Zazzle Shop

Screen printing

Monday, January 5, 2009

Time travel happens all the time

By Peter Becker/Gatehouse News Service


Westwood Press News RSS

By NASA/European Space Agency
This picture shows nebulous wisps of a supernova remnant, from a star that exploded thousands of years ago. Nicknamed the Pencil Nebula, it was formed by a shock wave encountering dense interstellar gas. The bright star in center is a foreground star, in the constellation Vela.">STAR25.jpeg
By NASA/European Space Agency
This picture shows nebulous wisps of a supernova remnant, from a star that exploded thousands of years ago. Nicknamed the Pencil Nebula, it was formed by a shock wave encountering dense interstellar gas. The bright star in center is a foreground star, in the constellation Vela.

Westwood - Time travel seems like stuff of science fiction, but in a sense, astronomers do it all the time. The night sky before us is a vista of time, as we look further and further back in the hundreds or thousands of years it takes starlight to reach our eyes. Another record of time is etched on the sky by way of “light echoes.”


Sky and Telescope reports that astronomers have found away to examine the light from a supernova blast that erupted, and faded away, more than 400 years ago. The astronomer’s time machine is his or her telescope, attached with a spectrograph that splits the light into its rainbow of colors and records the data the spectrum contains.
Supernovae are stars that blow up. That doesn’t sound scientific enough, but that’s what happens. Not all stars blow up, thank heavens. Those that do briefly outshine the galaxy and make a show for the broader Universe to see, a grand finale of a star’s time to shine. On the average, one will occur every 50 years or so in the Milky Way Galaxy and the only reason we don’t see them very often is the enormous plane of cosmic dust that acts as a veil on much of the stellar background.


That very dust, however, has allowed astronomers to detect light from the supernova of November 11, 1572, which was noticed by Danish astronomer Tycho Brahe who was startled to see a bright new star in the constellation Cassiopeia. He watched it night to night as the star grew brighter than Venus, and was visible in the blue daylight sky for two weeks. The mysterious star took 16 months to fade away from view, in the age before telescopes.


This event alerted Tycho that the stars were not eternal and unchanging, but there was a lot more to seek out and understand.


All that is left of the actual site of the supernova is a wisp of expanding debris which astronomers can best detect from radio emission, infrared light and X-rays given off. The evidence suggests this was a classic type of supernova known as “Type 1a” which involves a runaway thermonuclear blast of a white dwarf star. These type of supernovae have an intrinsic luminosity- they give out a certain amount of light more or less common to them all. Knowing this output and the faintness of the light they see in their telescope, astronomers can use them to deduce the distance. This is invaluable for estimating the distance of far away galaxies, where on occasion, a supernova will be revealed.
In September, a team from Germany, Netherlands and Japan did some time traveling. They were able to identify the light echo of the original supernova light, reflecting off a nebula of cosmic dust. This expanse of dust is many light years to the side and rear of the supernova Tycho saw 436 years ago, far enough away to give the supernova light 436 years of time to reach the nebula and then reflect back to our eyes in the year 2008.
This light echo is extremely faint, but the researchers were able to detect it and resolve a spectrum of colors, complete with the identifying lines of elements that made up the exploding star. Those elements absorb a thin slice (frequency) of the light depending on what type of element. Like an identifying fingerprint, dark lines in the spectrum of color tell us what the source of the light is made of.


From this study, Tycho’s supernova does appear to be a classic “Type 1a.”
As the decades and centuries go by, that light echo will reach further in the dusty plane of the galaxy, presumably allowing future generations of astronomers, hopefully with more advanced technology, to further examine the stellar wonder of November 11, 1572.
Although far beyond our reach today, perhaps some day someone will be able to detect light echoes that reflected off the Earth in the distant past and take a look back into time. Maybe they’ll see me typing away this column, though I doubt it since I’m inside a building and not near a window and its cloudy today anyway... just in case, I’ll remember to smile!


0 comments: