EGS8p7 was on researchers’ radar after it was observed by NASA’s Hubble Space Telescope and the Spitzer Space Telescope. Using the MOSFIRE spectrometer at the W.M. Keck Observatory in Hawaii, researchers took another look at the galaxy. A spectrographic analysis of the galaxy was performed to determine its redshift.
W.M. Keck Observatory
Redshift and the Doppler effect
We all see examples of the Doppler effect everyday. You know how an ambulance siren sounds higher in pitch when it is coming towards you, then after it passes? That’s the Doppler effect. The frequency of a sound wave changes depending on where you are in relation to the object producing the sound. Redshift is similar. But instead of sound, it’s light. Light is shifted from the actual color to redder wavelengths.
With redshift, the light source is moving away from you. The opposite of this would be blueshift, or a light source moving towards you.
Redshift and Galaxies
Redshift is the typical method used by scientists to measure the distance to galaxies. But, finding the most distant galaxy brings its own challenges. I’ll let the Caltech press release explain:
Immediately after the Big Bang, the universe was a soup of charged particles—electrons and protons—and light (photons). Because these photons were scattered by free electrons, the early universe could not transmit light.
After about 380,000 years, the universe cooled enough for protons and free electrons to combine and form neutral hydrogen atoms. About 500,000 years after the Big Bang, the first galaxies switched on and reionized the neutral gas.
Detecting galaxies before reionization was believed to be impossible. Clouds of neutral hydrogen atoms would have absorbed certain radiation emitted by the first galaxies. This includes a spectral signature known as the Lyman-alpha line.
“If you look at the galaxies in the early universe, there is a lot of neutral hydrogen that is not transparent to this emission,” says Adi Zitrin, a NASA Hubble Postdoctoral Scholar in Astronomy at Caltech. “We expect that most of the radiation from this galaxy would be absorbed by the hydrogen in the intervening space. Yet still we see Lyman-alpha from this galaxy.”
The redshift for EGS8p7 came in at 8.68. Before this discovery, the most distant galaxy had a redshift of 7.73.
Why can EGS8p7 be seen? Researchers say it could be because hydrogen reionization was not consistent. “Evidence from several observations indicate that the reionization process probably is patchy,” Zitrin says.
Sirio Belli, a Caltech graduate student who assisted Zitrin on the project, explains how EGS8p7 could have ionized hydrogen earlier than other galaxies.
“The galaxy we have observed, EGS8p7, which is unusually luminous, may be powered by a population of unusually hot stars, and it may have special properties that enabled it to create a large bubble of ionized hydrogen much earlier than is possible for more typical galaxies at these times,” says Belli.
This finding could have huge implications for astronomy. The timeline for reionization may even need to be revised according to Zitrin.