Astronomy & Astrophysics

Astronomy & Astrophysics

  • H. T. Liu added an answer:
    Does a gravitation wave change propagation direction passing near a massive gravitation center (star)?

    As we know light wave passing near a gravitation center (star) changes its propagation direction. Is this true for a gravitation wave? 

    H. T. Liu · Chinese Academy of Sciences

    Whether or not the  waves (electromagnetic or gravitational) propagate along the same directions in the Universe will depend on the spacetime. The curved spacetime will make the waves travel along the curved  trajectories. so, the gravitational waves will be deflected as passing near a gravitation center.

  • Cesare D. La Padula added an answer:
    Could it be a new discovery?

    This picture was taken through my telescope (150/1400) from Tripoli (north of Lebanon). Briefly, the story of this picture is that when I was taking arbitrary pictures of the sky with my camera which was connected to my telescope, I saw something strange -maybe never seen before- (a group of blue stars surrounded by a group of red stars, attached photos). I thought that the blue dots were “Neptune” planet, but after focusing I have deduced that my thought was false because I saw a group of blue stars surrounded by a group of red stars. I didn't recognize what I saw but I was sure that it wasn't an artifact or an out of focus picture. To identify this picture, I have asked many specialists and amateurs of astronomy for help and explanation. None of them gave me a convincing answer. Some of them told me that it was a globular cluster, others talked about planetary nebula like ring nebula or owl nebula. Many specialists asked me about the coordinates of that location (RA/DEC) but the problem is that I didn't take into consideration these parameters and I can't review it now because I don't know its exact location in the sky. Keep in mind that there were no lights in the street, the place was totally obscured. The size of these points in the picture is not their actual size but red points appear only after enlarging it many times. So, before zooming there was only blue points and after zooming red and blue stars could be seen.

    Cesare D. La Padula · National Institute of Astrophysics

    Dear Ahmad,
    as you know alt-azimuthal coordinates are geographic and time dependent. If you can provide azimuth, elevation from horizon, time (UTC) AND (it's very important) the DATE of the observation; then it is still possible to compute equatorial coordinates. Of course the precision depends of how accurate those necessary data are.
    Regards, Cesare.

  • Stephane Erard added an answer:
    Do you know free multispectral remote sensing datasets from other planets for teaching purposes?

    Hi Everyone, in my university course for geography students "Introduction to Remote Sensing" the students asked if there are missions and data from other planets than earth (Mars, moons of Saturn, our moon...). We are mainly working with data from sensors like WV-2, Landsat 8, Aster... It would be nice to give them some data from other planets to load into the software (Envi, 5.1), the missing ground data is not a problem as they currently learning how to load data into the software and explore metadata. It would be nice if the data is ready for envi and the metadata can be loaded with a metadatafile. Also the data has to be free of charge. A multispectral or hyperspectral datasets would be ideal as this concept has just been explained. I think it is a interesting topic but have never had the time to really study such data.

    Stephane Erard · Observatoire de Paris

    Hello

    Space agencies make their data available for free, of course. You only have to search for PDS (Nasa, several sites) or PSA (ESA). JAXA and ISRO also have data distribution systems. IKI data may be more difficult to access, but some Soviet missions/instruments have been archived by Nasa or ESA.

    The problem you will face is that the current, usual archive format (PDS3) is not exactly user friendly - but there are at least two solutions from PDS small bodies node and Observatory of Paris to read PDS3 data under IDL/Envi (http://voparis-europlanet.obspm.fr/othertool.shtml).

    You may be interested in the very nice Planetary GIS workshop which took place last week at ESA: https://issues.cosmos.esa.int/psawiki/display/GISWS

    - Regards

  • Robert Shuler added an answer:
    What is the three dimensional external graphical representation of black hole?

    .

    Robert Shuler · NASA

    Up to the event horizon is easy, it is just Schwarzschild coordinates R,θ,φ and to find the local coordinates, apply the metric transform.  You can represent the local (curved) spatial coordinates in a couple of different ways, shown in the figure below, and explained in https://www.researchgate.net/publication/265906651_Paths_to_static_spacetime_curvature .

    I find it unhelpful to try to draw a time coordinate for two reasons ... too many dimensions, and the sign difference between spatial and time coordinates squared (i.e. one of them is imaginary).  Instead just imagine or draw clocks and show a smaller time interval on the ones at smaller radius that are running slower.

  • Kenneth M Towe added an answer:
    What types of organic polymers made or found on Earth have affinities to those found in insoluble organic residues from carbonaceous meteorites?

    Insoluble organic matter residues are the remaining insoluble organic material after extreme acid digestion of the extraterrestrial material. They contain complex morphologies that exist as either: isolated spherical compounded shapes; hollow spherical objects or irregular (non spherical) shapes which internally often contain the same conglomeration of spherical features. Please see attached DF STEM images of some of these morphologies from two organic rich carbonaceous chondrites. As the residues are a product of the removal of surrounding mineralogy (i.e. context in situ is lost), connected features on the submicron to micron scale in the images, by approximation, should only be considered. Thanks!   

  • E. Nihal Ercan added an answer:
    What radiation processes are used to fit the observed spectra from the accretion disk around a supermassive black hole?

    Which forms are radiations are dominant in the case of AGNs or in general a super massive black holes?

    E. Nihal Ercan · Bogazici University

    mostly non-thermal mechanisms should be considered.

  • Clifford Miller added an answer:
    Can Popperian falsifiability be applied to cosmology science?

    While scientific cosmology rarely occurs in the work Karl Popper, nevertheless it is a subject that interested him. The problem now is whether falsifiability criterion can be used for cosmology theories.

    For instance, there are certain issues in cosmology which have never been refuted, but instead the same methods are used over and over despite their lack of observational support, for instance mutliverse idea (often used in string theory) and also Wheeler DeWitt equation (often used in quantum cosmology).

    So do you think that Popperian falsifiability can be applied to cosmology science too? Your comments are welcome.

    Clifford Miller · Clifford Miller

    Charles,

    I agree.  I also always appreciate your responses because you always answer with depth [and humour me politely].

    What I believe also however is that all thinking in mathematics and the exact sciences should start from a consideration of a state of chaos in an absolute sense.  A state of absolute chaos is of course difficult to envisage, perhaps more so than an infinity.

    Would such a state tend to an equilibrium, a form of order? If so, what would determine that and which form of order might prevail?  Or could any form prevail as if say by chance?

    Or working backwards from the world we observe, is the ordered universe an inevitable development or evolution of a state of chaos and if so, how and why could one form of order prevail over any other?

    It is of course unfathomable or at least I think so, but worth contemplating.

    Which brings me to your postulates.  All three appear consequent upon and reduce to the existence of a single universal form of order.  Enigmatically, complexity suggests that even if there is such a single form of order, we can never devise a single coherent theory to describe and to predict the behaviours found in the universe.  Even if it were possible it would be impossible to verify.

    These are musings and of course may never be any more than that.

  • Matts Roos added an answer:
    Is not the second law of thermodynamics violated in cyclic cosmology?
    It was shown by Tolmann that if the cosmological constant is zero then no minimum radius of universe exists (rate of expansion becomes negative infinite at R=0). Now dark energy gives a cosmological constant. So cyclic model came in again. But what about the entropy? Generally it is assumed that entropy of the universe during big bang is very low. Now if CC holds then according to 2nd law each cycle would produce a very high entropy. So it seemed that during big bang entropy of the universe was very high according to CC model.
    Matts Roos · University of Helsinki

    Michael,

    Maybe your full paper was clearer. Here you have reduced it beyond comprehensibility.

  • Eric J. Hallman added an answer:
    What is the physical meaning of Integrated Sachs-Wolfe effect, and how is it different to the Rees-Sciama effect?

    I found some papers discussing ISW as a proof of dark energy, but what is its physical meaning? What is your opinion? And how to calculate it?

    Eric J. Hallman · Tech-X Corporation

    I think I didn't answer your question regarding the "physical meaning" of these effects.  Physically, they are a result of the frequency shifting of CMB photons due to the change in size of the gravitational potential they are traveling through during that travel time.  Meaning, the photon enters the potential, and is blueshifted traveling down into the potential well.  The large size of the cosmological potential wells means that as the photon travels, and is still under the influence of the object's gravity, it can grow in mass, deepening the potential.  Therefore, when the photon climbs out of the potential, being redshifted by that travel, the corresponding redshift from leaving the deeper potential is larger than the size of the blueshift it encountered when entering the potential.  Therefore, on scales relevant to the size of the potentials that are important (for ISW it's large angular scales, for RS it's smaller scales), there is a distortion in the CMB that does not correspond to effects that occur at recombination.

  • Patricia J Lampens added an answer:
    Can you identify?

    I am a science professor at the Lebanese university, and I have interests about astronomy physics... I have a telescope (150/1400 mm). I have observed something strange (a group of blue stars surrounded by a group of red stars),(photos attached). I believe that it is a globular cluster but I'm not sure, and I'm certain that isn't out of focus. Can you please recognize what i have observed and if it is discovered ?.

    Patricia J Lampens · Royal Observatory of Belgium

    Hello, it seems to me that it is an instrumental pattern (maybe some faint stars superposed too). What type of camera did you use? To know for sure, you need to take a few calibration frames such as a bias, dark (subtraction) and flat-field (division). Only after taking out these effects, could you tell what you observed on the image. There is an additional edge effect too, which makes the halo appear asymmetric.  You could consult a manual from any software application useful for this, and find some basic information on the internet , e.g. even from a company which sells CCD camera's.

    For example, some definitions are given at https://www.sbig.com/astronomy/about-ccd-imaging/ccd-imaging-101/

  • Parviz Parvin added an answer:
    The sun is a critical fusion reactor and needs negative feedback control. How does the sun stabilize itself?
    Negative feedback is essential for the steady state operation of any dynamic system. The sun generates heat based on nuclear fusion. Therefore the sun is a nuclear reactor operating in a critical condition. How does the sun remain stable? What mechanisms are the control feedback of sun?
    Parviz Parvin · Amirkabir University of Technology

    I have not found a perfect answer to my question:

    What are the dominant mechanisms to feedback control the sun ?

  • Akira Kanda added an answer:
    Is dark energy merely an illusion?

    According to a report by Carlo Iorio and Timothy Clifton, dark energy may be an illusion. And LTb model or variations of it can be promising candidates to get rid of it. What do you think?

    Akira Kanda · University of Toronto

    DEAR NICHOLAS,

    I will stop to take part in a community where this kind of personal attack is allowed and criticizing established theories are considered to be offensive. I have a record of the whole communication here.

    Sincerely yours,

    Dr. Akira Kanda

    -------- Original Message --------
    Subject: Re: Your Posts on ResearchGate Q&A
    Date: 2015-03-10 23:34
    From: kanda <kanda@cs.toronto.edu>
    To: 54ff0736d3df3e27688b46bb@support.researchgate.net

    On 2015-03-10 17:44, kanda wrote:

    Hello Nick,

    Here is another one:
    Charles Francis · 58.39 · 29.12 · Jesus College, Cambridge

    Akira, in a recent thread you challenged the work-energy relation, on the grounds that you do not know enough mathematics to integrate Newton's second law with respect to distance. This is high school maths, without which you could not get into any reputable institution of higher education to study mathematics. Any pretense that you are a mathematician is an absurdity. You do not get the names of mathematicians right. Any pretense you are an academic is almost equally frivolous. What are you at the university of toronto. One might think you are a janitor, according to your knowledge of mathematics, physics, logic and the philosophy of science. It is certain you have a great dislike for anyone who has studied anything.
    This appeared in [Do you know of any case in which physicists accepted a basic theory based on a derivation from accepted theories, or its mathematical structure?]

    -------- Original Message --------
    Subject: Re: Your Posts on ResearchGate Q&A
    Date: 2015-03-10 17:31
    From: kanda <kanda@cs.toronto.edu>
    To: 54ff0736d3df3e27688b46bb@support.researchgate.net

    Hellow Nick,

    I am not terribly enthusiastic about doing things like this.

    To my recollection, I refrain myself in attacking some individuals personally. This is my policy. However, I do question existing theories when I have to. I trust that you are not saying that this kind of scientific communication should not be done in RG.

    For that very rarely I receive what can be regarded as scientific responses. I usually do no bother dealing with these seriously. So though most of them are direct personal attacks. I did not report you.

    To begin with

    I have been receiving the following posts many times in RG from the same poster:

    **********
    Ulrich Mutze · 84.99 · 16.21

    Akira,

    since in your opinion there is hardly anything in physics on which physicists have a correct view, I extrapolate that you will be able to produce hundreds of pages with ignorant and arrogant statements that will disgust people and make them adding their own hundreds of pages. So, I kindly ask you to discontinue this unworthy game.

    [It appeared in Why does the Schroedinger equation for a free particle contain the particle mass?]

    Akira kanda

    -------- Original Message --------
    Subject: Fwd: Re: Your Posts on ResearchGate Q&A
    Date: 2015-03-10 13:17
    From: kanda <kanda@cs.toronto.edu>
    To: 54ff0736d3df3e27688b46bb@support.researchgate.net

    On 2015-01-07 04:37, ResearchGate Community Support wrote:

    Dear Akira,

    Thanks for getting in touch, and for bringing this to our attention. We will look into this matter and take the appropriate measures.

    Kind regards,

    Maarten
    RG Community Support


    Have any more questions? Check out ResearchGate's Help Center: https://explore.researchgate.net/display/support/Help+CenterAkira Kanda wrote on Jan 7, 2015:

    I find that the following post by Charles Francis in the thred "Who rewrote General Relativity?" stepped out of the norm of scientific communication: "Akira, if you wish to participate in a scientific forum, you should first study some science. There are many sources readily available. Do not expect anyone to put time and effort into teaching you that which you have already shown no interest in studying. Please stop spamming the forum with demonstrations of ignorance."

    -------- Original Message --------
    Subject: Re: Your Posts on ResearchGate Q&A
    Date: 2015-03-10 11:26
    From: kanda <kanda@cs.toronto.edu>
    To: ResearchGate Community Support <54ff0736d3df3e27688b46bb@support.researchgate.net>

    Thank you for the message.

    My criticisms are targeted to the theories and disciplines.

    It is my personal feelings that I have been targeted for personal attacks.

    I appreciate your concern and I will respect your request.

    I do not receive the first warning, btw.

    Akira Kanda

    On 2015-03-10 10:10, ResearchGate Community Support wrote:

    Dear Akira,

    Thank you for being such an active member of our network. We appreciate your enthusiasm in posting in ResearchGate Q&A, however, researchers have flagged some of your posts as offensive.

    We would like to kindly request that you refrain from posting comments that might be interpreted as insulting to other researchers.

    Thank you for keeping this in mind when posting comments in the future.

    Please note that this is your second warning. One more will mean that we lock your account.

    Kind regards,

    Nicholas
    RG Community Support

    Have any more questions? Check out ResearchGate's Help Center: https://explore.researchgate.net/display/support/Help+Center



  • Charles Francis added an answer:
    Why are there different gases for different galaxies?
    In different galaxies there appear different gas structures. What is the mechanism adapting certain gases in certain galaxies while excluding the other gases?
    Charles Francis · Jesus College, Cambridge

    Of relevance may be that there is continuing star formation in spiral galaxies, but not in elliptical galaxies.

  • James Overduin added an answer:
    How do cosmologists determine the curvature of the universe based on astronomical data?

    Almost all cosmologists agree that the curvature of the universe is “flat” (k=0). Obviously this conclusion is based on solid astronomical observations - data. My question then is: Is there direct observational evidence that shows the universe is flat or is this conclusion solely a model-dependant parameter?

    James Overduin · Towson University

    Observational data (primarily the CMB) tell us that the curvature must be close to flat, but do not tell us that it is exactly flat. The belief that k=0 is a theoretical prejudice, usually based on fine-tuning arguments. For example, the "flatness problem" is the argument that any departure from flatness at the present time would imply that the total density of the universe at early times would have to be fantastically close to (but not equal to) the critical density. While widely believed, this argument has little logical force because the fine-tuning parameter here is simply an artifact of the definition of critical density (which evolves strongly with time). When curvature is expressed by more physical parameters, the fine tuning disappears and universes with nonzero curvature are found to be perfectly compatible with current and forseeable future CMB data. Some relevant papers here are by Adler & Overduin (gr-qc/0501061), Lake (astro-ph/0404319), and more recently by Carroll (1406.3057). In this context it is interesting to note that the Planck 2015 results (1502.01589) report a "2-sigma detection of positive curvature", which disappears when Planck data are combined with other datasets. A nice early discussion of these issues was by White and Scott (astro-ph/9508157).

    It's worth appreciating how impressive the CMB measurement of curvature really is. It is very much akin to the measurement that might be made by creatures in a 2D universe who measure the curvature of their world by adding up the angles in a triangle to see if they are equal to 180 degrees. In our case the "baseline of the triangle" is the patch of sky occupied by the largest fluctuations in the primordial plasma at the moment when the universe became transparent to light. This method gets its power from the fact that it leapfrogs "local" systems whose interpretation is messy and complex (supernovae, galaxies, quasars) and goes directly back to the radiation-dominated era when physics was simpler.

  • Mohamed Th. S. Heikal added an answer:
    Is it possible to find pure iron phase in meteorite without any inclusions?

    In the Chelyabinsk meteorite in particular.

    Mohamed Th. S. Heikal · Tanta University

    Iron meteorites were strongly used by ancient Egyptians as a tool in agriculture and other uses. I strongly  some colleagues about pure iron associated with Ni & Co as mentioned in Kamel impact crater crater of Egypt.

  • Arno Gorgels added an answer:
    As a researcher claimed that black holes do not exist , is any one interested in finding non singular general relativity?

    A researcher claimed that black holes do not exist the link is:

    http://phys.org/news/2014-09-black-holes.html

    https://www.researchgate.net/publication/265415056_Back-reaction_of_the_Hawking_radiation_flux_on_a_gravitationally_collapsing_star_II_Fireworks_instead_of_firewalls

    Is any one interested in solving the singularity problem in general relativity?

    What are the suggested ideas?

    Arno Gorgels · Principia Naturae

    Bon appetit, dear Daniele

  • Barry Turner added an answer:
    How significant is the discovery of Kepler-186f, an earth-sized habitable zone planet?
    Kepler-186f is the first earth-sized planet located in the habitable zone of another star that has been discovered. With this discovery, the search for life on other planets has entered into a new zone of discovery.
    Barry Turner · University of Lincoln

    Louis

    As you know I hope I am totally wrong in my pessimism about space travel or being able to communicate with other intelligent life forms.  I am not however optimistic that the quantum world offers us much assistance since we do not actually live in it.  You are quite right about general relativity and even Einstein accepted it was seriously flawed but we live in a universe of matter and energy for certain and it poses the problem.

    One of the biggest problems with travelling through space is the fact that it is not empty.  Since at present it is only feasible that humans would have to be in an energy propelled vessel to make a space voyage the presence of particles on matter in space would be a huge problem.

    Any space ship travelling through interstellar space at the speed of light, were that possible would be destroyed by the huge energy released by collision with even a tiny particle.  They would be unavoidable in a long space mission.

    Similarly navigation would be impossible due to the relative position of interstellar bodies being shifted.  

    Warp drive is the only possible method by which we could travel these distances but the physics of that require energy levels similar to those emitted from a quasar.  It is inconceivable that we could control let alone generate such forces.

    As I say, I hope I am wrong and physics is due for an overhaul!  

  • Mohammad Ayaz Ahmad added an answer:
    What is the structure of black holes?
    In some books popularizing science (e.g. “Astronomy for dummies” by S.P. Maran) it is written that black holes have the following structure: falling matter, event horizon, singularity. This structure does not coincide with the classification used in special literature where the accretion disk forming by falling matter is included. Is the black hole structure in the book above an adequate explanation for non-specialists?
    Mohammad Ayaz Ahmad · University of Tabuk

    Really, we do not know what the inside of a black hole. Describing the characteristics of the structure of a black hole still remains one of the challenges of modern relativistic astrophysics.

  • V. G. Kurt added an answer:
    What are the popular plotting softwares that astromomers and astrophysicists use for publication? I am using XMGRACE and GNUPLOT? What about Matlab?

    Supermongo and IDL are also very popular among astrophysicists. Are Matlab, Mathematica, Xmgrace, Gnuplot also popular among some groups?

    V. G. Kurt · Russian Academy of Sciences

    I prefere MATLAB, but I know some my friends which like MATCAD. I suppose that all depend from personal experiance. For plot of results of calculation by MATLAD I preferre very simple program which made my friend Alex Berezin special for this purpose. Vladimir G. Kurt. 

  • Xiangqian Wu added an answer:
    How can I calculate or where can I find the selenographic coordinate of the point where the Sun is at zenith?

    I need to know the time-varying location, in terms of selenographic latitude and longitude, of the point where the line connecting the centers of the Sun and Moon intersects with the lunar surface, to the accuracy of second and kilometer, from 2000 to 2020. Thanks!

    Xiangqian Wu · National Oceanic and Atmospheric Administration

    Thanks a lot!

  • Michael Peck added an answer:
    What is causing Dark Flow?

    Dark flow is an astrophysical term describing a possible non-random component of the peculiar velocity of galaxy clusters. The actual measured velocity is the sum of the velocity predicted by Hubble's Law plus a possible small and unexplained (or dark) velocity flowing in a common direction.

    Does Dark flow exits ? If yes what is the cause of it?

    1. There are many affects due to sample dependence, analytical methods and luminosity distance; I'm in no way saying you are unaware of them. However, I do think it is important to consider that the great attractor is estimated to be 80 Mpc away relative to the extent of the dark flow (at least 800 Mpc or almost 0.2z).

    2. I've only looked at articles by Kashlinsky and/or Atrio-Barandela, as there was controversy surrounding the Planck analysis by others.

    3. The question was asking about the source of the dark flow, which I suppose I can offer an answer to. Consider a sink-source universe with a cosmological scale gravitation potential, i.e. no energy is created or destroyed. The simplest solution would be a continuous, but collaminated 'big bang' arising from the center of the potential (CMB -> gravitational redshift). This than forms into the locally hot x-ray clusters, various galaxies and a Hubble flow, where the bulk flow begins to fall back into the potential (the "dark flow"). Gravitational lensing will then project local geodesics towards the center; i.e. we are observing objects accelerating back into a global gravitational potential through a cosmological-scale lens. This would further explain why volume element/angular scale observations support a static metric, increased entropy with redshift (cold baryonic matter, metallicity and mergers) and hemispherical anomalies versus homogenous universe.

  • Nestor Roman Voronka added an answer:
    What is the best model to predict Solar Cycle 25??

    Prediction of Solar cycle 24 based on various models that is a less active cycle is well known. What is the best model or way to predict Solar cycle 25?

    Nestor Roman Voronka · M42 Technologies

    I second the use of Dr. Ken Schatten's model - he is now a senior scientist at a.i. solutions.  You should also check out the work that Dr. W Dean Pesnell has been doing at NASA/GSFC for comparison.

    https://www.linkedin.com/pub/kenneth-schatten/33/aa5/978

    https://www.linkedin.com/pub/dean-pesnell/73/a23/405

  • Robert Loughnane added an answer:
    Is there a database of community-available antennas - beam size and efficiencies?

    Is it possible to source a URL or database of the available antennas in the field of millimeter and submillimeter astronomy?

    I need to be able to tabulate available frequency-dependent beamsizes and antenna efficiencies.

    Robert Loughnane · Universidad Nacional Autónoma de México

    True Johannes, but the beamsizes usually stated in the observing section of a specified article generally represent a frequency range. However, your point is noted. Thanks.

  • Parviz Parvin added an answer:
    An old question that is still fresh: Is gravity a Newtonian force or Einstein space-time curvature?
    No gravitational wave was measured yet, no graviton was detected accordingly. On the other hand no space- time curvature was observable. There is no successful experiment to validate the current theories. What is the nature of the mysterious gravity? What is the velocity of this effect ?
    Parviz Parvin · Amirkabir University of Technology

    Dear Tolga

    Happy new year.

  • Fatemeh Tabatabaei added an answer:
    What methods are the best to measure the metallicity in the ISM?

    There are several methods and observers which can be used to estimate the metallicity in the interstellar medium, most of which are based on the measurements in the HII regions. First, what methods give the most reliable estimate? Second, has there been any measurement in more diffuse ISM in the Milky Way?

    Fatemeh Tabatabaei · Max Planck Institute for Astronomy

    The radial gradient is an observational fact (which even could have been complicated by migration of stars in some cases). In any case, the environmental effects and the star formation feedback should not be neglected.

  • Ksh. Newton Singh added an answer:
    What will be the speed of sound in quark star if we consider EOS proposed by MIT bag model for an anisotropic fluid?

    If we consider MIT Bag Model EOS, the square of speed of sound for quark star should be around 0.33. But whether this is true for an anisotropic quark star or not. So whether EOS from MIT Bag Model is for isotropic or anisotropic matter or for both?

    Ksh. Newton Singh · National Defence Academy, Khadakwasla, Pune, India

    Thanks Prof. Uechi

  • Ksh. Newton Singh added an answer:
    Does a free fall collapsing dust radiate gravitational waves?

    A collapsing star when explode (supernova), due to the sudden ejection of massive mass around the central core, there is a disturbance in space-time leading to emission of gravitational waves. But what will happen if a collapsing goes on till black hole is formed, without any explosion? Will there be an emission of gravitational waves due to the continuous grow in curvature because of the growing mass?

    Ksh. Newton Singh · National Defence Academy, Khadakwasla, Pune, India

    Thank You Dr. Yang

  • Marshall Eubanks added an answer:
    How do I determine the spin rate of solivagant exoplanets and substellar objects?

    Solivagant (nomadic) planets are roaming the interstellar space. Depending on the steepness of the mass ditribution law, There may be significantly more substellar objects in the vicinity of the Sun than there are normal stars. A few nearby extremely cool object of super-Jupiter mass have been discovered (e.g., one with WISE). Despite the absence of light, such systems of planetary mass may be teeming with life. According to M. Eubanks, more solivagant planets will be observed in the future with JWST, ALMA and SPICA. My calculations show that the tidal heating of Earth generated by the Moon may presently come up to ~5 TW. A heat source of this order can sustain a massive subsurface ocean on a lonely exoearth for gigayears. The question is, how to observationally verify that nearby solivagant planets rapidly rotate? The spin rate of some stars has been determined photometrically from the modulations caused by persistent features (dark or hot spots) on the photospheres. Would that be the best way to observe the spin of very cold planets? Are there other possibilities?

    Marshall Eubanks · Asteroid Initiatives LLC

    Most galaxies, projected on the sky, are elliptical, and so there are a number of papers dealing with lens ellipticity (oblateness) for strong lensing (see below). I  do not think there will be much difficulty in introducing this into the microlensing formalism. Whether or not the data will be good enough to actually determine nomad rotation oblateness is, of course, another question. 

    http://iopscience.iop.org/0004-637X/482/2/604/pdf/0004-637X_482_2_604.pdf

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