astrobites 2018

Find out the latest thinking about our universe.
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Teaching Machines to find Fast Radio Bursts

Post by bystander » Thu Sep 27, 2018 4:12 pm

Teaching Machines to find Fast Radio Bursts
Astrobites | 2018 Sep 24
Joshua Kerrigan wrote:
Today’s astrobite combines two independently fascinating topics for a very interesting result, machine learning and fast radio bursts (FRBs). The field of Machine Learning is moving at an unprecedented pace with fascinating new results. FRBs have entirely unknown origins and experiments to detect more of them are gearing up. So let’s jump right into it and take a look at how the authors of today’s astrobite got a machine to identify fast radio bursts. ...

Fast Radio Burst 121102 Pulse Detection and Periodicity: A Machine Learning Approach ~ Yunfan Gerry Zhang et al
viewtopic.php?t=38683
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What Should We Assume?

Post by bystander » Thu Sep 27, 2018 4:19 pm

What Should We Assume?
Astrobites | 2018 Sep 25
Emily Sandford wrote:
Everyone warns you: don’t make assumptions, because when you ASSUME, you look as foolish AS a SUM of Elephant seals, or however it goes.

But assumptions are useful, as long as they’re based on facts! On the weekends, for example, I just assume, based on prior experience, that an NYC subway journey will take about twenty minutes longer than it’s supposed to because of crowds and construction. More often than not, I arrive about when I expect based on that assumption.

Of course, if the transit authority magically got its act together, I’d have to update my beliefs—I wouldn’t let an old assumption about slow subways mislead me into showing up awkwardly early for things forever. It would probably only take two or three fast train journeys before I stopped building in that extra 20 minutes. My observations, in other words, would take precedence over my assumptions.

But what if I couldn’t test my assumptions against the real world so effectively? What if I were working from very limited data? In the subway analogy, what if I had moved away from New York years ago, but I were still advising tourists about travel time based on how things used to be? My advice might be better than nothing, but still inadequate or misleading.

Today’s authors investigate: What happens when data are scarce, and you have to let your assumptions guide you? How do you choose your assumptions wisely, so you’re misled as rarely as possible? ...

Improving Orbit Estimates for Incomplete Orbits with a New Approach to Priors –
with Applications from Black Holes to Planets
~ K. Kosmo O'Neil et al
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Going Against the Galactic Flow

Post by bystander » Thu Sep 27, 2018 4:31 pm

Going Against the Galactic Flow
Astrobites | 2018 Sep 26
Tomer Yavetz wrote:
More often than not, when you hear an astrophysicist talking about a galactic rotation curve, you can expect their next sentence to be somehow related to dark matter. Indeed, one of the main reasons to believe that dark matter exists in the first place is the ubiquity of flat rotation curves in observations of galaxies. But today’s article focuses on a couple of galaxies with rotation curves that have an additional quirky feature – a large “counter-rotating” group of stars that seem to be moving in the opposite direction as the rest of the galaxy. ...

The properties of the kinematically distinct components in NGC 448 and NGC 4365 ~ B. Nedelchev et al
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Changing with the Tide

Post by bystander » Thu Sep 27, 2018 4:37 pm

Changing with the Tide
Astrobites | 2018 Sep 27
Mara Zimmerman wrote:
Systems of planets and stars influence each other’s every movement; anyone on Earth needs to only look outside to remind themselves of that. But how do these bodies influence each other over long periods of time? The authors of today’s paper attempt to answer this broad question as it pertains to WASP 12. ...

Understanding WASP-12b ~ Avery Bailey, Jeremy Goodman
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Gravitational Redshift and the Pup

Post by bystander » Wed Oct 03, 2018 4:07 pm

Gravitational Redshift and the Pup:
Measuring the Mass of Sirius B

Astrobites | 2018 Oct 02
Daniel Berke wrote:
White dwarfs are fascinating stellar remnants left over at the end of the lifetimes of many stars. Only about the size of Earth, these tiny objects can potentially be more massive than the Sun. And unlike many of the exotic objects we study in astronomy we have one situated right next door to us! Located a mere 8.6 light-years away, Sirius (the brightest star in the night sky), is actually a binary system. Sirius A, the one we see, is a main sequence A-type star, while its invisible companion Sirius B is a white dwarf. (Sirius B is also affectionately called “the Pup” due to Sirius A being known historically as the “Dog Star.”)

Sirius B was discovered on January 31, 1862, and was recognized as a white dwarf in 1915, only the second one to be discovered (after 40 Eridani B, as related in this astrobite). A year later in 1916 Einstein published his theory of General Relativity, with one of its predictions being that light leaving a star should be affected by gravitational redshift. (This is where light climbing out of a gravitational well loses energy and appears redder.) In 1924 the astronomer Arthur Eddington realized that, since Sirius B was so small and dense, it should show a measurable gravitational redshift. This was measured for the first time in 1925 by Walter Adams at the Mt. Wilson Observatory and considered a big success for General Relativity. (Although we now know that both the predicted and measured shift were about four times too low; it’s speculated that the spectra of Sirius B may have been contaminated by light from Sirius A which is very nearby on the sky.)

By measuring the gravitational redshift of a star with a known radius we can also measure its mass, since for a typical stellar object (i.e., not a neutron star or black hole) the gravitational redshift depends only on those two quantities. We can measure the distance to Sirius B using its parallax very well since it’s so nearby, and by measuring its luminosity (based on its brightness and temperature) we can work out its radius. We can also measure its mass dynamically, by observing how it and Sirius A orbit around their common center of mass and applying Kepler’s laws of orbital motion, but there’s a small problem: estimates of Sirius B’s mass based on measurements of its gravitational redshift have historically differed from its dynamically-measured mass by about 10% (to be clear, this is from new measurements taken after the original ones were realized to be wrong).

To clear up this long-standing confusion, the authors of today’s paper used the Hubble Space Telescope to take spectra of both Sirius A and B in order to perform a differential measurement of the gravitational redshifts of both. Differential measurement is a useful tool as it helps eliminate a lot of systematic errors that might be present in an instrument, since any that exist will affect all observations equally. The gravitational redshift of Sirius A is better known than for Sirius B, so by measuring both, finding the difference between them, and correcting for the known value of Sirius A’s redshift it’s possible to make a more precise and accurate measurement of the gravitational redshift of Sirius B than would be possible by observing it alone. ...

The gravitational redshift of Sirius B ~ Simon R.G. Joyce et al
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Some Like it Hot

Post by bystander » Wed Oct 03, 2018 4:15 pm

Some Like it Hot
Astrobites | 2018 Oct 03
Eckhart Spalding wrote:
Direct imaging has turned up only a handful of planets. However, as observing sensitivities get better in the coming years, the technique will become a powerful probe of planet formation physics. Part of the reason planets are so challenging to image is that planets don’t carry out fusion themselves, so they just slowly cool and become dimmer with time.

How, exactly, do they cool? We need to know this in order to convert the measured luminosity of a planet into meaningful data, like the planet’s mass. For that, we have to mostly rely on evolutionary models to predict the cooling curve. The authors of today’s paper do this by tackling the physics of the accretion process during its most rapid phase, when the growing protoplanet’s gravitational well consumes material as fast as the surrounding disk can supply it.

In the field of planet formation physics, “hot start” and “cold start” and a gradient of “warm” starts in between refer to the starting entropies of planets. These terms do not necessarily indicate the formation mechanism. The authors of today’s paper specifically investigate the core accretion mechanism to see what interior entropies, and by extension luminosities, it can lead to. ...

The Evolution of Gas Giant Entropy During Formation by Runaway Accretion ~ David Berardo et al
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How Many Planets Will We Find Around White Dwarfs?

Post by bystander » Sat Oct 06, 2018 1:56 pm

How Many Planets Will We Find Around White Dwarfs?
Astrobites | 2018 Oct 04
Matthew Green wrote:
Do white dwarfs have planets? The short answer is yes—but they’re difficult to detect by the traditional methods people use to look for exoplanets. In the next decade this might change thanks to a ground-breaking project called the Large Synoptic Survey Telescope, or LSST. Today’s paper uses simulations to estimate what LSST will see. ...

On the detectability of transiting planets orbiting white dwarfs using LSST ~ Jorge Cortes, David M. Kipping
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LISA forewarnings can help LIGO study black holes

Post by bystander » Sat Oct 06, 2018 2:10 pm

LISA forewarnings can help LIGO study black holes
Astrobites | 2018 Oct 05
Lisa Drummond wrote:
We have now detected several gravitational wave events (including one event with an electromagnetic counterpart, GW170817) since the first was detected on September 14th, 2015. So far, all the signals have been produced by compact binary mergers and observed using the ground-based detector LIGO (Laser Interferometer Gravitational Wave Observatory) and, more recently, VIRGO, another ground-based detector in Europe. In the future, space-based detector LISA (Laser Interferometer Space Antenna) will also detect gravitational waves (see Figure 1), and in particular will be sensitive to the lower-frequency band of the gravitational-wave spectrum.

Today’s paper focuses on how we can exploit LIGO and LISA in conjunction to greatly enhance our understanding of the nature of black holes. LISA will be able to detect the early inspiral stages of the compact binary, thereby giving a “forewarning” of when the signal will be detectable in the LIGO band (the waves become higher frequency later on). With weeks to years of advance warning due to LISA, LIGO can be optimised to make the most of the future detection of the predicted signal. ...

Optimizing LIGO with LISA forewarnings to improve black-hole spectroscopy ~ Rhondale Tso, Davide Gerosa, Yanbei Chen
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What is going on in the disk around HD 142527?

Post by bystander » Wed Oct 10, 2018 5:13 pm

A beautiful, yet complicated painting:
What is going on in the disk around HD 142527?

Astrobites | 2018 Oct 09
Arianna Musso Barcucci wrote:
We are currently in a golden era of circumstellar disk imaging: new instruments like ALMA and SPHERE (both located in Chile) are gifting us with stunning images of systems surrounding nearby stars, with their glowing disks, neatly carved gaps, rings, and beautiful spiral arms (check this astrobite for a good review on protoplanetary disks).

While most disks show only one or two of the aforementioned features, HD 142527 decided to make it big: the system around this 5-million-year-old star (Figure 1) is nothing short of spectacular.

But the wide variety of features and phenomena taking place at the same time makes this disk a puzzle to interpret! So far, there is no explanation for the entire artwork at once. ...

Circumbinary, not transitional: On the spiral arms, cavity, shadows,
fast radial flows, streamers and horseshoe in the HD142527 disc
~ Daniel J. Price et al
viewtopic.php?t=35642
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Magnetar Madness in Super Luminous Supernovae

Post by bystander » Wed Oct 10, 2018 5:29 pm

Magnetar Madness in Super Luminous Supernovae
Astrobites | 2018 Oct 10
Lauren Sgro wrote:
There are a lot of scary things out there in space: you know – like giant stars, black holes, aliens. But have you ever heard of a magnetar? On Earth’s surface, we experience a magnetic field less than 1 Gauss. The Sun’s magnetic field is not much more at about 25 Gauss. But a neutron star? Try a trillion Gauss. A magnetar is basically a neutron star on steroids with a magnetic field 1,000 times that of its normal counterpart. (You can read more about magnetars themselves in this astrobite).

Magnetars can be formed in supernovae explosions, just like neutron stars (the details of what makes them so magnetic is up for debate). The authors of today’s paper are studying some strange supernovae, and they want to know if the observations can be explained by modeling those supernovae with a magnetar at the center instead of the ordinary neutron star.

The authors are looking into two types of supernovae events, specifically: a type of hydrogen-rich super luminous supernovae (SLSNe II) and what we call Type II-P supernovae (SNe). Type II-P SNe are also hydrogen-rich, but they have a plateau in their light curve, meaning that as the luminosity declines from its peak, it hits a stretch where it declines at a very slow rate. For the case of SLSNe II, magnetars are typically used to model H-free SLSNe (SLSNe I), while interactions with circumstellar material are used to explain SLSNe II. What happens if a magnetar is used to model SLSNe II instead of space stuff around the progenitor star? ...

Systematic study of magnetar-powered hydrogen-rich supernovae ~ M. Orellana, M.C. Bersten, T.J. Moriya
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59 Binary Neutron Star Merger Simulations

Post by bystander » Sat Oct 13, 2018 3:52 pm

59 (Fifty-nine!) Binary Neutron Star Merger Simulations
Astrobites | 2018 Oct 11
Sanjana Curtis wrote:
Neutron star mergers are absolutely fascinating. These events are not just sources of gravitational waves but of electromagnetic radiation all across the spectrum – and of neutrinos as well. If you missed the amazing multimessenger observations last year that gave us a peek into what binary neutron star (BNS) systems are up to, please check out this bite about GW170817! The observations had major implications for many fundamental questions in astrophysics. The gravitational wave signal from the merger was detected along with the electromagnetic radiation produced. As a result, we were able to confirm that neutron star mergers are a site where heavy elements (those beyond iron) can be made via the r-process.

While all of this has undoubtedly been extremely cool (and we’re holding our collective breath for more data), there’s a lot of work that remains to be done. We need accurate predictions of the quantity and composition of material ejected in mergers in order to fully understand the origin of the heavy elements, and to say whether BNS mergers are the only r-process site. To investigate such questions, we require theoretical models that include all the relevant physics. Today’s paper presents the largest set of NS merger simulations with realistic microphysics to date. By realistic microphysics, we mean that the simulations also take into account what the atoms and subatomic particles are doing. This is done by using nuclear theory based descriptions of the matter in neutron stars, and by including composition and energy changes due to neutrinos (albeit in an approximate way). ...

Binary Neutron Star Mergers: Mass Ejection, Electromagnetic Counterparts and Nucleosynthesis ~ David Radice et al
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How can planets be heavier than the disks that formed them?

Post by bystander » Wed Oct 17, 2018 2:40 pm

How can planets be heavier than the disks that formed them?
Astrobites | 2018 Oct 15
Emma Foxell wrote:
Planets form from the dust and gas in protoplanetary disks, so we expect that the mass of these disks must be at least the same as the mass of the resulting planets. As this process takes millions of years, we cannot watch a given disk form planets. So the authors of today’s paper compare young protoplanetary disk masses with the masses of exoplanets that have already formed. ...

Why do protoplanetary disks appear not massive enough to form
the known exoplanet population?
~ C.F. Manara, A. Morbidelli, T. Guillot
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Full Metal Sky

Post by bystander » Fri Oct 19, 2018 4:00 pm

Full Metal Sky
Astrobites | 2018 Oct 17
Vatsal Panwar wrote:
Ultra-hot Jupiters are the new showstoppers in the field of exoplanets. Commonly detected by ground-based wide-angle surveys (like WASP, KELT and MASCARA), they are mostly nestled in tightly close orbits around bright early-type stars which irradiate the upper atmospheres of these planets to equilibrium temperatures of more than 2000 K – as hot as the photospheres of some of the cooler stars. However, these planets are less massive than cool stars. A combination of their lower surface gravities (as compared to that of stars) and the high equilibrium temperature of ultra-hot Jupiters leads to some exotic chemistry in their atmospheres. One direct consequence of their scorching hot temperatures is that their atmospheres can be treated as systems in chemical equilibrium, and most likely cloud free as it is likely that any possible cloud condensates would be thermally dissociated at these temperatures. This makes life much easier for astronomers studying exoplanet atmospheres. As predicted by recent studies, atmospheres of ultra-hot Jupiters should have metals like iron and titanium existing in their atomic form (molecular compounds like oxides are thermally dissociated at such high temperatures). Today’s paper reports the first detection of atomic iron and titanium in the atmosphere of one such ultra-hot Jupiter: KELT-9b. ...

Atomic Iron and Titanium in the Atmosphere of the Exoplanet KELT-9b - H. Jens Hoeijmakers et al
viewtopic.php?t=37256
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It’s a bird, it’s a planet, it’s a … speckle?

Post by bystander » Fri Oct 19, 2018 4:11 pm

It’s a bird, it’s a planet, it’s a … speckle?
Astrobites | 2018 Oct 18
Eckhart Spalding wrote:
The world’s state-of-the-art exoplanet imaging projects include the VLT’s SPHERE, Gemini’s GPI, Subaru’s SCExAO, Palomar’s Project 1640, and the LBT’s LEECH survey. As next-generation imagers come online, we need to think carefully about what the data say as sensitivities push closer in to the host stars. This Astrobite is the first of two which look at papers that change the way we think about exoplanet imaging data.

Traditionally, high-contrast imaging programs calculate a “contrast curve“, or a 1-D plot that shows the difference in contrast that could exist between a host star and a detectable low-mass companion (Fig. 1). The authors of today’s paper examine some of the statistical weirdness that happens as we get closer in, and how this can have a dramatic effect on the scientific implications. ...

Fundamental Limitations of High Contrast Imaging Set by Small Sample Statistics ~ Dimitri Mawet et al
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Heading to Titan? Bring a Swiffer!

Post by bystander » Tue Oct 23, 2018 2:34 pm

Heading to Titan? Bring a Swiffer!
Astrobites | 2018 Oct 19
Jessica Roberts wrote:
Before the Cassini satellite began touring the Saturn system, very little was known about Titan (one of Saturn’s many moons). When Voyager flew past Titan in 1981 on its way out of the Solar System, it sent back an image of a brownish yellow ball of haze (see Figure 1). For the next 24 years we were left with the nagging question: What could possibly lurk on Titan’s surface, hidden from view by its thick atmosphere?

This question was answered in 2004 when Cassini, equipped with multi-wavelength instruments, arrived at the Saturn system. By using different wavelengths, we were able to image different layers of Titan’s atmosphere, and at certain wavelengths, we could even observe its surface. In doing so, we discovered that Titan is actually fairly similar in some respects to Earth albeit with a chilly surface temperature of less than 100K. One notable similarity is the methane cycle on Titan is almost equivalent to the hydrological cycle on Earth. Astronomers observed huge methane storms in the atmosphere, liquid methane lakes near the poles and an arid region of dune fields probably made out of some type of frozen methane or other hydrocarbon “sand” surrounding Titan’s equator. These dune fields are the subject of today’s paper as the authors noted that an unusual bright spot appeared in this region three times during Cassini’s 13 year visit. ...

Observational Evidence for Active Dust Storms on Titan at Equinox ~ S. Rodriguez et al
viewtopic.php?t=38728
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How the Milky Way Got its Spiral Arms

Post by bystander » Tue Oct 23, 2018 2:41 pm

How the Milky Way Got its Spiral Arms
Astrobites | 2018 Oct 22
Tomer Yavetz wrote:
Spiral galaxies are named after their most prominent and stunning features – their spiral arms. These tightly wound filaments of stars and dust are undoubtedly one of the main reasons that pictures of spiral galaxies, originally taken for research purposes, often double as popular desktop backgrounds or as the centerfolds of coffee table books. Intuition correctly links the spiral structure to the rotational motion of these galaxies, yet the precise mechanism responsible for the formation of the spiral arms is still poorly understood. The goal of today’s paper is to improve on this picture by comparing maps generated from the second data release from the Gaia space telescope to simulations. ...

Discriminating among Theories of Spiral Structure using Gaia DR2 ~ J.A. Sellwood et al
viewtopic.php?t=38230
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Mind the (Gaia) Gap

Post by bystander » Fri Oct 26, 2018 9:48 pm

Mind the (Gaia) Gap
Astrobites | 2018 Oct 23
Lauren Sgro wrote:
By this point you have probably heard of Gaia, ESA’s amazing instrument that has cataloged over a billion stars, providing unprecedented precision in parallax measurements. Since its second data release in April, tons of discoveries have already been made (here and here and here). Several of these have been made by creating a simple HR diagram (HRD) of Gaia’s stars.

Because parallax information allows for distance measurements (which are needed to calculate luminosity), Gaia has been a great resource in studying the HRD. In today’s paper, the authors discover and explore a strange feature of the Gaia HRD concerning low-mass, M type stars. ...

A Gap in the Lower Main Sequence Revealed by Gaia Data Release 2 ~ Wei-Chun Jao et al
viewtopic.php?t=38740
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When is the next glitch on pulsar J0537-6910?

Post by bystander » Fri Oct 26, 2018 10:07 pm

When is the next glitch on pulsar J0537-6910?
Astrobites | 2018 Oct 24
Lisa Drummond wrote:
Pulsars (rotating, magnetised neutron stars) emit radiation that sweeps periodically over the earth (like the beam of a lighthouse sweeping across the ocean). We detect this radiation as a sequence of pulses, with the frequency of the pulse corresponding to the frequency of rotation of the star. Pulsars will typically spin down over their life time, due to electromagnetic braking, but this is a fairly slow process. Occasionally, in some pulsars, we will detect sudden increase in the frequency of the pulses. This is called a pulsar glitch. Essentially, the mismatch in the rotation of the fluid inside the star and the solid crust on the outside of the star causes a catastrophic event that we see as an increase in the frequency of the pulses.

The question that today’s paper seeks to answer is: can you predict the next glitch in a pulsar? In general, this is a challenging task, with different pulsars exhibiting different glitching behaviours that need to be captured in your model. However, for one particular pulsar (PSR J0537-6910) this can be accomplished fairly straightforwardly due to the strong correlation between the size of a glitch and the waiting time until the next glitch. The authors of today’s paper exploit this correlation to develop a method to predict the next starquake on PSR J0537-6910. ...

Predicting the Starquakes in PSR J0537–6910 ~ John Middleditch et al
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Building Butterflies from Starlight

Post by bystander » Fri Oct 26, 2018 10:21 pm

Building Butterflies from Starlight
Astrobites | 2018 Oct 25
Jamila Pegues wrote:
The Sun may be the closest star to us here on Earth, but there’s plenty about the Sun that we still don’t understand. One of the ongoing mysteries of the Sun, and really of stars in general, is their magnetic fields.

Astronomers believe that the magnetic field of a star, which is invisible to the human eye, drives some of the stellar activity that we can observe. Starspots, like those seen on the Sun in Figure 1, are examples of such stellar activity. These dark spots appear in places where the star’s magnetic field is highly concentrated.

One way that astronomers have catalogued stellar activity for the Sun, so as to better learn about and model the Sun’s underlying magnetic field, is with butterfly diagrams. Butterfly diagrams, the like one for the Sun shown here, illustrate how the latitude of a star’s active regions change with time. ...

Today’s authors present an entirely new approach that circumvents these issues. Their approach uses both photometric and asteroseismic data to assemble butterfly diagrams. They demonstrate their approach for the Sun-like star known as HD 173701. ...

Butterfly diagram of a Sun-like star observed using asteroseismology ~ M. Bazot et al
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Additional Arguments that Aboriginal Australians Observed Variable Stars

Post by bystander » Fri Oct 26, 2018 10:57 pm

Additional Arguments that Aboriginal Australians Observed Variable Stars
Astrobites | 2018 Oct 26
Avery Schiff wrote:
Stargazing is a global phenomenon. Despite the preponderance of Greek mythology in the modern constellations, ancient civilizations from China to Polynesia practiced early astronomy and developed their own mythologies. One culture with a particularly rich history of astronomical observation is that of Aboriginal Australians. Earlier this year, a researcher at the Monash Indigenous Studies Centre published a paper arguing that various Aboriginal groups correctly identified variable stars and incorporated their periodic behavior into constellation lore. Today’s paper, by Bradley E. Schaefer, focuses on one of the stars discussed in that publication, Betelgeuse, and provides additional evidence that Aboriginal astronomers discovered its variability. ...

Yes, Aboriginal Australians Can and Did Discover the Variability of Betelgeuse ~ Bradley E. Schaefer
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BepiColombo blasts off in pursuit of Einstein

Post by bystander » Tue Oct 30, 2018 4:14 pm

BepiColombo blasts off in pursuit of Einstein
Astrobites | 2018 Oct 29
Philippa Cole wrote:
On the 20th October, BepiColombo blasted off from Kourou on a five-year voyage to Mercury. BepiColombo is a joint mission between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), which aims to explore the smallest and least-studied planet of the inner solar system. It’s made up of two science orbiters which will be carried to Mercury by a transfer module, harnessing solar electric propulsion and gravity assist flybys to place them into orbit around Mercury in 2025. BepiColombo will need to withstand pizza oven temperatures (up to 450°C/840°F), as well as battle against the Sun’s enormous gravitational pull in order to successfully orbit the Sun’s nearest neighbour.

NASA’s Messenger mission was the last spacecraft to venture so close to the Sun, and while many questions were answered with the 4 years of observations, many more were opened up. BepiColombo is now off to hunt down those answers. Whilst there are many science goals concerning Mercury’s geology and magnetosphere — for example why is it shrinking?! — the authors of today’s paper explain that BepiColombo can also put Einstein to the test (again). ...

A new general relativistic contribution to Mercury's perihelion advance ~ Clifford M. Will
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Re: BepiColombo blasts off in pursuit of Einstein

Post by BDanielMayfield » Tue Oct 30, 2018 4:28 pm

I don't think they'll ever catch him.
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Glimpsing the fingerprints of gravitational waves in the early universe

Post by bystander » Tue Oct 30, 2018 4:31 pm

Glimpsing the fingerprints of gravitational waves in the early universe
Astrobites | 2018 Oct 30
Grace Chesmore wrote:
Fourteen billion years ago, our universe came into existence, rapidly inflating for a fraction of a second and subsequently coasting outward. Around 380,000 years after this Big Bang, the universe cooled enough for photons to escape and our universe became transparent. Scientists call these early photons the “Cosmic Microwave Background” (CMB).

Gravitational waves, which are ‘ripples’ in the fabric of space-time, left imprints in the polarization of the CMB during the early universe. The polarizations of interest are called B-mode and we can detect them with the Planck telescope, which maps out the fluctuations in the CMB. In 2017, LIGO detected gravitational waves from an amazing binary star collision – now scientists can study gravitational waves from the earliest moments of our universe in these tiny B-mode signals in the CMB using neural networks. ...

Confirmation of the detection of B-modes in the Planck polarization maps ~ H. U. Nørgaard-Nielsen
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The Spooky Origins of the Solar System

Post by bystander » Sun Nov 04, 2018 4:03 pm

The Spooky Origins of the Solar System
Astrobites | 2018 Oct 31
Emily Sandford wrote: ...
The early days of the Solar System, like much of what happens in space, were indeed spooky. We know this because (a) there’s a Monster Mash verse about it and (b) like all great spooky scenes, they’ve left behind enduring mysteries.

For one: how did the oldest meteorites, which contain minerals that form at very high temperatures and minerals that form at much lower temperatures, come to be? More specifically, how did those minerals get all mixed up together in the first few thousand years of the Solar System? ...

Today’s authors take this picture of a protoplanetary disk evolving even as the star’s big spherical birth cloud is still collapsing, and simulate it in the simplest possible terms. They start with a small disk with a source of light and heat at the center (to represent the protostar), and then they let a big spherical gaseous envelope gradually collapse into the disk. ...

Making the Planetary Material Diversity During the Early Assembling of the Solar System ~ Francesco C. Pignatale et al
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How to Diagnose the Light from Early Galaxies

Post by bystander » Sun Nov 04, 2018 4:12 pm

How to Diagnose the Light from Early Galaxies
Astrobites | 2018 Nov 02
Caitlin Doughty wrote:
Astronomers run into a predicament when attempting to study galaxies as they existed when the Universe was only about 1 billion years old (or even younger!), namely that these galaxies are quite far away and appear exceedingly dim in detector images, even when using large telescopes. How is one to learn what typical galaxies were like and how they were evolving if they are so difficult to see? Luckily, there is a special sort of light that is so bright it can even be seen from enormous distances. Called Lyman α (pronounced as “lyman alpha”), this form of light provides a possible way of studying some of the earliest galaxies to understand their evolution and structure. Today’s study takes a look at how Lyman α radiation is created within galaxies and how it escapes their boundaries to traverse the rest of space. ...

The physics of Lyman-alpha escape from high-redshift galaxies ~ Aaron Smith et al
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