UMass astronomer identifies earliest galaxy ever detected

By Cecilia Prado

University of Massachusetts astronomer Mauro Giavalisco, along with scientists from several other institutions around the globe, has successfully identified the most distant, and therefore earliest, galaxy ever studied, according to a UMass press release.

NASA Goddard Space Flight Center/Flickr

The discovery came during a new survey of the distant universe conducted from the NASA Hubble Space Telescope.

Although previous Hubble-based observations have been able to identify other distant galaxies in the early universe, this is the farthest and earliest galaxy whose span can be clearly confirmed with continuous observations from the Keck I telescope, according to the release.

The survey was the largest investigation of the early universe ever made with the Hubble telescope, and two special cameras were required to measure the distance of the galaxy. The research team consisted of scientists from Israel, Italy, Arizona, Maryland, California and Kentucky, as well as scientists from UMass and the University of Texas.

The team used a technique that Giavalisco helped develop in the early 1990s called “Lyman-break selection,” which involves enhancing the apparent colors of galaxies in order to determine their distance. This technique was useful in differentiating this distant galaxy from closer galaxies that obscure the light of other celestial objects.

This technique, however, can only provide vague distance estimates. Therefore, Giavalisco and his team had to calculate the distance of pre-selected, far-off galaxies, and estimate the age at which they are being observed. This was necessary to date the galaxy properly and measure its mass, luminosity and star-formation rate, according to the release.

In the release, Giavalisco said that colors can be indicators of a variety of physical processes happening inside a galaxy—for example, whether or not the galaxies form stars and how much dust is in them. Giavalisco said that dust makes the color of stars more red because it dims stellar light. According to the release, the team required very powerful spectroscopic telescopes to detect the Lyman-alpha emission line. This is a specific spectral feature emitted by hydrogen in a particularly narrow range of ultraviolet wavelengths, which is invisible to the human eye, the release said. The Lyman-alpha emission was necessary in order to measure how far away this galaxy is from our own.

The telescope used in the study was the Keck 10-meter telescope in Hawaii, one of the most powerful spectroscopic instruments available. It was used to detect the Lyman-alpha emission and to confirm its nature.

The distance of the galaxy discovered by Giavalisco was recorded at a redshift of 7.51, meaning that it is the farthest ever recorded. The results indicate that at the time the galaxy was formed, the universe was 700 million years old. Today, it is 13.8 billion years old. During the time it was formed, the universe was eight and a half times smaller than it is today and 600 times denser, and it was expanding eight and a half times faster, according to the release.

The discovery of such a young, distant galaxy by a survey that was not originally designed to do so came as a surprise to the researchers. According to first author, Steve Finkelstein, from the University of Texas, Giavalisco and others in a recent article published in Nature Journal, this discovery suggests that the infant universe may contain a much larger number of intense star-forming galaxies than astronomers believed possible. Because of this, theories and predictive models of the distribution of star formation in galaxies may need updating, the release said.

In the press release, Giavalisco used the analogy of how a brick being thrown through a window is expected to produce a large number of small glass shards and a few large glass shards to explain the beginning hypothesis of his team.

“We expected to find a lot more small objects with this survey,” said Giavalisco in the release. He said that their survey was not originally designed to find these distant galaxies with such a high rate of star formation. He and his team, however, were able to observe the highly active object on the first try. This could indicate a stroke of great luck, or it could mean that their predictive models were slightly off.

The astronomer said that the high level of luminosity that is powered by the star formation activity of this new galaxy “raised a tantalizing question about whether we’ve got the theory of galaxy formation correct in its fundamental ideas.” He added, “These mechanisms are not yet fully understood.”

Cecilia Prado can be reached at [email protected].