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Space Science

Light Echoes Solve Mystery of Tycho's Supernova 98

Ponca City, We love you writes "Powerful telescopes in Hawaii and Spain are using 'light echoes' from the original supernova explosion that have bounced off dust in the surrounding interstellar clouds to identify the precise type of supernova that Tycho Brahe saw 436 years ago. Although the echoed light from Tycho's supernova is around 20 billion times fainter than the original light observed in 1572, the team took identical images of the sky a few months apart and then digitally subtracted one from the other to find evidence for several sets of light echoes rippling across patches of dust in the northern Milky Way. 'Using light echoes in supernova remnants is time-travelling in a way, in that it allows us to go back hundreds of years to observe the first light from a supernova event. We got to relive a significant historical moment and see it as the famed astronomer Tycho Brahe did hundreds of years ago,' said Tomonori Usuda, of the Subaru Telescope in Hawaii. Tycho's original observations were particularly important as he immediately concluded that the new star, visible even by day, could not be closer than the Moon challenging the Aristotelian view of the cosmos, widely accepted since ancient times, which held that the sky beyond the Moon never changed."
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Light Echoes Solve Mystery of Tycho's Supernova

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  • by mangu ( 126918 ) on Friday December 05, 2008 @10:22AM (#26002345)

    This could be used to determine distances very precisely. If we know when that light was emitted and we know the speed of light, then we can calculate with great precision the distance from the star to the reflecting dust cloud.

  • Re:Light echoes? (Score:5, Interesting)

    by Sockatume ( 732728 ) on Friday December 05, 2008 @10:24AM (#26002357)
    "Echoes" evokes the idea that the light from the star first reaches us directly, then a delayed reflection of that light reaches us afterwards. "Reflections" are colloquially assumed to be instantaneous. I think it's a neat bit of semantics, really.
  • Re:Light echoes? (Score:3, Interesting)

    by nschubach ( 922175 ) on Friday December 05, 2008 @10:49AM (#26002629) Journal

    That's alright, I'm still trying to figure out which way is 'North' in space... Does North always point to the magnetic pole of Earth even on Mars? Has someone studied the Milky Way and determined that there's a magnetic ring perpendicular to the dish?

  • by TheThiefMaster ( 992038 ) on Friday December 05, 2008 @11:34AM (#26003095)

    xxx times less than yyy == yyy/xxx.
    It's common language these days, learn it!

  • Re:Light echoes? (Score:2, Interesting)

    by mrsquid0 ( 1335303 ) on Friday December 05, 2008 @11:38AM (#26003151) Homepage

    Hmm... I made a mistake. I should have said that supergalactic coordinates are described here: []

  • by Doc Ruby ( 173196 ) on Friday December 05, 2008 @12:29PM (#26003825) Homepage Journal

    A telescope array [] acting as an interferometer doesn't need to be a single large sensor like that. We can orbit the array with separations of 1E13, just beyond Neptune. That would give us resolution of something like 5.8E-20 arcseconds. The radius of that regular polygon with 10cm sides is about 7E21m, or about 740,000 light years. Which would show light that left Earth about 1.48 million years ago. Orbital arrays much closer to Earth are sufficient for looking for apples only 175ly away.

    The signal to noise is of course extremely high ("astronomical"). That's why I mentioned the combined computing power of all the world's computers. We're gonna need a bigger boat, but that's a good sea to sail her on, to catch this shark :).

  • by mangu ( 126918 ) on Friday December 05, 2008 @01:40PM (#26004713)

    You also have to account for any differences between the earth-star distance and the earth-cloud distance

    One could start by assuming that the points which are being illuminated now and have the biggest angular separation from the star are at the same distance from earth as the star. Those points form a circle with a 436 light-year radius. The size of that circle as seen from earth will give you the distance to the star.

    I'm assuming that there is enough dust everywhere in space to return a detectable reflection, but even if this isn't true an imperfect circle would still give us usable data. At the distance that star is, about 7500 light-years, this would probably more accurate than other methods.

    Supernova 1987A [] has had its distance measured by a similar method, look in this picture [] how the reflections appear.

  • by CrimsonAvenger ( 580665 ) on Friday December 05, 2008 @02:09PM (#26005125)

    But seriously, if something is 20 billion times fainter it's going to be barely visible, regardless of how bright the original is.

    Our sun is ~20 billion times fainter than it will be when it supernovas. And seems to be bright enough to light up the world nicely. OP is right, it would be nice to know how bright the original was.

  • by AlejoHausner ( 1047558 ) on Friday December 05, 2008 @03:36PM (#26006241) Homepage
    Here is a link to an article by one of the researchers involved in this work []

    As the article suggests, the biggest benefit of using light echoes is that the SPECTRUM of the original supernova can be obtained. In other words, while today we mostly see the direct-path light emitted by the supernova's gas remnant, light echoes let us see all the wavelengths of the light emitted at the time of the explosion.


  • by AlejoHausner ( 1047558 ) on Friday December 05, 2008 @10:32PM (#26010299) Homepage
    This would definitely not work. There is no imaging (no lens, or pinhole) at work. What you are proposing is analogous to sitting in a dark room with white walls with the television on: you will see areas of color on the wall, but you will be unable to deduce from these reflections what the picture on the TV looks like (beyond getting the average color of the TV picture). Of course, if the wall were a mirror, you could do it, but walls are diffuse reflectors, which means that, at each point on the wall, any light arriving is scattered into a 180-degree hemisphere of directions. The light reaching your eye from any point on the wall comes from the whole TV screen. You can't easily undo what is, effectively, a massive blurring operation.

    To make matters worse, room walls are white, and reflect light back and forth to each other, so a large fraction of the light you see on the wall has already bounced off one or more other walls. Thus it's undergone several blurring passes.

    This latter inter-reflection problem will, of course, happen in space too. There's lots of nebula to scatter light.

    And, what's worse, we don't know exactly where those nebular are, at least not precisely enough to get the data needed to undo the blurring, assuming that were at all feasible.


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