the carbon-based compounds in the laboratory. The Australian-Turkish team discovered more than expected: 10 billion trillion trillion tonnes of gloop, or enough for 40 trillion trillion trillion packs of butter.
Prof Tim Schmidt, a chemist at the University of New South Wales, Sydney and co-author of the study, said that the windscreen of a future spaceship travelling through interstellar space might be expected to get a sticky coating.
“Amongst other stuff it’ll run into is interstellar dust, which is partly grease, partly soot and partly silicates like sand,” he said, adding that the grease is swept away within our own solar system by the solar wind.

https://www.theguardian.com/science/2018/jun/27/space-is-full-of-dirty-toxic-grease-scientists-reveal

Offline Star One

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Re: Astronomy Thread
« Reply #477 on: 06/27/2018 08:50 PM »
Complex molecules found on Enceladus

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The discovery of complex organic molecules on Enceladus makes Saturn's moon the only known body apart from Earth to satisfy the requirements for life as we know it.

http://m.skyatnightmagazine.com/news/complex-organic-molecules-found-moon-enceladus

Offline Star One

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Astronomy Thread
« Reply #478 on: 07/02/2018 11:33 AM »
First confirmed image of a newborn planet revealed

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Nascent planet seen carving a path through the disc of gas and dust surrounding the very young star PDS70

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Captured by the Sphere instrument of the European Southern Observatory’s Very Large Telescope, the planet – a gas giant with a mass greater than Jupiter – is about as far from its star as Uranus is from our sun, with further analyses revealing that it appears to have a cloudy atmosphere and a surface temperature of 1000C.

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“The special thing about this new planet is that we can directly image it, so the ones by Kepler, for example, they were derived by indirect techniques,” she told the Guardian. “In this case we now have a direct image [of the planet] in its “birthplace”, which is the circumstellar disc. This is especially important because people have been wondering [for a long time], how these planets actually form and how the dust and the material in this disc forms [into] a planet, and now we can directly observe this.”

https://www.theguardian.com/science/2018/jul/02/first-confirmed-image-of-a-newborn-planet-revealed-pds70



ESOcast 169.
« Last Edit: 07/02/2018 11:38 AM by Star One »

Offline Star One

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Re: Astronomy Thread
« Reply #479 on: 07/04/2018 08:14 PM »
Einstein gets it right again—weak and strong gravity objects fall the same way

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In 2011, the National Science Foundation's (NSF) Green Bank Telescope (GBT) discovered a natural laboratory to test this theory in extreme conditions: a triple star system called PSR J0337+1715, located about 4,200 light-years from Earth. This system contains a neutron star in a 1.6-day orbit with a white dwarf star, and the pair in a 327-day orbit with another white dwarf further away.

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Through meticulous observations and careful calculations, the team was able to test the system's gravity using the pulses of the neutron star alone. They found that any acceleration difference between the neutron star and inner white dwarf is too small to detect.

"If there is a difference, it is no more than three parts in a million," said coauthor Nina Gusinskaia of the University of Amsterdam. This places severe constraints on any alternative theories to general relativity.

This result is ten times more precise that the previous best test of gravity, making the evidence for Einstein's Strong Equivalence Principle that much stronger. "We're always looking for better measurements in new places, so our quest to learn about new frontiers in our Universe is going to continue," concluded Ransom.

https://m.phys.org/news/2018-07-einstein-againweak-strong-gravity-fall.html