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NASA Science

Virtual Telescope Zooms In On Milky Way Black Hole 181

FiReaNGeL writes "An international team has obtained the closest views ever of what is believed to be a super-massive black hole at the center of the Milky Way galaxy. The astronomers used radio dishes in Hawaii, Arizona and California to create a virtual telescope more than 2,800 miles across that is capable of seeing details more than 1,000 times finer than the Hubble Space Telescope. The target of the observations was the source known as Sagittarius A* ("A-star"), long thought to mark the position of a black hole whose mass is 4 million times greater than the sun. Though Sagittarius A* was discovered 30 years ago, the new observations for the first time have an angular resolution, or ability to observe small details, that is matched to the size of the event horizon."
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Virtual Telescope Zooms In On Milky Way Black Hole

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  • Note (Score:3, Informative)

    by Colin Smith ( 2679 ) on Thursday September 04, 2008 @03:23AM (#24870569)

    The milky way is our galaxy.

    Also, 2 different brands of chocolate bar.


  • Interferometry (Score:5, Informative)

    by syousef ( 465911 ) on Thursday September 04, 2008 @03:31AM (#24870617) Journal

    Can we stop saying "virtual telescopes" and start using the proper grown up terms? Interferometry and Aperture Synthesis aren't hard to understand. It's a pet peeve of mine, and slashdotters should be of a level of intelligence that they can understand this stuff.

    http://en.wikipedia.org/wiki/Astronomical_interferometer [wikipedia.org]

    http://en.wikipedia.org/wiki/Aperture_synthesis [wikipedia.org]

    Yes you get the same angular resolution as a much larger telescope (one as big as the distance between the telescopes), which is why you do it. However it's important to note that you you don't increase the amount of radiation you're collecting - it's still just the sum of the telescopes you're using.

    I'll try to put it simply. Let's use optical telescopes as a familiar example. (In practice optical interferometry is much harder than radio astronomy, but I digress). The larger the diameter of the mirror (or lens) the more light we collect, and the smaller an object we can look at with reasonable detail (There is a physical relationship between the diameter of the telescope and the smallest thing you can resolve with it). We could space multiple telescopes a good distance apart and increase how small a piece of the sky we can look at in detail. The detail we could now resolve depends on the distance between the telescopes. However we're still only collecting as much light in total as the sum of the light collected by each scope. So even though we can look at a much smaller part of the sky, we won't be able to brighten up the image as much as if we had the larger telescope. It's still worth doing and it still yields discoveries, but it's not the same as having a massive telescope.

  • Re:Pics! (Score:3, Informative)

    by Normal Dan ( 1053064 ) on Thursday September 04, 2008 @04:04AM (#24870815)
    Here is the actual negative surrounded by brackets:
    [ ]
  • Re:also... (Score:5, Informative)

    by Muczachan ( 1012169 ) on Thursday September 04, 2008 @04:14AM (#24870867)
    Nope. Gravitic force gets weaker the further you get from the mass exerting it.
  • Re:Interferometry (Score:5, Informative)

    by Shag ( 3737 ) on Thursday September 04, 2008 @04:35AM (#24870957)

    Yes. Please.

    And while we're at it, can article-writers stop referring to the submillimeter/microwave portion of the spectrum as "radio"?

    Linking together radio dishes is not a big deal - radio astronomy goes back to the 1930s, and the Very Long Baseline Array has stretched from Hawaii to the Virgin Islands for decades now.

    Linking together JCMT and SMA with some dishes on the mainland is a big deal in submillimeter astronomy. The Cosmic Microwave Background wasn't even discovered until the 1960s, and then it took another couple decades to develop serious observing capabilities. There's plenty of interferometry on Mauna Kea, both within the SMA and between the SMA and JCMT and/or CalTech Submillimeter Observatory, but that's all relatively short-baseline.

  • Re:Interferometry (Score:4, Informative)

    by caluml ( 551744 ) <slashdot@@@spamgoeshere...calum...org> on Thursday September 04, 2008 @06:00AM (#24871283) Homepage

    And while we're at it, can article-writers stop referring to the submillimeter/microwave portion of the spectrum as "radio"?

    Just out of interest, why? It is part of the RF spectrum, just way way way up there. It's also good to call it that, because it reminds people that it's part of the same thing as light, xrays, Ham Radio, and mobile phones.

  • by Anonymous Coward on Thursday September 04, 2008 @06:45AM (#24871449)

    They both have angular resolution. The radio telescope in question still has 1000 times the angular resolution of Hubble.

    What, exactly, is your peeve here?

  • Re:Interferometry (Score:4, Informative)

    by syousef ( 465911 ) on Thursday September 04, 2008 @07:48AM (#24871779) Journal
  • Re:event horizon? (Score:3, Informative)

    by mbone ( 558574 ) on Thursday September 04, 2008 @08:09AM (#24871905)

    There is an accretion disk around the event horizon, where things (dust, gas) are orbiting around at nearly the speed of light. As these things rub together, and as new stuff gets added, there is lots of energy to be detected far away - especially in jets of very hot matter out of the poles.

    The event horizon itself, for a black hole of this size, is not detectable. (Very small black holes should glow with Hawking radiation.)

  • by mbone ( 558574 ) on Thursday September 04, 2008 @08:15AM (#24871957)

    If you had an array of Hubble sized telescopes in space and could put them whatever distance you'd like from each other, what sort of results could you get?

    That is basically the Space Interferometry Mission (SIM) [nasa.gov], which alas has had funding troubles recently. The component telescopes are not the size of the Hubble, but the idea is exactly as you suggest. One thing you could do with this is detect Earth sized planets in a solar system like ours out to a reasonable distance.

  • Re:event horizon? (Score:3, Informative)

    by NormalVisual ( 565491 ) on Thursday September 04, 2008 @08:16AM (#24871975)
    By definition, the event horizon is the area surrounding a black hole inside which the escape velocity exceeds the speed of light, therefore you can't see anything beyond it. You're probably thinking of the accretion disk.
  • Re:Interferometry (Score:3, Informative)

    by mbone ( 558574 ) on Thursday September 04, 2008 @08:21AM (#24872025)

    Yes, but in astronomy virtual telescope generally means a computer compilation of various sky surveys [nasa.gov], so you can type in a coordinate and see what is there. This is totally different, VLBI provides a real telescopic view, just synthesized by interferometry.

    As an analogy, Google Earth is a virtual spy satellite. An orbiting synthetic aperture radar is a real spy satellite, just with a synthesized image.

  • Re:also... (Score:1, Informative)

    by InfiniteLoopCounter ( 1355173 ) on Thursday September 04, 2008 @09:39AM (#24872727)

    That sounds mostly right.

    Here's my take as someone who has studied some basic astrophysics (apologies if it is too basic):

    The black hole is the core of a very large sun (larger than ours) that went supernovae. It has a huge mass that has collapsed down to a relatively small area. Inside a radius mapping out the event horizon light is not able to escape.

    Now, light always travels at the same speed from any viewpoint and the gravitation field warps space time. When light moves in a circle time will have stopped for observers at a greater radius (because the light will never reach them). You could imagine it spiraling many times before it reaches an outside observer. This delay is what causes the difference in perception of time.

    Black holes are thought to emit Hawking radiation [wikipedia.org] which ought to eventually release all the stuff inside and dissipate the black hole.

    Also, in space there is little friction (no air). So most object falling "towards" the black hole instead follow a very slow spiral path towards the black hole. This force is thought to affect everything in the universe, but decays fast with distance and this orbiting nature due to relative linear motions of things with mass keeps everything separate (plus, maybe the expansion of the universe that may/may not affect dark matter).

    From my experience (none) scientists hate infinities because you can't get any information from your data without getting rid of them.

    Actually, they like seem to like dealing (read complaining) about infinities a lot. In fact they use them (they are not all the same) just about as much as pure mathematicians do. For example, I think the volume as seen from inside the black hole comes out infinite!

  • Re:Interferometry (Score:4, Informative)

    by Muad'Dave ( 255648 ) on Thursday September 04, 2008 @09:43AM (#24872781) Homepage
    I disagree. Your cable modem [wikipedia.org] does indeed MOdulate and DEModulate digital signals to and from analog channels, just like the old-school telephone modem. Amateur radio folk call the things that convert digital signals to an analog representation and back 'modems'.
  • by Bragador ( 1036480 ) on Thursday September 04, 2008 @10:00AM (#24872979)
  • by TheSHAD0W ( 258774 ) on Thursday September 04, 2008 @11:18AM (#24874283) Homepage

    Here [mit.edu], actually.

  • Re:Interferometry (Score:3, Informative)

    by Mr Z ( 6791 ) on Thursday September 04, 2008 @12:30PM (#24875435) Homepage Journal

    Huh? I don't think so. [wikipedia.org] Microwaves sit smack between FM and Infrared. That's why your microwave oven, 802.11b radio and 2.4GHz cordless phone all don't get along so well. They're all in the lower part of the microwave spectrum.

    And to folks who say microwaves aren't radio, please explain to me what 802.11a are doing up in that band, or how we do microwave radio relay [wikipedia.org]?

  • Re:Pics! (Score:2, Informative)

    by JustOK ( 667959 ) on Thursday September 04, 2008 @01:37PM (#24876583) Journal

    thought that was ( * )


    Technically I think the gravitational field would be more accurately represented as:

    ( o )

    but the gravity can also distort the frame of reference

All seems condemned in the long run to approximate a state akin to Gaussian noise. -- James Martin