Astronomers discover earliest galaxy
Washington: In a major new survey of the early universe conducted from the NASA`s Hubble Space Telescope, astronomers have identified the most distant, thus the earliest galaxy ever detected.
The team, with researchers from Israel, Italy, Arizona, Maryland, California and Kentucky with UMass Amherst and UT, used two special cameras on Hubble as part of the largest investigation of the distant universe ever made with the space telescope.
To identify this distant galaxy from among myriads of other, closer faint galaxies that obscure deep images of the sky, they used a technique called the "Lyman-break selection" developed by University of Massachusetts Amherst astronomer Mauro Giavalisco and others in the 1990s. It exploits the apparent colours of galaxies as a crude distance indicator.
Giavalisco said that colours encode a lot of physical processes at work in them like whether they form stars or not and how much dust is in them, because dust dims stellar light and makes their colours redder.
To measure the distance to this record-breaking galaxy, Finkelstein, Giavalisco and colleagues needed very sensitive spectroscopic telescopes to detect a specific spectral feature emitted by hydrogen known as the Lyman-alpha emission line.
It is emitted in a very narrow range of ultraviolet wavelengths, invisible to the human eye.
To detect the Lyman-alpha emission from such a distant galaxy and fully confirm its nature, the team used the Keck 10-meter telescope in Hawaii, a very powerful spectroscopic instrument.
Results yielded a redshift parameter, that is an indicator of distance, of z = 7.51, by far the most distant galaxy ever recorded. At that time the universe was only 700 million years old, compared to 13.8 billion years today. It was 8.5 times smaller than today, 600 times more dense and expanding 8.5 times faster.
The study has been published in journal Nature.
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