Light Echoes Solve Mystery of Tycho's Supernova

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."

Comments

I want to play.

[suso]

That is really cool. Like some kind of galactic diff.

Wikipedia links just for the sake of completeness

[Anonymous Coward]

Here's a link to the supernova in question. Also, here's Brahe himself. Remember that all his observations were naked-eye - pre telescopes.

Re:Light echoes?

[Vellmont]

Is there something wrong with the word "reflections" now?

In human experience, a reflection is instantaneous, where an echo appears after a period of time. Thus echo is more descriptive to layman (remember them?). You know and I know that a reflection isn't instantaneous, it's just not generally perceptible to our eyes like an echo is perceptible to our ears.

A galactic yardstick?

[mangu]

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?

[Sockatume]

"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.

Reverse Ray Tracing

[Doc Ruby]

When can we point our telescopes at an object hundreds or thousands of lightyears distant, and pick up the light reflected back at us that previously traveled from Earth to that object, then reassemble it into images? Images of the Earth's past, twice as old as the lightyear distance of the object?

We could look at an object 1000 lightyears distant for reflections of Jesus being crucified. Search among objects 250-600 lightyears distant for reflections of people arriving in the "Americas" on ships before Columbus. 176ly distant objects could show us images of Newton getting hit by a falling apple.

Finally a use for the combined computing power of all Earth's computers.

Re:Reverse Ray Tracing

[glaswegian]

We would need monumentally large telescopes for this. The largest optical telescope on earth, the Keck, has a diameter of 10m. Using the Rayleigh Criterion, we can calculate the minimum resolvable detail at a given distance. For example, we can resolve details on the surface of the moon (in the visible) that are around ~20 meters across. If you want to resolve an apple falling on somebodies head you need ~10 cm resolution. So to see this happening on the moon we would need a telescope with a primary mirror ~ 2.6 km across. To see the same thing echoed back from a dust cloud near the closest star to our sun (4 ly * 2), you would need a telescope with a primary ~ 7e+10 m across or around half the distance between the earth and the sun. Not to mention that the signal would be very weak and completely lost in noise.

Re:Reverse Ray Tracing

[Doc Ruby]

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 :).

Tycho Brahe - Amazing

[Aladrin]

I'm amazed that he was able to observe that and figure out that the common concept of the sky was wrong at the time. I can't imagine how much thought must have gone into something like that.

Re:Light echoes?

[Yvan256]

HA-ha! You like semantics! /Nelson Muntz

Re:Light echoes?

[mrsquid0]

North in the sky is defined to be the point directly above the Earth North Pole of rotation. The northern half of the sky is the part of the sky between the celestial equator and the north celestial pole. For a planet north is defined using the right hand rule of rotation. Curl the fingers of your right hand. That is the direction of the planet's rotation. Stick out your right thumb. That is the direction of the planet's north pole. The same rule applies to Galactic north. Just apply the rotation rule to the Galaxy. Once you get outside the Galaxy supergalactic coordinates are used, which are defined here: http://en.wikipedia.org/wiki/Supergalactic_plane.

Re:20 billion times fainter?

[TheThiefMaster]

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