“It’s the great mystery of human life that old grief passes gradually into quiet, tender joy. The mild serenity of age takes the place of the riotous blood of youth. I bless the rising sun each day, and, as before, my heart sings to meet it, but now I love even more its setting, its long slanting rays and the soft, tender, gentle memories that come with them…” –Fyodor Dostoevsky, The Brothers Karamazov
Just last week, I wrote to you about one of the deepest images of the distant Universe, the Hubble Ultra Deep Field.
And in particular, how we’re able to find and identify some incredibly ultra-distant galaxies — despite their incredibly large redshifts — thanks to the magnification from the gravity of intervening matter.
Those are visual candidates in the green circles, where some of the light still appears red, and purely infrared candidates in the red circles, which is right at the limit of what Hubble can detect!
Completely invisible in ultraviolet and visible light, the light that was emitted in the ultraviolet (UV) from this galaxy is so severely redshifted that it appears at the far edge of what Hubble can see in the infrared (IR)! In fact, this galaxy — at a redshift of 10.3 — is a record breaker, and the only one known of its kind (although there are other candidates out that far).
In addition to being so far away and so redshifted due to the expansion of the Universe, these ultra-distant galaxies — the ones beyond a redshift of 6.5 (or back when the Universe was less than 800 million years old, as opposed to the 13.7 billion years old it is today) — have to contend with something else.
There’s neutral gas out there, blocking the starlight coming from these distant galaxies! And just like you’d expect, the more neutral gas you have to pass through, the brighter you need to be in order to make it through!
Well, going to higher and higher redshifts is, to put it mildly, harsh.
- To see something at a redshift of 7, you’ve got to go through about 50 million light-years of space where around 1% of the gas living there is neutral.
- To see something at a redshift of 8, you’ve got to go through an extra 100 million light-years of space where around 3% of the gas living there is neutral, in addition to the stuff you need to get here from a redshift of 7.
- And to see something at a redshift of 10, in addition to what happens at a redshift of 8, you’ve got to go through an additional 150 million light-years of space where something like 6% of the gas is neutral!
Well, unsurprisingly, people are already talking about how there should be more galaxies at this redshift than we’re seeing.
And that’s insane. First off, astronomically, you’re always going to see the brightest distant objects first. That’s a well-known effect. Second, the Universe is already 500 million years old by a redshift of 10, which means, conservatively, that we’ve had plenty of galaxies around for at least two-to-three hundred million years by then.
But it is amazing to be seeing and identifying galaxies this young, and we’re doing it for the first time ever. And this is just the tip of the iceberg; things are only going to get better from here!