Astronomy & Astrophysics

Astronomy & Astrophysics

  • 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 · University of Colorado at Boulder

    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

  • 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


    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 <>

    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 <>

    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


    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 <>

    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,

    RG Community Support

    Have any more questions? Check out ResearchGate's Help Center: 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 <>
    To: ResearchGate Community Support <>

    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,

    RG Community Support

    Have any more questions? Check out ResearchGate's Help Center:

  • Naïma Amrani asked a question:
    What is the three dimensional external graphical representation of black hole?


  • 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:

    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


    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.

  • Dhanraj Sitaram Warjurkar 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?

    Dhanraj Sitaram Warjurkar · Seoul National University

    MatLab is very good tool for plotting ...

  • 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.

  • 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, Khadakwas, 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, Khadakwas, 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.

  • Alexander Yurkin added an answer:
    Is there a future for ground-based astrometry after GAIA?
    Considering the revolution that occurred in terms of optical astrometry due to astrometric satellites such as Hipparcos (even though there were parallel developments and major improvements on ground-based astrometric telescopes), an even larger jump is about to occur with the GAIA astrometric mission. Much work will need to be done to tie the radio reference frame (ICRF2) to the GAIA optical reference frame. There will be ground-based follow-up work following GAIA detections, proper motions and parallax work, as satellite missions are relatively short lived and expensive. But, what does the future hold for ground-based astrometry? Near Earth objects? Solar system measurements? Reference frame maintenance?
    Alexander Yurkin · Russian Academy of Sciences

    Dear Sirs,

     I the first time answered this question by means of a joke, but this time I will give two serious forecasts and in advance I ask astrophysicists not to appropriate two of my deep theoretical scientific results.

    1. It is necessary to leave telescopes and field-glasses on Earth since in space there was a lot of space debris which strongly scratches glasses of space telescopes, sharply lowering their resolution therefore in them it is visible nothing.

    2. Industrial activity of the person causes greenhouse effect and destruction of the Terrestrial atmosphere. Soon on our planet Earth the atmosphere will become same transparent as on the planet Mars both all stars and black holes can be observed without hindrances through magnifying glass of an average aperture.

    Sincerely, Alexander

  • Rudolph E. Schild 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?

    Rudolph E. Schild · Smithsonian Institution

    The Shakura and Sunyaev (1973) model is accepted by many, but cannot be the entire story. Recall that the inner part of the accretion disc is inferred from microlensing observations to be a powerful X-ray source at 0.1 to 10 Kev, so something besides the SS model is present. Moreover, the X-ray observations show that most of the X-ray emission comes from a much larger source, which must therefore be farther away from the central black hole.

    Similarly optical observations of microlensing of the radiation show that the SS (1973) emission also has a reverberation in the quasar outer structure at 437 light days. See J. Lovegrove et al 2011.  It has been measured that 3/4 of the light at optical frequencies from this large outer reverberating source in all quasars. Recall that quasars have brightness fluctuation from microlensing that are just a few percent. The quasar microlensing signal from a star is a 30% brightness increase with a 30-year time scale. If the microlensing were of a point source as in MACHO searches, the amplitude would be a factor 10-30. From this we conclude that only a small fraction of the quasar microlensing is due to a compact central source, like the accretion disc inner edge at 6 R_S

    Microlensing from a single planet mass body has an amplitude of only 10%. This is understood to mean that the SS radiation mentioned by Nozhan arising from the inner edge of the accretion disc can only be a small fraction of the total quasar emission, and most of the emission you would see with your eye comes from the larger outer region.

    A good description of quasar structure observed in optical. radio, and X-ray regions can be found in Schild, Leiter, and Robertson, AJ, 2006. It gives the size scales of the luminous structures and their locations, in cm. 

  • Marcelo Negri Soares added an answer:
    What is antigravity?
    I want to know the basics.
    Marcelo Negri Soares · Universidade Nove de Julho

    Anti-gravity is an idea of creating a place or object that is free from the force of gravity. It does not refer to the lack of weight under gravity experienced in free fall or orbit, or to balancing the force of gravity with some other force, such as electromagnetism or aerodynamic lift. Anti-gravity is a recurring concept in science fiction, particularly in the context of spacecraft propulsion. An early example is the gravity blocking substance "Cavorite" in H. G. Wells' The First Men in the Moon.

    In Newton's law of universal gravitation, gravity was an external force transmitted by unknown means. In the 20th century, Newton's model was replaced by general relativity where gravity is not a force but the result of the geometry of spacetime. Under general relativity, anti-gravity is impossible except under contrived circumstances. Quantum physicists have postulated the existence of gravitons, a set of massless elementary particles that transmit the force, and the possibility of creating or destroying these is unclear.

    "Anti-gravity" is often used colloquially to refer to devices that look as if they reverse gravity even though they operate through other means, such as lifters, which fly in the air by using electromagnetic fields.

  • Alexander Chepick added an answer:
    How can we explain Tifft's quantization of galaxy redshift?
    The reports by Tifft on quantization of galactic redshift are well-known to astronomers. Read for example See also a recent review on redshift theories by Marmet at

    I don't have articles on Tifft's quantization, but I will send you two of my articles on static models.
    I think that the space of the Universe is not expanding. Test Tifft's quantization will show it, because in the framework of GR the distance between galaxies previously had to be less than it is now. Therefore, in GR dependence should be approximately inversely proportional to z.

  • Rahul K Sharma added an answer:
    Does CME affect the pulse of the heart?
    CME can leads to blackout on Earth due to disturbance in Earth's magnetic field.
    Rahul K Sharma · National Association of Nanotechnology and Ultra-science(NANU)

    Yuri, thank you very much.its english is not very nice.Sure i will read the book u have mentioned. i am following both link in researchgate.thanks for those links.They are Russians.I am in Russia now.It is really helpful.Though I am far from Moscow, it will be easier for me in future. after reading book i will connect with them. If any thing i will not understand about CME or anything related to concerned topic, i will bother you for help.thanks a lot for kind replies..

  • Raul Simon added an answer:
    How energy is transfered from photosphere to corona on the bais of elemental abundance variation from photosphere to corona ?

    As some of the research papers suggest that low FIP (below 10 KeV) elements get enhance by factor of 3-4 in Corona from Photosphere, while high FIP (above 10 KeV) elements don't show this characteristics.

    Does this effect conclude anything about energy transfer from Photospere to Corona ?

    Raul Simon · L A M B

    Thanks, Phil.

  • John Houghton added an answer:
    Proton- proton reaction in star center can anyone help?
    The proton-proton reaction in star center goes on for billions of years. But when the reaction starts on the surface as in the case of the nova, it only lasts for a few weeks. Can somebody explain this difference?

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