Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 04/08/2015 18:50:01

Title: Can we tell whether star light is old or new?
Post by: thedoc on 04/08/2015 18:50:01

Patrick Ivers asked the Naked Scientists:
   
Consider the following scenario: The starlight from one of the earliest stars to form in our Universe, a few hundred million years after the Big Bang, is blocked for several thousand years by a barrier less than 10,000 years ago before moving away. Between the time of the star's formation & the present, both the star & the Earth have receded from each other in an expanding cosmos so that the distance now separating them is tens of billions of light years. My inquiry: Would astronomers be able to discern a gap, based on the changing positions of the Earth & the star, between when the starlight was blocked & now?  Would telescopes be able to collect light from the star's earlier location & radiation before the obstruction as well as from it after the disappearance of the barrier, thus producing the appearance of two stars? Finally, if a barrier had formed several thousand years ago, isolating our Solar System from all celestial illumination beyond our Sun, lasting at least several hundred years before completely dissipating, would astronomers be able to provide evidence of this event by means of recognizing a gap in the starlight reaching us today? Would we be able to see more points of light in the night sky because of the changing in the position of the Earth in relation to all other stars during the darkout?

What do you think?

Title: Re: Can we tell whether star light is old or new?
Post by: evan_au on 04/08/2015 21:48:17

I don't understand the premise behind this question, but perhaps I can address one small part of it...

Quote from: Patrick

Would telescopes be able to collect light from the star's earlier location & radiation before the obstruction as well as from it after the disappearance of the barrier

When we observe distant quasars in the universe, this light has passed through many intervening galaxy clusters and their associated clouds of cold hydrogen.

Due to the general expansion of the universe, these closer clouds of gas have less velocity than the quasar itself, resulting in a "forest" of absorption lines (https://en.wikipedia.org/wiki/Lyman-alpha_forest) at different redshifts within the broad emission spectrum of the quasar.
 
Effectively, astronomers today are seeing a history of the path traveled by the light from the quasar to us. It records the history of this beam of light over long periods of time. This history is visible to us now, despite some hypothetical barrier that may have blocked the light from this quasar in the past.