T. McGrath

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About T. McGrath

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    Meson

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  • Favorite Area of Science
    Astrophysics
  1. Source of High Energy Neutrinos and Cosmic Rays:

    What is wrong with these people? Are they stuck in the 1960s? Blazars and quasars are what the ignorant call Active Galactic Nuclei. Blazar and quasar were merely placeholders for something we had no idea how to describe at the time. There was only a brief period (between 1963 and 1969) when we had no idea what these objects were. By the 1970s they knew the source were active galaxies, and thus began calling them Active Galactic Nuclei. Then we have the above paper, which is a throw back to 50 years ago.
  2. In December 2016 the United Nations General Assembly adopted resolution A/RES/71/90, declaring 30 June "International Asteroid Day" in order to "observe each year at the international level the anniversary of the Tunguska impact over Siberia, Russian Federation, on 30 June 1908, and to raise public awareness about the asteroid impact hazard." Since then it really has become an International Asteroid Awareness Week, with events planned in numerous countries beginning June 25th and extending until June 30th.
  3. There were actually two missions to Mercury. The 1973 launch of Mariner 10 made its closest approach to Mercury in 1975 as it flew by. Then there was the MESSENGER (MErcury Space, Surface ENvironment, GEochemistry, and Ranging) probe, launched in August 2004 and made its first flyby of Mercury in 2008. The MESSENGER probe made a total of three flybys of Mercury, two flybys of Venus, and a flyby of Earth between 2008 and 2011 before settling into orbit around Mercury. The spacecraft remained in orbit around Mercury between 2011 and 2015, before it ran out of fuel and crashed into Mercury in 2015. See also Mercury's Secrets Revealed by Soon-to-Crash Spacecraft
  4. Is this the Dark Matter Particle?

    According to the Standard Model of particle physics neutrinos are supposed to be massless. If you start giving mass to neutrinos then explaining how neutrinos are able to travel at the speed of light becomes problematic.
  5. Black Holes and/or Wormholes:

    Isn't a wormhole a black hole at either end, with a conjoined singularity? How could a wormhole not have an event horizon? If black holes don't exist, what was that accretion disc orbiting in Cygnus X-1? I'm willing to discuss the possibility that we may not know precisely what happens after the matter collapses beyond its Schwarzschild radius, but the fact that matter does indeed collapse at least to that point is irrefutable. We have witnessed too many core collapse supernovae and measured stars orbiting extremely massive, yet invisible, objects to simply dismiss black holes out of hand.
  6. One black hole or two?

    Since they are talking about hot ionized gas, shouldn't they be calling it plasma? I suppose I should be happy they are referring to it as an "active galactic nuclei" and not a "quasar" or "blazar" from the 1960s, before we knew what they were. Which many still do. I was very surprised by the outflow being measured at only a few thousands of kilometers per second. That close to the event horizon I was expecting much faster relativistic speeds. I was expecting closer to supernovae speeds (10,000 km/s), or even faster since the plasma is only a few light-days away from the event horizon. They made some really nice observations. Thanks for sharing.
  7. The discovery of those "hot Jupiters" was certainly the impetus behind the theory that our gas giants also moved inward initially. I do not recall seeing anything on the subject until after 1995. The theory would explain many things, such as the small size of Mars and of course the asteroid belt. If the theory is valid, then we were very fortunate. Those other "hot Jupiters" did not have a Saturn to pull them back out again. They suggest that Jupiter initially formed somewhere beyond the frost line, > ~3 AU, and then migrated inward until it got to about where Mars is now (~1.5 AU). When Saturn got into a certain orbital resonance with Jupiter it managed to pull Jupiter back out to its current location of 5.2 AU. This would also cause Uranus and Neptune to first move inward, and then outward. How all this planetary movement effected the creation and orbits of the Galilean satellites and other "natural" satellites (as opposed to captured) I don't think will ever be known, but it is certainly interesting to speculate.
  8. Science theories and all that:

    Well said. I would like to add that having good reference material to support one's assertions also helps. New ideas are always more palatable when others have had similar ideas that can be referenced. At the very least the reference material may demonstrate where this new theory originates or whether it has merit or is fundamentally flawed. One's references can either strengthen or weaken a theory.
  9. "Discovery of an Extraordinary Binary System"

    I would not say that the limits established by Chandrasekhar and Tolman-Oppenheimer-Volkoff were "wrong." Just not complete. I have absolutely no doubt that the maximum mass of a non-rotating, non-magnetic white dwarf is precisely as Chandrasekhar calculated it to be. Chandrasekhar did not take into consideration a rapidly rotating or a highly magnetic white dwarf when calculating the maximum mass of a white dwarf. Therefore, his answer is not "wrong," it just does not include all the possibilities. Compared to its red giant companion, any neutron star or white dwarf in an ~83-day orbit will be virtually invisible to us. We can obviously detect the mass of the object from its gravitational effects on its companion, which is what they did, but there is no way we would be able to "see" it.
  10. "Discovery of an Extraordinary Binary System"

    All they know for certain is that the red giant is being orbited by an unseen companion with a mass between 2.5 − 5.8 M☉. They are simply guessing that this object may be a black-hole. This unseen mass is within the Tolman-Oppenheimer-Volkoff limit, although it has been recently suggested that the maximum mass for a neutron star can only be 2.16 M☉. Another possibility that they have not considered is that this unseen mass may be a rapidly rotating and/or highly magnetic white dwarf. Recent discoveries have placed the maximum mass of white dwarfs well beyond Chandrasekhar limit of 1.44 M☉. New estimates of rapidly rotating and/or highly magnetic white dwarfs places their maximum mass between 2.3 and 2.8 M☉. Sources: Using Gravitational-Wave Observations and Quasi-Universal Relations to Constrain the Maximum Mass of Neutron Stars - The Astrophysical Journal Letters, Volume 852, Number 2, January 2018. (free preprint) Nearby Supernova Factory Observation of SN 2007if: First Total Mass Measurement of a Super-Chandrasekhar-Mass Progenitor - The Astrophyisical Journal, Volume 713, Number 2, March 2010 (free issue) Significantly Super-Chandrasekhar Limiting Mass White Dwarfs as Progenitors for Peculiar Over-Luminous Type Ia Supernovae - arXiv : 1509.09008, September 2015
  11. An Outstanding yet Grim Discovery:

    Anyone who wasn't a Roman was considered a "barbarian" by the Romans. The meaning of the word "barbarian" today is very different from what it meant then. If their language and/or culture was different from Rome, then they are considered "barbarians" by the Romans. It doesn't mean that they were technologically inferior to Rome. The Romans also lost between 15,000 and 20,000 in the Battle of the Teutoburg Forest (which isn't very far east from that bog in Denmark) 2,009 years ago, where Varus lost three Roman legions to those German "barbarians."
  12. Fastest Growing Black Hole:

    The last half of the first paragraph of the introduction of the paper says it all: Direct collapse would appear to be the only way you can get a 20 billion solar mass super massive black hole in under a billion years, but they have yet to explain the mechanism behind the super-Eddington collapse rates.
  13. Weird cave

    It is not a spoof. The language being spoken in the video is Hmong, which would suggest the cave is located in southeast Asia. There are other examples of caves that have very different atmospheres than can be found on the surface. For example, the Movile Cave in Romania. That cave only has a concentration of oxygen between 7% and 10%, and carbon dioxide levels that are 100 times surface levels. The cave in Romania also has high concentrations of methane and hydrogen sulfide. Which may explain why you do not see anyone in your video actually entering the cave without protection.
  14. Whenever discussing stars we also need to take into consideration all the other "stuff" that formed in addition to the star. I have no doubt that the first Population III stars would have had planets, asteroids, comets, and everything else we find in solar systems. However, it has been suggested that these first stars would have been massive, anywhere from 100 to 1,000 solar masses. If that is true then these first stars would have had very short lives indeed. Perhaps just a few million years. While that may be sufficient time to produce the first 26 elements on the Periodic Table, it is far too short a time for life to develop. At best life would just be getting started, only to be wiped out by the resulting hypernova when the Pop III star dies. I think life has its best shot beginning with Pop II stars. The metal-poor stars in the halo of our Milky Way, for example, have been dated to 12+ billion years. Since we only have one example to go by, it is rather difficult to say with any certainty how long it takes to evolve beyond primordial life. I would imagine that it very much depends on the conditions. On Earth it took just over 700 million years before life first appeared, and then another 3.3+ billion years before we get to the Cambrian. That is a long time for a planet to remain relatively stable. Too long for any star with greater than just a couple of solar masses. Given that Pop. III stars would have been short lived, the Pop. II stars would have formed shortly after the Pop. III stars. Certainly within the first billion years after the Big Bang. Therefore, I would not rule out the possibility of life being 12.8+ billion years old. Source: The Formation of First Stars. I. The Primordial Star-forming Cloud - The Astrophysical Journal, Volume 564, Number 1, 2002 (free preprint)