A galaxy known as “z8_GND_5296” — the red blob in the box to the right — has just been confirmed as the oldest known galaxy we’ve seen, formed just 700 million years after the universe’s birth.
The galaxy seems to be pumping out new stars much faster — hundreds of times — than modern galaxies like our Milky Way.
The findings were reported Wednesday, Oct. 23, in the journal Nature.
Most astronomers believe that the universe was created 13.7 billion years ago in the “Big Bang,” when an unimaginably dense clump of matter exploded outwards.
For around 300,000 years after the Big Bang, the universe was filled with a hot, dense fog of plasma that was opaque to ultraviolet light. The universe only became truly transparent during an epoch known as known as “reionization” — between 200 million and 1 billion years after the Big Bang — when the first stars and galaxies formed. Ultraviolet light could be seen through the fog of hydrogen gas for the first time.
Scientists observe the faint light from distant galaxies to determine their distance, and therefore, age. The light from a galaxy is redshifted, or stretched to longer wavelengths, by the expansion of the universe. So, the farther the galaxy, the greater the redshift.
Young galaxies in the universe can often be identified by the emission of Lyman-alpha radiation generated by hydrogen gas because it produces the brightest ultraviolet emission line. However, the Lyman-alpha line of hydrogen emitted by older galaxies is often hard to see because it gets red-shifted out of the spectrum that most telescopes can detect. Although there are many galaxy candidates with high redshifts, it’s hard to confirm the existence of those with a redshift that is greater than seven.
Now, a new, more sensitive instrument on the Keck I telescope has allowed researchers to see the lyman-alpha emission of one galaxy with a redshift of 7.51, meaning it was formed when the universe was only 700 million years old. This is a new distance record.
There are potentially many older galaxies out there, but there existence can’t be confirmed due to the limitations of measuring galaxy redshift. As our instruments improve, including the launch of the James Webb Space Telescope in the next decade, we will be able to positively identify even more distant galaxies.
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