Tagged: Astrobites Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 12:16 pm on October 20, 2017 Permalink | Reply
    Tags: Astrobites, , , , , ,   

    From astrobites: “Energy transport in white dwarfs: what about magnetic fields?” 

    Astrobites bloc

    astrobites

    Oct 20, 2017
    Ingrid Pelisoli

    Title: Can magnetic fields suppress convection in the atmosphere of cool white dwarfs? A case study on WD2105-820
    Authors: N. P. Gentile Fusillo, P.-E. Tremblay, S. Jordan, B. T. Gänsicke, J. S. Kalirai, J. Cummings
    First Author’s Institution: University of Warwick, UK

    Status: Submitted to MNRAS, open access

    Did you know that the bright yellow ball that shines in the sky, which we call the Sun, is also a huge magnet? However, it is huge only in terms of spatial dimensions – the strength of the magnetic field is only about 1 Gauss (G), or 10-4 Tesla (T). This is 10,000 weaker than the strongest magnet you can buy. The strongest magnet ever built on Earth produces a magnetic field of at least 45 T. Meanwhile, there are some other tiny dots in the sky with fields as strong as 108G, or 104T!

    Tiny giant magnets

    These tiny dots are white dwarf stars, which are about the size of the Earth, but with a mass comparable to the Sun. They maintain their hydrostatic equilibrium thanks to the Pauli exclusion principle: gravity can not further compress the object without pushing electrons into the same energy states, so the electrons push back, causing what is known as degeneracy pressure. The high field observed in some white dwarf stars is probably related to the fact that they are tiny: their progenitors had much smaller fields, but when they are compressed into a planetary size, the field is strengthened due to the magnetic flux being conserved. However, the process of evolution involves lots of mass being lost, and we don’t know exactly what happens to the magnetic field during these stages. As a result, we cannot fully understand the origin of such high magnetic fields.

    1
    Figure 1: The author’s spectral fit to the hydrogen Balmer lines, from H8 to Hß. The top panel shows the best fit using a convective model, and the bottom panel shows the best radiative model. The obtained values of effective temperature and logarithm of the surface gravity are indicated. Figure 1 in the paper

    With the data release 2 of Gaia, which has made many astronomers draw a big circle around April 2018 on their calendars, we should identify hundreds of thousands of new white dwarfs. Something between 5 and 30% of them should be magnetic, based on the fraction of known magnetic white dwarfs. So it’s about time we start learning more about these objects! One particular problem we currently have is that it is very hard to estimate the mass of magnetic white dwarfs. We usually cannot apply spectroscopic analysis, our main method of estimating masses, because the spectral lines of magnetic white dwarfs are affected by the Zeeman effect. This effect causes an extra broadening which we have not (yet) been able to model together with the other important effects. In summary, no complete model exists! Gaia will give us a hand with that by allowing us to estimate the radius of white dwarfs – which is related to their mass (more about it in this bite). But we still have to know the temperature of the white dwarf to be able to do further cool science, such as estimating the age of stellar populations (like here and here).

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

    Advertisements
     
  • richardmitnick 9:58 am on October 19, 2017 Permalink | Reply
    Tags: Astrobites, , , , , , Proof that standard sirens work!   

    From astrobites: “Proof that standard sirens work!” 

    Astrobites bloc

    astrobites

    Oct 19, 2017
    Kelly Malone.

    Title: A gravitational-wave standard siren measurement of the Hubble constant
    Authors: The LIGO Scientific Collaboration, the Virgo Collaboration, The 1M2H Collaboration, The Dark Energy Camera GW-EM Collaboration, The DES Collaboration, The DLT40 Collaboration, The Las Cumbres Observatory Collaboration, The VINROUGE Collaboration, and the MASTER Collaboration



    1M2H


    Status: Accepted by Nature (in press) [open access]

    By now, you’ve almost certainly heard about this week’s big scientific announcement: a binary neutron star merger resulting in the observation of both gravitational waves and counterparts all over the electromagnetic spectrum (you can read Astrobites’ coverage here). Astronomers are very excited about this event; as the first of its type to be observed, it ushers in a new era of multi-messenger astronomy as well as confirms that neutron star mergers are a source of short gamma-ray bursts.

    However, there is a lot of other interesting science we can get out of this event as well, which implications for many subfields of astrophysics. Just scan this list of 81 (at last count) papers about the event for an idea of the magnitude of physics we can do here. Today’s paper goes all the way into the field of cosmology and uses the event to derive the Hubble Constant completely independently of existing calculations.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 9:39 am on October 18, 2017 Permalink | Reply
    Tags: Astrobites, , , , , Observing a Strange Pulsar in X-ray and Radio   

    From astrobites: “Observing a Strange Pulsar in X-ray and Radio” 

    Astrobites bloc

    astrobites

    Title: SIMULTANEOUS CHANDRA AND VLA OBSERVATIONS OF THE TRANSITIONAL MILLISECOND PULSAR PSR J1023+0038: ANTI-CORRELATED X-RAY AND RADIO VARIABILITY
    Authors: Slavko Bogdanov, Adam T. Deller, James C. A. Miller-Jones, Anne M. Archibald, Jason W. T. Hessels, Amruta Jaodand, Alessandro Patruno, Cees Bassa & Caroline D’Angelo
    First Author’s Institution: Columbia Astrophysics Laboratory, Columbia University, New York, NY
    2
    Status: Submitted to ApJ, open access

    What’s more interesting than a rapidly spinning neutron star that emits electromagnetic radiation parallel to it’s magnetic poles? One that doesn’t exactly behave as expected of course. This weirdly acting pulsar, PSR J1023+0038 is a transitional millisecond pulsar (tMSP) which is fancy speak for a pulsar with a millisecond or so rotational period that switches between radio and x-ray emission on a several year timescale. However emitting in both x-ray and radio on these longer timescales isn’t what piques the interest of astronomers in the case of this astrobite.

    Weird Pulsar Behavior

    3
    Figure 1: Radio emissions (black) and x-ray emissions (blue) recorded by the VLA and Chandra respectively over time showing that when radio emissions drop off, x-ray emissions pick up.

    Beyond the basic idea of a pulsar, they typically can fall into one of the following categories. Radio pulsars are powered by exchanging rotational energy from the spinning neutron star into emitting radiation. This means that their rotation slows and their pulse length increases. Meanwhile, x-ray pulsars are accretion powered, meaning they turn infalling matter that is heated up into x-ray emission. What distinguishes PSR J1023+0038 from the background of pulsars that switch between accretion powered x-ray and rotation powered radio pulsars is that it has a simultaneous anti-correlated x-ray and radio emission. The authors looked at about 5 hours of overlapping and concurrent observations from the Chandra X-ray Observatory and the Very Large Array (VLA) to try and understand this weird relationship between the x-ray and radio emissions.

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

    This is very clearly shown in Fig. 1 where we can see a tiny sample of time of overlapping x-ray and radio flux measurements. The anti-correlation is quite strong, meaning that when the x-ray emissions are weakest, the radio emission is strongest.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 7:20 am on October 18, 2017 Permalink | Reply
    Tags: Astrobites, , , , , Lucky planets?   

    From astrobites: “Lucky planets?” 

    Astrobites bloc

    astrobites

    Oct 17, 2017
    Elisabeth Matthews

    Title: High-resolution Transiting Extrasolar Planetary systems (HITEP) II: Lucky Imaging results from 2015 to 2016
    Authors: Dan Evans, John Southworth, Barry Smalley et al.
    First Author’s Institution: Keele University, UK
    1
    Status: Accepted to A&A, open access

    We might have mentioned this before once or twice (or three or four or five times…) but dynamically hot Jupiters (exoplanets the size of Jupiter, but extremely close to their host stars) are really really weird. They shouldn’t be able to form so close to their host stars (or maybe they should?) but there’s a fair few of them floating around, so something has to be shunting them extremely close to their stars – and their orbits are often observed to be at very high eccentricities. If that doesn’t surprise you, minute physics have a great video explaining why all our solar system planets are in a plane, and why we’d expect the same for exoplanet systems: the stellar spin and any planetary orbits and spins should all be aligned.

    2
    Figure 1. An artist’s impression of a planet in a binary system, orbiting one of the two stars. Credit: Gould et. al/Ohio State University

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 11:28 am on October 17, 2017 Permalink | Reply
    Tags: Astrobites, , , , , , SO-2   

    From astrobites: ” Is S0-2 a Binary Star?” 

    Astrobites bloc

    astrobites

    Title: Investigating the Binarity of S0-2: Implications for its Origins and Robustness as a Probe of the Laws of Gravity around a Supermassive Black Hole
    Authors: D. S. Chu, T. Do, A. Hees, A. Ghez, et al.
    First Author’s Institution: University of California, Los Angeles

    Status: Submitted to ApJ, open access

    The most exciting discoveries in astronomy all have something in common: they let us marvel at the fact that nature obeys laws of physics. The star S0-2 is one of these exciting discoveries. S0-2 (also known as S2) is a fast-moving star that has been observed to follow a full elliptical, 16-year orbit around the Milky Way’s central supermassive black hole, precisely according to Kepler’s laws of planetary motion.

    2
    S0-2

    SGR A* NASA’s Chandra X-Ray Observatory

    Serving as a test-particle probe of the gravitational potential, S0-2 provides some of the best constraints on the black hole’s mass and distance yet. S0-2 is the brightest of the S-stars, a group of young main-sequence stars concentrated within the inner 1” (0.13 ly) of the nuclear star cluster.

    The next time S0-2 reaches its closest approach to the black hole, in 2018, there will exist a unique opportunity to detect a deviation from Keplerian motion — namely the relativistic redshift of S0-2’s radial (line-of-sight) velocity — in a direct measurement. In anticipation of this event, the authors of today’s paper investigate possible consequences of S0-2 being not a single star, but a spectroscopic binary, which would complicate this measurement.

    3
    Figure 1: Top: Radial velocity measurements of S0-2 over time. Bottom: Residual velocities after subtraction of the best-fit model for the orbital motion. [Chu et al. 2017]

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 6:11 am on October 12, 2017 Permalink | Reply
    Tags: Astrobites, , , , , Exoplanet atmospheres, Illusion and reality   

    From Astrobites: “Illusion and reality” 

    Astrobites bloc

    Astrobites

    Oct 12, 2017
    Eckhart Spalding

    Title: Illusion and reality in the atmospheres of exoplanets
    Authors: Drake Deming, Sara Seager
    First Author’s Institution: University of Maryland, College Park

    Status: Published in the Journal of Geophysical Research: Planets (open access)

    In discussions of exoplanet atmospheres, variations of the word “illusion” come up a lot. They pop up 27 times in today’s sobering article, which takes stock of the current state of knowledge and observational techniques. The fact is, real science is much messier than the popular image of science as a streamlined and systematic process of establishing truths. Despite scientists’ best efforts, published results sometimes turn out to be illusions.

    This has certainly been the case in the field of exoplanet atmospheres, where the observational signals are extremely small, often measured in hundreds of parts-per-million or less. They are usually made using detectors that were never built with exoplanets in mind, and faint signals have to be sieved painfully from the fuzz of detector noise. Furthermore, sources of systematic error have been poorly understood, as one might expect in any new field. This has led to a litany of published results which have later vanished like a mirage.

    Debunked findings have included a variety of claimed atmospheric molecular detections. For example, transmission spectroscopy observations using the Hubble Space Telescope’s (HST) NICMOS detector were used to claim the presence of water vapor, methane, and carbon dioxide in an exoplanet’s atmosphere. As people’s understanding of NICMOS systematics improved, it became clear that the detector suffers strong systematics which can masquerade as signals. In addition, the same dataset could yield different apparent signals depending on which data reductions techniques were used.

    It seems unavoidable that obtaining reliable information about exoplanet atmospheres requires huge telescopes, enormous expense, and lots of manpower. With some understatement, the modeler Adam Burrows wrote in a 2014 review article that knowledge of “exoplanet atmospheres is small and by no means commensurate with the effort expended”. But exoplanet atmospheres are worth the effort, because they provide us virtually all the information about the planet other than the planet’s mass, radius, and the characteristics of its orbit.

    What discoveries have proven to be on firm ground? Well, for one thing, the zeroth-order conclusion that exoplanet atmospheres exist. (Checkmark.) Some of the more extended known atmospheres have had absorption lines directly characterized by HST or Spitzer, and other atmospheres have been inferred indirectly from the large apparent radii of some planets (which would have unphysical densities if planets were assumed to be solid).

    1
    Fig. 1: A transmission spectrum of HD 209458b, representing current state-of-the-art observations using HST/WFC3. The big bump is water absorption. (Fig. 10 in Deming+ 2013)

    In fact, results from the Kepler spacecraft have led to the conclusion that planets with radii above ~1.6 Earth radii will, as a rule, have thick atmospheres. Smaller planets tend to be rocky orbs for which atmospheres are optional (like Venus vs. Mercury). We currently know next to nothing about super-Earth atmospheres, though HST/WFC3 observations are trying to chip away at this.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 8:38 am on October 11, 2017 Permalink | Reply
    Tags: A Helium-Powered Supernova, A supernova called MUSSES1604D, Astrobites, , , , , Subaru Hyper Suprime-Cam instrument,   

    From Astrobites: “A Helium-Powered Supernova” 

    Astrobites bloc

    Astrobites

    Oct 11, 2017
    Matthew Green

    Title: A hybrid type Ia supernova with an early flash triggered by helium-shell detonation
    Authors: Ji-an Jiang, Mamoru Doi, Keiichi Maeda, et al.
    First Author’s Institution: Institute of Astronomy, The University of Tokyo, Japan
    1
    Status: Accepted by Nature, open access

    Today we’re going to be talking about an unusual supernova, MUSSES1604D, which appears to be the first strong evidence for one of the proposed models of Type Ia Supernovae. First, we should talk about what the model is.

    2
    5
    http://www.swinburne.edu.au/news/latest-news/2017/10/surface-explosion-may-trigger-stellar-death.php

    Type Ia Supernovae, and Where They Come From

    3
    Figure 1: Artist’s impression of the ignition of an accreting white dwarf. Credit: David A. Hardy, STFC.

    Everyone loves a good explosion, and supernovae are among the biggest. They’re also complicated, and there exists a whole menagerie of different classes. Today we’re going to be talking about one particular subclass, ‘Type Ia Supernovae‘ (SNe Ia). These supernovae get a lot of press. As well as being interesting for their own sake, they are useful objects for astronomy as a whole, because they allow us to measure the distances of far-off galaxies. This comes from the fact that the brightness of an SN Ia is easy to calculate from other properties of the supernova. If we know how bright a supernova is, and we can measure how much of its light we receive, it’s relatively straightforward to work out how far away that supernova is. A lot of interesting science regarding the most distant galaxies is based on distance measurements that required SNe Ia.

    Despite this, there is a nagging problem with SNe Ia: we still don’t fully understand how exactly SNe Ia happen. We do know that SNe Ia result from exploding white dwarfs. A white dwarf has a maximum mass (named the Chandrasekhar mass after the theoretician who first proposed it) beyond which it cannot support itself against its own gravity. If a white dwarf grows to be heavier than the Chandrasekhar mass, it will collapse in upon itself. Collapsing causes the matter that makes up the white dwarf to become incredibly hot and dense. Past a certain point, atoms of carbon and oxygen can undergo nuclear fusion in a runaway nuclear reaction, causing an explosion which rips the white dwarf apart. This is the standard picture of what causes SNe Ia.

    This basic idea still has a number of unsolved problems surrounding it, however. For today, the most important problem is this: there just don’t seem to be enough high-mass white dwarfs to match the rate of supernovae that we see. As a result, an alternative model has been developed over the past few years, which would allow white dwarfs to explode without needing to reach the Chandrasekhar limit: the so-called ‘double detonation’ model. This model needs a white dwarf composed mostly of carbon and oxygen, surrounded by a thin atmosphere of helium. If the helium is hot and dense enough to trigger nuclear burning, this can ignite an explosion that sweeps through the entire helium atmosphere. Then, a resulting shockwave through the body of the white dwarf can trigger a second explosion in the core, ripping the white dwarf apart and creating a supernova even if the white dwarf is below the Chandrasekhar mass limit.

    MUSSES1604D: The First Helium-Triggered Supernova?

    4
    Figure 2: Brightness of the supernova over time, as observed through blue (left) and green (right) filters. The measured brightness of the supernova is shown by the coloured squares, while various model fits are shown by different lines. It isn’t clear from the data that the team collected whether the supernova dips in brightness as the models predict, or whether it just plateaus for a few days. Either way there are clearly two separate periods in which the source is brightening. This is Figure 3 in today’s paper.

    Today’s paper is about a supernova called MUSSES1604D, which was first detected in April 2016. It was discovered by a survey using the impressively named Hyper Suprime-Cam instrument (a camera which is larger than a person and heavier than the average car).

    NAOJ Subaru Hyper Suprime-Cam


    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level

    This survey is optimised towards finding supernovae in the first few days after they start, while their brightness is still shooting up. While the team were watching MUSSES1604D it did several interesting things. Firstly it showed signs of what they call an ‘early flash’: an initial period in which the supernova was growing brighter, after which it seemed to either stall or fade in brightness for several days before continuing to brighten. Secondly, during this early flash the supernova turned very red, before becoming blue again during the main explosion.

    5
    Figure 3: Spectra of MUSSES1604D, compared with models from various helium shell ignition models. Heavy metals in the supernova produce the features at the left hand side of the spectrum, while the dips on the right hand side (beyond around 6000 angstroms) are produced by silicon. Note that the models do not quite fit with the data, implying some further development of the models might be necessary. This is Figure 4 in today’s paper.

    A spectrum taken of the supernova showed that its composition was also odd. The elements that you see in an SN Ia are generally dependent on the temperature of the explosion. Most of the features in the spectrum MUSSES1604D are from silicon and indicate a fairly average temperature — which agrees with the brightness that they measure. However, the spectrum also shows the presence of heavy metals, such as iron and titanium. These would generally be found in cooler SNe Ia. The presence of these heavy metals is probably linked to the red colour of the explosion’s early flash, as these elements tend to absorb a lot of blue light.

    These unusual characteristics — the early flash, its red colour, and the odd mix of elements — are difficult to explain with any of the classical models of SNe Ia. However, these traits do fit rather well with the double detonation model. In this model, the early flash would come from the ignition of the white dwarf’s helium atmosphere, before the main peak in brightness which comes from the explosion of the white dwarf core. The first explosion would, through nuclear fusion, produce a burst of heavy elements that cause it to appear red. These heavy elements would then hang around during the main explosion, causing the unusual mix of elements seen in MUSSES1604D.

    This is the first strong evidence we have of an SN Ia with an early helium explosion. It’s a promising sign that the double detonation model can explain at least some supernovae, and gives theorists a known example to constrain their models. This is an exciting result for the field, and brings us closer to solving the decades-long question about how SNe Ia occur.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 2:55 pm on October 10, 2017 Permalink | Reply
    Tags: A Neptune in the Nearby Hyades, Astrobites, , , , , K2-NnnA and K2-NnnB make up a binary system   

    From Astrobites: “A Neptune in the Nearby Hyades” 

    Astrobites bloc

    Astrobites

    Oct 10, 2017
    Mara Zimmerman

    Title: K2-NnnA b: A Binary System In The Hyades Cluster Hosting A Neptune-Sized Planet
    Authors: David R. Ciardi, Ian J. M. Crossfield, Adina D. Feinstein et al.
    Lead Author’s Institution: Caltech/IPAC-NASA Exoplanet Science Institute Pasadena, CA USA
    1
    Status: Submitted to AAS Journals [open access]

    The authors of today’s paper report the discovery of a Neptune-sized planet in the nearby Hyades Cluster around a binary star.

    2
    http://www.nightskyinfo.com/archive/hyades/

    A binary is just two stars mutually orbiting their center of gravity; the larger star is called the primary and the smaller is the secondary. In a close binary where the stars are separated only by a short distance, the two stars affect the evolution and size of each other. Planets in binaries have to survive in an extreme environment for an incredibly long time. This binary system is referred to as EPIC 247589423 (also called LP 358-348), but the primary and secondary stars within this system are called K2-NnnA and K2-NnnB, respectively. Since this planet was discovered orbiting just the primary star, the authors of this paper have decided to refer to it as K2-NnnA b: exoplanets are generally named after their host star and then have another letter added to the end. However, this planet does not yet officially have a name, so there is hope that it will be called something that rolls off the tongue a bit more easily.

    Significance to Planetary Formation and Evolution

    Planets in binaries must form under the influence of two stars, which is an extreme environment, particularly if the two stars are close. The system EPIC 247589423 has a very close separation of 40 AU, which is roughly the distance from Pluto to the Sun. Using out system as an example, if we replaced Pluto with another star, it is easy to see that the rotation and generally everything about the planets would be drastically affected. By studying planets in these environments, we can learn the extremes of planet formation.

    These extreme planets test the robustness of planet formation, since these have to survive in an extreme environment for a long time. These also test how often planets are retained by their host star rather than destroyed by the changing gravitational field. By finding and studying planets in clusters, we may begin to understand how planetary systems form and evolve and find out the timescale for such events.

    K2 and Follow-up Observations

    K2, or as I like to call it, Zombie Kepler [not nice, unnecessary, beneath dignity], is the current mission for the Kepler Space Telescope.

    NASA Kepler Telescope

    The Kepler Space Telescope was launched in 2009 with the mission of finding exoplanets through transit photometry. The method of transit photometry means recording the brightness of the star for an extended period of time, then looking for any small periodic ‘dips’ in this where an exoplanet eclipsed a small part of the star.

    Planet transit. NASA/Ames

    This data is generally referred to as a light curve, since there is a rounded dip where the exoplanet eclipses the star. After a mechanical mishap in 2013 with the Kepler Space Telescope, the scientists working on this mission still found a way to use the telescope to look for transiting exoplanets. Instead of observing one single part of the sky for an extended period of time as before, K2 now observes smaller patches of the sky for shorter amounts of time. Figure 1 shows several stages of the light curve analysis from K2.

    3
    Figure 1: This shows the light curve in various stages of analysis from K2. The topmost panel shows the light curve with the telescope rotation removed. The second panel shows the binned version of the top panel. The third shows the data with the stellar variability removed, and the lowest panel shows the folded and binned result for the planet transit.

    These scientists used the K2 data to discover this short period exoplanet by looking at the starEPIC 247589423. Since this planet is in a binary system, the researchers had to first remove the stellar variability inherent in the data. The two stars within the binary already eclipse each other and cause dips in the light curve, which can make it difficult to find a much smaller dip from the planet. After removing the eclipse variability, they found the planet and solved for the period and radius of K2-NnnA b.

    After the initial discovery with K2, the researchers followed up their discovery with new observations and archival data to confirm their discovery. They used the archival data from 1950 Palomar Observatory Sky Survey to rule out any other object that could be causing the dip in the light curve.

    Caltech Palomar Observatory, located in San Diego County, California, US

    For example, if another eclipsing binary was behind this system, the variation in that system could be mistaken for a planet. However, by analyzing the data, these researcher ruled out those possibilities, then made observations using the Keck I telescope.


    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft) above sea level

    K2-nnnA b: Planet Properties

    K2-NnnA and K2-NnnB make up a binary system in the nearby Hyades cluster. They are separated by about 40 AU. The planet orbits the K2-NnnA with a period of 17.3, and its transit lasts roughly of 3 hours.

    K2-NnnA b is one of the first Neptune-sized planets that has been observed orbiting in a binary system within an open cluster. This cluster, the Hyades, is the nearest star cluster to the Sun and is roughly 750 Myr old. The discovery of this planet can provide us with a better understanding of the planet population in stellar clusters and allow us to place more limits on planetary formation and evolution.

    The authors of this paper say planets discovered in nearby star clusters ‘provide snapshots in time and represent the first steps in mapping out [planetary] evolution,’ and I wholeheartedly agree. The discovery of K2-NnnA b brings with it new understanding of planet formation in star clusters and in binary systems. The possibilities of planet formation and evolution are certainly not limitless, and with more and more discoveries like K2-NnnA b, we can hopefully find the extremes of planetary systems.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 11:54 am on October 5, 2017 Permalink | Reply
    Tags: Astrobites, , , , , Nuclear Pasta in Neutron Stars   

    From astrobites: “Nuclear Pasta in Neutron Stars” 

    Astrobites bloc

    Astrobites

    Oct 5, 2017
    Lisa Drummond

    Title: Astromaterial Science and Nuclear Pasta
    https://arxiv.org/abs/1606.03646
    Authors: M. E. Caplan, C. J. Horowitz
    First Author’s Institution: Indiana University, USA

    Status: arXiv.org, open access

    Inside a neutron star

    Neutron stars are the densest objects in the universe. Naturally, the matter inside of them is exotic and unlike anything on Earth — imagine squashing the mass of our Sun into a star only 10 km across! As one might guess from their name, neutron stars are comprised of mostly neutrons, with a small fraction of electrons and protons also contributing to their mass. A neutron star can be thought of as analogous to a giant atomic nucleus, bound by gravitational forces rather than the strong force. Under the pressure exerted by gravity, matter is compressed to the same density as the nuclei of atoms; properties of the high density matter in neutron stars are discussed in this bite.

    Now, let us visualise descending through the crust of a neutron star. Figure 1 provides a schematic of the stratified layers we encounter during our descent. In the outer crust, neutrons combine into nuclei which form a solid lattice. As we descend deeper into the crust, the nuclei become increasingly giant and neutron-rich. Beyond a certain size, the neutrons begin to overflow from the nuclei and drip out, forming an ocean of free neutrons in which the lattice of nuclei is immersed. This signifies our transition into the inner crust. Here, at the base of the crust (or “mantle”), we discover the intricate nuclear structures that today’s paper is concerned with. Usually we expect nuclei to be spherical, but here the nuclei deform and fuse, forming clusters of exotic shapes called “nuclear pasta”. Beyond this point, we enter the core of the star where we find uniform nuclear matter: a neutron superfluid (a substance that flows without friction) coexists with a proton superconductor (a material that conducts electricity without resistance).

    1
    Figure 1: (a) Structure of a neutron star. Symbols N, n, p, e, μ correspond to nuclei, fluid neutrons and protons, electrons, and muons respectively. (b) Composition of the inner crust of a neutron star. Source: https://compstar.uni-frankfurt.de/outreach/short-articles/the-nuclear-pasta-phase/

    Nuclear Pasta

    Under the extreme, high-density conditions inside a neutron star, the competition between nuclear attraction and Coulomb repulsion yields exotic structures called nuclear pasta. Ravenhall, Pethick, and Wilson were the first to investigate these unusual configurations of nuclear matter. Nuclear pasta is characterised by complex, non-spherical patterns such as tubes, sheets and bubbles; these configurations minimize their energy (see Figure 2). The name “nuclear pasta” arose due to a resemblance to different varieties of pasta — such as lasagna, gnocchi and spaghetti!

    Presently, our understanding of nuclear pasta in neutron stars is largely based on theoretical calculations. However, some observational evidence does exist that supports the existence of nuclear pasta in the crust. For example, Pons, Vigano and Rea postulate that the pasta phase limits the maximum spin period of rotating neutron stars (pulsars). They suggest that the absence of isolated X-ray pulsars with spin periods greater than 12 seconds may be observational evidence of nuclear pasta. Hunting for observational signatures of the nuclear pasta layer is a research topic of great interest.

    3
    Figure 2: Examples of different nuclear pasta phases. Figure 3 in paper.

    Results

    In this paper, the authors conduct semi-classical molecular dynamics simulations of nuclear pasta. The semi-classical approach is justified because the relevant behaviours involve clusters of thousands of nucleons and these heavy clusters can be treated classically. The quantum effects present at smaller scales are put in by hand through the parameters in the semi-classical model.

    The authors model the geometry and topology of the complex pasta structures pictured in Figure 2 and extract useful properties of the material, such as thermal and electrical conductivity. The authors discuss how the presence of a pasta layer at the base of the neutron star crust could influence observations of astrophysical phenomena such as supernova neutrinos, magnetic field decay and crust cooling of accreting neutron stars.

    Above we discussed the paper written by Pons et al. in which nuclear pasta phases are expected to contain impurities. The impurities cause the magnetic field of the neutron star to decay over 0.1-1 Myr, consistent with the observed population of isolated X-ray pulsars having spin periods less than 12 seconds. Molecular dynamics simulations in today’s paper provide evidence to support Pon’s assumption that the pasta has a high impurity parameter. Therefore, another piece of the puzzle fits together and we have even more reason to believe that nuclear pasta exists inside neutron stars.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 10:52 am on October 4, 2017 Permalink | Reply
    Tags: Astrobites, , , , , , How Plural are Singularities?   

    From astrobites: “How Plural are Singularities?” 

    Astrobites bloc

    Astrobites

    Oct 4, 2017
    Bhawna Motwani

    Title: Counting Black Holes: The Cosmic Stellar Remnant Population and Implications for LIGO
    Authors: Oliver D. Elbert et al.
    First Author’s Institution: University of California, Irvine, CA, USA

    Status: Published in Monthly Notices of the Royal Astronomical Society, open access via arXiv

    As the joy from yesterday’s Nobel Prize announcement continues to linger far and wide, I’d like to lend words to my delight by talking a bit about black holes. And LIGO. Well, black holes seen(heard?) by LIGO.

    Only a short while ago, in September 2015, the Laser Interferometer Gravitational-Wave Observatory (LIGO) made its maiden detection of the ripples travelling in spacetime, known as gravitational waves.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    The detection of these waves, a key prediction made by the Einstein’s Theory of General Relativity, has since revolutionalised the field of astronomy by presenting a novel avenue for us to understand the workings of the ever-so-elusive-and-vast cosmos.

    In the discovery that LIGO made, it sensed the gravitational waves created by the merger of two distant black holes, each about as massive as 30 Suns. For scientists specializing in black hole physics, as well as others with a keen excitement about the field, this event immediately triggered the question: how many more events will we see, and how often?

    Motivated by this curiosity, the authors of today’s paper have analyzed the gravitational wave signals from the first three binary black hole mergers detected by LIGO, and developed an understanding of their characteristics in the context of our current knowledge about galaxy formation. Based on what we know about the formation of stars, the relationship between their ages/metallicities and the mass of their host galaxy, as well the overall number density of galaxies in our universe, the authors infer the age and mass distribution of black holes in different types of galaxies. For their analysis, Elbert et al. assumed that the extant population of black holes is attained solely from the death of massive stars, and does not feature any primordial black holes, allowing them to make confident estimates from reasonably well quantified galaxy observables.

    How many black holes in store?

    Through their study, Elbert et al. found out that the total number of black holes of all masses increases linearly with galaxy mass for galaxies with stellar masses ≲1010 solar masses (M⊙); see Fig 1. For instance, the Milky Way would host up to 100 million black holes, 10 million of which would weigh about 30 M⊙ such as those detected by LIGO, whereas dwarf satellite galaxies like Draco, orbiting the Milky Way, may be home to just about 100 black holes.

    2

    Furthermore, considering the relationship between the mass and metallicity of a galaxy, the authors predict that most low-mass black holes (~10 M⊙) should reside in massive galaxies like our own. This is because larger galaxies have more metal-rich stars that undergo vigorous mass-loss over their lifetimes, thereby ending up as low mass black holes. Contrarily, dwarf galaxies predominantly host metal-poor massive stars that do not shed as much of their mass and hence result in more massive black holes (~50 M⊙).

    How often do they collide?

    In the case of binary black hole mergers, it can often be difficult to say whether the pair of merging black holes was created way back in the past and took a long time to merge, or whether it was newly minted and merged soon after. To demystify this situation, the authors, in addition to the original black hole census, also sought to develop a framework for predicting the frequency of future merger events.

    Depending on the probability that certain black holes will occur in binary systems and an estimate of the typical timescale of their merger, the results indicate that a range of merger efficiencies (0.1-1%), albeit very low, is needed to explain the characteristics of existing LIGO detections. Conversely, fixing the value of merger efficiency to a value necessitates a range of merger timescales to accommodate the data. Constraining the value of both the merger efficiency and merger timescales would require knowledge about the size of host galaxy population (massive vs. dwarf).

    For a nominal efficiency of 1% applied to the current detections, the results from this study indicate a merger density of 12–213 per cubic gigaparsec, or a merger timescale of ≲5 Gyrs, for ~50 M⊙ black holes. Such a high merger density suggests that mergers involving ~50 M⊙ black holes should be detected by LIGO within a decade.

    _________________________________________________________
    With another merger already under LIGO’s belt since this study was published, impending detections seem galore. There is no doubt that enthusiastic scientists all over the world will have a lasting opportunity to shine light on the exact physics driving the exotic phenomena that are binary black hole mergers.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: