"We’ve taken a major step back in time, beyond what we’d ever expected to be able to do with Hubble. We see GN-z11 at a time when the universe was only three percent of its current age." -Pascal Oesch
Arriving at our eyes after a journey of 13.4 billion years, the light from galaxy GN-z11 has been traveling towards us for 97% of the Universe’s present age. It’s detection and discovery, however, was a lot more complicated than simply opening up your telescope’s eyes and collecting enough light; a confluence of four separate things needed to happen all at once to make it possible.
The telescope itself needed to be configured to detect light that had been shifted by the Universe’s expansion from ultraviolet to infrared. The volume of the Universe, from here to there, needed to be reionized enough to allow light to pass through it. Gravitational lensing needed to magnify the background galaxy to make it detectable. And spectroscopic confirmation was needed to ensure that the galaxy wasn’t an impostor.
If it had to be lensed by a foreground galaxy so we could see it, why doesn't it appear as a ring? (And why don't we see the foreground galaxy in the images?)
By the way there's a great animated zoom to this galaxy here: https://www.nasa.gov/feature/goddard/2016/hubble-team-breaks-cosmic-dis…
1) Perfect alignment is required to form a ring. I leave it as an exercise for the reader to compute the probability (simplify to fraction of solid angle) needed to make an Einstein ring out of a background galaxy at z=11, from a foreground galaxy at z<1. For simplicity, assume both galaxies have a true diameter of 100 kpc.
2) If the lensing galaxy is itself at sufficient z, it may not be strong in the visible spectrum.
3) Lensing need to be by a single galaxy; a galaxy cluster with sufficient mass would not be apparent to a casual observer.
Michael Kelsey #2: thanks. I assumed that for it to be such a record-breaker, it would have to benefit from the greatest possible lensing magnification, which I thought would happen if it was well aligned and formed a ring. Looking at the picture, it isn't even noticably curved into an arc, the way I've seen lensed galaxies look before when they weren't spread out all around the foreground galaxy.
I think in your number (3) you're missing a "doesn't".
I understand your number (2). I'll take your word for it. But it sure is hard to picture that a galaxy (or galaxy cluster) too dim to be seen at all by Hubble can cause an even dimmer galaxy behind it to leap into focus for us.
Actually, far be it from me to question Ethan, but I wonder if he hasn't conflated two distant galaxies in this post. The previous record holder for age and distance was indeed lensed: https://www.nasa.gov/press/2014/july/hubble-shows-farthest-lensing-gala…
The lensing is apparent in those pictures of the previous record holder from 2014. But NASA's article about the new record holder says nothing about lensing. What do you think Michael?
@Jonathan: I think you're right. EGSY8p7, which was discovered by the same team, was visibly lensed (magnified), while the publication of GN-z11 (https://arxiv.org/pdf/1603.00461.pdf) doesn't mention any lensing at all, and in particular describes the candidate as "remarkably bright." If it were thought to be lensed, there would need to be some discussion and estimate of the magnification ratio.
wow what a great achievement..
AFL Sports News #6: thanks, it wasn't really such an amazing achievement, I just noticed that the photo was... oh wait, I see what you are saying. Never mind. :)