Looking at the universe with a telescope means looking back in time, since the speed of light is so slow that even the light from nearby stars in our own galaxy takes years or millennia to reach us. As such, the very distant galaxies also offer humans a glimpse into the universe’s past – making the discovery of the most distant galaxy ever found the oldest.
According to a new study published on December 14 In the journal Nature Astronomy, astronomers have confirmed the most distant galaxy in our universe. The galaxy, called GN-z11, is so distant that it is believed to form the boundary of the universe at 13.4 billion light years or 134 million kilometers from Earth, meaning that the light we see from it is 13.4 billion years ago – just 400 million years after the big bang.
Nobunari Kashikawa of the School of Science at the University of Tokyo, a co-author of the study, explained to Salon that the current designation for GN-z11 as the “oldest” galaxy may be short lived, as telescopes are constantly scanning the sky .
“GN-z11 is the most distant galaxy known to date, and we may find a more distant galaxy tomorrow,” Kashikawa wrote via email.
Although the distant galaxy was originally spotted by the Hubble Space Telescope in 2016, Kashikawa and his team used the Keck I telescope in Hawaii to confirm its age and distance. At the time of its discovery, astronomers estimated it to be 13.4 billion light years away, based on the discovery of what appeared to be a fracture, known as the ‘Lyman Fault’, in the ‘spectrum characteristic of distant galaxies’ , Kashikawa explained. .
In an attempt to spot such a distant, faint galaxy, the Hubble Space Telescope pushed it to its limits.
“Our spectroscopic observations show that the Milky Way is even further away than we initially thought, right at the distance limit of what Hubble can observe,” said Gabriel Brammer, author of the 2016 study, in a statement. statement.
Astronomers measure the distance of a galaxy by determining its redshift, which is a measure of how fast it is moving away from Earth. As the universe expands, any object in the sky that is not gravity bound to our own galaxy retreats from Earth; while they do, these objects’ light extends over longer and therefore redder wavelengths. The farther the galaxy, the greater the redshift.
To determine how far GN-z11 was from Earth, Kashikawa’s team studied its spectral features, as research into the Hubble Space Telescope’s observations was limited.
“Even Hubble cannot resolve the ultraviolet emission lines to the extent we need,” Kashikawa said in a statement. statement. So we turned to a more up-to-date ground spectrograph, an instrument to measure emission lines called MOSFIRE, which is mounted on the Keck I telescope in Hawaii. “
Kashikawa told Salon it was “difficult” to determine whether or not there really was a break in the spectrum. In particular, the team turned to look at ultraviolet light to find the redshifted chemical signatures. The bottom line was having the right equipment to confirm and identify the spectral fraction.
“Because the wavelength cannot be accurately measured, the accuracy of determining the distance to the galaxy was uncertain,” Kashikawa told Salon via email. “Once we believe that the carbon and oxygen emission lines we have detected at this point are real, it is not that difficult to calculate the distance to them.”
Although this galaxy is far, far away, astronomers hope it contains information we can learn about our own galaxy and the universe.
“The detected light from carbon and oxygen suggests special physical conditions that do not exist in current galaxies,” Kashikawa told Salon. “The age of GN-z11 is estimated to be only 70 million years and its estimated mass one billion times that of the Sun (the stellar component) suggests that this young galaxy was born and grew rapidly.”
Kashikawa added, “The fact that carbon and oxygen were found in GN-z11 indicates that this galaxy is not the first (metal-free) galaxy in the universe.” Since elements heavier than hydrogen and helium are only forged into massive stars, the presence of heavier elements such as carbon indicates that the stars in the galaxy are at least second-generation, meaning one generation of large suns has already lived and died and expelled their metals. in the galaxy.
This means, Kashikawa said, that the first galaxies in the universe are still “in a more distant universe unknown to mankind.”
Next year is going to be a big year for astronomy, especially when it comes to how we better understand the universe.
“The boundary of the farthest reaches of space is expected to expand dramatically,” said Kashikawa.
And that’s partly because the James Webb Space Telescope is scheduled to launch from French Guiana on October 31, 2021, building on the legacy of the Hubble telescope. In particular, it will observe the infrared universe and detect light from distant, ancient galaxies. Infrared light cannot be properly detected from Earth due to interference from the atmosphere, so a space telescope is needed to explore the universe in infrared.
“The [James Webb Space Telescope] The observatory will detect light from the first generation of galaxies that formed in the early universe after the Big Bang and study the atmospheres of nearby exoplanets for possible signs of habitability, ” said Eric Smith, NASA Webb’s program scientist at the agency’s headquarters. statement earlier.