Astronomers find baby blue galaxy close to dawn of time

Astronomers have discovered a baby blue galaxy that is the furthest away

in distance and time – 13.1 billion years – that they’ve ever seen. Photo: Pascal Oesch and Ivelina Momcheva, NASA, European Space Agency via AP

Excerpt from smh.com.au

A team of astronomers peering deep into the heavens have discovered

the earliest, most distant galaxy yet, just 670 million years after the

Big Bang.

Close-up of the blue galaxy

The findings, described in Astrophysical Journal Letters,

reveal a surprisingly active, bright galaxy near the very dawn of the

cosmos that could shed light on what the universe, now 13.8 billion

years old, was really like in its young, formative years.

“We’re

actually looking back through 95 per cent of all time to see this

galaxy,” said study co-author Garth Illingworth, an astronomer at the

University of California, Santa Cruz.

“It’s really a galaxy in its infancy … when the universe was in its infancy.”

Capturing an image from a far-off light source is like looking back

in time. When we look at the sun, we’re seeing a snapshot of what it

looked like eight minutes ago.

The same principle applies for the

light coming from the galaxy known as EGS-zs8-1. We are seeing this

distant galaxy as it existed roughly 13.1 billion years ago.

EGS-zs8-1

is so far away that the light coming from it is exceedingly faint. And

yet, compared with other distant galaxies, it is surprisingly active and

bright, forming stars at roughly 80 times the rate the Milky Way does

today.

This precocious little galaxy has built up the mass

equivalent to about 8 billion suns, more than 15 per cent of the mass of

the Milky Way, even though it appears to have been in existence for a

mere fraction of the Milky Way’s more than 13 billion years.

“If

it was a galaxy near the Milky Way [today], it would be this vivid blue

colour, just because it’s forming so many stars,” Illingworth said.

One

of the many challenges with looking for such faint galaxies is that

it’s hard to tell if they’re bright and far, or dim and near. Astronomers can usually figure out which it is by measuring how much

that distant starlight gets stretched, “redshifted”, from higher-energy

light such as ultraviolet down to optical and then infrared wavelengths.

The universe is expanding faster and faster, so the further away a

galaxy is, the faster it’s going, and the more stretched, or

“redder”, those wavelengths of light will be.

The astronomers

studied the faint light from this galaxy using NASA’s Hubble and Spitzer

space telescopes. But EGS-zs8-1 seemed to be too bright to be coming

from the vast distances that the Hubble data suggested.

To narrow

in, they used the MOSFIRE infrared spectrograph at the Keck I telescope

in Hawaii to search for a particularly reliable fingerprint of hydrogen

in the starlight known as the Lyman-alpha line. This fingerprint lies in

the ultraviolet part of the light spectrum, but has been shifted to

redder, longer wavelengths over the vast distance between the galaxy and

Earth.

It’s a dependable line on which to base redshift (and

distance) estimates, Illingworth said – and with that settled, the team

could put constraints on the star mass, star formation rate and

formation epoch of this galaxy.

The telltale Lyman-alpha line also

reveals the process through which the universe’s haze of neutral

hydrogen cleared up, a period called the epoch of reionisation. As stars

formed and galaxies grew, their ultraviolet radiation eventually

ionised the hydrogen and ended the “dark ages” of the cosmos.

Early

galaxies-such as EGS-zs8-1 – are “probably the source of ultraviolet

radiation that ionised the whole universe”, Illingworth said.

Scientists

have looked for the Lyman-alpha line in other distant galaxies and come

up empty, which might mean that their light was still being blocked by a

haze of neutral hydrogen that had not been ionised yet.

But it’s

hard to say with just isolated examples, Illingworth pointed out. If

scientists can survey many galaxies from different points in the

universe’s very early history, they can have a better sense of how

reionisation may have progressed.

“We’re trying to understand how

many galaxies do have this line – and that gives us some measure of when

the universe itself was reionised,” Illingworth said.

“One

[galaxy] is interesting, but it’s when you have 50 that you can really

say something about what galaxies were really like then.”
As

astronomers push the limits of current telescopes and await the

completion of NASA’s James Webb Space Telescope, set for launch in 2018,

scientists may soon find more of these galaxies even closer to the

birth of the universe than this new record breaker.

“You don’t get

to be record holder very long in this business,” Illingworth said,

“which is good because ultimately we are trying to learn about the

universe. So more is better.”

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Astronomers find baby blue galaxy close to dawn of time