NASA’s Hubble telescope discovers 250 small galaxies!

A team of astronomers has discovered 250 tiny galaxies that existed 600 to 900 million years after the Big Bang. Observations by the NASA/ESA Hubble Space Telescope have taken advantage of gravitational lensing to reveal the largest sample of the faintest and earliest known galaxies in the Universe.

Some of these galaxies formed just 600 million years after the Big Bang and are fainter than any other galaxy yet uncovered by Hubble. The team has determined, for the first time, with some confidence that these small galaxies were vital to creating the Universe that we see today.

The international team, led by Hakim Atek of the Ecole Polytechnique Federale de Lausanne, Switzerland, has discovered one of the largest samples of dwarf galaxies yet to be discovered at these epochs. The light from these galaxies took over 12 billion years to reach the telescope, allowing the astronomers to look back in time when the universe was still very young.

Although impressive, the number of galaxies found at this early epoch is not the team’s only remarkable breakthrough, as Johan Richard points out, “The faintest galaxies detected in these Hubble observations are fainter than any other yet uncovered in the deepest Hubble observations.”

The  constellation of Ursa Major (The Great Bear) is home to Messier 101,  the Pinwheel Galaxy. One of the biggest and brightest spiral galaxies in  the night sky, Messier 101 is also the subject of one of Hubble's most  famous images (heic0602). Like the Milky Way, Messier 101 is not alone, with smaller dwarf galaxies in its neighbourhood. NGC  5477, one of these dwarf galaxies in the Messier 101 group, is the  subject of this image from the NASA/ESA Hubble Space Telescope. Without  obvious structure, but with visible signs of ongoing starbirth, NGC 5477  looks much like an archetypal dwarf irregular galaxy. The bright  nebulae that extend across much of the galaxy are clouds of glowing  hydrogen gas in which new stars are forming. These glow pinkish red in  real life, although the selection of green and infrared filters through  which this image was taken makes them appear almost white. The  observations were taken as part of a project to measure accurate  distances to a range of galaxies within about 30 million light-years  from Earth, by studying the brightness of red giant stars. In  addition to NGC 5477, the image includes numerous galaxies in the  background, including some that are visible right through NGC 5477. This  serves as a reminder that galaxies, far from being solid, opaque  objects, are actually largely made up of the empty space between their  stars. This  image is a combination of exposures taken through green and infrared  filters using Hubble's Advanced Camera for Surveys. The field of view is  approximately 3.3 by 3.3 arcminutes. 

The constellation of Ursa Major (The Great Bear) is home to Messier 101, the Pinwheel Galaxy. One of the biggest and brightest spiral galaxies in the night sky, Messier 101 is also the subject of one of Hubble’s most famous images (heic0602). Like the Milky Way, Messier 101 is not alone, with smaller dwarf galaxies in its neighbourhood. NGC 5477, one of these dwarf galaxies in the Messier 101 group, is the subject of this image from the NASA/ESA Hubble Space Telescope. Without obvious structure, but with visible signs of ongoing starbirth, NGC 5477 looks much like an archetypal dwarf irregular galaxy. The bright nebulae that extend across much of the galaxy are clouds of glowing hydrogen gas in which new stars are forming. These glow pinkish red in real life, although the selection of green and infrared filters through which this image was taken makes them appear almost white. The observations were taken as part of a project to measure accurate distances to a range of galaxies within about 30 million light-years from Earth, by studying the brightness of red giant stars. In addition to NGC 5477, the image includes numerous galaxies in the background, including some that are visible right through NGC 5477. This serves as a reminder that galaxies, far from being solid, opaque objects, are actually largely made up of the empty space between their stars. This image is a combination of exposures taken through green and infrared filters using Hubble’s Advanced Camera for Surveys. The field of view is approximately 3.3 by 3.3 arcminutes.

By looking at the light coming from the galaxies, the team discovered that the accumulated light emitted by these galaxies could have played a major role in one of the most mysterious periods of the Universe’s early history — the epoch of reionisation. Reionisation started when the thick fog of hydrogen gas that cloaked the early Universe began to clear. Ultraviolet light was now able to travel over larger distances without being blocked and the Universe became transparent to ultraviolet light.

Lead author Atek explained, “If we took into account only the contributions from bright and massive galaxies, we found that these were insufficient to reionise the Universe. We also needed to add in the contribution of a more abundant population of faint dwarf galaxies.”

These results highlight the impressive possibilities of the Frontier Fields programme with more galaxies, at the even earlier time, likely to be revealed when Hubble peers at three more of these galaxy clusters in the near future.

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