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Nearest galaxy

  1. Nov 6, 2003 #1
    "The nearest galaxy to our own Milky Way has been revealed. It is so close that the Milky Way is gradually consuming it by pulling in its stars. But it will be few billion years before it is entirely swallowed up.

    The previously unknown galaxy lies about 25,000 light years from Earth and 42,000 light years from the centre of the Milky Way, beyond the stars in the constellation Canis Major. It is twice as close to the centre of our galaxy than the previous record holder, the Sagittarius Dwarf Galaxy, which was discovered in 1994."

    Seems like the Milky Way is enjoying a big meal

    http://www.newscientist.com/news/news.jsp?id=ns99994342
     
    Last edited: Nov 6, 2003
  2. jcsd
  3. Nov 7, 2003 #2
    Last edited: Nov 7, 2003
  4. Nov 7, 2003 #3
    Actually the closest Galaxy to the Milky Way is a Dawarf by the name of Sgr and there is upwards of 20 glalaxies in what is called the LOCAL GROUP. Starting at our galaxy and extending 500 Kpc out in every direction making what looks like a sphere. Five years ago counsil called the Nuker Team did research on a theory of Super-Massive Balck Holes. Using a certain lens on a 67" telescope in Hawaii they searched for these "Super-Massive Black Holes" in nearby Galaxies. They were unsucessful in finding them because the galaxies were so far away. They were seaching in the center of our galaxy for traces of primordial dust with the same technology as used to locate "Super-Massive Black Holes" and to their greatest fears they located a Super-Massive Black Hole in the center of the Galaxy. Because of the powerful gravitational force in Quasars, which are Super-Massive Black Holes (they light up because of the friction between the molecules of the primordial dust) they pull on other galaxies, and thats why galaxies orbit galaxies and galaxies collide with other galaxies.
     
  5. Nov 7, 2003 #4
    But our Galaxy is the big guy? Everyone else orbits us?
    Actually, the article says that some Galaxy located in Canis Major has been found to be closer than Sag (by 8000ly).
    Out of curiousity, how do they measure distances to such far away objects?
    How exactly do we detect black holes? And how would we measure how massive it is?
     
  6. Nov 8, 2003 #5

    NateTG

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    A generally accepted theory (due to Hubble) is that the universe is expanding. Since the universe is expanding, the further something is from us, the faster it is moving away from us.
    Light that's coming to us from objects that are far away is red-shifted because they are moving away from us at great speed.
    We can determine the relative velocity from the red shift, which allows us to determine the distance based on the theory. There's a bunch of extra stuff that goes into this, like comparing the distances to objects that we know are close to each other, knowing what color light started out as and so on.

    For nearby objects like (perhaps) Alpha Centauri, the distance can also be calculated by taking pictures in sumer and winter. This allows us to make measurements of the distance by the change in angle (called parralax). For distant objects, the change in angle is too small.

    According to currently popular theory, black holes are sources of gamma radiation. In general, they are not directly observed, but instead located based on the movement of visible objects that are near then.
     
  7. Nov 8, 2003 #6
    We detect Black Holes by the gravitational influences on other galaxies and the more influence one galaxy has the larger the Quasar. Our Galaxy is pretty big and i believe we are the largest galaxy in the LOCAL GROUP but M31 the Amdromeda Galaxy happens to be the runner up and it is just slightly smaller than ours, and believe it or not M31 has already collided and almost swollowed another very small Dwarf glaxay called M32 (Cited : Starry Night Pro). Lots of Galaxies orbit ours, and one happens to be the Andromeda Galaxy which we happen to be pulling closer to us. I am not to sure about this but i believe Canis Major is a Star Cluster.
     
  8. Nov 10, 2003 #7
    There are lots of ways of measuring the distances to astronomical objects. The most successful of these for measuring cosmologically distant objects (i.e. other galaxies) are Type 1a supernovae. These events occur in a very predictable manner, allowing us to determine the distance to the galaxy in which the supernova occurs.

    How we detect black holes depends on the scale that you are looking at. For small black holes (a few times the mass of the Sun) we generally find them by looking at a class of objects known as Galactic X-ray binaries. These are binary star systems where one star is either a black hole or neutron star and the companion is a normal star. The X-rays are produced by the neutron star/black hole accreting material from the companion. Angular momentum considerations mean that this material forms a disk around the neutron star/black hole, and friction and viscous forces cause this material to heat up, producing X-rays in the centre of the accretion disk. Whether the dark companion is a neutron star or a black hole is determined by looking at the spectrum of the normal star as it orbits the companion.

    For the supermassive black holes that are thought to exist in the centres of all galaxies with bulges (like our own), there are a number of ways of determining the mass. If the galaxy is close enough and the telescope has sufficient angular resolution (e.g. HST) then you can trace the orbits of the stars in the bulge and determine whether the mass they enclose is significantly larger than the mass implied by the visible star light. This is only possible for a few galaxies (17 or so), out to about the distance of the Virgo cluster. Observing the dynamics of the gas in the galaxy is easier, but gives less accurate results.

    Recently, the number of (quiescent) galaxies for which the mass of the central black hole has been measured has grown considerably (see any article by John Kormendy, Karl Gebhardt or Doug Richstone for a review), and has allowed us to relate the mass of the central BH to properties of the host galaxy itself. The two most useful of the relations that we have found are the Magorrian relation (which relates the mass of the host galaxy bulge to the mass of the central BH) and the relation between the velocity dispersion of the stars in the bulge to the mass of the central black hole. These are useful because they allow us to estimate black hole masses in active nuclei, which are frequently too far away to allow measurements from either stellar kinematics or gas dynamics. This allows us to look into BH formation and evolution and the evolution and structure of active galaxies.


    Jess
     
  9. Nov 10, 2003 #8

    Phobos

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    We detect BHs by their influence on surrounding matter...usually stars (not galaxies, which are usually too big to be affected by a single black hole). However, it is becoming apparent that most large galaxies like our own have a supermassive black hole in the center (so I suppose in that case, a black hole can significantly affect a galaxy). Black holes at the centers of early-galaxies are a good candidate for the source of quasars, but that's not very certain, AFAIK. But quasars are only associated with galaxies from the early universe.

    I don't think the Milky Way has been found to be the center of the Local Group. I suspect the gravitational center of the Local Group is somewhere between the Milky Way and Andromeda galaxies (the two big players in the group...the other are all small galaxies). The Milky Way and Andromeda are moving toward each other (due to gravity of course) and may "collide" in about 6 billion years. I put collide in quotes because galaxies are mostly empty space and even with a direct hit, there will be few direct impacts of any stars. The two galaxies will fly through each other and dramatically reshape the overall spiral structures (probably won't be spiral galaxies anymore) and will probably cause a sudden increase in star formation. It may be a grazing hit too (not necessarily a direct impact) which would still mess with the spiral structure, etc. due to gravitational forces.
     
  10. Nov 10, 2003 #9

    Phobos

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    p.s. This should have been like 4 different topics.
     
  11. Nov 11, 2003 #10
    There are problems with the current AGN model IMHO, but accretion onto a black hole is definitely the best model simply for energy generation.

    Also; quasars are only associated with galaxies at high redshifts (z >~ 1), that's true. But active nuclei are seen in late-type local galaxies (e.g. NGC 4395, which is at redshift 0.001) as well. In fact recent studies of local bright galaxies show some form of AGN activity in half of the nearly 500 galaxies studied. So the phenomenon is very widespread indeed.

    Jess
     
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